Variation among foliar isolates of Colletotrichum sublineolum of sorghum in Nigeria

Abstract

Foliar anthracnose, caused by Colletotrichum sublineolum, is a major disease of sorghum in Nigeria. Pathogenic diversity was studied among foliar isolates of C. sublineolum collected from sorghum cultivars in farmers fields in the Sahel, Sudan, northern Guinea and southern Guinea zones of Nigeria during the 1997 crop season. For the study a total of 50 isolates were identified based on typical symptom types and cultural characteristics. On the basis of growth in culture and morphological characteristics, the isolates were classified into nine morphological groups (MGs). Pathogenicity tests were done on a set of known sorghum differential lines by inoculating pot-grown seedlings in a greenhouse. On the basis of disease reaction and disease severity scores on the differential lines, the 50 isolates were classified into seven pathogenic groups (PGs). Sixteen representative isolates of the MGs and the PGs were further evaluated for virulence and aggressiveness on the differential lines and were classified into five distinct groups using the centroid method of cluster analysis. The existence of five races of C. sublineolum in major sorghum growing zones of Nigeria is suggested.