Phenotypic response and quantitative trait loci for resistance to Cephalosporium gramineum in winter wheat

Cephalosporium stripe (Cephalosporium gramineum) is an important disease limiting adoption of conservation tillage practices in the Pacific Northwest. The disease can cause severe loss of grain yield and quality in winter wheat (Triticum aestivum L.). Modified cultural practices can reduce disease incidence, but are not always dependable because of variation in climatic conditions and conflicts with soil conservations goals. The most desirable method of control would be planting of resistant cultivars. Improving disease resistance is problematic, however, as infection and disease response are environmentally dependent. Little is known about inheritance and level of resistance required to minimize grain yield loss. A combination of field trials and molecular genotyping was used to investigate the genetics and inheritance of resistance to Cephalosporium gramineum. Yield loss and impact on kernel characteristics was examined using 12 cultivars in field trials comparing inoculated and non-inoculated treatments. Negligible reduction in grain yield or test weight was observed with disease ratings of less than 5% whiteheads (sterile heads caused by pathogen infection). However, grain yield of the susceptible cultivar Stephens was reduced by 1.7 t ha⁻¹ with addition of inoculum. Response to Cephalosporium stripe was positively correlated with uniformity in kernel size, possibly a function of reduced number of seeds per spike. A recombinant inbred line (RIL) population derived from a cross between two commercially grown winter wheat cultivars was studied. Whiteheads and kernel characteristics were measured on each RIL. Quantitative trait loci (QTL) analysis identified seven regions associated with resistance to Cephalosporium stripe, with approximately equal effects, four derived from the susceptible parent (Brundage) and three from the resistant parent (Coda). Additivity of QTL effects was confirmed through regression analysis. Two resistance QTL were found to be related to head morphology traits. A promising QTL located on chromosome 5B could be related to toxin insensitivity genes described for other wheat pathogens. This study confirms the importance of Cephalosporium stripe as a threat to grain yield for wheat growers in the Pacific Northwest. Molecular markers can be effectively used to identify and combine QTL and provide higher levels of genetic resistance than available in commercial cultivars