TRANSGRESSIVE SEGREGATION FOR RESISTANCE TO PYRENOPHORA-TERES IN BARLEY

Populations of F1, F2, F1 x parent 1 (BC1), F1 x parent 2 (BC2), and F 3 resulting from two crosses between four susceptible varieties of bar ley used in national and international breeding programmes were tested at the seedling stage for their resistance to an isolate of Pyrenopho ra teres which is virulent to the parental varieties. Infection type, average lesion size, and number of lesions per unit leaf area were use d to assess disease reaction. In the two crosses, F2 and especially F3 generations (produced by self pollination of selected resistant F2 pl ants) showed more resistance expressed by infection type and average l esion size than either parent. The frequency distributions of F2 and F 3 generations derived from these crosses were continuous and showed tr ansgressive segregation for resistance. The results indicated that the four cultivars used in this study possessed additive genes for resist ance to P. teres. Thus useful resistance could be obtained following c rossing of susceptible cultivars and selection in succeeding generatio ns.