Study On The Regulation And Mechanism Of Two Quarterly Fruiting And Fruit Of Lemon In Dehong,Yunnan Province

Lemon（Citrus limon（L.）Burm.F.）is an evergreen fruit tree belonging to citrus in Rutaceae.It has a unique flavor and is rich in a variety of vitamin C and other bioactive compounds,with dual-purpose value of medicine and food.Yunnan lemon has two concentrated batches of fruits in a year,namely spring-flowered fruit（spring flowers mature in summer from July to October）and autumn-flowered fruit（autumn flowers mature in spring from March to June）,mainly spring-flowered fruit accounting for about 75%.However,lemon autumn-flowered fruit in Yunnan is a rare special batch of fruit,harvested in the off-season of fresh fruit,which has high economic benefits.Due to the lack of targeted flower regulation technology,the output of lemon autumn-flowered fruit fluctuates greatly.Technology of regulating lemon autumn-flowered fruit to achieve two-season output of lemon is required by the high-quality development of local lemon industry and market.Therefore,this study used multi-point questionnaire and sampling survey to explore the effects of nutrient management,soil nutrients and tree nutrients on lemon quality and fruit yield.Field experiments were conducted to explore the effects of fruit thinning,water stress and hormones on the yield and quality of lemon fruit in two seasons.Pot experiment was conducted to reveal the autumn-flowered regulation mechanism of flower bud differentiation in the process of autumn-flowered fruit development from the aspects of morphology,physiological metabolism and molecular biology.The main results were as follows:（1）Adjustment of nutrient status and fertilization on fruit yield and quality in spring-flowered and autumn-flowered in lemon orchards.29 representative lemon orchards in Dehong prefecture were investigated.It was found that the yield of spring-flowered fruit was significantly higher than that of autumn-flowered fruit.The fruit quality of autumn-flowered fruit was significantly better than that of spring-flowered g fruit.The contents of VC,TSS and TA of autumn-flowered fruit were significantly higher than that of spring-flowered fruit.There were significant differences in the content and accumulation of mineral nutrients in leaves and fruits between spring and autumn-flowered fruits.The analysis of tree nutrient content showed that the contents of N and K in autumn-flowered fruit leaves were significantly higher than those in spring-flowered fruit leaves,and the contents of Ca and Mg in leaves were lower than those in spring-flowered fruit leaves.There was significant difference in the accumulation of N,K,Fe,Zn and B between spring-flowered fruit and autumn-flowered fruit,the accumulation of K,Fe,Zn and B in autumn-flowered fruit was higher than that in spring-flowered fruit.Rich organic matter and high contents of Mg,Mn,B,K and Ca were important soil conditions for good quality of fruits in two seasons.They could increase the fruit longitudinal diameter and TSS content of fruits in spring and autumn,and promote the increase of fruit transverse diameter and VC content of autumn-flowered fruit.High soil K and Ca content decreased the TA content of fruit,but high soil available N content affected the titratable acid,soluble solid content and juice yield of autumn-flowered fruit,decreased the VC content,while high soil Cu,Fe,P content increased the VC content.The above results show that the soil acidification of lemon orchards in Dehong area was serious,and the fertilization of orchards was mainly chemical fertilizer.It was suggested to appropriately adjust the soil p H,increase the soil organic matter,increase the fertilization proportion of K fertilizer,and pay attention to the application of medium and trace elements Ca,Mg,B and Zn fertilizer.The nutrient content of lemon leaves can affect the fruit quality index of spring-flowered fruits,but it had little effect on the quality of autumn-flowered fruits.The content of P and Mn in leaves was positively correlated with the content of VC in spring-flowered fruits,and the content of Mn,P,N,Zn,Mg and Ca in leaves was positively correlated with the content of TA in autumn-flowered fruits.The leaf nutrient content had an effect on the yield of lemon,and the leaf P and Mn contents were positively correlated with the yield of spring-flowered fruits and the total yield of the two seasons.The nutrient content of lemon fruit had little effect on fruit quality,and has no significant effect on lemon yield.The content of Mg and K in fruit was positively correlated with the yield of spring-flowered fruits and the total yield of two seasons,and the content of Mn in fruit was positively correlated with the yield of autumn-flowered fruits.These results indicate that nutrient management can regulate the yield and quality of lemons in two seasons.