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Indole-3-Acetic Acid Improves Postharvest Biological Control of Blue Mold Rot of Apple by Cryptococcus laurentii

Cryptococcus laurentii is a well-known postharvest biocontrol yeast; however, it cannot provide satisfactory levels of decay control when used alone. Here, we evaluated the effects of indole-3-acetic acid (IAA), a plant growth regulator, on the biocontrol efficacy of the yeast antagonist C. laurentii against blue mold rot caused by Penicillium expansum in apple fruit. Results showed that the addition of IAA at 20 μg/ml to suspensions of C. laurentii greatly enhanced inhibition of mold rot in apple wounds compared with that observed with C. laurentii alone. The addition of IAA at 20 μg/ml or lower did not influence the population growth of C. laurentii in wounds, but adverse effects were seen on C. laurentii when the concentration of IAA was increased to 200 μg/ml or above in vitro and in vivo. P. expansum infection in apple wounds was not inhibited when the pathogen was inoculated into the fruit wounds within 2 h after application of IAA; however, infection was reduced when inoculated more than 12 h after IAA application. Treatment of wounds with IAA at 20 μg/ml 24 h before pathogen inoculation resulted in significant inhibition of P. expansum spore germination and host infection. Application of IAA at 20 μg/ml also reduced P. expansum infection when it was applied 48 h before pathogen inoculation in the intact fruit. Thus, IAA could reinforce the biocontrol efficacy of C. laurentii in inhibiting blue mold of apple fruit by induction of the natural resistance of the fruit.