ABSTRACT
In Switzerland, the use of phenylpyrrole, anilinopyrimidine, and hydroxyanilide fungicides for control of Botryotinia fuckeliana, causal agent of gray mold in grapes, has been restricted to one treatment per fungicide class per year as part of an anti-resistance strategy. Resistance development in B. fuckeliana was monitored from 1995 to 2001 for the anilinopyrimidine cyprodinil and the phenylpyrrole fludioxonil and from 1997 to 2001 for the hydroxyanilide fenhexamid in experimental vineyards in Richterswil and Stäfa, Switzerland. In total, over 2,400 field isolates were tested. In 1996, the first case of field resistance to anilinopyrimidines was encountered in Richterswil. Efficacy of the anilinopyrimidine cyprodinil decreased significantly, and 54% of the isolates were resistant to anilinopyrimidines. During 7 years of monitoring, one field isolate was found that showed a slightly decreased sensitivity to the phenylpyrrole fludioxonil. Resistance to the hydroxyanilide fenhexamid was not found in 1997 and 1998. From 1999 to 2001, the level of fenhexamid-resistant isolates increased to 100% in Stäfa. The analysis of monitoring and efficacy data showed that subpopulations of B. fuckeliana resistant to cyprodinil and fenhexamid have increased significantly; however, the efficacy of a mixture of fludioxonil and cyprodinil and of fenhexamid alone was still effective. The objective of this study was to initiate long-term monitoring in order to establish an early resistance-detection system as a tool to assess the effectiveness of the anti-resistance strategy used in Switzerland.
ABSTRACT
The anilinopyrimidines constitute a new class of mainly protective, broad-spectrum fungicides with a high activity against Botryotinia fuckeliana, the causal agent of gray mold on a wide range of host plants. The present study was initiated to investigate the genetic basis of resistance to anilinopyrimidines in B. fuckeliana and to assess the frequency of resistant isolates in vineyards in Switzerland exposed to experimental applications of anilinopyrimidines. In mating experiments, two sensitive reference isolates were crossed with three anilinopyrimidine-resistant field isolates. The analysis of 72 sexual progeny from six apothecia demonstrated that resistance to the anilinopyrimidine fungicide cyprodinil segregated in a 1:1 ratio and is therefore monogenic. The same segregation ratio was found for resistance to the dicarboximide fungicide vinclozolin. Resistance to cyprodinil segregated independently from resistance to vinclozolin. From 1993 to 1995, isolates of B. fuckeliana were collected in Switzerland from five vineyards that differed in their anilinopyrimidine spray history. Of a total of 303 isolates tested in vitro, three anilinopyrimidine-resistant isolates were detected in two vineyards where the cumulative number of treatments was between two and nine. The results of the study are discussed with respect to the implementation of an antiresistance strategy in Switzerland.
