Institut für Phytomedizin

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Effect of mulch application in combination with NPK fertilizer in cowpea (Vigna unguiculata (L.) Walp.; Leg.) on two key pests, M. vitrata F. (Lepidoptera: Pyralidae) and M. sjostedti Trybom (Thysanoptera: Thripidae), and their respective parasitoids
(1999) Zenz, Nikolaus; Zebitz, Claus P. W.
African farmers use mulch to preserve soils from physical and nutritional degradation. No clear evidence exists whether mulch may also be used successfully to control pests. This study aimed to assess the effect of mulch in combination with NPK fertilizer on two key pests of cowpea (Vigna unguiculata (L.) Walp.; Leguminosae), the legume pod borer Maruca vitrata F. (Lepidoptera: Pyralidae) and the flower thrips Megalurothrips sjostedti Trybom (Thysanoptera: Thripidae), inclusive of their parasitoids. Trials were carried out in three regions of Benin, West Africa, from 1995 to 1997. This study focused on plant physiology, soil properties, climate as well as habitat structure, all of which were assumed to have a strong influence on pest abundance. Data on plant development represented by number of nodes, flowers, and pods were collected periodically. Flowers were sampled in parallel to monitor the abundance of both pests. Eggs and living larvae of M. vitrata and larvae of M. sjostedti were collected periodically and reared for studies on parasitism. Mortalities due to three braconid parasitoids were assessed belonging to the order of hymenoptera, Dolichogenidea sp., Phanerotoma leucobasis Kriechbaumer, and Braunsia kriegeri Enderlein, which represented the dominant species on larvae of M. vitrata. Ceranisus menes Walker (Hymenoptera: Eulophidae) was the only parasitoid found on M. sjostedti. Pods were harvested and assessed for damage of M. vitrata. Pod number, weight per pod, relative pod and grain damage were investigated and estimates were made of the yield losses. Yield of cowpea was measured and related to preceding pest abundance. Pods were counted, weighed, and husked, and grains were weighed. Flowers were collected from potential wild host species of both pests in the vicinity of cowpea fields. Insect counts from flowers in the adjacent cowpea fields served as comparison.
Strategien zur Regulierung des Fruchtschalenwicklers Adoxophyes orana F.v.R. (Lepidoptera: Tortricidae) mit Kombinationen des Neem-Präparates NeemAzal-T/S und Entomopathogenen
(2002) Kumpmann, Sophia Katharina; Zebitz, Claus P. W.
The summer fruit tortrix moth Adoxophyes orana F.v.R. is known as a serious pest in pome fruits in Central Europe. According the new laws on plant protection in Germany, only few registered products are left which may be used in organic and conventional farming at present. The registered products used in organic farming base on the specific Adoxophyes orana granulovirus (AoGV; tradename: Capex) and Bacillus thuringiensis (Bt). The application of Capex in order to reduce high population densities led to various results, some of which proved to be insufficient. The results of Bt application were not satisfying, either. The application of 3 l/ha NeemAzal-T/S, a product based on Neem (Azadirachta indica A. Juss.) -extracts and plant oil, for aphid control in apple orchards shows promising side effects on Adoxophyes orana with a mortality rate of about 60 - 70%. However, the efficacy of the recommended dose of 3 l/ha at red bud stage is not high enough to obtain a satisfying control of A. orana in orchards with medium and high population densities. A possible positive aspect may be the long-term effect upon the population of A. orana following the application of both, Capex or NeemAzal-T/S. Until now, however, long-term effects have not been considered in control strategies. Thus, this study aimed towards to take advantage of these side effects of the application of NeemAzal-T/S in combination strategies with Bacillus thuringiensis or Capex for efficient and economically interesting control of this pest. Field and laboratory tests were carried out to test different strategies of combinations including short-term and long-term effects of the products. In addition, the aim of some laboratory trials was to test appropriate Bt-products and further additives for A. orana regulation. Combination of NeemAzal-T/S and a Bt-product In laboratory trials and field tests, different concentrations of NeemAzal-T/S and Bt were combined and sprayed at the same time to assess the effects of this strategy on the larvae of A. orana. This combination showed neither additive nor synergistic effects, no matter the concentration used. A successive strategy with a first application of NeemAzal-T/S either with or without adding 0,4 kg/ha Bt and with a second application of 0.6 ? 1.0 kg/ha Bt lead to high efficacy. Application of NeemAzal-T/S ? in doses of 2 l/ha or 3 l/ha in the first treatment ? turned out to be an important factor to achieve a good result. The addition of 0.4 kg/ha Bt to the first application did neither show a better nor a worse result. Obviously, this successive combination strategy leads to lower negative influence of the feeding inhibition, which seems to be partly responsible for the negative effects on A. orana when both products were applied at the same time. Combination of NeemAzal-T/S and Capex In organic farming, Capex at 100 ml/ha is applied two times in spring. Aim of the following tests was to minimise the risk of failure of a treatment with Capex by taking advantage of the positive side effects of the application of NeemAzal-T/S and to find out whether a reduction of the amount of Capex may be possible in this combination. In laboratory trials, no synergistic effects of a combined application of both products could be observed. In fields, Capex applications leading to 50 ? 60 % efficiency could be raised to 81 ? 94% by adding of NeemAzal-T/S. When Capex applications led to a larval mortality rate of 90% or more, the addition of NeemAzal-T/S showed no effects. Furthermore, the long-term effects of the combination of NeemAzal-T/S and Capex were taken into account. One trial showed that the increased efficiency of the combination was higher when considering also the number of larvae of the subsequent two generations, than assessing the larval mortality rate in the treated generation only. This leads to the conclusion that either the long-term effect of NeemAzal-T/S alone or of both products together reduces the population density of A. orana in the generations following the treatment. Long-term effects of Capex Aim of this part of the studies was to estimate whether an application of a small amount of Capex in summer in addition to the usual spraying in spring leads to a higher infection potential in the orchard. With the additional treatment, the rate of infected larvae in summer could be increased from 8% to 22%, and the amout of damaged fruits from 0.2 % to 0.6%. But both infestation rates were very low and, thus, too weak to support any interpretation. Thus, the additional treatment in the summer turned out to be of economical advantage. The repeated use of this virus product in various concentrations and against various generations of A. orana seems to be a very promising strategy. It remains to further research and long-term studies to elucidate the most efficient sequence, amount and dates of application of the virus to obtain maximum control of A. orana.
Mechanismen der Resistenzinduktion nach Blattbehandlungen mit Phosphaten
(2002) Orober, Miroslav; Buchenauer, Heinrich
In this study the induction of resistance against plant diseases following foliar application of phosphates was investigated. The early biochemical responses of the resistance activation by phosphates have been compared with other forms of induction of SAR such as the biotic induction with pathogens and treatment with synthetic plant defense activators. In cucumber plants foliar applications of phosphates lead to increased local and systemic acquired resistance against fungal pathogens such as Colletotrichum lagenarium, Sphaerotheca fuliginea and Pseudoperonospora cubensis. In tobacco foliar phosphate application enhanced resistance against TMV. For successful induction of SAR the occurrence of chlorotic/necrotic lesions on the phosphate treated inducer leaves was necessary. These reactions were accompanied by the occurrence of localized cell death, which was preceded by the generation of reactive oxygen species such as superoxide anions and hydrogen peroxide. Enhanced lipid peroxidation was observed in the treated leaves. Local phosphate treatments induced an increase of the concentrations of free and bound salicylic acid in the treated and distal leaves. Experiments with transgenic nahG-tobacco plants showed that the expression of SAR by phosphate treatments and TNV-inoculation was strictly dependent on the accumulation of salicylic acid. The activities of characteristic defense-related enzymes like peroxidases and polyphenoloxidases were highly increased in treated and in the distal leaves, respectively. In this study it could be shown that treatments with necrotizing chemicals such as phosphates cause similar cellular reactions as observed after biotic induction with pathogens which resulted in expression of SAR. Therefore it can be assumed that foliar phosphate treatments imitate the biotic induction of systemic acquired resistance.
