Regulation Of Temperature And Growth Regulators On Sex Differentiation Of Watermelon

Watermelon（Citrullus lanatus）is an annual herb of the watermelon genus（Citrullus）in the family Cucurbitaceae.In the process of watermelon hybrid seed production,the castration work on the female parent and the work of removing female flowers on male parent is time-consuming and labor-intensive,and accounts for a large part of the pollination cost.If the opening time of the female and male flowers of watermelon can be regulated by external factors,artificial input can be greatly reduced,and artificial pollination can be replaced by bumblebee pollination or other techniques,which is of great significance for watermelon seed production and breeding.In this study,different treatments of watermelon were carried out on the seedling stage to determine the endogenous hormones of the watermelon stem tips,to count the watermelon sex differentiation expression and to analyze the watermelon sex differentiation expression related gene expression.In order to explore the regularity of the occurrence of female and male flowers of watermelon,and regulate the flowering sequence of watermelon,so that the female and male parents only open one type of flower within a certain period of time,which can simplify the castration work on female parent and the work of removing female flowers on male parent in the process of hybrid watermelon seed production.The main findings are as follows:1.At low night temperatures,the first female flower node and the first male flower node of watermelon are both significantly reduced,and the number of female flowers is significantly increased,of which 12℃is the night temperature setting with the best treatment effect.In this paper,24℃night temperature is the stagnation temperature,at which the first male flower node and the first female flower node of watermelon changes drastically.Above this night temperature,the position of the first male flower of watermelon is significantly increased,and the number of female watermelon flowers is significantly reduced.Below this night temperature,the position of the first female flower of watermelon is significantly decreased,and the number of female watermelon is significantly increased.2.The effect of mepiquat chloride on the sex differentiation of watermelon is related to temperature,specifically as follows:（1）At 30/25℃and 25/20℃and with treatment of mepiquat chloride,the first male flower node and the first female flower node of watermelon decreased significantly,and the number of female flowers increased significantly.under the treatment with mepiquat chloride at 20/15℃,the first male flower node and the first female flower node of watermelon increased significantly,and the number of female flowers decreased significantly.（2）Spraying mepiquat chloride at 30/25℃and 25/20℃can promote flowering,and the first male flower node and the first female flower node of the watermelon at 30/25℃increased with the increase of the concentration of mepiquat chloride,and there was a decreased trend of the number of female flowers.However,at 25/20℃,there was a tendency to decrease the position of the first male flower and the first female flower of watermelon with the increase of the mepiquat chloride concentration,and the number of female flowers remained stable.3.The effects of ethephon on watermelon sex differentiation are significant:The three concentrations of ethephon greatly delayed the formation of the watermelon female flower.In the first 30 knots,there was no female flower development expression but only male flower formation,which can achieve the purpose of removing the female flowers in male parent.In addition,when ethephon and mepiquat chloride are sprayed simultaneously,the effect of ethephon is dominant.4.The high night temperature condition makes the overall content of GA₁ and GA₃ of watermelon seedlings stem apexes higher than that of watermelon under low night temperature,and the endogenous GA₃,GA₄ and GA₇ content of three-leaf one-heart stage watermelon seedlings during high night temperature is much higher than that of low night temperature condition.So that the number of female flowers of watermelon decreased significantly under high night temperature.At low night temperatures,the IAA content increases with increasing seedling age.At high night temperatures,the IAA content decreases with increasing seedling age.The variation regularity of ABA and JA content is completely opposite to IAA,which decreases with increasing seedling age at low night temperatures.Under high night temperature,it increases with the increase of seedling age.While at 24℃night temperature,the contents of IAA,JAA,and BAB increase with the increase of seedling age,which also shows the particularity of this night temperature.The high level of endogenous IAA content is closely related to the differentiation expression of watermelon female flowers,which can significantly increase the number of watermelon female flowers.When the content of endogenous ABA and JA in watermelon stem tips are low,it is conducive to the formation of female flowers,otherwise it is conducive to the formation of male flowers.5.After watermelon seedlings were sprayed with ethephon,the relative expression levels of the Cit ACS4 gene and CIWIP1 gene increased with time increase,and the maximum expression level was at12 hours after treatment.At this time,the relative expression level of the Cit ACS4 gene was about 20times that of the control The relative expression of CIWIP1 gene was 46.5 times that of the control.Then both they returned to a level comparable to that before spraying.Both Cit ACS4 and CIWIP1 in the watermelon stem tips responded quickly to ethephon,and they responded to ethephon within 6 hours.At this time,the relative expression levels of the two genes both increased obviously.