DNA RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISMS IN MYCOSPHAERELLA SPECIES THAT CAUSE BANANA LEAF-SPOT DISEASES

Restriction fragment length polymorphisms (RFLPs) of leaf spot pathoge ns of bananas, Mycosphaerella spp., were examined with low-copy nuclea r DNA probes isolated from a M. fijiensis cosmid library. The two rela ted fungi, M. musicola and M. fijiensis, displayed different RFLP patt erns and hybridization intensities, suggesting considerable interspeci fic genetic divergence. The synonymy of M. fijiensis var. difformis wi th M. fijiensis was supported because RFLP patterns were similar and d id not reflect morphological variations between these fungi. Fifty-sev en isolates of M. fijiensis with different geographic origins were ass ayed for RFLPs. The highest level of genetic diversity in this pathoge n was found in Southeast Asia, the region where it probably originated according to the chronological spread of M. fijiensis in the world. I n other areas, isolates formed genetically homogeneous groups specific for each region (Africa, Pacific islands, and Latin America). Such ge ographical differentiation suggests that there was limited introductio n of M. fijiensis into each of these regions.