Components of rust resistance in peanut genotypes.

Components of resistance to peanut rust were evaluated in 144 genotypes with the detached-leaf technique. All components of disease resistance ― infection frequency, incubation period, lesion diameter, percentage of leaf area damage, and sporulation index ― were significantly correlated with each other and with mean field rust scores. Incubation period was negatively correlated with all other components, which were positively correlated with one another. Significant differences among genotypes were observed for each component. The greatest variability among genotypes was observed for incubation period and percentage of leaf area damage. Of 144, 17 genotypes had a low sporulation index (1.3-2.5) and long incubation period (17.1-21 days). Components of resistance were further examined in 20 selected genotypes (based on sporulation index and incubation period levels), including the rust-susceptible cultivar TMV 2. Different components of resistance were not found in all genotypes; complementation of components was evident in genotypes ICG 10890 and 10881. The interrelationships among the components are described, and the usefulness of the incubation period and sporulation index is discussed in relation to selection for rust resistance