ASSOCIATIONS AND GENETICS OF 3 COMPONENTS OF SLOW RUSTING IN LEAF RUST OF WHEAT

Forty F6 lines, the two parental lines, and a susceptible check cultiv ar of wheat (Triticum aestivum L.) were inoculated in the young flag l eaf stage with leaf rust (Puccinia recondita f.sp. tritici) and evalua ted for latent period, receptivity, and uredinium size in a greenhouse experiment. Genotypic (r(g)) and phenotypic (r(p)) correlations betwe en latent period and uredinium size were - 0.81 and - 0.62, respective ly. A negative correlation (r(g) = - 0.50, r(p) = - 0.41) was found be tween latent period and receptivity and a positive correlation (r(g) = 0.28, r(p) = 0.26) between uredinium size and receptivity was found. Area under the disease progress curve (AUDPC) and final rust severity (FRS) obtained from a subsequent field study with common entries were negatively correlated with latent period and positively correlated wit h uredinium size. Correlations of receptivity with both AUDPC and FRS were not significant. The distributions of F6 family mean uredinia siz e and latent period were continuous between slow rusting and fast rust ing parents: however, the distribution for receptivity was discrete. N arrow-sense heritability estimates were 63%, 57%, and 47% for urediniu m size, latent period, and receptivity, respectively. Estimates of the minimum number of effective factors were three for latent period and three or four for the uredinium size and receptivity. The components a re controlled by closely linked genes or due to pleotropic effects of the same gene.