Germplsm Screening, Combining Ability Analysis, And Mapping Of QTLs For Resistance To DON Accumulation Of Chinese Common Wheat

Wheat Fusarium head blight(FHB) caused by Fusarium graminearum, also called scab, is a destructive disease of wheat worldwide. Infection of this disease results in both yield losses and deterioration of grains quality. Particularly, contamination of mycotoxin in the infected grains is very harmful to the healthy of human and livestock. Deoxynivalenol(DON) is the dominant mycotoxin form in China. Development of varieties with FHB resistance, especially DON accumulation resistance, is an efficient way to protect from the threat.Among the classified five types of FHB resistance, Typeâ… (resistance to the initial infection) and Typeâ…¡(resistance to the spread of infection) have been intensively studied. Until recently, with the increasing attention on food safety issue, more and more studies were initiated on Typeâ…¢(resistance for toxin accumulation). However, very few reports of Typeâ…¢were from China. CINAU(Cytogenetics Institute, Nanjing Agricultural University), as a scab research group, has been worked consistently for more than 20 years on the discovery and transferring of scab resistance genes from alien species into common wheat. Based on the previous study on wheat scab in CINAU, in this study, 39 Chinese wheat landraces with good scab resistance, progenies from an 8×8 diallel crosses of Griffingâ…¡between eight wheat landraces or lines with different DON accumulation levels, and lines of a DH population constructed between Wangshuibai and Alondra's were inoculation with a high DON-yielding isolate B4-1 of Fusarium graminearum by single floret injection for 2 years(2004 and 2005). Their grains were harvested and DON content in grains were determined by both DON-test HPLC and GC-MS. The DON content in grains was used as a index to reflect the DON accumulation resistance, combined with molecular marker and genetic mapping analysis, the research aims at(1)discovering new wheat germplasm with low DON accumulation and with distinct genetic background other than that of Sumai 3 and Wangshibai;(2)revealing the combining ability of DON accumulation resistance;(3) mapping QTLs conferred resistance for DON accumulation, elucidating the relationships of different scab resistance parameters. The results were as the following:For test of DON content in the diseased wheat grains, two kinds of method were adopted and compared. The linear limit of DON test-HPLC was as low as 0.10ng.μL^-1 with an average recovery rate 85.80%, while the limit of GC-MS was 0.025ng.μL^-1 with a recovery rate 94.68%. The first method is more flexible for large samples and the second one best for small samples and detection of DON derivatives. Significant correlations(R²=0.9928) was found between two methods.Variance analysis on the DON content tested in the 42 landraces or lines with three replications after inoculated with B4-1 in 2005 revealed significant differences of wheat genotypes, which indicated that resistance for DON accumulation in wheat was mainly controlled by the genetic factors within the same environment. DON content varied from 0.44 mg·kg^-1 to 9.25 mg·kg^-1. Combined with the DON content of 2003 and 2004 and other scab resistance parameters, Fanshanxiaomai, Sumai 3, Yangmai and Wangshuibai showed more stable resistance for DON accumulation. Amplification of wheat SSR markers linked with QTLs for scab resistance on chromosomes 2D, 3B, 5A and 5B revealed that 18 landraces including Yangmai etc had new resistance alleles different from that of Sumai 3. In the diallel crossing combinations, significant differences of GCA(General combining ability) and SCA(special combining ability) for DON accumulation resistance were observed among the eight parents. Among them, Sumai 3 showed the lowest DON content(0.5715 mg·kg^-1) and with the highest negative GCA values(-1.26). Negative GCA effects of Sumai 3(-1.26), Wangshuibai(-1.16) and Fanshanxiaomai(-1.13) were similar and significant for decreasing DON content, while Alondra's with the highest DON content(13.5560mg·kg^-1) and positive GCA values(2.96). Resistance for DON accumulation in wheat grains was mainly controlled by additive genetic components, while affected by partial dominance effects. Significant positive correlations among DON content, number of the diseased spikelets, percentages of diseased spikelets and diseased grains were described(r=0.5980～0.9889). The narrow sense heritability of DON accumulation resistance was 74.54%, indicating this kind of resistance might be selected in the earlier generations in breeding programs.Composite interval mapping in a DH population derived from Wangshuibai×Alondra'S F₁(120 DH lines) revealed that nine QTLs located on chromosomes 2D, 3B, 3D, 4B, 5A, 5B, 7A and 7B, respectively were associated with DON accumulation resistance of Wangshuibai. Among them, two QTLs showed higher effect, one was in the interval of Xgwm533-Xgwm493 on chromosome 3BS, and another was in the interval of Xgwm129-Xgwm156 on chromosome 5AS. Chromosomes carrying the QTLs for both DON content and percentages of diseased grains were almost the same. This indicated that the resistance for DON accumulation and the percentages of diseased grains were closely related. Resistance for DON accumulation was dominated by additive effects with a genetic contribution as 40-50%, the effect of additive epistasis effects was 20%, and additive effect×environment interaction was 10%, while the lowest effect was additive epistasis×environment interaction. Resistance for DON accumulation in wheat was mainly controlled by genetic components.