Study On Effect And Mechanism Of Hot Air Treatment Combined With MeJA On Postharvest Disease Of Strawberry Fruit

Strawberry is a highly nutritional fruit with soft and juicy. However, due to the high water content of strawberry fruit and easily infection by postharvest disease. Grey mold decay caused by Botrytis cinerea is the major postharvest fungal disease on strawberry. The study was designed to investigate the effect of hot air treatment (HAT) and methyl jasmonate (MeJA) alone on inhibiting major fungal disease of grey mold decay on strawbrry fruit (Fragaria×ananassa Duch. cv. Fengxiang) and the possible mechanisms involved. Furthermore, the effectiveness of HAT in combination with MeJA on postharvest disease on strawberry fruit was also assessed, in order to supply a gist for the new preservation technique. The results were as follows:(1) HAT at 45℃for 3 h effectively restrained grey mold decay caused by B. cinerea and reduced the degree of the disease. On the one hand, HAT could induce the activity of chitinase,β-1,3-glucanase, and POD, promote the synthesization of the total polyphenol, enhance the resistance. On the other hand, the in vitro experiment showed that HAT significantly inhibited spore germination, germ tube elongation and mycelial growth of B.cinerea. These results indicate that HAT can effectively reduce fruit decay possibly by directly inhibiting pathogen growth and indirectly inducing disease resistance.(2) The results demonstrated that treatment with 1μmol/L MeJA could significantly inhibit the grey mold decay caused by B.cinerea on strawberry fruit. MeJA treatment in reducing the decay on strawberry could be related to the priming for defense responses, which indirectly induced the activity of chitinase,β-1,3-glucanase, and POD, stimulated biosynthesis of total phenolics and phytoalexin when the fruit was challenged or infected by pathogen, rather than a direct activation of defense responses. In addition, the in vitro experiment showed that MeJA couldn't directly inhibit spore germination and germ tube elongation of B. cinerea. Thus, these results MeJA can effectively reduce fruit decay possibly by priming action for "preserve the disease resistance", rather than a direct inhibitory action on pathogen growth.(3) The effect of HAT combined with MeJA on the quality of apples was evaluated by response surface method (RSM) with different temperature (42～48℃)-time (2～4 h)-concentrate (5～15μmol/L) combinations. The changes of decay index, firmness, TSS and TA of fuits were measured. Four second order quadratic equations for hot-air treatment combined with MeJA were established. 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 are 45℃,3 h and 10μmol/L.(4) The combined treatment of 10μmol/L MeJA vapor with HAT (45℃,3 h) showed the lower incidence of fruit decay caused by B.cinerea than alone treatment. It reduced the decline of Vc and firmness, maintained TSS and TA contents and accelerated the composition of total phenolics, further higher scavenging capacity against DPPH radicals. The combined treatment maintained the balance of active oxygen metabolism. Meanwhile, the combined treatment induced higher activities of the defense-related enzymes includingβ-1,3-glucanase, chitinase and PAL in strawberry fruit than applying either alone to enhance the resistance. Thus, these results suggested that the combination of HAT treatment and MeJA might be a more useful technique to reduce fruit decay and maintain quality in strawberries during postharvest storage compared with the HAT or MeJA alone.