Effect Of Preharvest Stroby Treatments Induced Resistance Of Postharvest Muskmelons And Its Effects On Fruit Quality

Stroby is a biological fungicide, which can effectively control the field disease of crops, but also has potentially induced resistance to postharvest fruit. In this study, 4 times 400 ppm Stroby spraying during the ‘ Manao’ muskmelons growth and development period. We researched partial mechanisms of treatment on induced disease of muskmelons at postharvest, meanwhile, discussed the effect of treatment on physiology and quality of fruits. The results showed that:1. Preharvest Stroby treatment can effectively inhibited the expansion of the lesion diameter of fruit inoculated with A. alternate, F. sulphureum and T. roseum and the fruit natural infection rate. Which the inhibitory effect is most obvious to F. sulphureum and the lesion diameter was significantly lower than the control by 40.41%.2. Stroby treatment obvious increased the activity and expression of the corresponding genes of PAL, 4CL and C4 H of harvest and postharvest fruit, the results also showed that the trends on expression and activity of these enzymes were roughly consistent. Similarly, it also promoted the accumulation of the lignin, total phenols and flavonoids harvest and postharvest fruit. In addition, Stroby treatment also induced increase of the activity and gene expression of CHT and GLU in fruit.3. Stroby treatment can suppressed the excessive accumulation of O2-· and H2O2 and the addition of the membrane permeability and the content of MDA during later storage period, and also had various degrees of regulation on activity and gene expression of NOX, SOD, POD and CAT. Stroby treatment may promoted activity and gene expression of APX, GR, DHAR and MDHAR of ASA-GSH cycle. In addition, it effectively improved the content of ASA and GSH, and inhibited the accumulation of DHA and GSSG.4. Preharvest Stroby treatment effectively delayed the postharvest respiration and ethylene peak, maintained the firmness of harvest and postharvest fruit, reduced the decline of TSS and TA and inhibited yellowing of the peel, thereby maintained the good quality of fruit.Furthermore, the content of kresoxim-methyl of fruit peel was lower than the national standard at harvest and kresoxim-methyl can degraded quickly during storage. After storage 28 d, the content of kresoxim-methyl significantly reduced about 90% than harvest after storage 28 d.In summary, preharvest Stroby treatment improved the activity and gene expression of SOD and other antioxidant enzymes, accelerated the accumulation of lignin and other antibacterial substances of melon fruit by activated the phenylpropanoid metabolic pathway and reactive oxygen metabolism included ASA-GSH cycle, thus effectively improved reduced resistance of postharvest fruit. Preharvest Stroby treatment delayed the ripening and aging process of fruit by inhibited the respiration intensity and ethylene production, maintained the good quality of fruit. Preharvest Stroby treatment had lower residual amount in fruit, and has higher edible security.