该研究以哈密瓜为材料,分别接种链格孢、粉红单端孢,采用扫描电镜观察病原菌繁殖和细胞壁结构,结合发病情况和细胞壁降解酶活性,以及细胞壁降解导致的品质变化,探讨病原菌侵染引起哈密瓜腐烂机制。结果表明,打孔接种哈密瓜发病最严重,1 d后哈密瓜就出现病害,第4天时,接菌组发病率均达到100%。两接菌组比较,粉红单端孢侵染病斑面积扩大的比链格孢侵染快。扫描电镜观察发现,贮藏期间对照组细胞壁结构完整,第7天时表面有真菌生长,但未造成细胞结构降解;链格孢和粉红单端孢接种组,第3天时细胞内已长满菌丝,细胞壁塌陷,第7天时,粉红单端孢组出现组织破裂。β-半乳糖苷酶、多聚半乳糖醛酸酶、羧甲基纤维素酶、β-葡萄糖苷酶活性缓慢升高,接种病原菌组酶活显著高于对照组,酶活是对照组的1.28~1.85倍。与对照组相比,链格孢和粉红单端孢接种组的哈密瓜色泽变暗,呼吸速率加快,失重率增加,相对电导率升高,硬度下降。研究结果可为解析病原菌的侵染过程和哈密瓜的病害防治提供一定理论基础。
The postharvest diseases accounted for 20%-30% of the total loss of Hami melon, resulting in huge economic losses. The objective of this study is to investigate the physiological changes of Hami melon and to clarify the decay mechanism caused by Alternaria alternata and Trichothecium roseum. The propagation of pathogenic fungi and cell wall structure of melon were observed by scanning electron microscope (SEM). The disease symptoms, the activity of cell wall degradation enzyme, as well as the quality changes caused by cell wall degradation were discussed. The results showed that compared with different inoculation methods, the inoculation on holes exhibited the most serious spoilage, showed disease symptom after 1 d, and the disease incidence reached 100% on the 4th day. Comparing the two pathogenic fungus inoculated groups, the lesion area of melon infected by T. roseum expanded faster than that of A. alternata. SEM observation showed that during storage, the cell wall structure of the control group was complete, and fungi grew on the surface on the 7th day, but did not cause the degradation of the cell structure. In the group inoculated with A. alternata and T. roseum, the cells were covered with fungus and the cell wall collapsed on the 3rd day, and the tissue ruptured in the T. roseum group on the 7th day. The activities of β-galactosidase, polygalacturonase, carboxymethyl cellulase and β-glucuronidase in Hami melon pericarp after inoculation increased slowly. The enzyme activity in the inoculated group (1.28-1.85 times of the control group) was significantly higher than that in the control group. The respiration rate, weightlessness rate and relative conductivity of Hami melon inoculated with spoilage fungus were higher than those in the control group, but the hardness was lower than that of the control group. These results provide a theoretical basis for the infection process of pathogenic fungus and the disease control of melon.
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