Correlation and genetic analysis of fruit traits in F1 hybrid population of loquat generated from Ninghaibai × Dafang

Abstract: 【Objective】This paper aimed to complement the correlation genetic analysis of the important traits of loquat (Eriobotrya japonica Lindl.) fruits in the F1 population generated from the white flesh cultivar Ninghaibai crossed with the yellow flesh cultivar Dafang in order to provide the reference for the parent selection and seedling screening in loquat breeding【. Methods】A total of 130 plants of F1 hy- brid population of Ninghaibai × Dafang were used as experimental materials. The samples were collect- ed at the maturity stage from May to June in 2020, and 30 fruits were randomly selected from the mid- dle and upper part of the crown of each tree. The longitudinal diameter, transverse diameter and pulp thickness of the fruits were measured with digital display vernier caliper.The Fruit weight and seed weight were measured with electronic balance (1/100). Soluble solid content (TSS) in fruit flesh was determined by ATAGO handheld digital refractometer. The number of seeds was also recorded. Excel 2016 was used to organize data and draw tables. IBM SPSS Statistics 25.0 was used to test normality, draw frequency histogram and perform correlation analysis.【Results】The results of genetic analysis showed that the seven important fruit traits were normally distributed. The average values of fruit weight, fruit longitudinal diameter, fruit transverse diameter and fruit flesh thickness were lower than the mid-parent value or even lower than the low parental value. The genetic transmission ability was between 90.40%-96.46%, all lower than 100%, and the dominant rate was all negative. The heterosis was not significant, the genetic tendency was small, and most of the hybrid offspring showed the phe- nomenon of character decline. The decline in flesh thickness was the most serious, 73.08% were thin-ner than the low parent and 11.54% were thicker than the high parent. Although fruit weight, fruit lon- gitudinal diameter and fruit transverse diameter showed a genetic tendency to be lower, the high paren- tal rate was 24.62% to 33.08%. The average values of TSS, seed weight, seed number were higher than that of high value, genetic heritability were higher than 100% and between 102.26 and 121.23%. Heter- otic rate showed strong heterotic, genetic tendency represented as high genetic predisposition. Among them, the heterotic rates of seed weight and seed number reached 21.23% and 15.20%, showing the most significant heterosis performance. The results of correlation analysis showed that the fruit weight was positively correlated with the vertical diameter, horizontal diameter, flesh thickness, seed weight and seed number, but negatively related to TSS. Through stepwise regression analysis, the optimal mul- tiple linear regression equation for fruit weight was expressed as: Y=- 41.861 + 0.317X1 + 0.795X2 + 2.975X3+2.208X5-0.879X6 (Y= fruit weight, X1= fruit longitudinal diameter, X2= fruit transverse diame- ter, X3= flesh thickness, X5= seed weight, X6= seed number; R = 0.991, R2 = 0.981, e = 0.138), which in- dicated that the fruit longitudinal diameter, fruit transverse diameter, flesh thickness, seed weight and seed number were the main factors affecting fruit weight. Path analysis results showed that the fruit transverse diameter, fruit longitudinal diameter, flesh thickness, seed weight and seed number were the important traits that affected fruit weight. The order of simple correlation coefficient between five traits and fruit weight was the fruit transverse diameter (0.974) > seed weight (0.859) > flesh thickness (0.847) > longitudinal diameter (0.820) > seed number (0.323). The order of direct path coefficient be- tween five traits was the seed weight (0.383) > transverse diameter (0.338) > flesh thickness (0.227) > longitudinal diameter (0.136) > seed number (-0.070). The order of decision coefficient was the fruit transverse diameter (0.544) > seed weight (0.511) > flesh thickness (0.393) > longitudinal diameter (0.204) > seed number (-0.050).【Conclusion】The fruit weight, fruit transverse diameter, fruit longitu- dinal diameter, flesh thickness, TSS, seed weight and seed number were all quantitative traits con- trolled by multiple genes. Among them, the genetic tendency of the fruit weight, fruit transverse diame- ter, fruit longitudinal diameter and flesh thickness tended to be smaller, while the genetic tendency of the TSS, seed weight and seed number tended to be higher. The fruit weight was significantly positive- ly correlated with the longitudinal diameter, transverse diameter, flesh thickness, seed weight and seed number, but negatively correlated with the TSS. In conclusion, the longitudinal diameter, transverse di- ameter, flesh thickness, seed weight and seed number are the main factors affecting fruit weight, among them the transverse diameter and seed weight had the greatest effect on fruit weight, whereas the seed number had the least effect.