Genotypic variation for resistance to Septoria nodorum in triticale

Abstract

Septoria nodorum leaf and glume blotch is an important disease of triticale (×_Triticosecale Wittm.) and can cause severe losses of grain yield in some regions. Quantitative genetic parameters for resistance were estimated for 2 years in two locations in triticale genotypes artificially inoculated with S. nodorum. The effect of infection was assessed by a visual symptom rating of flag leaves and spikes and by grain yield traits relative to an uninoculated control. The mean ratings of flag leaves and spikes, calculated from two to four ratings, were 2.6 and 3.9, respectively, with a range of six ratings for spikes and over five for flag leaves. Infection caused an 11.5% mean reduction in kernel weight per spike, which was the result of 13.2% lower 1000-kernel weight. The number of kernels per spike and 50-ml weight were little affected. For all relative grain yield traits, genotypic variation was small with high genotype-environment interaction effects and thus moderate to low heritabilities. In contrast, for visual ratings genotypic variation was high, with low interaction effects leading to high heritabilities. Phenotypic correlation between flag leaf and spike ratings was low, indicating independent disease resistance mechanisms. The best association, although still moderate, was obtained between flag leaf rating and relative 1000-kernel weight. Therefore, visual disease ratings do not satisfactorily assess the effect of Septoria infection on grain yield traits. The reduction in 1000-kernel and possibly 50-ml weight are good indicators, provided that multi-environment tests are conducted.