Browsing by Subject "Corn salad"

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Genetic diversity in germplasm of cornsalad (Valerianella locusta L.), radish (Raphanus sativus L.), and celeriac (Apium graveolens L. var. rapaceum), investigated with PCR-based molecular markers
(2004) Muminovic, Jasmina; Melchinger, Albrecht E.
During the last couple of decades, production and economic importance of cornsalad (Valerianella locusta L.; fam. Valerianaceae), radish (Raphanus sativus L. var. sativus convar. radicula; fam. Brassicaceae), and celeriac (Apium graveolens L. var. rapaceum; fam. Apiaceae) have been considerably increasing in Europe. Nevertheless, genetic diversity currently utilized for breeding cornsalad, radish, and celeriac is narrow, whereas their germplasm collections in gene banks are relatively poor. Assessment of genetic diversity among breeding materials and genetic resources is an important consideration for the optimal design of further breeding programs. The major objective of this study was to investigate genetic diversity in germplasm of cornsalad, radish, and celeriac, applying amplified fragment length polymorphisms (AFLPs) and inter simple sequence repeats (ISSRs) molecular markers. In particular, the objectives were to (i) analyze relationships among breeding materials of the three vegetable crops (referred to as elite germplasm), as well as among their formerly grown varieties, gene bank and botanical garden accessions (referred to as exotic germplasm), (ii) reveal genetic structure of radish germplasm to establish heterotic pools for hybrid breeding, and (iii) evaluate the usefulness of introducing exotic materials for broadening of the elite germplasm in cornsalad, radish, and celeriac. Average genetic similarity in 34 elite varieties of cornsalad was very high (GS = 0.90), which is comparable with other autogamous crops. The majority of elite varieties clustered closely applying the UPGMA analysis because of a narrow-based germplasm in cornsalad breeding. A substantial level of genetic diversity (GS = 0.47) was detected in 30 cornsalad varieties representing exotic germplasm. Exotic varieties that interspersed the sub-clusters of the elite may serve as a direct genetic resource for broadening the elite cornsalad germplasm base, whereas Valerianella locusta-related species that were distinct from cultivated germplasm can contribute to the introgression of new (resistance) genes. Sixty-eight varieties of cultivated radish (garden and Black radish) created sub-clusters with GS estimates higher than 0.70, thus supporting the assumption that the currently used radish germplasm in Europe relies on a narrow genetic base. Owing to a high degree of heterogeneity and heterozygosity within radish varieties, the detected between-variety diversity was low, but there still was a substantial overall diversity in available radish germplasm. Applying both UPGMA and principal coordinate analyses, Black radish varieties were distinct from garden radish. A further unambiguous division within garden radish germplasm was revealed with the model-based clustering approach. These sub-groups can be employed for establishment of heterotic pools within European modern cultivars of garden radish. In addition, ISSRs can substantially reduce hybrid radish production costs by an early detection of two closely related weed species (R. raphanistrum and R. sativus L. var. sativus convar. sinensis). AFLPs and the evaluation of morphological traits were used to investigate genetic diversity in 34 varieties of elite celeriac germplasm and 35 accessions of exotic germplasm. Only two morphological traits supported the clustering pattern obtained with UPGMA analysis of morphological distance estimates. AFLP-based GS estimates offered a clearer view of diversity present in elite (GS = 0.68-0.95) and exotic germplasm (GS = 0.05-0.95), and clustered the two sets in distinct UPGMA-based sub-clusters. This indicated that only a small fraction of available genetic diversity is exploited for current breeding of celeriac. Exotic celeriac germplasm as well as varieties of celery and leaf celery might substantially improve commercial celeriac breeding. Wild relatives of Apium graveolens are valuable resources for the introgression of resistance genes. Regarding the generally high level of GS in celeriac germplasm conserved in the German gene bank, a broadening of the germplasm collection was suggested. This study demonstrated the capacity of molecular markers to be highly discriminating among varieties of cornsalad, radish, and celeriac. AFLP-based genetic similarity estimates in the three vegetable crops (i) allowed the first insight into the genetic diversity and structure present in the germplasm, (ii) offered suggestions for germplasm broadening, and (iii) proposed a way of rationalization and utilization of available germplasm resources.
Untersuchungen zur bakteriellen Erkrankung Acidovorax valerianellae an Feldsalat
(2012) Braje, Inga; Hinrichs-Berger, Jan
The aim of this study was to contribute to clarifying the epidemiology of the phytopathogenic bacterium Acidovorax valerianellae on corn salad [Valerianella locusta (L.)]. To this end, research was conducted on infection conditions, cultivar sensitivities, transmission paths and seeds. Based on these results, control strategies shall be demonstrated. The tests performed under infectious conditions revealed that the infection of A. valerianellae is dependent on temperature, leaf age, inoculum concentration and leaf moisture, as well as the relative humidity. Inoculation was possible at temperatures between 10 °C and 30 °C. It was possible for leaves of any age to be infected. Moreover, infection was independent of the inoculum concentration, and occurred between 102 and 107 cfu/ml. The speed of infection and the characteristics of the symptoms increased with increasing temperature, leaf age and inoculum concentration. Both the duration of leaf moisture and the relative humidity played a crucial role in the infection process. Under dry conditions, inoculated corn salad plants developed no symptoms. However, infestation increased significantly under humid conditions or during humid periods. Five hours of leaf moisture sufficed for an infection to occur. It was demonstrated that targeted dry growth conditions with short leaf moisture periods constitute an option for controlling A. valerianellae. All 13 tested commercial corn salad cultivars were prone to A. valerianellae. However, the resistance of the wild type V. rimosa was confirmed. For this reason, it seems advisable to cross the wild type with commercial cultivars. A. valerianellae endured for up to eleven months in the soil. Some of the corn salad cultivars cultivated immediately (and one up to eleven months, respectively) after infected plants were severely infected. The number of infected plants decreased in line with increased rotting of infected old plant material. A cultivation break of at least twelve months and the rotation of crops therefore appear to be appropriate ways to eliminate A. valerianellae from the soil. No alternative hosts were detected in the experiments or in the literature. In addition, this study revealed that A. valerianellae is transmitted via seeds. It is therefore important to focus on healthy seeds to prevent the further dissemination of this hazardous disease to uncontaminated crop land. Seeds with natural A. valerianellae contamination were tested using a variety of decontamination methods. Warm water treatment (43 °C for 20 minutes, 55 °C for 20 minutes, 60 °C for 5 minutes) or hot steam treatment (66 °C for 105 seconds) managed to reduce the contamination rate. However, it was not possible to completely eliminate the bacterium. In summary, sowing healthy seeds after a cultivation break of at least twelve months and under dry growth conditions may reduce the infestation of corn salad with A. valerianellae.