CORRELATION BETWEEN HYPOVIRUS TRANSMISSION AND THE NUMBER OF VEGETATIVE INCOMPATIBILITY (VIC) GENES DIFFERENT AMONG ISOLATES FROM A NATURAL-POPULATION OF CRYPHONECTRIA-PARASITICA
Yc. Liu et Mg. Milgroom, CORRELATION BETWEEN HYPOVIRUS TRANSMISSION AND THE NUMBER OF VEGETATIVE INCOMPATIBILITY (VIC) GENES DIFFERENT AMONG ISOLATES FROM A NATURAL-POPULATION OF CRYPHONECTRIA-PARASITICA, Phytopathology, 86(1), 1996, pp. 79-86
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.