Values of Stress Resistance Genes Relative to Dry Weight Accumulation in Wheat Seedlings

Abstract

Biotic stresses on winter wheat (Triticum aestivum L.) seedlings can be extremely damaging. Many genes for resistance to insects and pathogens have been introduced into wheat; however, no quantitative estimates are available regarding the effectiveness of such genes with regard to seedling traits. In this study we used closely related lines derived from backcrossing using a single recurrent parent to assist in estimating genotypic values for four resistance genes Pm17, for resistance to powdery mildew; Gb2, for resistance to biotype ‘C’ greenbug; and two sources of resistance to biotype ‘E’ greenbug, Gb3 and Gb6. All genes were present in the TAM-105 background. The genotypes were evaluated for dry matter accumulation during a 5-week period, beginning at the two-leaf stage. For each greenbug resistance gene, two initial infestation rates were examined, 0.5 and 5.0 aphids per plant. Powdery mildew damage to susceptible seedlings developed more slowly than did greenbug damage at either infestation rate. Resistance conferred by Pm17 was completely effective in maintaining seedling dry weight in inoculated vs. uninoculated plants, while greenbug infestation of any of the resistant genotypes at 5.0 aphids per plant resulted in significantly reduced dry matter accumulation, compared to uninfested control plants by the end of the study. In TAM-105, which is susceptible to both greenbug biotypes, reduced dry weight occurred earlier when infested with biotype ‘E’ than with biotype ‘C’. Also, while both TAM-105 and TAM-107 are susceptible to biotype ‘E’, when infested with that biotype, TAM-105 exhibited reduced dry weight sooner than did TAM-107, which possesses biotype ‘C’ resistance. These results that biotype ‘E’ is the more damaging of the two biotypes, but that biotype ‘C’ resistance confers some delay in development of symptoms to biotype ‘E’.