Effect Of The Blue Light:Red Light Ratio In Supplemental Light On Pitaya Flower Bud Differentiation And Fruit Quality

Pitaya is a kind of cultivated plant with high nutritive value,long production period and simple cultivation method.The cultivation area has been expanding since it was introduced to Zhejiang in 2000.However,the temperature in Zhejiang Province changes greatly in spring,and there are many rainy days,which led to low yield of the first batch of Pitaya fruits under protected cultivation.Supplemental light is one of the significant ways to achieve good quality and high yield of plants,which has been widely used in greenhouse culture of flowers and vegetables.Light-Emitting Diode(LED)has played an important role in plant light supplement in recent years due to its narrow wave width and low energy consumption.In this thesis,we used a red pitaya cultivar,'Zimilong' for this study.We set up 5 levels of blue to red light ratios(1:8,1:6,1:4,1:3 and 1:2)in LED to treat the pitayas,and the rest treated with white LED light acted as controls.By comparing the flower bud differentiation,phenology and fruit quality,we attempt to find out the best light supplement ratio to advance spring budding,increase the amount of budding as well as improve the quality in pitaya.Besides,the study also aimed at revealing the effect of supplemental lighting on flower bud differentiation and fruit quality in pitaya by comparing the changes of carbon-nitrogen mass ratio,hormone content,activity of sugar related metabolizing enzymes and sugar content during fruit maturation between different treatments and controls.Furthermore,the results provide a foundation for establishing Protected Cultivation Techniques of pitaya in Zhejiang Province.The results are follows:1.By comparing the flower bud differentiation and fruit quality,we attempt to choose the best light supplement that would advance spring budding,increase the amount of budding and also improve the quality in pitaya.The results showed that 1:4 and 1:2 light supplementation treatment could significantly increase the number of flower buds in the first batch of pitaya fruit in spring,with the yield increased 238%and 112%respectively.Meanwhile,the treatment 1:2 could also significantly increase TSS and soluble sugar content in pitaya.2.The number of flower buds in light supplementation treatment was significantly higher than that in non-light supplementation treatment;with the blue-red ratio of 1:4 being the largest.Before the emergence of flower buds,C/N in leaves of two light supplemental treatments were significantly higher than control,and treatment 1:4 was higher than treatment 1:2.The peak of ABA in leaves of light supplemental treatment appeared earlier than control.GA in leaves of light supplementation treatment was significantly lower than that of control before flower bud appeared.The correlation analysis showed that the content of C/N,ABA and ZR in the leaves of pitaya was positively correlated with number of flower buds,while GA was negatively correlated with number of flower buds.The first batch of flower bud of pitaya can be promoted by supplementing light with blue to red ratio of 1:4.Overall,light quality promoted ABA and ZR synthesis,inhibited GA synthesis and promotes flower formation by regulating the changes of endogenous hormones in pitaya.Meanwhile,regulating C/N in pitaya through photosynthesis,which created an environment with relatively more carbon and less nitrogen.All these result in more flower buds and flowers.3.The study preliminarily explored the mechanism of light supplementation regulating sugar accumulation by measuring the content of sucrose,glucose,fructose and activities of sucrose metabolism-related enzymes in the flesh of pitaya at young fruit stage,color-changing stage and mature stage.Results showed that the TSS,sucrose content in fruit of LED light supplementation with blue and red light ratio of 1:2 were higher than other treatments,and the activity of SPS and SS acted the same as well.While the activity of AI and NI in treatment 1:2 were lower than others.There was no significant difference except fructose content and AI activity in 1:4 mature fruit was lower than CK.Overall,LED light supplementation with blue and red light ratio of 1:2 improved the sucrose content of the first batch of spring pitaya.The mechanism may be less red light promoted sucrose,reduced glucose and fructose by inhibiting the activity of AI in pitaya fruiit.Meanwhile,regulating the activity of SPS and SS so as to provide more materials for glucose and fructose,and also promote sucrose in fruit.