Zur Diversität von Galium aparine L.-Herkünften
(2003) Ernst, Vera; Hurle, Karl
G. aparine is known as a very adaptable and worldwide distributed plant species. It is one of the worst weed species in numerous crops causing severe problems. Occasionally, a high degree of variability of G. aparine regarding to morphological and phenological characteristics was reported as well as to its herbicide susceptibility. Because of these observations and the necessity to gain more information about the biology and ecology of this species to perform a successful control of this weed in the field the variability of G. aparine was investigated. In comparative studies 24 field populations of different origins within Europe were used. For some of these populations the history of field management for the last few years was known. Additionally to the field populations one population from a hedgerow and one population of G. spurium has been further characterized. One central aim of these studies was the determination of the susceptibility of the populations against different herbicides. Furthermore the morphology and phenology of the different populations were also characterized. The variability of selected populations was examined by RAPD-PCR, too. The results of herbicide susceptibility tests showed that field populations of G. aparine reacted differently to the various herbicides. The largest differences in susceptibility were observed for the test herbicide, where one population showed a 6,8-fold higher tolerance than the most susceptible population (ED90). Low variability was detected for Mecoprop-P and Cinidon-ethyl, where populations differed at a factor of at most 1,5 and 1,7, respectively. Nearly all populations could be controlled with reduced herbicide concentrations compared to the recommended dosages. No resistant population was observed. Further, no significant differences between field populations and the hedgerow population could be detected. In several experiments the population of G. spurium tended to react slightly more susceptible towards the herbicides than G. aparine. A correlation between herbicide susceptibility and chemical control measures as described in the field history of the few past years could not be observed. The results with the test herbicide and Cinidon-ethyl might be interpreted as natural variability, because the active agents have not been on the market before sampling of the plants. Populations from adjacent fields showed as different susceptibilities as populations from distant fields, so that no regions with populations predominantly expressing significant levels of susceptibility or tolerance could be identified. The morphological and phenological tests showed that all populations differed regarding to many parameters. For most parameters the differences between the populations were in an identical range and persistently the populations differed at a maximum factor of 1,2-1,5. Higher differences than at this scale could be observed for the size of cotyledons, the number of seeds and the seminal yield. For the last parameter the largest differences could be observed with a maximum factor of 2,4 between the population with the smallest and highest seminal yield. Further, some populations showed a stronger habit than others. In a cluster analysis the G. aparine populations were divided into four groups. There was no difference between the field populations and the hedgerow population, but the population of G. spurium was, as expected, clearly different from G. aparine. An analysis of correlation revealed correlations for several parameters. For example, an early beginning of flowering was accompanied by a higher seminal yield. Some characteristics could furthermore be correlated with the geographic origin of the populations. Populations from northern and western locations often tended to have a less stronger habit than populations from the southern regions. Furthermore the onset of flowering was delayed compared to the populations from the more southern regions. The different characteristics could not been explained with the field history of the populations. Certainly the field history as well as climatic and geographic factors may have influenced the different morphology and phenology of the populations. In summary no morphological and phenological differences were detected between more sensitive or less sensitive populations. The results of the RAPD-PCR showed that 17 out of 40 tested primers were suitable to indicate polymorphisms between the different populations. They have been used to calculate the genetic similarity of the populations. The resulting genetic similarity of the G. aparine populations including the hedgerow population was between 93 and 97 %. G. spurium differed clearly from Galium aparine. No correlations could be detected between the results of the molecular and the morphological, phenological and herbicide susceptibility tests.
Unkrautbekämpfung in Zuckerrüben - Ermittlung der Kritischen Periode
(2003) Kobusch, Henner; Hurle, Karl
Early leaf stages of sugar beet are very sensitive to weed competition, which is a major reason for the absence of thresholds for weed control in sugar beet. In combination with non-selective herbicides, the use of herbicide resistant sugar beets appears to allow the control of weeds at a later date than usual applications of common selective herbicides. Therefore, it is necessary to know the critical period, in which the crop should be weed free in order not to loose yield. The influencing factors of the critical period are the moment until weed can be tolerated (beginning of the critical period) and the moment after weed can be tolerated (end of the critical period). The primary objective of the present work was the establishment of a parameter, which would allow a determination of the critical period independent of location and season. Therefore, triannual field trials were carried out at three different sites in the Ukraine and in Stuttgart-Hohenheim in order to evaluate the suitability of different parameters. In addition, by use of a glufosinat resistant sugar beet transformant, the practicability of the critical period was investigated. Application of the critical period and moreover the definition of a general period threshold requires a reference value defining the beginning and end of the critical period which is both independent of location and season. The primary aim of this work was to establish a parameter, which fulfills this condition. All parameters relate to the growth of sugar beet or of the weed quantify their interaction. The following parameters were investigated: the leaf stage of the sugar beet, the weed and sugar beet coverage level, the relative weed coverage, the temperature sum and the intensity of weed shading of the beets. The investigation took place at three separate sites in the Ukraine and in Stuttgart-Hohenheim enabling the effect of different sites to be taken into account. A uniform sugar beet leaf stage until and after weeds could be tolerated was not found. The leaf stage until weeds could be tolerated varied between the 2 and 10 leaf stage. Similarly the leaf stage after which the weeds could be tolerated varied between the 2 and 12 leaf stage of the beet. A uniform and therefore location and year-independent degree of sugar beet coverage and weed coverage relating to leaf stage was not found at the beginning of the critical period at the Hohenheim site (1999 and 2000) and Poltava (1999) in the Ukraine. The degree of weed cover varied at the beginning of the critical period between 96.7% and 66.5% in Hohenheim. The same applies to the degree of sugar beet coverage which varies between 5.3% and 15%. The difference between the two levels of coverage is almost completely compensated by the parameter relative weed coverage. At the Hohenheim site it only varied between 94.8% and 84.5%. The minimum value was found at Poltava with 83.8%. On this basis, a maximum relative weed coverage of 83 % can be tolerated without significant yield loss. Herewith, a decisive parameter is defined as a measure for timing weed control in sugar beets. However, an important requirement is the availability of efficient control methods at this certain point of time. In a further step an attempt was made to apply the critical period in relation to the leaf stage of the beet by using a glufosinate resistant sugar beet transformant. In no trail it could be waited with glufosinate applications until the beginning of the critical period. The latest leaf stage, when glufosinate application had to start in Poltava and Vinnitsa was the 6-leaf stage, whereas the critical period began at the 10- or 12-leaf stage. A limiting factor for the definitive application of the beginning of the critical period was shown in the field trials by a decreasing tolerance of the glufosinate resistant transformant at ever later leaf stages of beet development. Prediction model investigations confirmed this correlation. In addition to the effect of the leaf stage the effect of weather conditions was also apparent. The increase in air humidity from 50 % to 80 % led to an increase in NH3 concentration in the resistant transformant, regardless of its leaf stage. NH3 is found in non-resistant plants due to the inhibition of glutamine-synthetase by glufosinate, which leads to cell death. The largest increase in NH3 when the air humidity was increased from 50 % to 80 % occurred at the youngest leaf at the 6-leaf stage. In addition to the dependency of NH3 concentration on leaf stage the effect of leaf age was also apparent. Concluding, the control of weeds, related to the leaf stage of glufosinate resistant sugar beet, has to be done before the critical period begins. Unfortunately, technologies, which offer the possibility to control weeds by an integration of the critical period, are so far not available.
Prüfung von Citral als Zusatzstoff zu Pheromon zur Bekämpfung des Apfelwicklers Cydia pomonella L. (Lepidoptera, Tortricidae) und des Apfelbaumglasflüglers Synanthedon myopaeformis Borkh. (Lepidoptera, Sesiidae)
(2003) Hapke, Christine; Zebitz, Claus P. W.
