Effects Of Hot Air Treatment Combined With Meja On Harvested Peach Fruit Soft Rot And The Mechanisms

Peach is harvested in hot summer and has high water content. So peach is hard to store and easily infected by postharvest disease. Rhizopus stolonifer is the major postharvest fungal disease on peach. It caused soft rot on peach. The study was designed to investigate the effect of hot air treatment (HA) and methyl jasmonate (MeJA) alone to induce disease resistance in harvest "Baifeng" peach and the possible mechanism involved. Furthermore, the effectiveness of HA in combination with MeJA on postharvest disease on peach fruit was also assessed.(1) We screened out that45℃、2h hot air treatment is the best condition to induce the disease resistance and reduce the growth of lesion diameter on peach. On one hand, hot air treatment induced the content of hydroxybenzene on peach. On the other hand, it increased the activities of phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), peroxidase (POD), superoxide dismutase (SOD), catalase (CAT),β-1,3-glucanase and chitinase in peach fruit. Thus, HA treatment elicited disease resistance of peach fruit。(2) We found out that10μmol/L MeJA could significantly inhibit the soft rot decay caused by R. stolonifer on peach fruit. MeJA treatment induced the activity of chitinase, β-1,3-glucanase, and POD, stimulated biosynthesis of total phenolics and phytoalexin, thus it reduced the decay on peach. In addition, in vitro experiment results demonstrated that MeJA couldn’t directly inhibit spore germination and germ tube elongation of R. stolonifer. Thus, these results MeJA can effectively reduce fruit decay possibly by inducing disease resistance, rather than a direct inhibitory action on pathogen growth.(3) The effect of HA combined with MeJA on the quality of peaches was evaluated fvvby response surface method (RSM) with different temperature (40-50℃)-time (1-3h)-concentrate (5-15μmol/L) combinations. The lesion diameters of peaches after infection were measured. We established the second order quadratic equation for hot-air treatment combined with MeJA. The adequacy of the model equation for predicting the optimum response values was verified by the validated data. The optimum heated temperature, time and vapor concentrate are42℃,2h and10μmol/L.(4) The combined treatment of MeJA(10μmol/L) with HA (42℃,2h) showed the lower incidence of peach fruit disease and lesion diameter caused by R. stolonifer than alone treatment. The combined treatment could induce higher activities of the defense-related enzymes such as PAL and PPO in peach fruit than applying either alone to enhance the resistance. RT-PCR analysis showed that hot air treatment with10μmol/L MeJA significantly inhibited gene expression of GNS, NPR1-like and CHI12h after treatment. Thus, these results suggested that the combination of HA treatment with MeJA might be a more useful technique to induce disease resistance of peach fruit compared with the HA or MeJA alone.