Competition between aggressive and non-aggressive strains of Botrytis cinerea (Botryotinia fuckeliana) on French bean leaves

Competition was assessed between aggressive and non-aggressive strains of B otryris cinerea on French bean (Phaseolus vulgaris) leaves by inoculating s trains simultaneously and sequentially(6, 12 or 24 h later). The lesions pr oduced when an aggressive strain (forming large lesions) and a non-aggressi ve strain (forming small, restricted lesions) were inoculated simultaneousl y were intermediate in size between those produced by the strains when inoc ulated individually, suggesting that the two strains were co-existing in th e lesion. However, in sequential inoculation when the second inoculation wa s delayed 6 h or more, lesion sizes typical of the first inoculated strain were found indicating that the first strain to be inoculated dominated the infection site. Competition between two aggressive strains, individually id entifiable by genetic markers, was found to follow a similar pattern, sugge sting that the dominating effect of the first strain is a general phenomeno n. Domination of the lesion site by the nonaggressive strain prevented an a ggressive strain from forming spreading lesions suggesting a possible use f or these strains as a biocontrol agent in some disease situations.