In the years 1998 til 2000, a modification of the confusion technique was tested against two pest insects in apple, the Codling moth Cydia pomonella L. and the Apple clearwing Synanthedon myopaeformis Borkh. The respective pheromone was combined with the tentative monoterpene synergist Citral, and applied in the orchard at a density of 125 per hectare as recommended. Laboratory tests were conducted to characterize the effects of Citral mode on individuals of the pests. Field tests with Codling moth revealed no essential differences in the efficiency between the common confusion method with 500 pheromondispensers per hectare and the new technology with Citral (125 dispensers/ha) as expressed in numbers of male caught in pheromone traps or in percent fruit damage under low pest pressure. Both methods failed under high pest pressure. Weighing the dispensers weekly followed up the release of Citral and the pheromone. In semi-field tests in large cages (2 m  2 m  2 m) pest population density seemed to have no impact on control success. In small cages (30 cm height, 30 cm ) the copulation rate in the pheromone plot was significantly lesser than in the Citral-treated atmosphere and in the untreated control plot. Using a laboratory wind tunnel undiluted and 10-1 diluted Citral resulted in a significant decrease of the attractiveness of pheromone. After 24 hours this effect diminished. Half-life of released Citral was approximately two hours. After four hours about 100 µg/h 10-1 diluted Citral was still released into the tunnel. Electroantennogrammes of both, male and female antennae of C. pomonella showed a strong reaction to Citral. The reaction of the antennas to pheromone was strongly overlaid by Citral. In laboratory tests in a closed system, copulation of the moths could be prevented starting from a Citral concentration of 2000 mg/l. Male moths, previously exposed to Citral for 24 h, were not able to copulate with mature, unmated females. Citral-exposed females (24 h exposure time), however, were successfully mated by mature untretaed males. Any impact of Citral in concentrations up to 1,500 mg/l on oviposition could not be proven. Furthermore, first larvae of the Codling moth were not prevented to penetrate into an apple with up to 5,000 mg/l Citral. Field tests with the Apple clearwing proved significantly lesser pheromone trap catches in the Citral-treated plots than in the control plots on five alternatively six test orchards. The plots with 500 and 250 pheromone dispensers per hectare also exerted rates of confusion of up to 100 %. In a plot with 250 Citral dispensers per hectare, an effect of confusion could not be observed. Catches in lure pots showed no difference in the amount of mated or unmated females between plots. The amount of mated females in all plots was much higher than those of the unmated. The amount of fresh frass in treated and untreated plots was too small for proving a success of control. The quantitative preparation of the larvae in coincidentally selected trees on a plant showed a significant difference between the Citral-treated plot and the untreated control plot. However this difference is based only on a reduced number of larvae up to 7 mm body length. Tests with S. myopaeformis in a laboratory wind tunnel were not successful, because the attractiveness of the traps baited with pheromone were not very high. Investigating the environmental conditions for a successful copulation of S. myopaeformis the light intensity did not prove to play the major role. Temperature and wind velocity seem to possess a substantial meaning, dominating light. The copulation rate in small cages (30 cm height, 30 cm ) generally hardly reached 50 % and was very small thereby. In the laboratory moths of the apple clearwing could not be brought to copulation. Synergisation of pheromones with Citral seem to be not recommendable under practical conditions.
Vermehrungs- und Schadpotential der Grünen Gurkenlaus (Aphis gossypii Glover) an Gewächshausgurke (Cucumis sativus L.)
(2003) Bünger, Isa Brigitte Annemarie; Zebitz, Claus P. W.
The aim of this work was to collect basic data for the development of a model which could simulate the injury of greenhouse cucumbers caused by Aphis gossypii G.. This work mainly deals with two aspects: first it is the population dynamics of A. gossypii influenced by infestation density (initial infestation 2-10 individuals per plant) and host plant quality (age) and second it is the quantitative and qualitative assessment of damage by investigation of growth, yield, and chemical composition of the cucumber plants. The investigation took place under controlled, semicontrolld and practical conditions.
Bromus-Arten in Winterweizen: Verbreitung, Bedeutung und Populationsdynamik
(2005) Moray, Ralph; Hurle, Karl
The increase of reduced tillage in agriculture and winter cereal dominated crop rotations has lead to a rise of annual and perennial grass weeds in the last decades. One of these are Bromus species that occur worldwide in cereal growing areas. In Germany they also attract more and more interest because of their increasing distribution. Therefore an inves-tigation was conducted to assess the current situation of Bromus species in Germany, competition, population biology and control. Additionally, control strategies were designed on the basis of analyses of population-dynamical parameters. A survey carried out in Germany, showed that Bromus sterilis and B. secalinus were found to be the dominant species. The problems that were predominantly mentioned were yield loss and difficulties at harvest which mostly appear in winter wheat. Their occurrence is closely connected with reduced tillage, early seeding and winter cereal dominated crop rotations whereas Bromus densities can be reduced effectively with a mouldboard plough or the increase of spring crops in crop rotation. In dicot. crops the chemical control was regarded as very good, whereas in cereals between good to sufficient. All of the survey participants expected a further distribution of Bromus species on arable land. Field trials were conducted on three locations over a period of three years to investigate the competition of B. sterilis, B. secalinus, B. tectorum and B. japonicus in winter wheat. Weed density and seeding date of winter wheat were considered for the species competition studies. The trials showed that distinct yield losses could be recorded in winter wheat depending on the different Bromus species. Thresholds where calculated based on the relationship between weed density and yield loss. The thresholds for the Bromus species in winter wheat were below the values given in literature for other grass weeds in winter cereals. This highlights the strong competitiveness of the species. Additionally the results showed that with late seeding the weed density decreases distinctively and thereby the yield loss can be reduced by half. Greenhouse trials on the efficiency of the three in Germany registered herbicides for the control of Bromus species showed, that a sufficient control of B. sterilis and B. secalinus could not always be achieved with the recommended dose. The simulation of the population dynamics showed clearly that with reduced tillage and direct seeding in a winter wheat monoculture without control measures a very fast increase of densities within two growing seasons up to a density-dependent level where high yield losses can be expected. In contrast mouldboard ploughing can control the species to 100 % as a depth of seeds of 10 cm already reduces emergence by half and seeds in the trials showed to have longevity in soil of no longer that 12 months. Moreover, it was demonstrated that the soil cultivation has a higher influence on the development of the weed population than the different seeding dates of winter wheat. The simulation under the influ-ence of herbicide application suggested, that it is possible to practice a winter cereal dominated crop rotation without yield losses. From the results of the investigations it can be concluded that Bromus as a problem in win-ter cereal dominated crop rotation in our latitudes will increase. In fact the control with available herbicides is not always sufficient, but for economical reasons integrated control strategies can not always be considered although quite a good control is given. Therefore one can presume that in future the control of Bromus in winter cereals still will be based on the use of herbicides and that these weed species will be as common in win-ter cereals as it became Alopecurus myosuroides and Apera spica-venti.
Molecular systematics of selected Diadegma species (Hymenoptera: Ichneumonidae: Campoplegine) important in biological control
(2006) Wagener, Barbara; Zebitz, Claus P. W.
The genus Diadegma (Hymenoptera: Ichneumonidae: Campopleginae) represents a large group of parasitoids with 201 species worldwide. Adult Diadegma females parasitise larvae of various lepidopteran species and some species, in particular Diadegma insulare (Cresson) and D. semiclausum (Hellén), have gained economic importance as biological control agents of Plutella xylostella (Linnaeus). A low parasitism rate of <15 % of the parasitoid complex (Diadegma sp., Oomyces sokolowskii (Kurdjumov) and Diaplazon laetatorius (Fabricius)) in unsprayed cabbage and kale fields infested with P. xylostella in eastern and southern Africa was the starting point for the development of a biological control project for P. xylostella which was implemented by the International Centre of Insect Physiology and Ecology (ICIPE), Kenya. One of the objectives of the biocontrol project was to examine the taxonomic status of Diadegma species associated with P. xylostella in eastern and southern Africa and the exotic parasitoid D. semiclausum imported to Kenya from Taiwan (Asian Vegetable Research and Development Centre, AVRDC) by cross breeding experiments and molecular methods. Thus, two different molecular regions, a fragment of the mitochondrial cytochrome c oxidase subunit (COI) and the second internal transcribed spacer (ITS2) of ribosomal DNA were amplified utilising polymerase chain reaction (PCR) and digested afterwards with several restriction enzymes (PCR-Restriction Fragment Length Polymorphism-RFLP). In the due course of the study examinations of several Diadegma species attacking P. xylostella were undertaken with the PCR-RFLP method developed previously for the African Diadegma. This molecular method could solve some taxonomic difficulties of the genus Diadegma. Sequence analyses were used to investigate the phylogenetic relationship of nine Diadegma species (D. blackburni (Cameron), D. insulare, D. leontiniae (Brèthes), D. chrysostictos (Gmelin), D. armillata (Gravenhorst), D. fenestrale (Holmgren), D. mollipla (Holmgren), D. semiclausum, D. rapi (Cameron)) and the phylogenetic relationship of the genus Diadegma within the superfamily Ichneumonoidea. Cross breeding experiments were carried out between two populations of D. mollipla from eastern and southern Africa. No significant differences in the total number of progeny per female and the number of male offspring were obtained, whereas the female progeny showed significant differences. Hybrid females resulting from both reciprocal crosses were reproductively compatible with males of both parental lines, which indicated that no genetic incompatibility was apparent between the two D. mollipla populations. In contrast, crosses between D. mollipla and D. semiclausum resulted only in the occurrence of male offspring, which is typical for unfertilised progeny in Diadegma. The laboratory cultures of D. mollipla and D. semiclausum were highly male biased. Inbreeding, where homozygosity is much higher, is leading to a higher diploid male production. Diploid males can easily be detected by isoenzyme variations as a genetic marker. Heterozygote females/males of D. semiclausum and D. mollipla were identified by phosphoglucomutase (PGM) electrophoretic banding patterns. Crosses between a mother (heterozygote, diploid) and her son (homozygote, haploid) resulted in one diploid male in D. mollipla and none in D. semiclausum. Information about diploid males in D. semiclausum detected with PGM has already been published and different methodologies might be the reason why in D. semiclausum no diploid male was detected. Therefore the present analyses with PGM as molecular marker should be seen as a preliminary study.
