Browsing by Subject "Mykotoxin"

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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.
Effects of non-adapted quantitative trait loci (QTL) for Fusarium head blight resistance on European winter wheat and Fusarium isolates
(2010) Ohe, Christiane von der; Miedaner, Thomas
Fusarium head blight (FHB), caused by Fusarium graminearum and F. culmorum, is a devastating disease responsible for tremendous damage in wheat fields and contamination of grain with mycotoxins deoxynivalenol (DON) and nivalenol (NIV), rendering the harvest unsafe for human and animal consumption. The variability of Fusarium populations is high and changes in aggressiveness, chemotypes or species within and among Fusarium populations are known. Stable FHB resistance combined with high yield is one main target in wheat breeding programs. Mapping studies detected several quantitative trait loci (QTL) for FHB resistance in non-adapted sources, such as Sumai3 from China. The two most important and commonly used major QTL are located on chromosome 3BS (Fhb1) und 5A (Qfhs.ifa-5A). However, negative side effects of non-adapted resistance sources introgressed in elite winter wheat material are feared in Europe. Furthermore, the stability of the QTL effect against changing Fusarium populations is unknown. The objectives of this research were to analyze whether (1) the QTL Fhb1 and Qfhs.ifa-5A introgressed from a non-adapted resistance source into two winter wheat varieties have possible side effects on agronomic and quality performance, (2) 3-ADON and 15-ADON chemotypes are significantly different in their aggressiveness and DON production, (3) competition among Fusarium isolates in mixtures exists, and if so, how the resistant host will influence this competition. In conclusion, both resistance QTL are effective and stable in elite spring and winter wheat backgrounds. For improvement of FHB resistance both QTL are valuable, but Qfhs.ifa-5A would suffice for European breeding programs. Due to chemotype shifts, 3-ADON isolates could pose a greater risk to food safety than 15-ADON but breeding and use of highly resistant lines can reduce the risks associated with DON in wheat. Accordingly, resistant spring wheat lines were less affected by the tested Fusarium isolates and mixtures and, therefore, confirmed a high stability of these QTL. Directed selection of highly aggressive isolates due to the resistance QTL seems to be unlikely in the short term.
Genetic variation in early maturing European maize germplasm for resistance to ear rots and mycotoxin contamination caused by Fusarium spp.
(2010) Bolduan, Christof; Melchinger, Albrecht E.
Ear rots of maize, caused by Fusarium spp., are of major concern because they lead to losses in grain yield and contamination with mycotoxins which harm animals and humans. In the absence of other strategies, breeding maize for genetic resistance is currently the most promising avenue to control these rots and mycotoxin accumulation. The predominant pathogens in Central Europe are F. graminearum, the causative agent of Gibberella ear rot (GER), and F. verticillioides, the causative agent of Fusarium ear rot (FER). GER causes contamination with deoxynivalenol (DON), nivalenol and zearalenone (ZEA), whereas FER causes contamination with fumonisins (FUM). Information on the resistance to GER and FER and mycotoxin contamination is lacking for maize adapted to the cooler climatic conditions of Central Europe. In this study we investigated (1) the resistance of early maturing European elite inbred lines against GER and FER and contamination of mycotoxins, (2) the genetic variances and heritabilities for ear rot ratings and mycotoxin concentrations, (3) the correlations of ear rot ratings with mycotoxin concentrations, (4) the correlations between line per se (LP) and testcross performance (TP) for GER rating and DON concentration, (5) the aggressiveness of and mycotoxins produced by different isolates of F. graminearum and F. verticillioides, and (6) the potential of near infrared spectroscopy (NIRS) to estimate concentrations of DON and FUM in maize grains under artificial inoculation. Significant genotypic variances and moderate to high heritabilities were found for GER, DON and ZEA among the inbred lines and for GER and DON among the testcrosses, as well as for FER and FUM among the inbred lines. Further, genotype x environment