329 Alberto VIGNUTELLI, Maja HILBER-BODMER and Urs W. HILBER* Swiss Federal Research Station for Horticulture, 8820 Waedenswil, Switzerland. E-mail : urs.hilberfaw.admin.ch Received 25 May 2001 ; accepted 5 December 2001. This paper describes, as a part of the resistance risk assessment, the genetic analyses which were performed to evaluate the resistance risk of the phenylpyrrole fungicide fludioxonil and the implications for cross resistance with the dicarboximide vinclozolin. Cross resistance between dicarboximides and phenylpyrroles, often found in the laboratory, has been extremely rare in the field. Over seven years of monitoring in Switzerland no fludioxonil field resistant isolates were found. Sexual crosses between a fludioxonil field resistantvinclozolin field resistant strain isolated in France and a sensitive one showed an independent segregation of the resistance to the two fungicides, suggesting that different genes regulate field resistance to fludioxonil and vinclozolin. Sexual crosses between a fludioxonil field resistant B. fuckeliana strain and a fludioxonil laboratory resistant strain indicated that the two fludioxonil resistance phenotypes segregate independently. We concluded that fludioxonil resistance is influenced by at least two different genes. Genetic studies with laboratory strains resistant to both fungicides demonstrated a low segregation rate between fludioxonil and vinclozolin resistant phenotypes. These results let us hypothesize that fludioxonil and vinclozolin resistance induced in laboratory could be due to two genes closely linked. Finally, pathogenicity tests performed with progenies of sexual crosses showed a positive correlation between virulence and phenotypes. INTRODUCTION Fludioxonil and fenpiclonil belong to the phenylpyr- roles, a novel class of non systemic fungicides (Gehmann et al. 1990). The phenylpyrrole fungicides are derivates of the antibiotic pyrrolnitrin, which is produced by various bacteria species of the genera Pseudomonas (Arima et al. 1964, Imanaka et al. 1965). Together with anilinopyrimidines and dicarboximides, the phenylpyr- roles belong to the most powerful botryticides. Fludi- oxonil and vinclozolin (a dicarboximide) are chemically very different. Yet under laboratory conditions, it is easy to produce Botryotinia fuckeliana strains resistant to both groups of compounds (Faretra & Pollastro 1993, Hilber 1992). Faretra and Pollastro (1993) identified the gene Daf1 as responsible for cross resistance in laboratory strains which were resistant to both fludioxonil and vinclozolin. These two compounds induce similar yet abnormal changes of germ tube morphology in B. fuckeliana (Leroux, Lanen & Fritz 1992). Although the mode of action of phenylpyrroles is little understood (Jespers, Davidse & de Waard 1993, Jespers & de Waard 1995), the probable resistance mechanism of the phenylpyrrole * Corresponding author. fenpiclonil is similar to the one of dicarboximides (Leroux et al. 1992). It was found by many authors that dicarboximide resistant B. fuckeliana strains collected in the field did not loose their sensitivity to fludioxonil (Chapeland et al. 1999, Gullino et al. 1998, Leroux et al. 1999). Moreover different levels of resistance to vinclozolin have been found in laboratory and field resistant strains. This may indicate the presence of other gene(s) responsible for dicarboximide resistance according to Khai-Ahmed & Bompeix (1993). However, Faretra & Pollastro (1993) attributed the same effect to the presence of different alleles for the same gene. Faretra & Pollastro (1993) reported also the presence of a laboratory strain resistant to vinclozolin in which the fludioxonil sensitivity had not been altered. Genetic analyses revealed that in this case a distinct gene called Daf2 was responsible for resistance. It appears that in Neurospora crassa the mode of action of dicarboximides differs from that of phenylpyrroles (Pillonel & Meyer 1997), which may suggest the presence of different target genes to the fungicides fludioxonil and vinclo- zolin. After several years of monitoring in Swiss vineyards which were treated annually with SWITCH, a com- pound containing fludioxonil and cyprodinil, no fludi- Mycol. Res. 106 (3) : 329–335 (March 2002).  The British Mycological Society DOI : 10.1017S0953756202005683 Printed in the United Kingdom. Genetic analysis of resistance to the phenylpyrrole fludioxonil and the dicarboximide vinclozolin in Botryotinia fuckeliana (Botrytis cinerea)