Untersuchungen zur Bedeutung und Lebensweise phytophager Thripse (Insecta, Thysanoptera) als Verursacher von Austriebsstörungen an Reben als Grundlage zur Entwicklung umweltschonender Bekämpfungskonzepte
(2006) Wipfler, Rosi; Zebitz, Claus P. W.
Aim of this study was to gain basic knowledge of the biology of thrips pest species on grapevine. The results should provide the basics to develop environmentally compatible protection strategies. From 2002 to 2004, a monitoring of thrips infested vineyards was done in the vine growing region Palatinate. Thrips population dynamics and level of infestation were investigated in different newly planted vineyards and nurseries, as well as the damage caused by thrips. To answer the question, how and where thrips hibernate in vineyards, different collection techniques were tested to detect thrips in the soil and underneath the bark of vines. During the vegetation period, the flight activity of thrips was monitored in different vineyards and nurseries. Thrips species of vineyards, surrounding crops and shrubberies were compared to reveal possible ways of infestation by thrips on grapevine. Different insecticides were tested to control adult thrips and larvae in the field. Considering the collected thrips species, most striking result was the dominant abundance of the onion thrips, Thrips tabaci Lindeman, which caused most of the damage. The expected grapvine thrips Drepanothrips reuteri Uzel was of minor importance. Preferences for different grapevine varieties could not be found. Infestation mainly appeared in nurseries and newly planted vineyards. 30 different thrips species could be detected on grapevine. The results on level of infestation and phenology corresponded mostly with the literature data on D. reuteri. In the investigated vineyards, infestation was only detected in spring. In three years of investigation, infestation rates decreased from the middle of June onwards. The reason was mainly a migration of the polyphagous T. tabaci to other host plants. The detailed description and documentation of thrips infestation symptoms resulted in additions to already known symptoms. It was also possible to make further differentiations to infestation symptoms not caused by thrips. During the investigations it could be proved that different thrips species overwinter underneath the bark of vines and in the soil of vineyards. Therefore, thrips can rapidly infest vines in the following spring. Field experiments with yellow water traps showed that airborne adult thrips and thrips that actively migrate from surrounding crops are of major importance for the infestation of grapevines. Nurseries showed an increased risk of infestation, because they are usually located outside the grapevine areas and are surrounded by other crops. In this study it was not possible to gain any hint that thrips are transferred by grafted vine cuttings. The influence of shrubberies on thrips species in vineyards was of minor importance but needs further studying. It would also be of interest to investigate the influence of different culture techniques on the level of infestation and the phenology of thrips in vineyards. The insecticidal compounds spinosad, abamectin and imidacloprid proved to be effective to control thrips in the field. For newly planted vineyards, two treatments are recommended in spring: first against adult thrips at the beginning of May, and the second against the hatched larvae 14 to 21 days later. Treatment is necessary at levels of infestation of more than one thrips per shoot at the grapevine developmental stage BBCH 09 to 13, and with more than one thrips per leave at BBCH 14 to 17, respectively. Preventive treatment is recommended 1. for newly planted nurseries, if there is an increased risk of infestation because of surrounding crops with detected thrips infestation, and 2. at the beginning of budding for newly planted vineyards and one year old vineyards, especially if there was thrips infestation in the previous year and if predatory mites are absent. Control experiments in the laboratory could not be done, because it was not possible to establish a thrips colony to supply enough thrips material. The results of this study contributed to the approval of the compounds imidacloprid and abamectin for minor uses to control thrips on grapevine in 2006.
Teilschlagspezifische Unkrautbekämpfung durch raumbezogene Bildverarbeitung im Offline- und (Online-) Verfahren (TURBO)
(2006) Oebel, Horst; Gerhards, Roland
Georeferenced application maps (TURBO) is presented. The system was applied and analysed on agricultural fields from 2004 to 2005. The results can be summarized as followed: For online image acquisition bi-spectral cameras were developed which took homogeneous grey scale pictures with a strong contrast using a combination of two spectral channels in the near infrared and the visible spectrum. Three bi-spectral cameras were mounted in front of a prototype carrier vehicle. Using an automatic control of the exposure time, well focused pictures of weeds in cereals, maize, sugar beets, peas and oil seed rape were taken at a speed up to 10 km/h and stored together with their GPS coordinates. Under changing light conditions, bi-spectral images were free of faults. Stones, mulch and soil were not illustrated. The picture quality showed a clear improvement compared to current image analysis technologies using colour and infrared cameras in plant production. The geometric resolution of the cameras was sufficient for creating application maps. With a size of 0.014 m² per picture weed seedlings were representatively assessed. The dense grid of 3.500 sampling points per hectare allowed an efficient detection of weed distribution within agricultural fields. The procedure of shape analysis allowed precise identification of weed species in a speed of 20 images per second. The classification rate of unclassified plants using Fuzzy Logic or the principle of minimum distance was between 73 % (malt barley) and 85 % (oil seed rape). The calculation of discrimination functions to separate crops and weed classes by shape parameters allowed a better classification of unknown plants and increased the classification rate to 88.4 % (sugar beets) and 94 % (malt barley). Characteristic shape features of 45 weed species in the growth stages BBCH 10 to BBCH 14 were stored in a database and the classification of weed species in malt barley, maize and sugar beets was studied using discrimination analysis. In growth stage BBCH 10 weed species could be differentiated on average by 70 %. Crops were accurately differentiated from broadleaved weeds and grass weeds. Joining weeds species (BBCH 10) in the classes broadleaved weed species, grass weeds, Galium aparine and crop resulted in correct classification of 83 % in malt barley to 96 % in maize. With manual, GIS-based and image analysis sampling methods treatment maps for three weed species classes were created for site-specific weed control in cereals, sugar beet, maize, oil seed rape and peas on a total of 138 ha. Economic weed threshold were used as a decision rule for chemical weed control. Herbicides were only applied when the economic weed threshold was exceeded. Above the economic weed threshold the herbicide dosage was varied from 70 % to 100 % depending on the density of weed species. Herbicide application was performed with a newly developed multiple sprayer. The sprayer integrates three conventional sprayers on one machine including three separated hydraulic circuits, boom section control (3 m), dGPS for real time location and a central control unit. During application the on-board computer loading a georeferenced application maps was linked to the spray control system for precise application of up to three different herbicide mixtures. Herbicide savings using site-specific weed control depended on the cultivated crop, weed species composition and weed infestation levels. On average 47 % of herbicides for grass weeds and 35 % for broad-leaved weeds were saved. Herbicide use to control Galium aparine and Cirsium arvense was reduced by 71 %. The efficacy of site-specific weed control was documented by manual weed sampling before and after post emergent herbicide treatments. It ranged from 71.8 % to 98.8 %. Weed infestation level did not increase in the following crops. First results with yield mapping of experimental fields revealed that site-specific weed control did not cause yield reduction. On contrary, in cereals higher yields were observed at locations where no herbicides were applied. However, further studies are needed to prove this hypothesis. The economic evaluation of site-specific weed control over two years on practical farm sites showed that site-specific weed control was profitable. The average savings for herbicides were 27.61 ?/ha. This resulted in an average profit of 11.35 ?/ha using the system for site-specific weed control.
The host parasite relation of the parasitic mite Varroa destructor (Anderson and Trueman) and the honeybee races A. m. syriaca (Skorikov) and A. m. carnica (Pollmann) in Jordan.
(2006) Al-Attal, Yehya Zaki Khalid; Zebitz, Claus P. W.
