MOLECULAR VARIABILITY AMONG EXSEROHILUM-TURCICUM ISOLATES USING RAPD (RANDOM AMPLIFIED POLYMORPHIC DNA)

Thirteen isolates of Exserohilum turcicum races 0, 1, 2, 23, and N col lected in widely separated geographic regions from corn (Zea mays) and five isolates collected from Johnson grass (Sorghum halepense) were c haracterized for pathogenicity and aggressiveness on both Johnson gras s and corn. DNA variability between isolates of different host specifi city, different races and differ ent geographic sources was estimated by the random amplified polymorphic DNA (RAPD) technique with 20 arbit rary decamer primers. Most primers revealed scorable and reproducible polymorphism and a total of 157 bands were scored. Distances between p airs of isolates were calculated and cluster analysis was used to gene rate a dendrogram showing relationships between them. Race-specific di agnostic patterns were not found, but the results suggested that races 0, 1, and N may be grouped separately from race 23. Levels of polymor phism among the corn-derived isolates were low. Larger genetic distanc es were observed both among the Sorghum-derived isolates and between S orghum- and corn-derived isolates than within corn derived isolates. T wo 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.