Optimizing phenotypic and genotypic selection for Fusarium head blight resistance in wheat

Fusarium head blight (FHB), or head scab, is an economically important disease of wheat (Triticum aestivum L.). In developing FHB-resistant soft winter wheat cultivars, breeders have relied on phenotypic selection, marker assisted selection (MAS), or a combination of the two. The objectives of this study were to estimate heritability of resistance in a resistant × susceptible cross and to simulate selection in order to determine the optimal combination of phenotypic and genotypic selection. F₂ derived lines from the cross of KY93C-1238-17-2 (high yielding, susceptible) × VA01W-476 (resistant line with two exotic quantitative trait loci (QTL) and additional resistance) were grown under artificial inoculation in scab nurseries at Lexington (2007 and 2008) and Princeton (2008), KY. Visual symptoms were estimated on a 1-3 scale; percentage Fusarium damaged kernels (FDK), and deoxynivalenol (DON) concentration were measured. VA01W-476 contributed resistance alleles at two major QTL: Fhb1 and a QTL on chromosome 2DL, QFhs. nau-2DL. In this genetic background, the effect of QFhs. nau-2DL was more pronounced than that of Fhb1: 55 vs. 25% DON reduction and 40 vs. 32% FDK reduction. Genotypic selection based on both QTL was equivalent to phenotypic selection of the most resistant 28% of the population for DON and the most resistant 24% of the population for FDK. We propose that an initial round of phenotypic selection at moderate selection intensity will enrich the population with major QTL resistance alleles while maintaining variation at minor scab resistance loci and for other traits in general. Genotyping can then be used to extract lines whose phenotypic worth has been demonstrated and which are homozygous for resistance alleles at the major QTL.