Since the honeybee mite Varroa destructor (Anderson and Trueman) succeeded to parasitize the Western honeybee Apis mellifera L. and accept this species as a new host it became the most serious threat to Apiculture worldwide. The very few stable relations between Varroa mites and the new host are either associated with honeybees of African origin, or with tropical and sub-tropical climates. This balanced relations seems to be due to reduced fertility of the female mites in worker brood cells, a shorter post-capping period of the worker brood and a set of highly differentiated active defense traits of the host bees. In this work I investigated several aspects of the host parasite relation between the honeybee and the Varroa mites in Jordan. The endemic honeybee race of Jordan is A. m. syriaca Skorikov, which join African and European bee traits. The Jordanian beekeepers use this ?local? bee as well as its hybrids with imported European bees. Therefore, Jordan provides the possibility to prove the influence of different honeybee races and different climatic conditions on this host-parasite system. For a better direct comparison, I evaluated the host-parasite relation of two honeybee races at the same study site: the ?local? honeybee (A. m. syriaca) and the imported ?carnica? honeybee (A.m. carnica Pollmann), which is susceptible to Varroa infestation under Central Europe conditions.To assess the current status of Varroa mite in Jordan, we surveyed the infestation rates of in capped brood cells and on adult worker bees in 180 honeybee colonies at six locations. All colonies were kept untreated for at least 8 month. The results revealed high infestation rates, which exceed, in part, the thresholds for colony damages. No significant differences between honeybee races or climatic condition were visible. The population dynamics of the host and its parasite represents the most important parameter of the honeybee-Varroa relation and was described in the ?local? and the ?carnica? (imported from Hohenheim) honeybees at Baqa (dry Mediterranean climate) and Yadodeh (wet Mediterranean climate) for a one-year period. In all colonies the number of adult bees and brood cells were evaluated every three weeks by the ?Liebefeld? method. During all evaluations, samples of adult bees and capped brood of all colonies were analyzed to determine Varroa infestation rates. The population dynamics of the honeybee colonies revealed a significantly higher population density of the ?local? honeybee race compared to the ?carnica? colonies. The average number of adult worker bees was 8,368 ± 2,724 in the ?local? colonies and 6,447 ± 2,338 in the ?carnica? colonies, while the average number of capped worker brood cells was 9,164 ± 3,336 in the ?local? and 7,628 ± 3,166 in the ?carnica? colonies. Compared to colonies in Central Europe, my results indicate a surprisingly shorter life span of adult worker bees. The corresponding population dynamics of Varroa mites revealed an exponential growth phase till the maximum infestation and a decreasing phase until the beginning of the next season. The maximum Varroa population density ranged between 2,614 ± 2,190 mites in the ?carnica? colonies and 4,397 ± 2,746 mites in the ?local? colonies. Using an exponential function, growth rate = eb, the average exponential growth rate of Varroa population per three weeks interval ranged between 1.33 and 1.46 and was significantly different between both locations. The subsequent decrease in the mite population was two folds higher than the decrease in the effective bee population (adult bees plus capped worker brood cells together). Therefore, a higher mortality rate of the parasites or its host activity must contribute to the observed drastic decrease of the Varroa population. No significant race-specific differences in the infestation rates could be observed. However, the mortality rate was higher in the ?carnica? colonies (? 40%) compared the local colonies (? 10%). This indicates a general higher fitness of the ?local? colonies independent from Varroa infestation rates. As a threshold for the survival of honeybee colonies, maximum infestation rates of 20% in adult worker bees and 40% in capped worker brood were determined. The evaluated resistance mechanisms, which are considered to contribute to stable host-parasite relations, did not reveal any pre-adaptation of the ?local? honeybee to Varroa mite. Neither in the fertility of female mites nor in the reproductive rate significant differences between the local and the ?carnica? honey bee race could be detected. The post-capping period of the worker brood was nearly the same in both bee races and it corresponds to data from Central Europe. Also no significant difference could be revealed in the daily mite mortality between both races, which ranged between 0.8% and 1.5% of the total mite population in the colonies. Nevertheless, in few individual ?local? colonies, the mite mortality comprises a surprisingly high percentage of the total estimated number of the phoretic mites within the colonies. By RFLP of the CO-I unit, only the V. destructor Korean haplotype was detected in all examined mite samples from Jordan. Additionally, mite genotyping based on the sequences of two genetic markers shows very low genetic variability among different mite populations, which confirm recent publications and makes the hypothesis that differences in mite virulence could be responsible for a stable host parasite relationship, less probable. Conclusions ? The ?local? honeybee of Jordan is not more resistant to Varrosis compared to the susceptible European honeybee races. ? The Mediterranean climate has no significant inhibition effect on Varroa population dynamics. ? Varroa infested ?local? honey bee colonies revealed a significant higher survival rate than imported ?carnica? colonies under the same conditions. ? Variation in the mite infectivity between different V. destructor population is less probable.
Development of alternative strategies for the control of the important phytopathogens Phytophthora infestans (Mont.) and Erwinia amylovora (Burrill)
(2007) Swaidat, Ihsan; Buchenauer, Heinrich
Within the framework of two projects, financed by DBU (Deutsche Bundesstiftung Umwelt) and ProInno ("Förderung der Erhöhung der Innovationskompetenz mittelständischer Unternehmen"), respectively, in co-operation with an industrial partner, alternative phytosanitary compounds from natural sources have been screened. High throughput screening systems were developed and used for testing of large numbers of extracts of Actinomycetes in 96-well multiplates against Phytophthora infestans and Erwinia amylovora, the causal agents of tomato late blight and apple fire blight, respectively. These important phytopathogens were chosen as models. According to the Pflanzenschutzgesetz (PflSchG) §2 Nr. 10a, plant strengthening compounds (Pflanzenstärkungsmittel) should not act directly against the pathogen, but via an induction of plant resistance mechanisms. Therefore, one of the projects (DBU) aimed to exclude direct action on P. infestans. Based on the GFP-fluorescence of the P. infestans transformant 208m2, a fluorescence optical measurement of mycelium growth respectively growth inhibition was developed, to test the influence of the extracts and extract fractions. Only 52 out of 8335 extracts significantly inhibited the mycelium growth (Pi+) in this test, and thus had to be excluded according to §2 Nr.10a PflSchG for a potential commercial application. Searching for resistance inducing activity, all extracts were re-tested in parsley cell culture as a model for putative resistance induction characterised by formation of furanocoumarin phytoalexins. Only 42 out of the whole set of extracts tested, induced furanocoumarins (Pc+) significantly. In order to test if the induction correlates with a successful defence of host tissue against P. infestans, detached tomato leaves were treated with these Pc+ extracts. Only one extract resulted in formation of small sharp necrosis symptoms after pathogen inoculation, leading to strongly reduced infection and inhibited sporulation. The identification of the active ingredient is currently performed. When comparing the 52 direct acting substances (Pi+) with the potentially resistance inducing compounds (Pc+), three were also found actively inhibiting P. infestans in the host tissue. These three extracts also induced limited dark brown necrosis, suggesting an induction of hypersensitive reaction (HR). Infection area and sporulation level were reduced to levels below 25% of total leaf area. Microscopic investigations showed non-germinated or abnormally shaped germinated sporangia. Promising extracts were fractionated by the cooperation partner. Fraction 1 of one Pi+-extract (014 008-2) reduced the sporulation level and the size of the infection area to 5 and 25%, respectively, compared to the control. Application of fraction 2, although less effective than fraction 1, produced sporangiophores that were morphologically abnormal carrying no sporangia, indicating a possible highly specific action on a certain developmental step of the pathogen. In case of the extracts tested in vitro against E. amylovora, only 60 out of 5236 extracts inhibited bacterial growth. Only extracts showing a similar effect as the streptomycin positive control (12 extracts), were also tested in the cell culture of parsley for a potential resistance induction. The effect of such promising extract (000 391 CF) was compared in in vitro apple plantlets with two purified substances identified in the in vitro growth inhibition screening (tubercidin and streptothricin) and two commercially available resistance inducers (Prohexadion-Calcium, Bion®) in addition to streptomycin as control. Streptothricin was found nearly as effective as the streptomycin control (2 and 0% diseased shoots, respectively). 000 391 CF with chuanghsinmycin as active ingredient in unknown concentration, however, was less effective together with tubercidin; both compounds were originally classified effective in the in vitro screening (approximately 20 and 30%, respectively). The resistance inducers showed a maximal effectiveness of 20-25% approximately; however, in the highest concentration applied, they caused phytotoxic effects. As an alternative strategy of plant defence, an experiment was performed to silence the GFP-fluorescence of transformant 208m2 as a model for silencing fungal genes responsible for plant infection via the transgenic host. Two types of ?T0? transgenic tomato plants were produced from ?Hellfrucht? cultivar, one carrying the gfp-gene and the other carrying inverted repeat fragment of the gfp-gene (gpg). GFP-expressing plants could be identified by their green fluorescence under UV-A light. gpg-transformants were verified by PCR analysis of their genomic DNA and the formation of siRNAs by Northern blotting. In order to test the silencing effects in the plants Agrobacteria harbouring the gfp-gene or gpg-construct in a binary vector were infiltrated into tomato leaves. Leaves of agro-infiltrated (gfp) wild type plants were found to fluoresce, but no green fluorescence appeared when gpg-tomato leaves were infiltrated, due to the production of siRNAs resulting in gene silencing. The green fluorescence of gfp-tomato leaves disappeared gradually starting from the major vein expanding to small veins after infiltration of gpg-Agrobacteria due to the same phenomenon. However, no systemic silencing over the whole plant was observed; this may be due to the comparatively low expression of the gfp-gene in the?T0? plants used. However, the GFP in the P. infestans transformant 208m2 was not found to be silenced when leaves of gpg-plants were infected; this might be due to unsuccessful passing of siRNAs through haustorium?s membrane system, or due to the comparatively low amount of siRNAs in the gpg-tomato tissues.
