Methyl jasmonate does improve postharvest conservation of ‘Golden’ papaya fruit

ABSTRACT: Methyl jasmonate (MeJA) is recognized as a plant hormone that induces several biochemical changes related to improving fruit quality, but it is evident that the effect of MeJA during postharvest is very variable upon concentration, plant species, and even cultivars. The objective of this research was to relate the application of this regulator at low concentration (10 µmol L-1 for 24 h) to changes in postharvest physiology, on the incidence of anthracnose and quality of ‘Golden’ papaya fruit during storage at 24 ± 1°C. From the seventh day of storage, anthracnose incidence was reduced by more than 50% with MeJA treatment. The lesion area after infection was also reduced. Although, MeJA reduced fruit acidity, the ascorbic acid and soluble solids content were not altered during storage with the hormonal treatment. The skin color and pulp firmness showed slight retention. The reduction in ethylene production was accompanied by a reduction of respiration in treated fruits. MeJa increased CAT activity only in the skin whereas SOD activity was not induced by MeJA in both skin and pulp. Although, the increase of CAT from the third day of storage may have contributed to the reduction of lipid peroxidation in the skin, the MDA reduction in the pulp cannot be explained only by CAT activity. In summary, the application of MeJA in ‘Golden’ papaya reduced the incidence and severity of anthracnose, decreased respiration, ethylene production and lipid peroxidation. It is concluded that the application of MeJA at a low concentration (10 µmol L-1) may contribute to anthracnose control in ´Golden`papaya and slows the ripening of fruits.摘要：茉莉酸甲酯（Methyl jasmonate, MeJA）是一类可诱导多种与提升果实品质相关生化变化的植物激素，但现有研究证实，其采后施用效果会因浓度、植物种类乃至品种的不同而存在显著差异。本研究旨在探讨低浓度（10 µmol L⁻¹，处理24 h）下施用该调节剂，对‘Golden’番木瓜果实在24 ± 1℃条件下贮藏期间的采后生理变化、炭疽病发病率以及果实品质的影响。贮藏至第7天时，茉莉酸甲酯处理组的炭疽病发病率降低了50%以上，病原菌侵染后的病斑面积也显著减小。尽管茉莉酸甲酯处理降低了果实酸度，但经该激素处理的果实在整个贮藏期内，其抗坏血酸与可溶性固形物含量均未发生显著改变。果皮色泽与果肉硬度均得到小幅维持。处理组果实的乙烯生成量降低的同时，呼吸强度也随之下降。仅在果皮组织中，茉莉酸甲酯可提升过氧化氢酶（Catalase, CAT）活性；而在果皮与果肉中，茉莉酸甲酯均未诱导超氧化物歧化酶（Superoxide dismutase, SOD）活性升高。尽管贮藏第3天起CAT活性的提升可能有助于降低果皮的脂质过氧化程度，但果肉中丙二醛（MDA）含量的下降无法仅通过CAT活性变化来解释。综上，对‘Golden’番木瓜施用低浓度茉莉酸甲酯可降低炭疽病的发病率与病害严重度，同时减弱呼吸强度、减少乙烯生成并抑制脂质过氧化。研究表明，10 µmol L⁻¹浓度的茉莉酸甲酯处理可有效防控‘Golden’番木瓜的炭疽病，并延缓果实成熟进程。