GENETIC-RELATIONSHIPS BETWEEN REACTION TO COMMON ROOT-ROT AND YIELD IN THE PROGENY OF A BARLEY CROSS

The heritability of resistance to common root rot, caused by Cochliobolus sativus, in 125 progeny (F6-F8) of a cross between barley cultivars Argyle (resistant) and Melvin (tolerant) was 56.7% +/- 4.1 and the minimum number of genes by which the two parents differed for the expression of disease severity was three. The heritability of yield for the same population was 35.3% +/- 3.8, and the number of loci estimated was at least three. There was a greater range in yield and disease expression in the Peace region of Alberta than at Saskatoon, Saskatchewan. At sites in the Peace from 1988 to 1990, the means of some progeny exceeded those of the parents; this did not occur at Sasktoon. Cluster analysis grouped the progeny into three classes; 45% of the lines were resistant (similar to Argyle), 45% tolerant (similar to Melvin), and 10% were susceptible. The rank of lines for disease reaction was generally similar for most resistant and tolerant progeny at both locations. The regression of grain yield on disease severity with all progeny was negative (y = -4.9 X + 1625 at P = 0.01) but the correlation was weak (R = -0.24). This relationship was stronger when the tolerant group of lines was removed from the regression (R = -0.53, P < 0.001). The relationship between yield and disease among the resistant and tolerant lines was positive (y = 5.7 X + 1136, R = 0.28, P <0.01), yet a within-class correlation between yield and disease in the tolerant group indicated a negative association (R = -0.34, P < 0.01). This study suggests that a breeding strategy for developing lines resistant to common root rot, while maintaining high yield should involve screening to eliminate the highly susceptible lines from crosses and then selecting the best yielding lines with the lowest disease.