Evaluation of weed populations under the influence of site-specific weed control to derive decision rules for a sustainable weed management
(2008) Ritter, Carina; Gerhards, Roland
In context of reduction programs for chemical plant protection, herbicide use needs to be strictly controlled and reduced to the absolute necessary extent in order to minimise negative side effects for the environment and pesticide residues in the food chain. The site specific weed management is a promising way to reduce herbicide use. It aims at managing weeds with respects to their spatial and temporal variability. Post-emergence herbicides are only applied at highly infested locations in the fields. Several studies on site-specific weed control have shown that this practice is reasonable, and it has been successfully implemented in various crops, resulting in a considerable reduction of herbicide use, treatment costs, and consequently benefits to the environment. However, there is still lack of knowledge on the population dynamics of weeds and the interactions between crop and weeds under the site-specific weed management. Long term effects of the site-specific weed control have not been studied in detail yet. Additionally, an experimental approach was needed to create precise decision algorithms for site-specific weed management. Therefore the applied scientific objective of this research was: - to analyse the spatial and temporal distribution of weeds, - to provide information on weed population dynamics under the influence of the site-specific weed control, - to detect if site-specific weed management leads to an increase in weed density, and if weed patches remain stable in density and location over time, - to determine herbicide savings and efficacy of the site specific weed management, - to design an experimental on-farm approach to explain yield variation caused by within-field heterogeneity of weed density, soil quality and herbicide application, in order to derive decision rules for site-specific weed control. During the course of this work site specific weed management tested in field trails, long term effects were examined, population dynamics were analysed and a model approach to derive management decision was approved. It was proved that weed distribution was heterogeneous in all experimental fields. The average weed density remained stable when economical weed thresholds were applied. The application of effective herbicides in every year did not reduce density in high density weed patches. The patches were persistent over eight years, with slight variations in density from year to year. It is suggested that a combination of chemical, mechanical, and cultural weed management strategies would be necessary to effectively control weeds in high density locations. However, the knowledge about the spatial stability of weed patches of individual species offers possibilities to use this information for weed management strategies. Population dynamic parameters such as weed seedling emergence, crop-weed competition, seedlings mortality, herbicide efficacy, seed production and viability were found to be weed density dependent. With increasing weed density weed biomass and fecundity increased. These findings support that weed density has to be considered in weed management strategies. Site-specific weed management was effective over time. The amount of herbicides used could be decreased significantly due to site specific herbicide application, without loosing performance. Only 26-35 % of herbicides were sprayed compared to uniform application of herbicides that is still the standard method of weed control. Additionally, a new experimental design based on an anisotropic exponential model with nugget effect was established. The influences of the co-variables weed and soil on yield and the side-effects of herbicides were quantified separately with this model, by overlaying and spatially joining all data. Out of this information, yield losses due to weed and herbicide injury could be defined, and valid decision rules for site-specific weed management could be ascertained. For the first time the injury to the crop due to herbicide application could be numeralised with this experimental design. This large loss of yield can be avoided and considerable reductions in herbicide rates can be achieved by site-specific weed management based on weed thresholds. This experimental approach enables to explain the variation of yield within agricultural fields, and an understanding of the effects on yield of the factors and their causal interactions. This work is seen as a mayor step forward in order to precisely manage weeds with respect to their spatial and temporal dynamics.
Untersuchungen zur Grünfäule (Penicillium spec.) an Weintrauben
(2008) Walter, Ruth; Buchenauer, Heinrich
Since the end of the 90th increasing problems with the occurrence of secondary bunch rot pathogens could be observed in German vine growing regions. Thereby blue mould, caused by Penicillium species, plays a mayor role. Already small amounts of infected bunches can lead to economical losses by off-flavors in the wine, so that infected bunches have to be discarded before harvest. Only little was known about the pathogen on grapes. So questions about the causing species in German vineyards, the biology and epidemiology, the impact of cultivation methods on disease development, the competition with Botrytis cinerea and possible preventing strategies were investigated.
Characterization of mechanisms of resistance to common insecticides in noctuid pest species and resistance risk assessment for the new lepidopteran specific compound flubendiamide
(2009) Konanz, Stefanie; Zebitz, Claus P. W.
Noctuid species, such as the beet armyworm Spodoptera exigua, the cotton bollworm Helicoverpa armigera and the tobacco budworm Heliothis virescens, are well-known pests in many agricultural cropping systems worldwide. The extensive and widespread use of insecticides against these species has led to the development of resistance against almost all commercially used compounds. The focus of this thesis was on the novel lepidopteran specific compound flubendiamde, to get a detailed overview about the efficacy using different kinds of bioassays for a resistance risk assessment. On the other hand, the underlying possible resistance mechanisms of a S. exigua strain from southern Spain was investigated on the toxicological, biochemical, pharmacokinetic and molecular level. The basic of all further experiments was two bioassay techniques, a leaf-disc spray application and an artificial diet bioassay, on 2nd instar larvae. Flubendiamide and 11 competitors with different mode of actions were tested on three susceptible laboratory strains (HELI-AR, HELI-VI, SPOD-EX S) and one field strain from Spain (SPOD-EX E-98). The aim was to get baseline susceptibilities of the three noctuid species and additionally the resistance profile of strain SPOD-EX E-98 against the different insecticides. The results of the two bioassay techniques were comparable with each other, emamectin shown the highest efficacy followed by low EC50-values for flubendiamide, deltamethrin and indoxacarb. The robust artificial diet bioassay was used for a worldwide resistance monitoring for flubendiamide, and resulting in a mean efficacy of 93% in 18 test populations. An interesting cross-resistance pattern against insecticides with different mode of actions demonstrated the S. exigua strain SPOD-EX E-98, and can be called as ?multi-resistant?. High resistance to three classes of insecticides, pyrethroids, benzoylphenyl ureas and carbamates/organophosphates, was detected in this strain, also moderate resistance levels to endosulfan and indoxacarb. The in vivo application study with the synergist PBO (monooxygenase inhibitor) has shown an additionally participation of this enzyme system towards the deltamethrin resistance in this strain. Additionally, PBO and two esterase inhibitors had no effect to the resistance level of triflumuron (benzoylphenyl urea) and so target-site resistance is likely in this case. Using molecular biological methods, a point mutation (kdr) in the voltage-gated sodium channel of the resistant strain SPOD-EX E-98 was detected, this channel is the target of the pyrethroids. This target-site resistance is particularly responsible for the extremely high resistance factor (~900) of the pyrethroid deltamethrin detected in the bioassays. In order to investigate the pharmacokinetic profiles of deltamethrin, triflumuron and flubendiamide in S. exigua larvae radiolabelled compounds were used. No differences in penetration or excretion of the compounds were observed between the two strains. This suggests that physiological changes have not influence as a possible mechanism of deltamethrin and triflumuron resistance. Four biochemical markers, carboxylesterases (CEs), cytochrome P450-dependent monooxygenases (monooxygenases), glutathione S-transferases (GSTs) and acetylcholinesterases (AChEs), were investigated in both S. exigua strains. These enzyme systems are known to be linked with metabolic detoxification/resistance to diverse insecticides. With the exception of GST, in the multi-resistant SPOD-EX E-98 strain was found significantly higher enzyme activities to the other three marker enzymes. The higher CE activity in the multi-resistant strain SPOD-EX E-98 was further investigated, using an nPAGE to obtaining the iso-enzyme banding patterns of both strains. In comparison, the strain SPOD-EX E-98 exhibited an additional thick band and it was not possible to inhibiting this band in vitro through the esterase inhibitor DEF. It is possible that this result is involved in resistance, but only further investigations could be clarify the exact role of the additional band in this resistant strain. The AChE of both S. exigua strains was used for in vitro inhibition studies. The resistant strain SPOD-EX E-98 was insensitive against several organophosphates and carbamates compared with strain SPOD-EX S. Only one exception was detected, the AChE of the resistant strain was more sensible to carbofuran than the enzyme from strain SPOD-EX S. This phenomenon of ?negative cross-insensitivity? is generally correlated with an altered substrate binding site of the AChE. Further investigations of kinetic parameters exhibited a higher turnover of the substrate in strain SPOD-EX E-98. The bioassays confirmed these results and so the resistance mechanism of the two chemical classes is an altered AChE in the resistant strain.
