Effect of L-cysteine treatment to induce postharvest disease resistance of Monilinia fructicola in plum fruits and the possible mechanisms involved

Plum is an important stone fruit in China, but the fruit is easily perishable and susceptible to infection by pathogens. Traditionally, synthetic fungicides are used to control diseases. However, the side effects of fungicides should not be ignored. Cysteine, generally recognized as safe (GRAS) amino acid, has been reported to play roles in the plant abiotic stress response, but little is known about the role of cysteine to control postharvest diseases in fruits. Therefore, this study was designed to investigate the effect of L-cysteine treatment on control of postharvest brown rot in artificially inoculated plum fruits and the possible biocontrol mechanisms involved. Postharvest plum fruits were inoculated with 1, 10, 100 and 1000 mg L−1 L-cysteine. 100 mg L−1 L-cysteine treatment effectively controlled brown rot in artificially inoculated plum fruits by inducing resistance. Furthermore, 100 mg L−1 L-cysteine treatment increased the activities of glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH), enhanced the content of NADPH of the pentose phosphate pathway, as well as improved the contents of H2O2 and some amino acids in the artificially inoculated plum fruits. 100 mg L−1 L-cysteine treatment also elevated the antioxidant content (AsA, GSH) and the antioxidant enzymes activities (APX, GR, MDAR, DHAR) of the ascorbate-glutathione (AsA-GSH) pathway. The protective effects of L-cysteine treatment on postharvest plum fruits likely be due to activating some defense-related responses of the fruit against infection. L-cysteine treatment is a safe promising method for controlling postharvest brown rot in plum fruits.