Effects Of Exogenous Growth Substances On Plant Photosynthetic Traits, Fruit Development And Fruit Quality Of Netted Melon

Netted melon (Cucumis melo L. var. reticulatus Naud.) is a variety of Cucumis genus in Cucurbitaceae family. Netted melon is one type of thick-peel melon with the fruits for edible parts. It is called netted melon because there are netty flaws on peel of mature fruits. In southern area of China, fruit quality traits are usually poor because of low light and heavy rain in these areas. In this paper, effects of24-epibrassinolide (EBR) treatment before harvest on photosynthetic traits of netted melon plants and fruit postharvest qualities were studied. Influence of CPPU treatment at flowering stage on fruit setting rate, fruit growth and development, fruit visual quality, and nutritional qualities of netted melon were also investigated. Moreover, effects of postharvest1-MCP treatment on shelf life, visual quality, physiological and nutritional qualities of fruits stored under25℃and10℃were also investigated. The main purpose of the present study is to explore the mechanism and effects of these exogenous growth substances on plant photosynthesis, fruit development as well as fruit quality, expecting to provide theoretic and technological basis for improvement of fruit qualities by chemical regulation in netted melon. The main results are as follows:1. Different concentration of EBR was applied to netted melon plants at different developmental stages, and differences in photosynthetic parameters between EBR-treated and untreated plants were analyzed. After harvest, differences in fruit qualities between treated and untreated melon were studied. Our results showed that0.1mg I-1was the most effective EBR concentration to enhance photosynthetic rate of netted melon. In seedlings and early-flowering plants, EBR treatment increased net photosynthetic rate (Pn) and gas conductance (Gs). Meanwhile, it reduced intercellular CO2concentration (Ci) and transpiration rate (Tr) of melon plants. These results suggest that enhancement of photosynthetic rate by EBR is probably attributed to non-stomata factors in these two stages. In late-fruiting stage, Pn, Gs, and Ci of EBR-treated plants were all higher than that of the control, whereas Tr of treated plants is lower than that of the control. It is concluded that elevated photosynthetic capacity caused by EBR was probably due to stomata factors in late-fruiting stage. It is also found that EBR treatment effectively increased fruit longitudinal and horizontal diameters. In addition, fruit weight was also significantly increased after EBR treatment. These changes may be attributed to the direct promotion of cell growth and division by EBR treatment. Moreover, EBR significantly improved total soluble sugar content of netted melon. Therefore it is speculated that EBR might promote transportation of carbohydrate from leaves to fruits by uplifting photosynthesis rate.2. After different concentration of CPPU was sprayed onto ovaries of netted melon during flowering stage, fruit setting rate, fruit growth, and fruit quality traits of netted melon were investigated. The results demonstrated that CPPU significantly increased the fruit setting rate of netted melon from96.4%(control) to100%. This indicated that parthenocarpic fruits were successfully induced by CPPU. The research results showed that20mg I-1is the most appropriate concentration for CPPU application. Moreover, CPPU significantly increased the growth of treated fruits, enhanced the fruit weight and yield of netted melon. In addition, CPPU increased the contents of soluble sugar, sucrose, fructose, glucose and vitamin C of melon fruits, and therefore, the fruit quality was improved.3. Effects of1-methylcyclopropene (1-MCP) on shelf life, fruit visual quality and nutritional quality were investigated. Netted melons were fumigated with air (control) or0.6μl I-11-MCP in sealed condition at25℃for24h, then were stored at25℃or10℃. In the storage period,1-MCP significantly extended fruit shelf life, inhibited weight loss and delayed firmness decline of melon. Meantime, ethylene production and respiration rate were declined.1-MCP also retarded ACC increase and inhibited activities of ACS and ACO. In addition,1-MCP treatment reduced the decrease of total soluble solids and titratable acidity, as well as decrease of content of several sugars (sucrose, fructose and glucose). These results indicated that1-MCP treatment is an effective method to extend melon shelf life and maintain fruit quality, and the combination of1-MCP treatment with low temperature storage may result in more acceptable fruit quality.