Postharvest application of plasma-activated water delays anthracnose symptom development in apples

Apples rank among the most frequently consumed fruits, nevertheless, they are prone to microbial contamination after the harvest period. Anthracnose caused by Colletotrichum gloeosporioides is a serious postharvest disease. Plasma-activated water (PAW) has great potential as an efficient, cost-effective, and environmentally sustainable method of sterilizing food. This study investigated the effects of PAW with different activation times (100, 200, and 300 s of plasma exposure) on the infection process of C. gloeosporioides and the postharvest quality of apples. The results showed that PAW treatment could effectively inhibit mycelial growth, conidial germination, appressorium formation, and melanin accumulation in C. gloeosporioides , and could also suppress the manifestation of anthracnose symptoms in apples inoculated with C. gloeosporioides conidia during postharvest storage. Interestingly, PAW treatment reduced the transcriptional levels of genes ( CgCDC42 [cell polarity], CgRAC1 [cytoskeletal organization], CgRHO1 and CgRHO2 [cell wall synthesis]) related to the mycelial adhesion ability, conidia formation, appressorium shape, and establishment and maintenance of cell polarity in C. gloeosporioides . Simultaneously, it enhanced the expression levels of the marker gene ( MdPR1 ) of the salicylic acid (SA) pathway, key enzyme-encoding gene of phenylpropanoid metabolism ( MdPAL1 ), gene regulating the jasmonic acid (JA) response ( MdMYB108 ), and key enzyme-encoding genes of JA biosynthesis ( MdJAR4 / MdAOS2 ) in apples. This indicates that PAW may activate the SA, JA, and phenylpropanoid metabolic pathways in apples by generating reactive oxygen species (ROS) or nitrogen species (RNS), thereby enhancing their resistance to C. gloeosporioides . In addition, in response to the ROS burst induced by PAW, the antioxidant system of apples was activated, and the activities of the antioxidant enzymes Superoxide Dismutase (SOD), peroxidase (POD), Polyphenol Oxidase (PPO), and catalase (CAT) increased. Significantly, PAW not only enhances the resistance of apples to C. gloeosporioides but also increases the vitamin C and soluble sugar content of the fruit, thereby improving the sugar-acid ratio. In summary, PAW has the potential to replace traditional fungicides as an efficient technology for postharvest disease control and quality maintenance of apples. • Plasma-activated water (PAW) down-regulated the transcriptional levels of pathogenic-related genes in C . gloeosporioides . • PAW up-regulated the transcriptional levels of defense-response-related genes in apples. • PAW increase the vitamin C and soluble sugar content in apple fruit, and improve the sugar-acid ratio.