Presence of double-stranded RNA and virus-like particles in Botrytis cinerea

Abstract

Double-stranded RNA (dsRNA) was demonstrated in mycelial extracts in 143 of 200 isolates of Botrytis cinerea from a range of hosts in New Zealand. The dsRNA profiles differed widely between isolates in the number, size and relative concentration of dsRNA species present. Virus-like particles (VLPs) were observed by electron microscopy in partly purified virus preparations in three of five dsRNA-containing isolates examined. Morphological types present included isometric particles of varying size classes (approx. 30, 35, 40 and 45 nm) and bacilliform particles (approx. 25 × 63 nm). Such particles were not observed in five isolates apparently lacking dsRNA but flexuous rods with a modal length of approx. 720 nm were present in one. Total RNA extraction of partly purified VLP preparations gave similar profiles to those obtained from mycelial dsRNA extractions of the same isolates, suggesting that the VLPs represent encapsidated dsRNA. Comparison of 12 dsRNA-containing and 12 dsRNA-free isolates indicated slight differences between the two groups in radial growth rate, virulence on bean leaves and sclerotial number but the differences were minor and the ranges overlapped.