interaction variances were significant for all traits except FUM. Thus, the results underlined the presence of ample genotypic variation and the need to conduct multi-environment tests for reliable identification of resistant genotypes. Ear rot ratings and mycotoxin production of eight isolates each of F. graminearum and F. verticillioides differed significantly. Even though, isolate x inbred interactions were significant only in the case of F. graminearum, and no rank reversals occurred among the tested inbred lines. Most isolates differentiated the susceptible inbreds from the resistant ones for severity ratings. However, the differences between the two groups were smaller for the less aggressive isolates. Therefore, we recommend using a single, environmentally stable and sufficiently aggressive isolate for resistance screenings under artificial inoculation. Strong correlations between ear rot severity and mycotoxin concentrations indicated that selection for low ear rot severity under artificial inoculation will result in high correlated selection response for low mycotoxin concentration, particularly for GER and DON. Selection for ear rot severity is less resource-demanding and quicker than selection for mycotoxin concentration. Thus, it enables the breeder to maximize selection gain for a given budget. However, the selected elite material should be evaluated for mycotoxin concentrations in order to avoid ?false positives?. In this regard, NIRS showed high potential to predict DON concentrations in grain obtained from artificially inoculated maize. Compared to the commonly employed ELISA assay, NIRS assays are considerably cheaper, because no mycotoxin extractions and test kits are needed. We observed moderate positive correlations between GER and FER, and identified inbreds combining resistance to both ear rots. Therefore, selection for resistance to one pathogen is expected to result in indirect response to the other. Nevertheless, in advanced stages of each breeding cycle, lines preselected for other agronomically important traits should be evaluated for resistance to both pathogens. Genotypic variances for GER and DON were generally higher in LP than TP. Thus, assuming identical selection intensities for each scheme, the expected response to selection for LP should be higher than for TP. However, owing to moderate correlations between LP and TP for GER and DON, selection based on LP is not sufficient, because the ultimate goal is to develop resistant hybrids. Therefore, a multi-stage selection procedure is recommended with evaluation of agronomically promising lines for GER in only one environment in order to eliminate highly susceptible lines, followed by evaluation of TP of the selected lines for GER with one tester of moderate to high resistance level from the opposite heterotic pool in two to three environments.
Molecular and genetic analyses of aggressiveness in Fusarium graminearum populations and variation for Fusarium head blight resistance in durum wheat
(2011) Talas, Firas; Miedaner, Thomas
Fusarium head blight (FHB) is a devastating disease of wheat, barley and other cereals, which affects all wheat-growing areas of the world. The most prevalent species are Fusarium graminearum Schwabe (teleomorph: Gibberella zeae (Schweinitz) Petch) and Fusarium culmorum (W. G. Smith) Saccardo. Wheat breeding for FHB resistance has become the most effective and cost efficient strategy to combat this disease. Assisting long term stable breeding programs need a better understanding of the biology and dynamic changes of the population structure. Deoxyninalenol (DON) has the most economical impact among the other mycotoxin secreted by this fungus. Several chemotypes characterizes F. graminearum isolates. All chemotypes (3-ADON, 15-ADON, and NIV) were detected in Europe. The prevalent chemotype in Germany and UK is 15-ADON. Population structure is the result of evolutionary forces acting on the population in time and space together with mutation, recombination, and migration enhancing the genetic variance of a population, random drift and the selection reducing it. Aggressiveness in F. graminearum denotes the quantity of disease induced by a pathogenic isolate on a susceptible host in a non-race specific pathosystem, and is measured quantitatively. The quantitative traits such as aggressiveness and DON production mirror both the environmental changes and the genetic