Browsing by Subject "Fusariose"

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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.