Investigations on herbicide resistant grass weeds
(2009) Balgheim, Natalie; Balgheim, Natalie
Weeds are one of the most troublesome threats for farmers, causing high yield losses and serving as hosts for pathogens and insect pests. Since the introduction of chemical weed control agricultural production systems have changed. During the last years the number of herbicide resistant grass weeds is steadily increasing especially in cereal monocultures. These monocultures are characterised by the repeated use of herbicides with the same modes of action and minimum-tillage practices. All these factors can one by one or all together lead to the development of herbicide resistant grass weeds. In general herbicide resistance is the result of heritable changes to biochemical processes that enable plant survival when treated with herbicides. Two different mechanisms are commonly known to confer resistance: target-site resistance and non-target-site resistance. First is the result of an altered target enzyme, where a single point mutation is changing the amino acid structure and exclude herbicide from effectively binding to the target enzyme. The second one, non-target-site resistance, can be summarised as the mechanisms which includes all other mechanisms than target-site resistance, for example rapid metabolic degradation or translocation of herbicides. In Germany, the most trouble causing weeds associated with target-site resistance are the grass weeds Alopecurus myosuroides Huds. and A. spica-venti L. Beauv.. All investigations carried out during this thesis are dealing with those two weed species. Therefore the main objectives of this thesis are the following: To characterise the resistance levels and patterns of both species. To identify the underlying resistance mechanisms. To develop molecular markers for rapid detection of target-site based resistance. To get an idea of the spatial and temporal distribution of herbicide resistant grass weeds in arable fields. Both investigated species are highly adapted to cereals and developed resistance against ACCase and ALS inhibiting herbicides. So they are an increasing problem for German farmers and in consideration of the fact, that both weeds have developed multiple resistances, detecting and management strategies for controlling and preventing of these weeds are absolutely necessary. Carried out dose response relationships proved strong resistance of the A. myosuroides biotype BR(R) against cycloxydim and fenoxaprop, where low resistance was expressed against clethodim. However, biotype BL(R) showed resistance to fenoxaprop and clodinafop only. Dose response experiments carried out with the A. spica-venti biotype showed resistance to sulfosulfuron and iodo-/mesosulfuron. No cross resistances could be detected in both species. The carried out DNA analysis revealed target-site resistance as the underlying resistance mechanism. BR(R) and BL(R) showed well known substitutions: an amino acid change on position 1781 with in the CT domain result in a change of Leu to Ile which confers resistance to APPs and CHDs in the biotype BR(R). The mutation of Gly to Ala on position 2096 within the CT domain causes resistance to APPs only. Also in the A. spica-venti biotype a amino acid change is the responsible resistance mechanism: a change of Pro to Thr at position 197. These sequencing results serve as basis for the development molecular markers. Designed markers based on dCAPS technology. Such markers were developed to detect SNPs which can cause amino acid changes on the constitutive enzymes. Developed markers can rather differentiate between heterozygous and homozygous resistant alleles. Their technology is based on the fact that restriction endonucleases can cut DNA strands on specific recognition sites. This fact can be used for developing markers which are cutting the DNA in a previously generated PCR fragment on the mutation or wild-type sites, respectively. If there is no recognition site, it can be implemented by specific primers during the PCR. By these markers suspicious samples can be analysed and the results give an advice for management strategies, because target- and non-target-site resistance need different controlling strategies. Investigations on the spatial and temporal distribution of weed populations where carried out on an arable field, invested with herbicide resistant A. myosuroides. Collected and analysed leave samples give information about the spatial dynamics of homozygous, heterozygous and sensitive plants in the field. Results show that the distribution of resistant plants depends on the weed density. Besides the weeds are distributed heterogeneous on the field and occur in patches that are persistent over several years. This example revealed that herbicide resistance is rather associated with crop cultivation measurements. Changes in herbicidal and cultivation measurements shall be practiced to control and to prevent the occurrence of herbicide resistant grass weeds.
Modeling population dynamics and dispersion of Codling moth Cydia pomonella L. (Lepidoptera, Tortricidae)
(2009) Gharehkhani, Gholamhossein; Zebitz, Claus P. W.
The study of insect dispersal plays an essential role in estimating the spread of damage caused by a newly invaded pest or the spatial distribution of an insect during the active period in growing season. Moreover concerning dispersal, quantitative information performs a crucial role in the evaluation and implementation of pest control. Since rearing clean and healthy insects in sufficient numbers is the most important prerequisite for many basic research programs and for developing pest control strategies, mass rearing of the Codling moth on the artificial diet carried out as the first step at optimum conditions. With regard to the fundamental function of feeding and pre-releasing handling on insect biological attributes, we intended to evaluate the individual marking influence on longevity of Codling moths in the next step. For this purpose, one day old adult male and female moths were kept three and five minutes at -20°C to make them motionless, then immediately marked individually with felt tip pens and coded by the different colors, maintained under optimum condition and checked daily for 13 days. The proposed linear model accounted for 89 % of the variations. Numbing and marking process influenced of the moths longevity regardless of their sex while the duration of the anesthetize does not affect the survival of moths meaningfully. Regarding the obstacles associated with egg and pupa storage of Codling moth, we examined the possibility of adult moth?s storage in low temperature in order to evaluate its eﬀect on longevity of moths. Adult 12-24 h old male and female moths were treated separately and maintained in 4 ◦C and (0:24 h, L:D) photoperiod during the entire adult life. The survival rate evaluated with two days interval throughout 27 days. The effects of day and treatment were significant. It seems that the female moths tolerate the cold condition better and further than the male moths and live longer. Additionally the proposed models accounted for 71 % and 57 % of the variations for male and females respectively as verified more affection and debility of the males by the storage condition. Disadvantages of individual marking led us to test the mass marking and it?s influence on the survival of the moths. One-day-old moths were marked with fluorescent powder. Mortality of the males and females recorded daily for a 20 days period. Results indicated that the effects of the sex, the replications and interaction of them were significant as well as the effect of the day. The model accounted for 96 % of the variations. This study indicated that male and female moths were inﬂuenced by the ﬂuorescent powder. Findings of this study may facilitate the improvement of mark-release experiment results and interpretation more precisely in particular for dispersal studies. In the field experiments, firstly trade off trap structure in assessing the horizontal and vertical distribution of Codling moth carried out as well as outward and inward dispersal. Three different types of the traps including Delta pheromone traps, Delta Pear ester trap and Cylinder shape Pear ester traps were used in the research station of the Hohenheim University. Ninety six traps were suspended in eight compass directions in order of four traps per direction, at three heights in random arrangement in outward dispersal. In inward dispersal study the traps arrangement and number was the same but dissimilarly the releasing site was from borders of directions SW, NW, W, E, and SE. The traps were checked daily and followed nine days after release. Results demonstrated no significant differences between three types of traps in attracting the marked and feral females ?Fn?. Meanwhile significant dissimilarity in marked and feral male ?Mn? catches were traced. Reaction of the moths to the traps elevation was not similar in the vertical distribution study. whereas marked female moths exhibited significant differences to different heights, marked and feral male and ?Fn? moths revealed no difference reaction to traps in different heights.In horizontal distribution study marked female moths ?Fr? exhibited significant differences. It is revealed that dominant directions for marked and feral moths were different. Concerning inward distribution, both marked male ?Mr? and female demonstrated significant differences in their direction and distances. In regard to this findings and priceless and effortless manufacturing of the Cylinder traps, utilization of this trap in mark-release-recapture studies of female and male Codling moths is recommended. Effect of apple cultivar on pheromone and Pear ester trap efficiency studied as the next tread. In this experiment 32 Delta pheromone traps and 32 Cylinder-shape Pear ester traps impartially mounted on different varieties of apple trees. Artificially reared and marked 24 to 26 h old moths were released at 1 m height from a central point. Among the simple effects the most important explanatory variable for the response variables ?Mn? and ?Fn? moths was sampling dates of moths, while the variety and distance from the releasing point for ?Mn? and the variety and trap height for ?Fn? were the second and third influential variables respectively. Moreover among the nested effects the interaction of distance-height-variety was the most influential one for ?Mn? likewise the interactions of date, release point, direction and trap height with the variety were the most influential for ?Fn?. For the ?Mr? and ?Fr? moths releasing date was the most important influential variable, while the trap type and variety for ?Mr? and variety and trap height for the ?Fr? were the second and third influential variables respectively. Current study revealed that dispersal of the feral and marked-released male and female Codling moths