variation. Several genes are responsible for DON production; majority of these genes are grouped in TRI5 cluster. Few genes are known to be associated with F. graminearum aggressiveness such as MAP kinase genes, RAS2, and TRI14. Association between single nucleotide polymorphism and genetic variation of aggressiveness and DON production traits provide a clear identification of quantitative participation of different SNPs in expressing the trait. Also, this approach provides a good method to test the association between candidate genes and the traits. The objectives of this research were to (1) screen some durum wheat landraces for FHB resistance; (2) determine the genetic and chemotypic structure of natural population of F. graminearum in Germany; (3) determine the phenotypic variation in Aggressiveness and DON production, which come out one farmer wheat field; (4) compare the phenotypic variation and genetic variation occurring in one wheat field; and (5) associate the phenotypic traits with SNPs in candidate genes. Screening for FHB resistance was performed on sixty-eight entries form the Syrian landraces. The main characters of selection for resisting FHB disease are low mean value of infection and stability in different environments. Four genotypes (ICDW95842, ICDW92330, ICDW96165, Chahba) had small mean FHB value, small value of deviation form regression, and regression coefficient close to zero. These genotypes were considered as candidate resistant sources of FHB for further agronomic performance analysis through backcrossing generation. The causal agent of FHB in Germany is F. graminearum s.s. with a dominating rate of 64.9 % (out of 521 Fusarium spp. isolates). Nonetheless, the three chemotypes were detected in Germany and some times within one wheat field. The 15-ADON chemotype dominated the populations of F. graminearum s.s. in Germany followed by 3-ADON then NIV chemotype (92, 6.8, and 1.2%, respectively). High genetic diversity (Nei?s gene diversity ranged form 0.30 to 0.58) was detected on a single wheat field scale. Analysis of molecular variance (AMOVA) revealed a higher variance within populations (71.2%) than among populations (28.8%). Populations of F. graminearum s.s. in Germany display a tremendous genetic variation on a local scale with a restricted diversity among populations. Surprisingly the phenotypic variation of aggressiveness and DON production revealed a similar partitioning scale as the genetic variation. In other words, analyses of variance (ANOVA) revealed a higher variance within populations (72%) than between (28%) populations. The wide spectrum of aggressiveness (i.e., from 18 to 39%) and DON production (from 0.3 to 23 mg kg-1) within single wheat field simulate the global variation in both traits. Consequently, associating the observed variation of aggressiveness and DON production with detected single nucleotide polymorphism (SNPs) in some candidate genes revealed few but significant associations. According to Bonferroni-Holm adjustment, three SNPs were associated significantly with the aggressiveness, two in MetAP1 and one in Erf2 with explained proportions of genotypic variance (pG) of 25.6%, 0.5%, and 13.1%, respectively. One SNP in TRI1 was significantly associated with DON content on TRI1 (pG=4.4). The rapid decay of the LD facilitate a better high resolution of the association approach and is in turn suggest the need of higher number of SNP marker to facilitate a genome wide association study. The linkage disequilibrium between unlinked genes suggests the involvement of these genes in the same biosynthesis network. In conclusion, building wheat breeding program for FHB resistance depend initially on identifying sources of resistance among wheat varieties or wild relatives. Moreover, understanding the population structure of the pathogen and the selection forces causing genetic alteration of the population structure enable us employ a sufficient increase of the host resistance. Keeping such a balanced equilibrium between increasing host resistance and changes occur in genetic structure of F. graminearum population would insure no application of additional selection pressure. Further association of candidate genes with aggressiveness can provide effective information of the population development. Continuous observation of Fusarium population?s development is needed to insure a stable management of Fusarium head blight disease.
