dc.description.abstract |
Botrytis cinerea (teleomorph: Botryotinia fuckeliana) is a plant pathogenic fungus of significant economic interest for the international horticultural industry and control is complicated by resistance to current fungicides. Mycoviruses that alter the virulence of B. cinerea are therefore of interest as potential biological control agents. This thesis explored the effects of Botrytis virus X on B. cinerea and the hypothesis that sex in fungi provides a mechanism for the elimination of mycoviruses and avoidance of reinfection. There was an 89% retention rate of BVX in individual conidiospores from virus positive B. cinerea, indicating vertical transmission comparable to the more efficient dsRNA isometric viruses. Transmission through sexual spores did not eliminate BVX, with transmission rates of 36% and 55% in progeny from reciprocal crosses between BVX positive and BVX negative isolates, demonstrating that sex does not completely or largely eliminate BVX. Horizontal transmission through hyphal fusion was demonstrated using auxotrophic Nit mutants, with BVX being detected in two of twenty single conidiospore isolates post hyphal fusion. The phenotypic effects of BVX on B. cinerea were assessed in-vitro for linear growth, conidia production and sclerotia production, and in-vivo using an apple rot test. Growth of BVX positive B. cinerea on agar plates was significantly faster than that of BVX free isolates while, in contrast, BVX negative B. cinerea produced a statistically significant larger rot area in apples than BVX negative B. cinerea. In the majority of cases BVX presence had no significant effect on conidiospore and sclerotia production in vitro, although BVX positive isolates from the anastomosis experiment produced fewer sclerotia by day 14. Testing of New Zealand and international B. cinerea isolates for the presence of BVX, using RT-PCR, detected BVX-like sequences in isolates from New Zealand, Italy, Switzerland, England, Greece, Portugal, Belgium, Israel, France and USA. The sequences from different locales showed very little variation, providing strong circumstantial evidence that despite the large number of B. cinerea hyphal incompatibility groups these are not a major barrier to horizontal transmission. This is a critical factor if mycoviruses are to be considered as biological control agents for B. cinerea. |
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