influenced by host cultivars distinctly and decidedly. Meanwhile, quantifying these relationships and propose distinct model for marked and feral male and female moths are the exclusive characteristics of present findings. The next stage of present study related to study of climatic factors on dispersal of Codling moth. In this study, Hohenheim station climatic data were used. Several climatic elements including temperature, relative humidity, precipitation, wind speed in two different heights (2.5 m and 10 m), Day Degree, twilight temperature, wind speed and precipitation were utilized in the analysis. Diversity and high number of variables led us to use AIC method for selecting of appropriate regressors and fitted model. The main regressors that inföuenced the ?Fr? were flight height, ageing, twilight wind speed (2.5 m heights) and precipitation. For the ?Mr? the same regressors plus the distance from the releasing point were the best subset. In the case of the feral moths the flight height, relative humidity, Day Degree, twilight temperature and wind speed were the best subset regressors. Comprehensively we concluded that present study provides new knowledge in basic as well as in applied science. Twilight temperature, rainfall, wind speed and Day Degree impress the distribution of the moths in a superior way than the circadian weather data. This knowledge could mitigate confusion which arises from observations of erratic flight patterns and could lead to fewer treatment decision errors in the future. Also may accelerate and strengthen forecasting programs of this key pest as well as the related management tactics. The combination of mark-release-recapture and diffusion models have been shown to be effective for measuring insect dispersal. We attempted to measure the Codling moth dispersal using traps placed at different distances and heights. Diffusion coefficient calculated for horizontal and vertical dispersal of male and female moths distinctly using direct and indirect methods and resulting models were compared. We fitted the non-linear regression using the iterative process and estimating the parameters accuracy were tested according to the default asymptotic 95 % confidence intervals calculation in non-linear regression. Considering the overall models, suitability of three factors fitted models was more convincible than that of two factors model particularly for male moths. Meanwhile we found great difference in the diffusion coeffcient of direct and indirect methods. Regardless of the model type, the R2 was relatively high in our experiments which evaluate how well the model fits data. We have shown that the diffusion model leads to powerful techniques for the analysis of dispersal data at least for one economically important insect. In conclusion, the present study provides an estimate of population spread by Codling moth using estimated rates of reproduction and dispersal, quantified the association between various key factors and Codling moth movement for the first time using the diffusion model. By including additional parameter to the diffusion model the predictive explanatory potential of this method was improved for dispersal studies at least for a cosmopolitan and critical insect.
Resistenz von Hopfen, Humulus lupulus L., gegen die Hopfenblattlaus, Phorodon humuli (Schrank)
(2010) Kryvynets, Oleg; Zebitz, Claus P. W.
Non-chemical methods controlling the damson-hop aphid, Phorodon humuli (Schrank) have recently gained importance, due to its great economical relevance and increasing problems with its chemical control. Breeding for the classic 'Genetically controlled resistance', where the plant exerts negative influence on the pest's behaviour during feeding, in this case appears as the only promising method because so far no other efficient biological control methods are available. In order to analyse the host-parasite relationship between hop and damson-hop aphid, and to provide a reliable, standardised screening method based on line-specific host selection behaviour, 1. the composition of the aphid's food, 2. hardness of hop tissue, 3. host selection behaviour and 4. parameters of aphid growth and development were investigated. In the apoplast (Intercellular washing fluid) of leaves and cones from all hop lines resveratrol was found, which also indicates an accumulation of its glycosidic form in the plant tissue. In contrast, no resveratrol could be found in samples of non-transgenic hop. An analysis for bitter acids detected alpha- and beta-acids in the cones only, not however in the intercellular space of the leaves. In a comparative study of plant tissues the contents of lupulones in leaf extracts from transgenic plants (except Tk160 and Tk424) was lower, the contents of humulones higher compared with those from non-transgenic plants. Generally leaf extracts showed higher contents of alpha- than of beta-acids. Resveratrol was not found in any of the leaf- or cone-extracts. Tissue hardness differed between transgenic and non-transgenic plants as well as between those from the glasshouse and from open land. In the field-grown plants it was definitely higher. Leaves of transgenic lines were harder than those of non-transgenic ones. This difference was pronounced particularly in young leaves. Significant differences were observed among parameters of aphid growth and development. The individual transgenic lines exert significantly different influence on P. humuli in respect of relative growth rate of individuals, rate of population increase and fecundity. There was no significant difference between the variants regarding the parameters rDS-value, life span and number of embryos. Host selection behaviour was different on transgenic versus non-transgenic plants. On leaves of transgenic plants a slowing down of food intake from the phloem and an extension of water intake from the xylem were observed. On the cones no similar effect ? general reduction or extension of intake from phloem or xylem in comparison to non-transgenic plants ? could be ascertained. Generally a strong decrease in food intake from the phloem of cones compared to that of the leaves was observed, caused by frequent phases of aphid inactivity on cones. Aphid behaviour on artificial diets was definitely influenced by different concentrations of bitter acids and resveratrol. A gradual increase in bitter acid concentration first prolonged or raised some EPG-parameters and then shortened or reduced them subsequently. This means that the aphids first reacted negatively, from a certain concentration of bitter acids on, however, positively to these substances. A raise in resveratrol concentrations led in the whole course either to a notable increase or decrease of values for the individual EPG-parameters. This suggests a xenobiotic resistance effected by this substance. Correlations between the experimental data showed the following dependencies: The humulones and lupulones found in intercellular washing fluid and in tissue extracts influence EPG-parameters that indicate factors located in the mesophyll. The duration of those phases of the penetration that take place in the intercellular space is reduced with increasing concentrations of humulones and lupulones. Food quality and quantity in plants from the glasshouse had no negative effects on the damson-hop aphid. On field-grown plants different effects of alpha- and beta-acids in the extracts on the aphids were ascertained. The contents of lupulones in cone- and leaf-extracts exerted a more inhibiting, the humulones a more promotional effect on the aphids during feeding. As with the overall contents of humulone and lupulone a different influence of individual bitter acids on aphid behaviour was recognisable in EPG-parameters. On cones the strong behaviour modification by the examined substances took effect on the mesophyll level and in the phloem. Positive correlations between the adult weight of the aphids as well as the amount of offspring per life span per insect and the bitter acid contents indicate an influence in favour of the insect. Negative correlations between the rm -value and the bitter acid contents, however, show an influence on the aphids in favour of the plant. Higher bitter acid concentrations reduce the development rate of aphid populations. Notable differences between transgenic and non-transgenic plants as well as varying effects of examined substances on the aphids, partly favourable for the plant, partly favourable for the pest, were found. These differences were partially clarified by comparing the effects of the substances when administered with artificial diets. The exact mode of action of resveratrol and its derivatives in transgenic hop lines on the damson-hop aphid requires further examination. A direct toxic effect on the aphids is very probable. As a conclusion from the clustering by examined parameters the transgenic hop line Tk424 can be designated as optimal.
An image analysis and classification system for automatic weed species identification in different crops for precision weed management
(2010) Weis, Martin; Gerhards, Roland
A system for the automatic weed detection in arable fields was developed in this thesis. With the resulting maps, weeds in fields can be controlled on a sub-field level, according to their abundance. The system contributes to the emerging field of Precision Farming technologies. Precision Farming technologies have been developed during the last two decades to refine the agricultural management practise. The goal of Precision Farming is to vary treatments within fields, according to the local situation. These techniques lead to an optimisation of the management practice, thereby saving resources, increasing the farmers outcome, reducing the overall management costs and the environmental impact. A successful introduction of Precision Farming involves the development of application equipment capable of varying treatments and sensor technology to measure the spatial heterogeneity of important growth factors. Such systems are able to record, store and use large amounts of data gathered by the sensors. Decision components are needed to transform the measurements into practical management decisions. Since the treatments are varied spatially, positional data, usually measured using GPS technology, has to be processed. The located measurements lead to a delineation of management zones within a field and are represented by geo-data and can be visualised in maps. The improved, detailed knowledge of the situation within the field leads to new and extended scopes of applications and allows to document the management practices more precisely. In this work, parts of Precision Farming technology were developed for site-specific weed management. Five selected publications are presented, covering the technological prerequisites and details of the developed system.

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