Molecular mapping of resistance and aggressiveness in the cereal/Fusarium head blight pathosystem
(2016) Kalih, Rasha; Miedaner, Thomas
Fusarium head blight (FHB) is one of the most destructive fungal diseases in small-grain cereals worldwide causing significant yield losses and contamination of grain with mycotoxins e.g., deoxynivalenol (DON). This renders the grain unsuitable for human consumption and animal feeding. Exploring the genetic mechanism of FHB resistance is considered the key tool for modern cereal breeding activities. Triticale, the intergeneric hybrid between wheat and rye, is an important cereal crop in Poland and Germany. Resistance breeding using genetic mapping to identify quantitative-trait loci (QTL) associated with FHB resistance represents the best strategy for controlling the disease. In parallel, understanding the mechanism of aggressiveness and DON production of F. graminearum will be a significant contribution to improve FHB management. The objectives of the present work were (1) identification of QTL related to FHB resistance in triticale, together with the analysis of the correlation of FHB severity with other related traits such as plant height and heading stage, (2) correlation between DON production and FHB severity, (3) mapping of dwarfing gene Ddw1 in triticale and studying its effect on FHB resistance, plant height and heading stage, (4) detection of SNPs in candidate genes associated with aggressiveness and DON production of a large Fusarium graminearum population in bread wheat. To study the genetic architecture of FHB resistance in triticale, five doubled-haploid (DH) triticale populations with 120 to 200 progenies were successfully tested under field conditions by inoculation with Fusarium culmorum (FC46) in multiple environments. All genotypes were evaluated for FHB resistance, plant height and heading stage. DArT markers were used to genotype triticale populations. Significant genotypic variances (P<0.001) were observed for FHB severity in all populations combined with high heritability. Twenty-two QTLs for FHB resistance in triticale were reported with two to five QTL per population, thus confirming the quantitative inheritance of FHB resistance in triticale. The most prominent (R2 ≥ 35%) QTLs were located on chromosomes 6A, 3B, 4R, and 5R. QTLs for plant height and heading stage were also detected in our work, some of them were overlapping with QTLs for FHB resistance. Correlation between FHB severity, DON content and Fusarium damaged kernels (FDK) in triticale was studied in the population Lasko x Alamo. Significant genotypic variance was detected for all traits. However, low correlation between FHB severity and DON content (r=0.31) was found. Interestingly, correlation between FHB severity and FDK rating was considerably higher (r=0.57). For FHB severity, two QTLs were detected in this population. A QTL located on chromosome 2A with minor effect for FHB severity was also a common QTL for DON content and FDK rating and explained ≥34% of genotypic variance for these two traits. A second QTL on chromosome 5R was a major QTL but it has no effect on DON content or FDK rating. For analyzing the rye dwarfing gene Ddw1 derived from the father Pigmej, 199 (DH) progenies were genotyped with DArT markers and in addition with conserved ortholog set (COS) markers linked to the Ddw1 locus in rye. QTL analyses detected three, four, and six QTLs for FHB severity, plant height and heading stage, respectively. Two specific markers tightly linked with Ddw1 on rye chromosome 5R explained 48, 77, and 71 % of genotypic variation for FHB severity, plant height, and heading stage, respectively. This is strong evidence, that we indeed detected the rye gene Ddw1 in this triticale population. Another objective was to highlight the association between quantitative variation of aggressiveness and DON production of 152 F. graminearum isolates with single nucleotide polymorphism (SNP) markers in seven candidate genes. One to three significant SNPs (P < 0.01 using cross-validation) were associated to FHB severity in four genes (i.e., Gmpk1, Mgv1, TRI6, and Erf2). For DON content, just one significant SNP was detected in the gene Mgv1 explaining 6.5% of the total genotypic variance. In conclusion, wide genetic variation in FHB resistance in triticale has been observed in five populations. QTL mapping analyses revealed twenty-two QTLs for FHB resistance derived from wheat and rye genomes. QTLs located on the rye genome were reported here for the first time and they are a new source for FHB resistance in triticale. In parallel, analysis of the diversity of four pathogenicity genes in F. graminearum is an important first step in inferring the genetic network of pathogenicity in this fungal pathogen.
Resistance of Maize (Zea mays L.) Against the European Corn Borer (Ostrinia nubilalis Hb.) and its Association with Mycotoxins Produced by Fusarium spp.
(2004) Magg, Thomas; Melchinger, Albrecht E.
