Preharvest Harpin Treatment Induce Resistance In Fruit Of Muskmelon And Its Mechanisms

Harpin at 50mg/L was sprayed 4 times to melons (cv. Yindi and Huanghemi) in the field. The spray time was at 1 week before flowering, young fruit period, fruit enlarging period, and netting period. The latent infection, histology, physiological metabolization, postharvest resistance and some part of quantity of fruit were studied in this paper. The results indicated as below:1. The latent infection rate of fruit was reduced significantly with harpin treatment. The latent infection rate decreased with increasing of spraying times. The four times of spraying showed the best effective control.2. Treatment of preharvest Harpin enhanced activity of peroxidase (POD), poly- phenoloxidase (PPO), phenylalanine ammonia-lyase(PAL), 4-coumarate:CoA ligase (4CL),β-1,3-glucanase (GLU) and chitinase (CHT) in muskmelon, it also resulted in an increase of content of total phenolic, flavanoid , hydroxyproline-rich glycoprotein (HRGP) and lignin. Above-mentioned activity of defense enzyme and content of resistance-disease substances gradually increased along with Harpin treatment times. In addition, treatment of preharvest Harpin increased the activity of superoxide dismutase (SOD), enhanced the content of Hydrogen peroxide (H2O2) and reduced the activety of catalase (CAT).3. The preformed antifungal compounds was increased in melon's peel after treatment with Harpin.4. Tissues of cortex showed more tightness, and the array of cell became tighter and thickness of cell wall increased by preharvest treatment with Harpin,5. Disease incidence and lesion area of muskmelon inoculated with Trichothecium.roseum could be controlled effectively by preharvest Harpin treatment in the period of storage.6. Preharvest Harpin treatment didn't reduce sensory quality of fruit while improved some part of physiological and chemical quality.