Molecular variability among Exserohilum turcicum isolates using RAPD (random amplified polymorphic DNA)

Thirteen isolates of Exserohilum turcicum races 0, 1, 2, 23, and N collected in widely separated geographic regions from corn (Zea mays) and five isolates collected from Johnson grass (Sorghum halepense) were characterized for pathogenicity and aggressiveness on both Johnson grass and corn. DNA variability between isolates of different host specificity, different races and differ ent geographic sources was estimated by the random amplified polymorphic DNA (RAPD) technique with 20 arbitrary decamer primers. Most primers revealed scorable and reproducible polymorphism and a total of 157 bands were scored. Distances between pairs of isolates were calculated and cluster analysis was used to generate a dendrogram showing relationships between them. Race-specific diagnostic patterns were not found, but the results suggested that races 0, 1, and N may be grouped separately from race 23. Levels of polymorphism among the corn-derived isolates were low. Larger genetic distances were observed both among the Sorghum-derived isolates and between Sorghum- and corn-derived isolates than within corn derived isolates. Two Sorghum isolates, S-4 and S-5, can infect also corn. Our molecular data indicate that isolates S-4 and S-5 are closer to the corn-derived isolates than to the Sorghum specific ones.