CORRELATION BETWEEN HYPOVIRUS TRANSMISSION AND THE NUMBER OF VEGETATIVE INCOMPATIBILITY (VIC) GENES DIFFERENT AMONG ISOLATES FROM A NATURAL-POPULATION OF CRYPHONECTRIA-PARASITICA

Correlation between hypovirus transmission and the number of different vegetative incompatibility (vie) genes among isolates of Cryphonectri a parasitica was estimated using isolates sampled from a natural popul ation. We tested the hypothesis that transmission of hypoviruses among isolates is negatively correlated to the number of vic genes that are different between vegetative compatibility (vc) groups. In a sample o f 58 isolates collected from a population in Finzel, MD, eight isolate s, each in a different vc group, were randomly selected and infected w ith each of the Cryphonectria hypoviruses CHV1-EP43 and CHV2-NB58. The frequency and time required for virus transmission were estimated by pairing infected donor isolates with uninfected recipient isolates in vitro. The number of vic genes different between vc groups was estimat ed by crossing the donor and recipient isolates and determining the pr oportion of ascospore progeny that were vegetatively compatible with e ither parent. Hypovirus transmission occurred between all pairs of iso lates that were vegetatively compatible. The frequencies of transmissi on between vc groups that differed by one vic gene were 0,50 and 0.48 when the donor isolates were infected with CHV1-EP43 or CHV2-NB58, res pectively. Transmission frequencies decreased to 0.13 for CHV1-EP43 an d 0.14 for CHV2-NB58 when ve groups differed by two vic genes. When vc groups were different by more than two vic genes, transmission of hyp oviruses occurred in only one out of 37 pairs (3%) and one out of 25 p airs (4%) with CHV1-EP43 and CHV2-NB58 in the donor isolates, respecti vely. The transmission frequency was negatively correlated to the numb er of vic genes different between isolates (P < 0.01). In contrast, th e time taken for transmission to occur was only weakly correlated (r = 0.40, P = 0.05) to the number of vic genes different between vc group s. Unidirectional transmission of hypoviruses was observed between six pairs of vc groups. This study provides evidence for a significant ne gative correlation between the frequency of hypovirus transmission and the number of vic genes different between isolates of C. parasitica f rom a natural population.