Biocontrol activity and induced resistance as a possible mode of action for Aureobasidium pullulans against grey mould of strawberry fruit

Efficacy and mode of action were investigated for Aureobasidium pullulans, a potential biocontrol agent for grey mould on strawberry fruit. Wound inoculation of detached green strawberry cv. Elsanta fruit with Aureobasidium pullulans prevented grey mould rot on fruit inoculated 2 days later with Botrytis cinerea. Treatment of white, pink and red-ripe fruit did not, however, control grey mould. Treatment of wound sites on green fruit with both live and heat-killed A. pullulans cells reduced B. cinerea infection compared to controls. Dip-inoculation of unwounded green strawberry fruit with A. pullulans when still attached to the plant delayed the development of grey mould after harvest at the fully ripe stage. The (i) efficacy of A. pullulans on green but not on ripening fruit, (ii) partial inhibitory effect of both live and heat-killed A. pullulans cells and (iii) absence of evidence for antibiotic production from in vitro competition tests suggest that control of grey mould on green fruit is at least partly due to a mechanism other than antagonism and / or competition. Bioassays showed that skin tissue from green fruit treated with A. pullulans had greater antifungal activity than control tissue. Thus, enhanced natural disease resistance in green strawberry fruit contributed to grey mould rot suppression by A. pullulans.