Genetic resistance to and effect of leaf rust and powdery mildew on yield and its components in 50 soft red winter wheat cultivars

Effects of leaf rust (caused by Puccinia triticina f. sp. tritici Eriks.) and powdery mildew [caused by Blumeria graminis (DC.) E. O. Speer f. sp. tritici Em. Marchal], on performance of 50 soft red winter (SRW) wheat (Triticum aestivum L) cultivars were evaluated under natural field conditions. Widely grown cultivars released from 1919 to 2009 with varying disease resistance were grown in split-plot experiments in 2010 and 2011. Treated replications received seed treatments of triadimenol, captan and imidacloprid and foliar applications of propiconazole and prothioconazole + tebucanazole fungicides. Non-treated replications received only tebucanazole + metalaxyl + imazalil seed treatments. Final mean disease severity, agronomic, yield-related traits, yield components and spike characteristics were analyzed to determine individual and combined effects of leaf rust and powdery mildew on the cultivars. Yield losses as high as 54% were observed in the susceptible cultivar Red May. Average yield losses ranged from 1% to 21%. Yield losses primarily due to powdery mildew were as high as 14%, and losses primarily due to leaf rust were as high as 33%. Powdery mildew had the largest negative correlation with harvest index and seeds/spike. Leaf rust was most negatively correlated with plant biomass and harvest index, with a less consistent negative relationship with kernel weight.