Comprehensive evaluation on fruit quality of six hybrid pollination combinations of Majiayou based on the principal component analysis

Abstract: 【Objective】Different hybrid pollination combinations show significant differences in fruit quality of Majiayou. However, research on cross pollination of Majiayou mainly focuses on the evaluation and analysis of conventional quality. There are few studies that comprehensively evaluate the secondary metabolites such as important flesh color indicators like lycopene, flavor indicators like naringin, and aroma substances based on variety characteristics. In order to provide valuable information and evaluation tools for breeders, a total of 18 pomelo fruit quality traits were used for comprehensive evaluation to select suitable male parents for pollination and provide data support for production.【Methods】 The fruit setting rate, important secondary metabolites like lycopene and naringin, and major volatile substances of six hybrid pollination combinations of Majiayou were examined, and then the early data on 18 quality traits including single fruit weight, peel thickness, number of seeds, soluble solids, titratable acid, sucrose, glucose, fructose, citric acid, malic acid and sweetness value were used for coefficient of variation (CV) analysis, correlation analysis, principal component analysis (PCA), and comprehensive score ranking to evaluate the fruit quality traits of different hybrid pollination combinations in Majiayou.【Results】There were significant differences in the 18 quality traits of fruit among different hybrid pollinated combinations of pomelo, with a coefficient of variation ranging from 6.35% to 114.45%. Among them, the highest fruit setting rate hybrid combination was Majiayou × Tuyou No. 4 (T4) of 55.3%, while Majiayou × Cocktail grapefruit (JW) had the lowest fruit setting rate of 22.9%.The contents of lycopene, naringin, and volatile substances in the juice cells of different hybrid pollination combinations of pomelo were measured. The results showed that different male parents had a significant impact on the secondary metabolites in the juice cells of Majiayou. Among them, the contents of lycopene in Majiayou × Tuyou No. 1 (T1), Majiayou × Tuyou No. 2 (T2) and T4 treatments were significantly higher than those in natural pollination (control), while there was no significant difference between Majiayou × Tuyou No.3 (T3), Majiayou × HB pummelo (HB), and JW treatments and control. In terms of naringin content, HB treatment significantly reduced the naringin content in the fruit, being only 4.05 mg·g^-1 , and there was no significant difference between other treatments and control. The composition and proportion of volatile substances in fruits of different hybrid pollination combinations were as follows: the volatile substances in the juice cells of naturally pollinated Majiayou were mainly sesquiterpenoids, accounting for 44%; next were monoterpenoids, accounting for 24%; Aromatic hydrocarbons accounted for 13%; Other volatile substances (aldehydes, acids, esters and aldehydes) accounted for a total of 20%. Compared to control, there were significant differences in the proportion of main volatile substances of different hybrid pollination combinations, specifically manifested as an increase in the proportion of sesquiterpenoids and a decrease in the proportion of monoterpenes. The proportion of sesquiterpenoids of T1 increased to 60%, which was 16% higher than that of control; Monoterpenoids only accounted for 4%, a decrease of 20% compared to control. Except for T3, the proportion of volatile substances of the hybrid combinations was significantly different, while the proportion of various substances of other four male parents (T2, T4, JW and HB) was similar to that of T1. With T3 combination, the proportion of sesquiterpenoids and monoterpenes decreased to 34% and 9%, respectively, compared to control; Aromatic hydrocarbon substances increased to 16%. The proportion of other volatile substances increased to a certain extent, with aldehydes, acids, esters and aldehydes increasing by 11%, 5%, 5% and 1%, respectively. Analyzing the specific main volatile substances, T3 treatment with the highest content of gemacrene D. significantly reduced the content of gemacrene D in fruits, being only 11.71 μg · g^{- 1} compared to control, the decrease was 64.1%, and there was no significant difference in the fruits of the other five hybrid pollination combinations. The correlation between different indexes was analyzed. The quality traits of different hybrid pollination combinations were different, and the coefficient of variation ranged from 6.35% to 114.45%. Correlation analysis results showed there were extremely significant or significant correlations among them. The correlation analysis results indicated that there was a highly significant or significant correlation between similar indicators like sugar and acid components. In terms of appearance quality, there was a significant negative correlation between the number of seeds and the thickness of the fruit peel. In terms of nutritional color and flavor, ascorbic acid was significantly and positively correlated with fructose, glucose and malic acid, while naringin was significantly and positively correlated with ascorbic acid. The correlation results reflected consistency and also reflected differences in some indicators like fruit appearance and internal quality due to different parental choices. Principal component analysis was conducted on 18 standardized trait indicators, and a total of 5 principal components were extracted from the 18 quality indicators. The cumulative contribution rate of these 5 principal components reached 85.001%, indicating that the first 5 principal components had already covered most of the fruit quality trait information. The contribution rate of the first principal component was 30.416%, including soluble sugar, organic acid and sweetness value components: fructose (0.930), sucrose (0.832), glucose (0.938), citric acid (0.753), malic acid (0.722) and quinic acid (0.674) and those indicators had higher positive eigenvalues in PC1, indicating that as the contribution rate of the first principal component increased, the contents of sugar and acid related indicatorsincreased. Finally we ranked the scores of the 5 top principal components based on their variance contribution rates. Among them, JW had the highest comprehensive quality score of 1.39, T1 had a comprehensive quality score of 1.18, ranking second. The hybrid pollination treatments T3, T4, T2 and HB ranked 3-6 in sequence, and control ranked last, in which the comprehensive quality of the fruit was the worst.【Conclusion】The principal component factor score and ranking indicated that Cocktail grapefruit was the best male pollinator for Majiayou, followed by local resource Tuyou No. 1.