Browsing by Subject "Helianthus annuus"

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    Generation of high oleic acid sunflower lines using gamma radiation mutagenesis and high-throughput fatty acid profiling
    (2023) Rozhon, Wilfried; Ramirez, Veronica E.; Wieckhorst, Silke; Hahn, Volker; Poppenberger, Brigitte
    Sunflower (Helianthus annuus L.) is the second most important oil seed crop in Europe. The seeds are used as confection seeds and, more importantly, to generate an edible vegetable oil, which in normal varieties is rich in the polyunsaturated fatty acid linoleic acid. Linoleic acid is biosynthesized from oleic acid through activity of the oleate desaturase FATTY ACID DESATURASE 2 (FAD2), which in seeds is encoded by FAD2-1, a gene that’s present in single copy in sunflowers. Defective FAD2-1 expression enriches oleic acid, yielding the high oleic (HO) acid trait, which is of great interest in oil seed crops, since HO oil bears benefits for both food and non-food applications. Chemical mutagenesis has previously been used to generate sunflower mutants with reduced FAD2-1 expression and here it was aimed to produce further genetic material in which FAD2-1 activity is lost and the HO trait is stably expressed. For this purpose, a sunflower mutant population was created using gamma irradiation and screened for fad2-1 mutants with a newly developed HPLC-based fatty-acid profiling system that’s suitable for high-throughput analyses. With this approach fad2-1 knock-out mutants could be isolated, which stably hyper-accumulate oleic acid in concentrations of 85-90% of the total fatty acid pool. The genetic nature of these new sunflower lines was characterized and will facilitate marker development, for the rapid introgression of the trait into elite sunflower breeding material.
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    QTL mapping of resistance to Sclerotinia sclerotiorum (Lib.) De Bary in sunflower (Helianthus annuus L.)
    (2005) Micic, Zeljko; Melchinger, Albrecht E.
    Sclerotinia sclerotiorum (Lib.) de Bary is one of the most important pathogens of sunflower. Three different disease symptoms can be caused by S. sclerotiorum: Sclerotinia wilt, midstalk- and head rot. An improvement of the resistance against S. sclerotiorum would contribute to yield security and thus increase the profitability of sunflower cultivation. We investigated resistance to midstalk rot with respect to the prospects of marker-assisted selection (MAS). The bjectives were to (1) identify quantitative trait loci (QTL) involved in resistance against Sclerotinia sclerotiorum, (2) map their position in the genome, (3) characterize their gene effects, and (4) estimate their consistency across generations of the cross NDBLOSsel x CM625. Two sunflower lines with high resistance level to S. sclerotiorum and different genetic origins (NDBLOSsel and TUB-5-3234) were used as parents. They were crossed with a highly susceptible line CM625 to develop two mapping populations. A modified leaf test was used for the evaluation of midstalk-rot resistance. Three resistance traits and two morphological traits were measured. Disease resistance of 354 F3 families of the population NDBLOSsel x CM625 was screened in field trials with two different sowing times in 1999. A total 317 recombinant inbred lines (RIL) derived from F3 families were tested in 2002/2003. The 434 F3 families of cross CM625 x TUB-5-3234 were screened in 2000/2001. The field trials were conducted by using generalized lattice designs with three replications and five infected plants per replication. Highly significant genetic variation between F3 families and RIL was observed for the resistance traits in all field trials. Heritabilities ( ) were highest for stem lesion and lowest for leaf lesion for all three experiments. The resistance traits were moderately correlated with each other. For the construction of the genetic map of population NDBLOSsel x CM625, 352 F2 individuals were analyzed with 117 SSR marker loci. On the basis of results from the QTL mapping in F3 families, 41 markers were selected and genotyped in 248 RIL. A "selective genotyping" (SG) approach was used for population CM625 x TUB-5-3234. Based on the results measured in F3 families for stem lesion, the SSR genotype at 72 marker loci was determined for the 60 most resistant and 60 most susceptible F2 individuals. For QTL mapping and estimation, the method of the "composite interval of mapping" was used. For stem lesion in the population NDBLOSsel x CM625, eight QTL were detected explaining 33.7% of the genetic variance ( ). The QTL on LG8 explained 36.7% of the phenotypic variance (R2adj). All other QTL for this trait explained between 3.3 and 6.0% of R2adj. Nine QTL were detected for leaf lesion. The proportion of the phenotypic variance explained by individual QTL ranged from 3.4 to 11.3%. All detected QTL for leaf lesion explained 25.3% of the genetic variance in cross validation. For speed of fungal growth, 6 QTL were detected, which explained from 4.6 to 10.2% R2adj. Cross validation explained 24.4% of. Most QTL showed additive gene action. QTL occurring consistently across generations can be recommended for MAS and therefore, the QTL results between RIL and F3 families of population NDBLOSsel x CM625 were compared. One common QTL was identified for leaf lesion, two for stem lesion and three for speed of fungal growth. In population CM625 x TUB-5-3234, four QTL for stem lesion, three QTL for leaf lesion and three QTL for speed of fungal growth were identified. Owing to the SG approach we conjecture that not all QTL were found. The comparison of QTL results between two F3 populations showed two common QTL for stem lesion on LG4 and LG8. The QTL on LG4 originated from the susceptible parent CM625. The QTL on LG8 probably corresponds to the QTL with the largest effect determined in the population NDBLOSsel x CM625. Regarding MAS, our results indicate that two QTL detected for stem lesion and speed of fungal growth in population NDBLOSsel x CM625 are promising. They were consistent across environments, and showed no adverse correlation to leaf morphology in trials with the RIL. In mapping population CM625  TUB-5-3234, it remained unclear whether TUB-5-3234 can contribute new alleles with sufficiently large effects for resistance that were not identified in line NDBLOSsel and would be useful in MAS. The genomic region on LG10 should be analyzed in more detail with respect to its importance for resistance in multiple plant parts (head and stalk) and to verify its association with leaf morphology. Resistance breeding of sunflower against S. sclerotiorum is difficult due to the complex inheritance of the trait. This study showed that both the resistance source NDBLOSsel and the identified markers are promising in improving resistance by MAS. For a broader resistance against S. sclerotiorum, it is necessary to detect new resistance genes from different sources to pyramide them in elite lines.
