Preharvest Chitosan Treatment Inhibits Latent Infection And Induced Resistance In Muskmelon

Chitosan at 1 mg/ml was sprayed 4 times to melons (cv. Yindi) in the field. The spray time was at 1 week before flowering, young fruit period, fruit enlarging period, and netting period, respectively. The latent infection and postharvest resistance of fruit were investigated. Meanwhile, the change of resistance physiological response and histology were studied in this paper. The results indicated as below:1. Sprays with chitosan during melon growth reduced effectively latent infection of fruit. The latent infection rate of total, Alternaria and Fusarium decreased with increasing of spraying times. Three and four times of spraying showed the effective control.2. Control of latent infection with chitosan was related with inducing resistance in the fruit. Chitosan treatment enhanced activity of peroxidase (POD), polyphenoloxidase (PPO), phenylalanine ammonia-lyase (PAL),β-1,3-glucanase (GLU) and chitinase (CHT) in muskmelon. Chitosan also resulted in an increase of content of total phenolic and lignin. Chitosan treatment increased the activity of superoxide dismutase (SOD), enhanced the content of hydrogen peroxide (H2O2) and reduced the activety of catalase (CAT) in the fruit. The peel of fruit treated with chitosan had more preformed antifungal compounds than that in the control.3. The observation of histology indicated a more tightness tissues, a tighter the array of cell and a thicker of cell wall in the cortex of melon treated with chitosan.4. Lesion diameter was reduced effectively by chitosan treatment in harvested muskmelon inoculated with A. alternate, F. semitectum and T. roseum during an ambient storage. Disease incidence and disease index were also decreased significantly by chitosan treatment in stored melons. The effects of control decay by chitosan were enhanced with treatment times. Three and four times showed a better control.