Studies On Developmental Characteristics Of Fruit Quality Of Netted Muskmelon(Cucumis Melo L. Var. Reticulatus Naud.)

Netted muskmelon (Cucumis melo L. var. reticulatus Naud.) is a variety of melon species, a type of muskmelon. Because there is net on the rind of the mature fruit, which is for eating, we call it "netted muskmelon". In southern area of China, fruit quality factors, such as sugar content, fruit net, are always not good enough because of low light intensity and heavy rain. In this paper, the fruit development dynamic and the quality development, such as sugar accumulation, formation of muskmelon net, were studied. The main purpose is finding the mechanism in the growth and development of muskmelon fruit, and that, can serve as theory for improving the fruit qualities by cultivation and /or breeding. The main results were as follows:(1) In order to study the netted muskmelon fruit growth dynamic, fruits were sampled regularly after artificial pollination, fruit size, and sugar, protein, amino acid content were assayed, and the formation of net on the surface of muskmelon fruit was observed as well. It was found that fruit size and weight increased rapidly from 10 to 25 days after pollination, and then increased slowly. It was 15 days after pollination that the net began to form on the surface of the fruit, and the fruit net formation was ended at about 40 days after pollination. During the fruit growth period, the reduced sugar content changed slightly. The total soluble sugar and sucrose contents increased steadily from 30 days after pollination to fruit mature. The reduced sugar was the main composition of the total soluble sugar in fruit from anthesis to 30 days after pollination, but from 30 days after pollination to fruit mature, sucrose was the main composition of the total soluble sugar. During the early and late developing stage of fruit, the protein content was at a relative high level, and during the middle developing stage of fruit, the protein content was at a relative lower level. Content of amino acid increased from 25 days after pollination, and had a peak before the protein content rising, and then kept on rising after a short decrease stage.(2) Experimental data showed that the accumulation of sucrose was the result of co-reaction of AI/NI, SPS and SS during the development of melon fruit. By comparing the sucrose accumulation and its related enzyme activities during the development of muskmelon fruit, it was found that there was a high correlation coefficient between soluble sugar content and net activities of related enzyme. A significant correlation existed between SPS activity and sucrose accumulation. The activities decrease of AI/NI was the premise of sucrose accumulation during the fruit development, though no significant correlation was found between the AI/NI activities and soluble sugar content. No notablecorrelation was found between synthesized activity of SS and sugar accumulation. Statistical data showed that the correlation coefficient of sink activity and AI activity was up to 0.8566.(3) It was observed that the fruit net occurred during the maximal growth period of muskmelon fruit. The development of the fruit net could be divided into 4 stages: (i) At the beginning stage, one or two ring-like cracks emerged around the fruit stalk, this happened about 16 days after pollination, (ii) About 2 or 3 days after the first stage, vertical crack occurred gradually, (iii) About 20 days after pollination, transverse crack appeared between every two vertical creaks, and fruit net formed steadily, (iv) About 25 days after pollination, cracks covered the entire fruit, but cracks did not stop occurring until about 40 days after pollination. In the meantime, callus emerged on the cracks, and the net formed on the fruit surface. On the other hand, anatomical experiment showed that the tissue structure of fruit coat changed when the crack occurred. The cells of outer layer were almost 4 times larger than common cells and were covered with a heavy cuticle. When the fruit developed to 16 days after pollination, the arrangement of cells of fruit coat began to be disorder, and the cells under outer cells layer cracked.