Diallel analysis of fusarium head blight resistance in soft red winter wheat

Fusarium graminearum Schwabe, the causative agent of Fusarium head blight (FHB), is an economically important pathogen of wheat (Triticum aestivum L.). Breeding FHB resistant wheat requires knowledge of the underlying genetic control of FHB resistance. While soft red winter (SRW) wheat breeders have begun to characterize germplasm for resistance, little information is available on the value of cultivars as parents in breeding for FHB resistance. Two diallel series of crosses, each involving nine SRW parents, were evaluated in both the greenhouse and field near Lexington, KY. The progeny and parents from the diallels were point inoculated with F. graminearum in both environments. FHB severity, deoxynivalenol (DON) level, and kernel damage were recorded. FHB severity ranged from 4.9 to 84.3% in the greenhouse and from 16.4 to 86.7% in the field. Significant general and specific combining ability effects were observed in both diallels in both environments. The nature of the resistance varied with diallel and with screening environment. On the basis of ratios of variance components, resistance in diallel 1 depended primarily on additive genetic effects, while in diallel 2 in the field dominance effects prevailed. Correlations between the greenhouse and field screening environments were low (0.36 in diallel 1 and 0.14 in diallel 2). Genotype x environment interactions were highly significant and due almost exclusively to rank change interactions. These results do not support indirect selection in a greenhouse environment for resistance expressed in the field.