Effects Of Different Fruit Setting Techniques On The Fruit Enlargement And Quality Of Melon Under Protected Culture

Melon(Cucumis melo L.)is an important horticultural crop. China is the leading melon producer and it has a large consumer market. The plastic sheet which is widely used in melon cultivation set a barrier for the pollination insects, and the decline of insects have harmful effect on pollination leading to reduction of crop yield. The use of synthetic growth regulators like forchlorfenuron(CPPU) can promote fruit setting, but usually lead to deformity, quality deterioration and other problems when used in inappropriate concentration. Is there any alternative way, such as bee pollination, to solve this key problem? In this study, the melon cultivars ’Elizabeth’ was used as the material and three fruit setting methods(bee pollination, artificial pollination and CPPU treatment) was used to investigate the fruit enlargement process and fruit quality. The results are as follows:1. Effect of different fruit setting techniques on fruit enlargement process was done by measuring the fruit weight, vertical and horizontal diameter, size and number of cells and ploidy of cells in the developing melon fruit. The results showed that in the early fruit development period [0 days after anthesis(DAA)-7 days after anthesis(DAA)], the increase of the number of cells is the main reason for the enlargement in the various three treatments. The cell number rapidly increases on 1DAA when treated with CPPU than the other two treatments, and the numbers of 2C and 4C cells achieve balance earlier, which result in a most rapid increase in vertical and horizontal diameter and fruit weight in 3DAA-7DAA. In the medium-term of fruit development(7DAA-20DAA), the increase in cell size becomes the main reason for fruit-growth, at the same time the number of cross-section of the cell continues to increase with a increase in 8C and 16 C cells; In the late stage of fruit development(20DAA-32DAA), fruit weight, vertical and horizontal diameter of 3 treatments reached a stable high levels. At ripe stage(32DAA), the melon size was biggest with CPPU treatment, followed by bee pollination and artificial pollination.2. The changes of several endogenous hormones have been detected by enzyme-linked immunosorbent assays(ELISA) to compare different fruit setting techniques during fruit development. The results showed that, indole-3-acetic acid(IAA) and abscisic acid(ABA) content significantly increased on 1DAA, then quickly dropped to a lower level, again there was an upward trend but in the late stage of fruit development, and no significant difference in three treatments was observed. Gibberellic acid(GA3) content showed an upward in both treatments on 1DAA. The GA3 content in CPPU treatment were significantly higher than other treatments followed by a short time of decline, after that the level began to increase again in 3DAA and 15 DAA. The zeatin riboside(ZR) contents of bee pollinated and artificially pollinated fruit increased on 1DAA followed by a decline until 20 DAA, but ZR content in CPPU processing began to decline just after 1DAA which showed a significant difference from the other treatments.3. Soluble sugar, sucrose metabolizing enzymes and the expression of genes was measured to compare the effects of fruit setting techniques on melon fruit(10DAA-34DAA). The results of the accumulation of carbohydrate in melon fruit of different treatments showed that during the young fruits development phase, glucose and fructose were nearly all of sugar rather than sucrose. With the development of the fruit, sucrose began to accumulate and eventually became the major carbohydrate. In mature fruits, gene expression and enzyme activity demonstrated that the decreased activities of acid invertase(AI) and neutral invertase(NI) were the prerequisite for the accumulation of sucrose. While the increased sucrose phosphate synthase(SPS) activity in bee pollinated mature fruit was the main reason for its higher sucrose content on 32 DAA compared to other methods.4. We compared fruit quality with different fruit setting techniques in ripe melon fruit by analyzing the appearance, nutrient and flavour quality. The results showed that flesh firmness, flesh thickness, seed cavity length and width, fruit shape index and fruit set rate have no significant difference among three treatments, however the fruits with bee pollination got a highest score in tasting and skin color; nutritional quality is mainly composed of sugar and the results showed that the soluble solids, total soluble sugar by bees pollination were the highest in three treatment in ripe melon fruits; the flavor quality by bees pollination was the best among different treatments and the total peak area of volatiles proportion in bees pollinated melon was significantly higher than two other treatments. Esters were 50.73%, 43.60% and 33.79% of the total volatiles in bee pollination, artificial pollination and CPPU processing respectively.To sum up, results show that bee pollination has best fruit appearance, nutritional and flavor quality and taste among all the three treatments. The melon fruit weight with CPPU were higher than the other two treatments, but at the same time fruit cracking rate was the highest. In conclusion, bee pollination effectively ensure melon fruit yield and quality, is an efficient, high quality, labor-saving way, so it should be the first choice for melon fruit setting in production system on commercial scale.