Genotypic variation for resistance to Septoria nodorum in triticale

Septoria nodorum leaf and glume blotch is an important disease of triticale (x Triticosecale Wittm.) and can cause severe losses of grain yield in som e regions. Quantitative genetic parameters for resistance were estimated fo r 2 years in two locations in triticale genotypes artificially inoculated w ith S. nodorum. The effect of infection was assessed by a visual symptom ra ting of flag leaves and spikes and by grain yield traits relative to an uni noculated control. The mean ratings of flag leaves and spikes, calculated f rom two to four ratings, were 2.6 and 3.9, respectively. with a range of si x 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 varia tion was small with high genotype x environment interaction effects and thu s moderate to low heritabilities. In contrast, for visual ratings genotypic variation was high, with low interaction effects leading to high heritabil ities. 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 relativ e 1000-kernel weight. Therefore, visual disease ratings do not satisfactori ly assess the effect of Septoria in infection on grain yield traits. The re duction in 1000-kernel and possibly 50-ml weight are good indicators, provi ded that multi-environment tests are conducted.