Effectsofdifferentfruit Setting Techniquesonthe Growth And Quality Of Watermelon Fruit

With the continuous development of protected watermelon, the increase in labour cost and higher requirement of food security, the traditional fruit setting techniques, such as hand pollination and growth regulators (CPPU) treatment, cannot meet the needs of the future development of protected watermelon production. Exploring the fruit-setting technique with labour saving and high fruit quality is necessary and urgent. To discuss the possibility using bee pollination as a mean for fruit setting of watermelon, the present study assess the effects of hand pollination, CPPU treatment, bee pollination on the fruit yield and quality of watermelon (Zaojia8424). The main results were as follows.1. The fruit development was effected by different fruit setting techniques, and the bee-pollinated fruit was the largest. The weight of bee-pollinated watermelon fruit was186g higher than that of hand-pollinated fruit and118g than that of CPPU-treated fruit. The enlargement of watermelon fruit is mainly affected by the number of cells and cell size, fruit enlargement is caused mainly by an increase in the number of cells in the early development (1DAA-7DAA), while the fruit enlargement mainly attributed to the increase in cell size in the late stage of fruit development (12DAA-24DAA). The cell area of the longitudinal section of bee-pollinated watermelon fruit was107.10%and109.24%of that of hand-pollinatedandCPPU-treated fruit at33DAA, respectively. The cell area of the cross section of bee-pollinated watermelon fruit was102.74%and107.03%of that of hand-pollinated and CPPU-treated fruit at33DAA, respectively.2.The number of cells that has2C DNA content was equilibrated with the number of cells that has4C DNA contentat5DAA in the bee-pollinated fruit, but CPPU-treated fruit at3DAA.The proportion of cell numberwhich DNA content greater than4C was significantly increased in the bee-pollinated fruit, which is higher than CPPU treatment. Between1DAA-3DAA, the GA3content showed a downward trend in the bee-pollinated fruit, while CPPU treatment showed a rising trend; the GA3content of bee pollinated fruit reached the peak at18DAA, while in CPPU-treated fruits it was3DAA.3. The fruit quality was affectedby different fruit setting techniques, and the bee-treated watermelon has the best quality.In the mature fruits,the soluble solids content of bee-pollinated fruit was12.12%, which was higher than that of hand-pollinated and CPPU-treated fruit. The sucrose content of bee-pollinated fruit was67.40mg/100g FW, more than the hand-pollinated and CPPU-treated fruit by2.45mg/g,15.37mg/g, respectively. The fruit set rate of bee-pollinated watermelon was98%, which raises5.3%compared with hand-pollinated watermelon. The marketable fruit rate of bee-pollinated watermelon was95%, which up5.60%and11.76%, respectively compared with hand-pollinated and CPPU-treated fruit. The relative content of alcohols in bee-treated fruit was22.87%, which was7.45%,12.27%more than that of hand-pollinated and CPPU-treated watermelon, respectively. The relative content of aldehydes in bee-treated fruit was25.53%, which was4.92%,3.00%higher than that of hand-pollinated and CPPU-treated watermelon, respectively.4. Different techniques, mainly through fruit fruit of sucrose synthase, sucrose phosphate synthase to affectsugarccumulation of watermelon fruit In the phase of maturity (30DAA-36DAA), Sucrose synthase (SS) and sucrose phosphate synthase (SPS) activities in bee-pollinated fruit was significantly higher than those in CPPU-treated fruit, and insoluble acid invertase (IAI) activity in bee-pollinated watermelon fruit was significantly belowerthan that in CPPU-treated fruit. SS activity has a significant positive correlation with sucrose content(rSS(Hand)=0.957、rss(CPPU)=0.868、rss(Bee)=0.959), but IAI activity was significantly negatively correlated with sucrose content(rIAI(Hand)=-0.917、 rIAI(CPPU)=-0.959、、rIAI(Bee)=-0.973). Gene expression studies showed that bee-pollinated fruit increased SS activity through upregulating the expression of encoding gene SS2.Based on the comprehensive comparation between fruit development, quality, fruit setting cost, economic and other indicators, bee pollination has the best overall performance. As a fruitsetting technique that saving labour and raising fruit quality, it can be widely used in the protected watermelon production.