Genomic variation of Phymatotrichum omnivorum (Shear) Duggar revealed by restriction fragment length polymorphisms and random amplified polymorphic DNA

Vita.Phymatotrichum omnivorum (Shear) Duggar is a phytopathogenic fungus with one of the largest host ranges known, especially when considering its limited geographic range. Questions concerning the origin and the evolution of P. omnivorum and questions concerning the relationship between isolates of P. omnivorum remain unanswered after over a hundred years of research. The objective of this study was to determine whether a grouping of P. omnivorum isolates from various hosts and different geographic locations could be developed based on differences in their genetic composition. Additionally a single population from one infection locus was studied. Isolates were compared using the molecular techniques, restriction fragment length polymorphisms (RFLP) and random amplified polymorphic DNA (RAPD). Only one difference was detected with RFLP, although this difference was reproducible with different probes and different enzymes. The less stringent procedure, RAPD, detected variation between a larger number of isolates. There is no apparent variation in pathogenicity or virulence among isolates of P. omnivorum. The variability among isolates is limited, indicated by similarity coefficients among isolates and their determined RAPD groups of greater than 68%. Clusters of isolates determined by RAPD appear to maintain these groups when examined for vegetative/somatic compatibility. A greenhouse study of inoculated plants, with isolates within separate RAPD groups, does not establish that anastomosis or a parasexual mechanism among the isolates contributes significantly to even this low level of variation. The significance of this apparent genetic variation was not determined. The study of the proper taxonomic placement of P. omnivorum supports the separation of this genus from other Botrytis-like fungi, including other species originally placed in the genus Phymatotrichum. The analysis of the sequences of the ITS1, 5.8S and ITS2 ribosomal DNA region revealed P. omnivorum differed from the other genera examined, Botrytis Whetzel, Streptobotrys Whetzel, Amphobotrys n. g., Verrucobotrys Whetzel, Dichobotrys n. g., Chromelosporium Corda, and Pulchromyces n. g