Study On Prevention And Control Of ’Kanpei’ Citrus Fruit Cracking By Exogenous Hormone And Calcium Treatment

’Kanpei’is a new citrus variety bred from a cross between’Nishinokaori’and’Ponkan’.’Kanpei’has good quality and good taste,but it suffers from a severe fruit cracking problem,which has significantly affecting farmers’income.Therefore,we need to resolve the problem of’Kanpei’fruit cracking.This study use 7-year-old’Kanpei’citrus plants from the Fasi base in Jiangxia District,Wuhan as the subject.we aim to explore the main causes of’Kanpei’fruit cracking and investigate preliminary prevention and control technologies.The primary research findings are as follows:（1）By the statistical analysis of the growth and fruit cracking of’Kanpei’,we confirmed that’Kanpei’fruit cracking begins in July,peaks in mid-August.’Kanpei’citrus fruits undergo two distinct expansion periods,with the cracking peak occurring during the fruit’s slow growth stage.The primary types of cracking in’Kanpei’citrus are transverse,longitudinal.microscopic inspection exposed numerous voids,thickened cell walls,and folding depressions in fruit peel cells.（2）The fruit cracking of’Kanpei’is related to the environmental factors and physiological indexes of fruit.Regarding environmental factors,the incidence of’Kanpei’fruit cracking exhibits a positive correlation with the number of high-temperature days,indicating that a greater number of hot days increases the likelihood of fruit cracking.In terms of fruit physiological markers,the’Kanpei’fruit cracking rate has a negative correlation with fruit shape index and a positive correlation with fruit size,signifying that lower fruit shape indices and larger fruits and greater lateral diameter are more susceptible to cracking.The occurrence of’Kanpei’fruit cracking is positively associated with peel brittleness and negatively linked to peel thickness and hardness,suggesting that increased peel brittleness and decreased peel thickness and hardness contribute to fruit cracking.（3）By the analysis of the physiological and molecular mechanism of’Kanpei’cracked fruit,we found significant differences in GA₃ and abscisic acid（ABA）content exist in the epicarp and juice sacs of’Kanpei’citrus.GA₃ promotes normal fruit growth and exhibits a stronger expansion capacity than the peel.Furthermore,reduced ABA content in the peel leads to elevated peroxidase（POD）enzyme activity,resulting in lignin accumulation,decreased peel elasticity,increased brittleness,and exacerbated fruit cracking.Transcriptome and Real-time Quantitative PCR（qRT-PCR）analyses identified upregulated six differentially expressed genes in hormone and eight differentially expressed genes in lignin metabolism pathways,particularly in the albedo,indicating that the albedo is a sensitive site for fruit cracking.（4）By the prevention and control effect of exogenous and calcium treatment on’Kanpei’fruit cracking.We found GA₃’s significant impact on fruit cracking.So,a three-factor,three-level orthogonal experiment was designed with GA₃ at the core to treat’Kanpei’plants.Statistical analysis of fruit cracking rate,fruit peel physical properties,and fruit peel anatomical structure revealed that the optimal preventative and control strategy for’Kanpei’fruit cracking consists of a treatment combination of 10 mg/kg GA₃+0.08mg/kg BR,can reduce the fruit cracking rate during the cracking peak period by 50.96%compared to the control group.This study conducted a comprehensive analysis of’Kanpei’citrus fruit cracking rate,environmental factors,fruit physiological indicators,hormone content and cell wall metabolic enzyme activity.We preliminarily determined that an imbalance in endogenous hormones GA₃ and ABA distribution in the fruit and peel results in reduced peel expansion capacity and elasticity,leading to fruit cracking.We performed a three-factor,three-level orthogonal experiment with GA₃,BR,and Ca（NO₃）₂ to preliminary identify the optimal treatment combination:10 mg/kg GA₃+0.08 mg/kg BR.It lays the theoretical and practical foundation for reducing’Kanpei’fruit cracking.