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 Cochliobo lus sativus, in 125 progeny (F6-F8) of a cross between barley cultivar s Argyle (resistant) and Melvin (tolerant) was 56.7% +/- 4.1 and the m inimum number of genes by which the two parents differed for the expre ssion of disease severity was three. The heritability of yield for the same population was 35.3% +/- 3.8, and the number of loci estimated w as at least three. There was a greater range in yield and disease expr ession in the Peace region of Alberta than at Saskatoon, Saskatchewan. At sites in the Peace from 1988 to 1990, the means of some progeny ex ceeded those of the parents; this did not occur at Sasktoon. Cluster a nalysis grouped the progeny into three classes; 45% of the lines were resistant (similar to Argyle), 45% tolerant (similar to Melvin), and 1 0% were susceptible. The rank of lines for disease reaction was genera lly similar for most resistant and tolerant progeny at both locations. The regression of grain yield on disease severity with all progeny wa s negative (y = -4.9 X + 1625 at P = 0.01) but the correlation was wea k (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 r elationship 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 withi n-class correlation between yield and disease in the tolerant group in dicated a negative association (R = -0.34, P < 0.01). This study sugge sts that a breeding strategy for developing lines resistant to common root rot, while maintaining high yield should involve screening to eli minate the highly susceptible lines from crosses and then selecting th e best yielding lines with the lowest disease.