The European corn borer (ECB, Ostrinia nubilalis Hübner) is a major pest of maize (Zea mays L.) in Europe and continues to spread to northern maize growing regions. The ECB severely affects commercial maize production by decreasing yield stability. In addition, damaged plants often show an increased susceptibility to secondary infections caused by Fusarium spp.. Information about the potential of Bt hybrids (event 176, MON810) to reduce yield losses and mycotoxin contamination under Central European growing conditions is still lacking. However, such monogenic resistances with a strong negative effect on the ECB will break down rapidly. Improving the natural host plant resistance of maize could provide an economical and ecological tool for an integrated pest management system. The overall goal of this study was to evaluate alternative breeding strategies for improving resistance of maize against ECB damage and Fusarium spp.. The objectives were to (1) initiate a selection experiment in the early maturing European flint pool and evaluate a breeding program for ECB resistance in the European dent pool, (2) compare the efficiency of host plant resistance vs. Bt resistance in maize, (3) determine Fusarium-caused mycotoxin contamination of maize genotypes with improved host plant resistance to ECB, and (4) study the association between important agronomic traits, ECB resistance traits, and mycotoxin concentration in early European maize germplasm. The goal of the Hohenheim ECB breeding program, initiated in 1992, was to select lines with improved per se and testcross performance for multiple agronomic traits and ECB resistance. In the standard breeding scheme, line development started from a segregating S1 population. Genotypes were evaluated for their line per se ECB resistance in generations S1, S3, and S5. Lines from the S2, S4, and S5 generations were testcrossed and evaluated for their agronomic performance. Selection was based on ECB resistance and TC performance for grain yield and maturity. In order to compare transgenic Bt maize hybrids carrying event 176 or MON810 with their isogenic counterparts and commercial hybrids or experimental hybrids, field trials in multiple environments were conducted in 1998 to 2000. Furthermore, a laboratory bioassay with neonate ECB larvae was performed to assess mortality and subsequently the level of Bt antibiosis present in the used hybrids of 1998. Resistance traits such as damage rating of stalks, number of damaged plants, and number of larvae per plant were assessed exclusively in manually ECB infested plots. Grain yield, grain dry matter content and plant height were determined in the insecticide protected and the ECB infested main plots. In addition, grain samples from each subplot were drawn at random and analyzed separately for Fusarium mycotoxins such as type B trichothecenes (DON, NIV), Zearalenon (ZEN), Fumonisins (FUM), and Moniliformin (MON). The inbred lines displayed a significant genotypic variance for all ECB resistance traits evaluated. However, in the further course of selection and topcross testing, most dent and flint lines, especially those displaying improved resistance to ECB larvae feeding, were discarded because of their poor agronomic performance. Negative correlations between grain yield, early maturity and the damage rating of stalks were identified. However, three dent lines (P028, P029, P030) with moderate resistance to ECB were developed. In all experiments, Bt hybrids were superior to other hybrids in the control of ECB larvae. Non-Bt hybrids displayed a significant genotypic variance for all evaluated resistance traits; grain yield reductions ranged from 8.6 to 21.8% under manual infestation of ECB. All evaluated resistance traits were highly significantly correlated with each other and showed significant negative correlations to grain yield reduction. Bt hybrids did not differ from their isogenic counterparts for most agronomic traits. Highly significant location and genotype × location interactions were identified for all mycotoxins evaluated, except MON. MON concentration doubled under manual infestation of ECB compared to insecticide protected conditions and a similar trend was found for FUM. Bt hybrids displayed significantly lower MON concentrations than non-Bt hybrids and significantly lower DON concentrations than their isogenic counterparts under ECB infestation. Highly significant correlations between ECB resistance traits and MON were found. However, a significant genotypic variance was observed for DON, 15-A-DON, FUM, and MON concentrations, suggesting variation for resistance against Fusarium spp. in current elite hybrids. By combining different sources of monogenic Bt resistance and quantitatively inherited resistances to ECB, it may be possible to develop hybrids with multiple resistance by pyramiding the underlying genes in one genotype. Therefore, further research is required to identify new sources of ECB resistance and new breeding strategies should be developed. Furthermore, there is indication that an improved resistance against Fusarium spp. possesses a greater potential for reducing mycotoxin contamination of maize kernels than a high level of ECB resistance. Since resistance to ECB and resistance to Fusarium spp. are inherited fairly independently, simultaneous improvement of both resistances seems to be necessary for improving the stability and quality of future maize hybrids.