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    Strategies and mechanisms of cellular interaction between the parasitic weed Orobanche cumana WALLR. and its host Helianthus annuus L.
    (2020) Krupp, Anna Clarissa; Spring, Otmar
    Sunflower broomrape, Orobanche cumana WALLR., is a root parasitic plant causing considerable yield losses in sunflower cultivation in Europe, North Africa and Asia. Comprehensive knowledge about early interaction stages between host and parasite is necessary to find new ways of controlling this weed. In this thesis, three aspects regarding the biology of O. cumana were studied: 1) the chemotropism of O. cumana germtubes which bend towards the host root, 2) the development of O. cumana on resistant and susceptible sunflower lines and 3) the development of the phloem connection between the O. cumana haustorium and the sunflower host root. Sesquiterpene lactones in sunflower root exudates act as germination stimulants for O. cumana. As sesquiterpene lactones are known inhibitors of plant elongation growth and seem to play a role in the phototropic curvature of sunflower hypocotyls, a chemotropism bioassay on water agar was established to test if they also serve as chemotropic signals for the host-finding of O. cumana germtubes. When sesquiterpene lactone containing sunflower root exudate, sunflower seed oil extract or the sesquiterpene lactone reference costunolide were applied on filter discs, 70 % of the germtubes showed orientation towards them. The artificial strigolactone GR24, however, did not induce chemotropism. A concentration gradient of sesquiterpene lactones exudated from the host root is likely to be responsible for a stronger inhibition of elongation growth on the host-facing flank of the germtube. This would confer a double role of sesquiterpene lactones from root exudates in the sunflower-broomrape-interaction, namely as germination stimulants and as chemotropic signals. One way of controlling O. cumana is the cultivation of resistant sunflower lines. However, this resistance is rapidly overcome by more aggressive pathotypes of the parasite. Therefore, the resistance or tolerance reaction of the sunflower genotype T35001 was investigated in comparison to six other sunflower genotypes with different resistance characteristics. The development of O. cumana was monitored in a root chamber system which allowed permanent assessment of germination, attachment and tubercle formation in the different host-parasite-combinations. All seven tested sunflower lines induced germination and attachment of O. cumana, independent of the expected resistance or susceptibility of the host. A difference between compatibility or incompatibility of the interactions was only observed at the tubercle stage. On T35001, tubercles never occurred, neither in root chamber nor in pot experiments. To find out why the development stopped before the tubercle stage, samples of sunflower roots with attached O. cumana seedlings were analysed by bright field-, fluorescence- and transmission electron microscopy. Histological studies revealed that O. cumana penetrated the host root, but never reached the host’s vascular bundle. The root cortex cells surrounding the Orobanche haustorium showed no ultrastructural changes such as cell wall thickening. Fluorescence microscopy revealed no callose depositions or signs of phytoalexin release. However, ultrastructural examination of the host-parasite-interface showed degeneration processes in both cortex and haustorial cells. Cortex cells were flooded with bacteria, haustorium cells showed degeneration of cytoplasm and nuclei. The resistance mechanism that prevented further development of the O. cumana haustorium did not express itself in a histologically visible way. As holoparasite, O. cumana acquires its entire demand for water, minerals and organic nutrients from the host’s vascular system. The development of the xylem connection between O. cumana and sunflower had previously been reported, but the phloem connection is far more relevant for the parasite in terms of organic nutrients. Accordingly, the ultrastructure of the phloem connection between the haustorium of young O. cumana tubercles and the sunflower root was examined. Parasite and host tissues were intermingled at the contact site and difficult to distinguish, but sieve-tube elements of O. cumana and sunflower could be differentiated according to their plastid ultrastructure. While sieve-element plastids of O. cumana were larger, often irregular in shape and contained few, small starch inclusions, sieve-element plastids of the host were significantly smaller, always round with more and larger starch inclusions. This made it possible to trace the exact contact site of host and parasite sieve elements to show a direct symplastic phloem connection between the two species. The interspecific sieve plate showed more callose on the host side. This allowed detection of newly formed plasmodesmata between host sieve-tube elements and parenchymatic parasite cells, thus showing that undifferentiated cells of the parasite can connect to fully differentiated sieve elements of sunflower.