| Peach fruit is an important fruit in China, and is very popular for its juiceful texture, delicious flavor and rich in nutrient. Peaches are matured in mid-summer, and are highly susceptible to pathogenic infection and physiological deterioration during ambient temperature storage and ripening. Low temperature storage is effectively used to control postharvest disease and inhibited ripening of peach fruit. However, chilling injury, such as internal browning and flesh mealiness, is usually found in peach fruit stored at low temperature for long time. Thus, it is crucial to study the regulation and mechanism of disease resistant and chilling injury of peach fruit after harvest for transportation and storage.In this paper, the effect of MeJA and 1-MCP on the major fungal disease, such as blue mold, gray mold and soft rot caused by Penicillium expansum, Botrytis cinerea and Rhizopus stolonifer respectively, and chilling injury in peach fruit and the possible mechanisms involved were investigated. In addition, the effects of MeJA combined with low temperature conditioning (LTC) or with hot air (HA) treatment on alleviating chilling injury in peach fruit and the possible mechanisms involved were investigated. The results were as follows:1 Effects of MeJA treatment on postharvest disease in peach fruit and possible mechanisms involvedPeaches were treated with different concentrations of MeJA (1,10 or 100μmol/L) to investigate the effect of MeJA treatment on blue mold, gray mold and soft rot. We found that treatment with 1μmol/L MeJA was most effective in reducing fruit decay caused by P. expansum, B. cinerea and R. stolonifer infection, however,100μmol/L MeJA treatment had little effect. In addition, the in vitro experiment showed that MeJA inhibited mycelial growth, spore germination and germ tube length of P. expansum, B. cinerea and R. stolonifer. Thus,1μmol/L MeJA was chosen to investigate the effects of MeJA on reducing blue mold and the possible mechanisms involved in postharvest peach fruit. The MeJA-treatment enhanced the activities of chitinase,β-1,3-glucanase, phenylalanine ammonia-lyase (PAL), peroxidase (POD) and polyphenol oxidase (PPO), and maintained the higher level of total phenolic content in peach fruit, which is considered to play important roles in disease resistance. Moreover, MeJA-treatment induced accumulation of H2O2 content due to increased superoxide dismutase (SOD) activity, decreased catalase (CAT) and ascorbate peroxidase (APX) activities in peach fruit. The level of H2O2 induced by the treatment might also be related to the higher resistance of the MeJA-treated fruit to infection by the pathogen. These results indicated that MeJA inhibited postharvest disease probably due to suppressed pathogen growth directly and enhanced the disease resistance of fruit tissues by increasing anti-pathogenic proteins and antimicrobial phenolic compounds.2 MeJA combined with LTC treatment alleviates chilling injury in peach fruit and possible mechanisms involvedPeach fruits were treated with different concentrations of MeJA (1,10 or 100μmol/L) to investigate the effect of MeJA treatment on chilling injury and fruit quality. We found that treatment with 1μmol/L MeJA was most effective in reducing internal browning (IB) and flesh mealiness (FM) while maintaining higher level of TSS, TA and extractable juice in peach fruit, however,100 and 500μmol/L MeJA treatments had little effect. Thus,1μmol/L MeJA was chosen to combine with LTC treatment to investigate the effects of combination treatment on chilling tolerance and the influence on H2O2 and pectin metabolism. MeJA combined with LTC treatment alleviated chilling injury, maintained higher fruit quality in peach fruit during cold storage. The activities of PPO and POD were significantly inhibited, while the activities of antioxidant enzymes such as SOD, CAT, and APX were induced by MeJA combined with LTC treatment. In addition, the activities of PAL, polygalacturonase (PG) and the level of total phenolic content were enhanced by MeJA combined with LTC treatment. These results suggested that the effect of MeJA combined with LTC treatment on alleviating chilling injury of peaches during cold storage may be attributed to it ability to enhance defense system against cold stress, induce antioxidant system and affect the activities of pectin metabolism enzymes.3 MeJA combined with HA treatment alleviate chilling injury in peach fruit and possible mechanisms involved Peach fruits were treated with 1μmol/L MeJA combined with 38℃hot air treatment to investigate the effects of combination treatment on chilling tolerance and the influence on H2O2 and pectin metabolism. The results showed that the fruit treated with combined treatment showed the high quality and low percent of chilling injury symptom. HA treatment alone significantly inhibited IB, however, it showed more severe FM than other treatments, this side effect was counteracted by MeJA. In addition, MeJA combined with HA treatments exhibited the higher activities in PAL, SOD, CAT and PG, and showed the lower activities in PPO and POD. These results suggested that effect of MeJA combined with HA treatment on alleviating chilling injury of peaches during cold storage may be attributed to it ability to induce antioxidant system and affect the activities of pectin metabolism enzymes. The combination of MeJA and HA treatment could be a useful technique to alleviate the chilling injury and maintain fruit quality during cold storage.4 Effects of 1-MCP treatment on postharvest disease in peach fruit and possible mechanisms involvedPeaches were treated with different concentrations of 1-MCP (0.1,0.5 or 5μl/L) to investigate the effect of 1-MCP treatment on blue mold, gray mold and soft rot. We found that treatment with 0.5μl/L 1-MCP was most effective in reducing fruit decay caused by P. expansum, B. cinerea and R. stolonifer infection, however,0.1 or 5μl/L 1-MCP treatments had little effect. Thus,0.5μl/L 1-MCP was chosen to investigate the effects of 1-MCP on reducing blue mold and the possible mechanisms involved in postharvest peach fruit. The results shown that 1-MCP enhanced the activities of PAL and maintained the higher level of total phenolic content, which indicated that 1-MCP reduced postharvest disease probably due to increase antimicrobial phenolic compounds. In addition,1-MCP decreased accumulation of H2O2 content due to increased CAT and APX activities in peach fruit. However, little effect was found on chitinase andβ-1,3-glucanase activities in 1-MCP treated fruits. These results indicated that 1-MCP was not enhanced disease resistance of fruit tissues by increasing anti-pathogenic proteins or regulating H2O2 signal pathway. The effect of inhibiting fruit decay was probably due to maintaining higher level of antimicrobial phenolic compounds and delaying fruit ripening and senescence. 5 Effects of 1-MCP treatment on chilling injury in peach fruit and possible mechanisms involvedPeaches were treated with different concentrations of 1-MCP (0.1,0.5,5 or 10μl/L) to investigate the effect of 1-MCP treatment on chilling injury and fruit quality. We found that 0.5μl L-l 1-MCP was the optimal concentration to alleviate chilling injury and maintain higher quality of peach. However, higher concentration of 1-MCP treatment had little effect. The activities of PPO and POD were significantly inhibited, while the activities of antioxidant enzymes such as SOD, CAT, and APX were induced by 0.5μl L-1 1-MCP treatment.0.5μl L-1 1-MCP enhanced the activity of PG, which made the higher ratio of PG/PME and kept the balance of pectin metabolism. These results suggested that 0.5μl L-1 1-MCP treatment had considerable effect to alleviate the chilling injury rather than high concentration of 1-MCP applied in peach fruit during cold storage. The effect of low concentration of 1-MCP treatment on alleviating chilling injury of peaches during cold storage may be attributed to it ability to induce antioxidant system and affect the activities of pectin metabolism enzymes.
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