CHARACTERIZATION AND GENETIC-ANALYSIS OF FIELD ISOLATES OF BOTRYOTINIA-FUCKELIANA (BOTRYTIS-CINEREA) RESISTANT TO DICHLOFLUANID

Field isolates of Botryotinia fuckeliana were collected from naturally infected plants. Their responses to the multisite fungicide dichloflu anid in mycelium growth test fell into three phenotypic classes, chara cterized by the following EC(50) (and MIC) values in mu g ml(-1): sens itivity, 1-3 (6-10); low resistance, 3-10 (> 100); high resistance, 10 -30 (> 100). The corresponding values obtained for these classes in a spore germination test were respectively: congruent to 0.05 (0.2), 0.0 5-0.1 (0.5), 0.5-1 (0.9-1.5). Resistant isolates were crossed with two sensitive and two resistant strains of appropriate mating type to det ermine the genetic basis of resistance. Distribution of resistance phe notypes in ascospore progeny indicated that a gene, named Dic1, was pr obably responsible for the low or high resistance of 14 mutants select ively collected from experimental plots of greenhouse-grown gerbera sp rayed several times with dichlofluanid or tolyfluanid. A second gene, named Dic2, was probably responsible for the low resistance displayed by two isolates (from grapevine and from carnation) maintained in the laboratory collection. As a result of the investigation, the use of di chlofluanid in integrated management programmes against grey mould is discussed.