RAPD-PCR analysis of genetic variation among isolates of Alternaria solani and Alternaria alternata from potato and tomato

Random amplified polymorphic DNA-PCR (RAPD-PCR) analysis was used to investigate genetic variation among 35 isolates of Alternaria solani, the causal agent of early blight on solanaceous crops, and 30 isolates of A. alternata, an opportunistic pathogen. A symmetric dissimilarity matrix, based on Euclidean metric distances, was used to calculate interpopulation genetic distances (Phi(st)) between the fungal species, geographic origin, and host plant. Of the total genetic variation observed, 34% (Phi(st) = 0.340, P < 0.0001) resided between the two fungal species. A very highly significant interpopulation genetic distance (Phi(st) = 0.2275, P < 0.0001) was observed between isolates of A. solani collected from potato and tomato, suggesting the possibility of pathogenic specialization. There was a significant difference between isolates of A. solani (Phi(st) = 0.1569, P < 0.017) and A. alternata (Phi(st) = 0.1096, P = 0.02) from foreign and domestic sources, but no difference between isolates from Pennsylvania and other states. One primer, P248, generated polymorphisms that could be used to distinguish between the two fungal species.