Browsing by Subject "Ergot"

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Analyzing resistance to ergot caused by Claviceps purpurea [Fr.] Tul. and alkaloid contamination in winter rye (Secale cereale L.)
(2022) Kodisch, Anna; Miedaner, Thomas
Ergot caused by Claviceps purpurea [Fr.] Tul. is one of the oldest well-known plant diseases leading already in medieval times to severe epidemic outbreaks. After the occurrence of honeydew, the characteristic ergot bodies called sclerotia are formed on the ear. These are containing toxic ergot alkaloids (EAs). Strict limits are set within the European Union. Rye (Secale cereale L.) as cross-pollinating crop is particularly vulnerable to ergot since the competitive situation of fungal spores and pollen during flowering. Nevertheless, even today the threat is real as agricultural practice is changing and screening studies revealed EAs in samples of the whole cereal value chain frequently. The aims were to establish a harmonized method to test ergot resistance and EA contamination in winter rye, to clarify major significant factors and their relevance and to reveal the suitability of one commercial ELISA test. Further, effort was paid to examine the covariation of ergot amount and EA content considering different factors because of prospective legislative changes. Genotypes showed significant variation for ergot severity and pollen-fertility restoration after natural infection as well as artificial inoculation whereas a high positive correlation could be found between both treatments. Additionally, variances of environment, general combining ability (GCA), specific combining ability (SCA), and interactions were significant. Although male pollen-fertility restoration was of utmost importance, the female component was also significant. This illustrates that apart from promising selection of high restoration ability the maternal restorability could be exploited in future breeding programs especially when a high pollen amount is already reached. A large-scale calibration study was performed to clarify the covariation of ergot severity, EA content (HPLC, ELISA) considering genotypes, locations, countries, years, and isolates. EA profile was rather stable across country-specific isolates although large differences regarding the EA content were detected. The moderate covariation between ergot severity and EA content (HPLC) indicates that a reliable prediction of the EA content based on ergot severity is not possible what can also not be explained by grouping effects of the factors. Further, EAs seem not to act as virulence factor in the infection process since EA content showed no relationship to disease severity. Additionally, the missing correlation of ELISA and HPLC leads to the conclusion that the ELISA is not an appropriate tool what can be used safely to screen samples regarding ergot in the daily life. The genetic variation of male-sterile CMS-single crosses was analysed in a special design without pollen in field and greenhouse to identify resistance mechanisms and to clarify whether ergot can be reduced in the female flower. At this, comparison of needle and spray inoculation revealed medium to high correlations illustrating that both methods were suitable for this research. Significant environment and genotype by environment interaction variances were detected. So, testing across several environments is necessary also without pollen. Further, small but significant genotypic variation and identification of one more ergot-resilient candidate revealed that selection of female lines could be promising to further reduce ergot. The EA content was lower for less susceptible genotypes. Thus, EA content can be considerably reduced by breeding. A strong positive correlation could be found for ergot severity and EA content when analysing 15 factorial single crosses. The male pollen-fertility restoration was also here the most relevant component but the female component contributed an obviously higher proportion for the EA content than for ergot severity. In conclusion, this thesis demonstrate that implementing of a high and environmental stable male fertility restoration ability via exotic Rf genes can effectively reduce ergot although also the female restorability enables great opportunities. The unpredictable covariation between ergot amount and EA content illustrates that both traits have to be assessed, in particular the EA content by a valid HPLC approach to guarantee food and feed safety.
Genetische Variation für Resistenz gegen Mutterkorn (Claviceps purpurea [Fr.] Tul.) bei selbstinkompatiblen und selbstfertilen Roggenpopulationen
(2006) Mirdita, Vilson; Miedaner, Thomas
Ergot (Claviceps purpurea [Fr.] Tul.) is one of the most important diseases in rye. Infection during flowering results in the production of black, overwintering organs (sclerotia) instead of kernels, which contain harmful alcaloids. Three experiments were conducted to estimate quantitative-genetic parameters of the resistance of rye to ergot under the conditions of organic farming. The general aim was the estimation of genetic variation among and within self-incompatible rye populations and among CMS lines and their male-sterile testcrosses. In 2002 and 2004, genetic variation in resistance to ergot was tested among 65 rye populations at each of two locations (Experiment 1). Thirteen populations were registered rye varieties and the remaining 52 were genetic resources. To assess genetic variation within populations, 50 full-sib families (FSF) from each of five rye populations were developed and tested at four locations (Experiment 2). To test genetic differences in the susceptibility of ovaries towards fungal penetration in the absence of pollen, (i) 64 currently available CMS lines and (ii) their male-sterile crosses with three testers (=sets) were tested in 2003 and 2004, and in 2004, respectively. Inoculation was performed by spraying an aggressive mixture of isolates of Claviceps purpurea three times during the flowering period. The micro-plots were grown in a chess-board design separated by wheat plots to reduce the neighbouring effects. Traits of resistance were the proportion of infected spikes relative to the total number of spikes per plot, and the percentage by weight of ergot sclerotia in the grain. In Experiment 3, the weight of slcerotia per spike and per pair of spikelet were measured due to the absence of grain. Amount of pollen shedding was rated on the basis of the anther size and extrusion. Highly significant genotypic and genotype-environment interaction variances were found among rye populations in the percentage of ergot sclerotia in the grain. All genotypes were infected by ergot. No differences in mean among the registered rye varieties and genetic resources were detected. Because all populations were highly pollen shedding, the results indicate the existence of genetically determined resistance to ergot within the self-incompatible rye. Correlation between both resistance traits was significant (rp = 0.92). Genetic variation within populations was highly significant for all five populations. Individual progenies with resistance higher than the population mean were observed. The mean resistance of initial populations hardly differed from the mean of their progeny indicating a predominantly additive inheritance. Highly significant genetic variation in resistance to ergot was also detected among the currently available 64 CMS lines. Corresponding testcrosses mostly had a higher weight of sclerotia per spike than the lines. Considerable differences in the level of resistance were observed among testcrosses. Crosses with tester line 1 were substantially more susceptible, whereas those with tester 2 were hardly over the mean of the parental lines. The material showed a quantitative distribution of ergot resistance. Weak to medium-sized correlations (0.33 ? 0.47) between locations were detected among lines. The correlation between locations was even weaker in testcrosses. Weak correlations in ergot weight per spike were observed between CMS lines and their testcrosses in sets 2 and 3. In set 1, the estimated phenotypic correlation was higher (rp = 0.65). Estimates of error-corrected correlations were always higher than phenotypic correlations. No genetic difference was detected among the CMS lines for the amount of alkaloids in their sclerotia. This study shows that incompatible rye populations as well as self-fertile hybrid populations contain a substantial genetic variation for resistance to ergot that is inherited quantitatively. In both materials, mainly additive genetic variance was found. Because of a significant genotype-environment interaction, multi-environment trials are necessary to select for resistance. The results of this study nevertheless indicate good prospects to improve resistance to ergot in rye breeding in the long term.