Activity of adjuvants in ‘Aliette’ against Botryotinia fuckeliana (Botrytis cinerea) and their cross-resistance with benzimidazole fungicides

'Aliette', a formulation of the fungicide fosetyl-aluminium, is moderately active in vitro against the ascomycete Botryotinia fuckeliana (Botrytis cinerea). In contrast, fosetyl-aluminium and related chemicals, such as phosphonic acid and sodium phosphonate, have low efficacy, although it is enhanced by media with low phosphate content. This indicates that the effectiveness of 'Aliette' against B. fuckeliana is not due to fosetyl-aluminium but to adjuvants included in the formulation. The genetic basis of differences in sensitivity to 'Aliette' was investigated in field and laboratory isolates of B. fuckeliana. Genetic analysis showed that reduced sensitivity to 'Aliette' always co-segregated with resistance to benzimidazole fungicides in meiotic progeny of sexual crosses. This indicates that differences in sensitivity to 'Aliette' in B.fuckeliana are due to the major gene Mbc1 of resistance to benzimidazole fungicides and active adjuvant(s) present in 'Aliette' are linked to benzimidazoles by cross-resistance.