Effect of frequency of defoliation of 40 Stylosanthes guianensis genotypes on field reaction to anthracnose caused by Colletotrichum gloeosporioides

Abstract

Four different defoliation frequency treatments (uncut, or cut to approx, 10 cm every 4, 8, or 12 weeks) were imposed over 40 weeks on 40 S. guianensis genotypes to determine whether defoliation frequency can reliably be used to alter reproductive stage (as measured by visual score of flowering abundance) of the host plant and to determine the degree of association between anthracnose severity and reproductive stage. Flowering was more abundant and anthracnose more severe with less frequent defoliation. Flowering abundance was closely related with weeks of uninterrupted regrowth. Anthracnose severity was not closely associated either with weeks of uninterrupted regrowth nor with flowering abundance. The genotype-defoliation frequency interaction effect on anthracnose severity was very small compared to the main effects. Thus defoliation frequency of field trials should not affect reliability of estimation of relative genetic resistance to anthracnose. Flowering abundance was positively correlated with anthracnose susceptibility across genotypes, but the correlation was generally of only moderate magnitude.