Control of postharvest black rot caused by Alternaria alternata in strawberries by the combination of Cryptococcus laurentii and Benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester

The biological control activity of Cryptococcus laurentii alone or in combination with Benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH) against postharvest black rot caused by Alternaria alternata in strawberries was investigated. As a stand-alone treatment, C. laurentii significantly reduced the incidence and lesion diameter of black rot in strawberries at 20 °C. The incidence and lesion diameter in strawberries treated with BTH alone was not significantly different from that in the control. C. laurentii in combination with BTH (0.1 g L⁻¹) was more effective than C. laurentii alone or BTH alone. BTH only slightly increased the population of C. laurentii in strawberry wounds and nutrient yeast dextrose broth (NYDB) and had little inhibition effect on the growth of A. alternate in potato dextrose agar (PDA). The enzyme analysis results showed that BTH significantly increased the activity of defense enzymes, including polyphenol oxidase (PPO), peroxidase (POD), and catalase (CAT) in strawberries treated with C. laurentii in combination with BTH. All these results indicated that the action mode of BTH enhancing the biocontrol efficacy of C. laurentii against A. alternata may involve in its ability to induce defense enzymes including PPO, POD and CAT in strawberries rather than its direct effect on C. laurentii or A. alternata.