Effect Of Postharvest Oxalic Acid Treatment On Induced Resistance Of Muskmelon Fruit And Its Storage Quality

Effect of postharvest oxalic acid treatment on induced resistance of muskmelon fruit (cv. Yindi) and its storage quality were studied by inoculation and storage experiment in this paper. The results indicated as below:1.Oxalic acid significantly inhibited mycelial growth of Alternaria alternata,Fusarium semitectum and Trichothecium roseum in vitro. Postharvest dipping treatment with different concentration oxalic acid reduced the lesion diameter of fruit inoculated with three pathogens in vivo. Oxalic acid at 50mM dipping 10 mintues was the most effective treatment for reducing decay severity. Higher concentration and longer time failed to promote better resistance against decay-causing agent and to cause phytotoxicity. This treatment was also effectively reduced the disease index and incidence of fruit. Oxalic acid induced systemic acquired resistance against T. roseum.2.Treatment of oxalic acid increased activity of phenylalanine ammonia-lyase (PAL), peroxidase (POD), polyphenoloxidase (PPO), chitinase (CHT) andβ-1,3-glucanase (GLU) in fruit. Oxalic acid resulted in an increase in production of total phenolic, flavanoid and lignin. The challenge with T. roseum enhanced furthermore activity of PAL, POD, PPO, CHT and GLU in the melon with oxalic acid treated, more accumulation was also found in total phenolic, flavanoid and lignin. The control had an increase resistance reaction after challenge with T. roseum; however, the intensity was weaker than the treated.3.Treatment of oxalic acid increased the production of H202 and the activity of superoxide dismutase (SOD), and reduced the activity of catalase (CAT). The challenge with T. roseum enhanced furthermore accumulation of H202 and activity of SOD in oxalic acid treated. However, the activity of CAT was inhibited.4.The preformed antifungal compounds were accumulated in peel after treatment with oxalic acid. The challenge with T. roseum enhanced furthermore accumulation of the preformed antifungal compounds during storage. The oxalic acid treated was higher than control.5.Tissues of cortex showed more tightness, and the array of cell became tighter and thickness of cell wall and cuticle increased by treatment with oxalic acid. The challenge with T. roseum increased furthermore thickness of cell wall and cuticle. The oxalic acid treated was higher than control.6.Treatment of oxalic acid delayed the decrease of the soluble solid content (SSC) and firmness of fruit during storage, and didn't significantly influence chroma and Vitamine C content.