（2）Regulation of flower and fruit thinning measures on fruit yield,quality and nutrient accumulation of lemon in spring-and autumn-flowered fruits.The field plot experiment had been carried out for 4 consecutive years.It was found that the technical measures of flowers and fruits thinning significantly increased the yield of autumn-flowered fruits while reduced spring-flowered fruits.The total yield of the whole year reduced,but the economic benefit increased.The measures of thinning flowers and fruits significantly increased the longitudinal diameter,VC,TSS and TA contents.Thinning flowers and fruits significantly increased the nutrient contents of N,P and K in lemon autumn-flowered fruits,and significantly increased the contents of K and Ca in spring/autumn-flowered fruits.It significantly promoted the contents of N,P,Fe and Mn in autumn-flowered fruit,while significantly reduced the contents of N,P,Fe and Mn in spring-flowered fruit.It significantly decreased Mg,Zn and B content in autumn-flowered fruit,while increased Mg,Zn and B content in spring-flowered fruit.It shows that flower thinning and fruit thinning can not only increase the yield of autumn fruit and increase economic benefits,but also adjust nutrient content and improve quality.（3）Regulation of water stress and hormones on flowering,yield,quality and nutrient accumulation in lemon.The pot experiment was carried out to regulate autumn-flowered fruit under water stress and hormones.It was found that water stress could not only weaken the vegetative growth of trees,but also promoted flowered amount and fruit setting rate（6.7times that of the control）.Water stress significantly reduced the content of VC and TA in fruit,significantly increased the content of TSS in fruit.Water stress significantly increased the content of N,P,Fe and Cu in leaves,significantly reduced the content of Mn,and significantly reduced the C/N ratio.When the concentration of hormone PBZ was 600 mg/L,the number of flowered branches was the largest.Hormone PBZ treatment significantly reduced the single fruit weight,longitudinal diameter,transverse diameter,skin thickness and VC content of lemon,and significantly increased the juice yield and TSS content.However,spraying hormone GA inhibited the flowered of lemon.This shows that water control 15%,spraying PBZ 600 mg/L and the combination of the two（CW15+PBZ 600）all significantly improved the yield of autumn flowers,but had little effect on quality.（4）Mechanisms of water stress and hormone treatment inducing out-of-season flowering in lemon.Microscopic observation showed that water stress could significantly induce lemon flowering and promote the transformation from axillary buds to flower buds.A total of 1638differentially expressed genes（DEGs）were identified by RNA sequencing.DEGs were related to flowering,hormone biosynthesis or metabolism.Gene structure analyses of alternative splicing genes were performed,many alternative splicing of flowering-related gene were noted.Two alternative splicing transcripts of CiFT were isolated from lemon.The expression of some DEGs was associated with floral induction by real-time PCR analysis.Quantitative analysis of endogenous hormones under water stress showed that the content of IAA increased,while the content of GA₃ decreased.And the content of ABA was also induced by water stress treatment.The effect of exogenous plant hormone treatment on flowering related differentially expressed genes found that the expression of t CiFT in leaves could be significantly induced by ABA and PBZ treatment,and inhibited by GA₃ and NAA.The expression pattern of CiFTαand CiFTβwas similar to that of t CiFT.The expression of CiMFT was induced by NAA.The accumulation of CiBFT and CiTFL1 in buds was always induced by ABA.There were no significant change were found in CiELF3,CiELF4 and CiSPL6 genes.In conclusion,aiming at the industrial demand of lemon off-season production in Dehong,Yunnan to improve the yield and quality of autumn-flowered fruits,through investigation,analysis and experimental research,this study defines the role of nutrients,water,hormones and flower thinning and fruit thinning in regulating the yield,quality and nutrient accumulation of autumn flowered fruits of lemon.This study expounds the relationship between the yield and quality of lemon fruit in two seasons and fertilization,tree nutrients,flower and fruit management.It puts forward the nutrient management strategy of lemon"improving the quality of spring flowered fruits and increasing the yield of autumn flowered fruits",and forms a technical scheme of water stress and hormone to improve the yield and quality of lemon autumn flowers and fruits.It is found that the florigen gene FT is involved in the regulation of flowering by water through selective splicing,which adds a new dimension to the flower formation theory of perennial woody plants.molecular evidence of scientific importance.