Isozyme Analysis to Differentiate Species ofPeronosclerosporaCausing Downy Mildews of Maize

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Abstract
Isozymes from 10 fungal cultures representing 3 spp. of the genus Peronosclerospora were compared electrophoretically on starch gels to determine if isozyme analysis can be used to aid in species identification. Cultures of P. sorghi from Texas (USA), southern India and Brazil were nearly identical with apparent polymorphisms (allelic variations) at 3 of 13 presumed loci examined. Of 15 apparent alleles detected in an isolate of P. sorghi from Thailand, only 4 were in common with alleles in any of five other cultures of typical P. sorghi. Two cultures of P. philippinensis from the Philippines and 1 of P. sacchari from Taiwan had all 16 alleles in common indicating that they are most likely of the same species. In 4 cultures of the P. sacchari-P. philippinensis complex, apparent polymorphisms were evident in 6 of 13 loci examined. Considerable potential for variation exists in this "species." The isolate of P. sorghi from Thailand was more closely related to the P. sacchari-P. philippinensis complex than to the other isolates of P. sorghi. An average coefficient of similarity of 0.50 was estimated by comparing the Thailand culture with P. sacchari and P. philippinensis at 13 loci. Isozyme analysis is useful for distinguishing species of Peronosclerospora and elucidating phylogenetic relationships.