Infrequent Transmission of Double-stranded RNA Virus Particles but Absence of DNA Proviruses in Single Ascospore Cultures of Gaeumannomyces graminis

Abstract

SUMMARY A field isolate, 3b1a, of the wheat take-all fungus Gaeumannomyces graminis var. tritici, was previously shown to be infected with three serologically unrelated viruses, A, B, and C. It is now shown that virus B can be separated into two distinct strains, designated B1 and B2. All four viruses, A, B1, B2 and C, were faithfully transmitted into conidia. However, six out of eight single ascospore cultures derived from 3b1a single conidial cultures were shown to be virus-free. The remaining two single ascospore cultures each contained only one virus, which appeared to be the same in each culture. This virus was serologically indistinguishable from virus B1, but had dsRNA components of mol. wt. lower than those of virus B1 and had only the smaller of the two capsid polypeptide species of virus B1. No DNA provirus molecules homologous to viruses B1, B2 or C could be detected in two of the virus-free ascospore cultures or in one of the virus-infected ascospore cultures. Very low concentrations of virus particles were detected in hyphal tip isolates of G. graminis. After prolonged storage and subculturing of these isolates, the concentration of virus particles had increased to the level of the parent culture from which the hyphal tip isolates were derived.