Genetic Variability of Paecilomyces fumosoroseus Isolates Revealed by Molecular Markers

Abstract

Paecilomyces fumosoroseus (Deuteromycotina:Hyphomycetes) is a fungus that is potentially useful for the biocontrol of economically important agricultural pests, such as whitefly (Bemisia tabaci). Arbitrarily primed PCR and PCR with tRNA consensus primers were used to analyze genetic variability among 27 P. fumosoroseus isolates, 15 of which came from the same host, B. tabaci, one P. lilacinus isolate, used as an outgroup, 9 previously unidentified Paecilomyces isolates. Fifteen 10-mer oligonucleotide primers of arbitrary sequence revealed 322 scorable binary characters. Principal coordinates and cluster analysis of characters showed that most of the P. fumosoroseus and Paecilomyces sp. isolates were in three phenetic groups with >65% internal similarity. Two of the three arbitrary phenetic groups were closely related (76% similarity) 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 whitefly in Florida was detected. Isolates from B. tabaci were represented 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 genotypes, as has been shown in other entomopathogenic fungi. Three isolates morphologically classified as P. fumosoroseus were clustered in a phenetic group which displayed only 14% similarity to the other isolates of this species. Seven isolates that presented problems for morphological classification were found to be similar or, in three cases, identical 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 that what is morphologically classified as P. fumosoroseus likely represents a species aggregate, in agreement with studies of other entomopathogenic fungi. Phenetic analysis using arbitrarily primed PCR polymorphisms was concordant with a phylogenetic analysis of 107 amplified products (53 informative) obtained by PCR with four pairs of consensus tRNA gene primers. Molecular data suggested that a morphologically based taxonomy provides little insight to species, and perhaps, in some cases, even genera within imperfect fungi. Both the arbitrarily primed PCR and the tRNA fingerprinting were found to be powerful tools for improving the taxonomy of the genus Paecilomyces and other imperfect fungi.