Reduction of postharvest diseases of loquat fruit by serine protease and possible mechanisms involved

Abstract

Anthracnose caused by Colletotrichum acutatumis the most common disease-causing decay duringthe postharvest storage of loquat fruit.The use of serine proteasecould reduce decay of the fresh fruits during storage. However, the postharvest studies with the serine protease are limited. This study explored the mechanism of keeping loquat fruit fresh by serine protease. In vitro, SP treatment resulted in abnormal hyphae of C. acutatum, damaged plasma membrane integrity and decreased spore germination rate. Then we applied the best concentration of SP of 120 mg•L−1to explore its effect on loquat fruit. Test fruits were exposed to 2 different treatments, which are (i) serine protease (120 mg•L−1)+ C. acutatum, (ii)sterile water + C. acutatum as control. In vivo, SP treatment could regulate reactive oxygen species (ROS) metabolism of loquat fruit by enhancing the activities of catalase (CAT), superoxide dismutase (SOD) and ascorbate peroxidase (APX), and activating AsA-GSH circulatory system. SP treatment improved the disease resistance of loquat fruit to C. acutatum by enhancing the activities of phenylalanine ammonia lyase (PAL), peroxidase (POD), polyphenol oxidase (PPO), chitinase (CHI) and β-1,3-glucanase (GLU), promoting the accumulation of total phenolics and flavonoid. In addition, Spraying SP could increase the relative expression of genes related to fruit disease resistance (PAL, PPO, PR-1, TLP, ERF2, ERF4, WRKY22, GST). The results showed that the SP could inhibit the growth of C. acutatum, enhance the resistance of loquat fruit to pathogenic fungi, reduce postharvest decay, maintain postharvest quality and it was an effective biological preservative.