GENETIC-VARIABILITY OF PAECILOMYCES-FUMOSOROSEUS ISOLATES REVEALED BYMOLECULAR MARKERS

Paecilomyces fumosoroseus (Deuteromycotina:Hyphomycetes) is a fungus t hat is potentially useful for the biocontrol of economically important agricultural pests, such as whitefly (Bemisia tabaci). Arbitrarily pr imed PCR and PCR with tRNA consensus primers were used to analyze gene tic variability among 27 P. fumosoroseus isolates, 15 of which came fr om the same host, B. tabaci, one P. lilacinus isolate, used as an outg roup, 9 previously unidentified Paecilomyces isolates. Fifteen 10-mer oligonucleotide primers of arbitrary sequence revealed 322 scorable bi nary characters. Principal coordinates and cluster analysis of charact ers showed that most of the P. fumosoroseus and Paecilomyces sp. isola tes were in three phenetic groups with >65% internal similarity. Two o f the three arbitrary phenetic groups were closely related (76% simila rity) with the third group quite different (only 14% similarity) from the first two. The phenetic groups did not correlate with geographical origin or host species. Genetic variability of isolates infecting whi tefly in Florida was detected. Isolates from B. tabaci were represente d in two of the three groups, and different genotypes were identified even when they were isolated from an epizootic population in India and Pakistan. There was no evidence of host-specific selection of genotyp es, as has been shown in other entomopathogenic fungi. Three isolates morphologically classified as P. fumosoroseus were clustered in a phen etic group which displayed only 14% similarity to the other isolates o f this species. Seven isolates that presented problems for morphologic al classification were found to be similar or, in three cases, identic al to other P. fumosoroseus isolates that did not present problems for morphological classification. Two of the three difficult-to-classify isolates clearly belonged to other species, based on their low degree (<13%) of similarity in relation to the three main phenetic groups of P. fumosoroseus and to each other. This level of divergence suggests t hat what is morphologically classified as P. fumosoroseus likely repre sents a species aggregate, in agreement with studies of other entomopa thogenic fungi. Phenetic analysis using arbitrarily primed PCR polymor phisms was concordant with a phylogenetic analysis of 107 amplified pr oducts (53 informative) obtained by PCR with four pairs of consensus t RNA gene primers. Molecular data suggested that a morphologically base d taxonomy provides little insight to species, and perhaps, in some ca ses, even genera within imperfect fungi. Both the arbitrarily primed P CR and the tRNA fingerprinting were found to be powerful tools for imp roving the taxonomy of the genus Paecilomyces and other imperfect fung i. (C) 1995 Academic Press, Inc.