| Botrytis cinerea Pers., the causal agent of grey mould disease, infects an extremely wide range of host plants. Previous studies showed that the mycelium of B. cinerea Pers. is heterocaryotic. Thus B. cinerea has high potential to produce a genetical diverse population, especially when B. cinerea population is subjected to a fungicide selection pressure, the fungicide-resistant subpopulation would be selected and built up rapidly. By the consequence of fungicide-resistant subpopulation emeraging, the control effect of the fungicide to grey mold would be decreased or even resulted in the failure of control. Among numerous fungicides that used to against the grey mould, pyrimethanil is one of the most effective fungicides. However, it was demonstrated that under intensive using of pyrimethanil the subpopulation of pyrimethanil-resistant B. cinerea emerged rapidly in the field because the pyrimethanil-resistance was manipulated by a single gene. Pyrimethanil was introduced into Zhejiang since 1999. The decreasing of control effect was reported occasionally. In order to control grey mold disease effectively by properly using fungicides, we assayed the sensitivity of B. cinerea populaton isolated from Solanaceae vegetable crops to pyrimethanil. The in vitro fitness, pathogenicity and the ability in pectase and cellulase-producing between the subpopulations of pyrimethanil-sensitive and resistant B. cinerea was compared and the results were summarized as follow.Sensitivities to pyrimethanil of 48 isolates isolated from protecting fields in Ningbo, Jinhua, Jiaxing, Hangzhou in Zhejiang Province were determined by mycelial growth test on medium amended with different dose of pyrimethanil. Among them, 4 isolates (8.33%) showed high resistant (HR), 2 isolates (4.17%) showed middle resistant (MR), 6 isolates (12.5%) showed low resistant (LR), whereas 36 isolates were pyrimethanil-sensitive. Resistance to pyrimethanil for B. cinerea is genetically stable demonstrated by the successive subcultures for 10 times in fungicide free medium.To compare the in vitro fitness of pyrimethanil-resistant and pyrimethanil-sensitive B. cinerea populations, isolates BC-T-4-28 (S) , BC-T-4-69 (MR) and BC-T-l-37(HR)were chosen to assay their growth rates and spore production on solid PDA, mycelium gross in liquid PDA. The results showed that the growth rate between isolates of pyrimethanil-resistant and pyrimethanil-sensitive was not different significantly (PO.05), whereas the mycelium gross and spore production decreased significantly (PO.05) as the increasing of pyrimethanil resistance. This results indicates that the in vitro fitness of B. cinerea decreases as its pyrimethanil resistance emerages.To understand the inhibtion mechanism of pyrimethanil, the pathogenicities of above three B. cinerea isolates were compared via inoculation tomato fruits, and their abilities in pectase and cellulase-producing were assayed. The result showed that both pathogenicity, pectase and cellulase-production decreasesd in some degree as the its pyrimethanil resistance increased. This result is consistent with that pyrimethanil may protect plants from the damage of B. cinerea by inhibiting its secretion of the ectoenzymes.One feature of B. cinerea population is that it consisted of at least two sympatric sibling species, characterized by the presence (transposa) or absence (yacumd) of the transposable elements Boty and Flipper. To elucidate if the isolates of B. cinerea we collected contain transposa, and the characteristic of the transposa, two pairs of primers, which aimed to amplify the transposable elements Boty and Flipper were synthesised according to the reported sequences of these elements, and 123 isolates were analysed in this study. The result demonstrated that 8 isolates (6.5%) have Boty only, 31 isolates (25.2%) have Flipper only, 53 isolates (43.1%) have both Boty and Flipper, whereas 31 isolates (25.2%) do not have any transposable element. Our analysis indicates that pyrimethanil resistance of B. cinerea is not associated with the presence of transposable elements.
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