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 the barley cultivars Argyle (resistant) and Melvin (tolerant) was 56.7±4.1% and the min. number of genes by which the 2 parents differed for the expression of disease severity was 3. The heritability of yield for the same population was 35.3±3.8%, and the number of loci estimated was at least 3. There was a greater range in yield and disease expression in the Peace region of Alberta than at Saskatoon, Saskatchewan, Canada. At sites in the Peace region during 1988-90, the means of some progeny exceeded those of the parents; this did not occur at Saskatoon. Cluster analysis grouped the progeny into 3 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). It is suggested 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.