Genetic variation analysis of fruit sugar and acid components in triploid hybrids of Dongzao × Chenguang

【Objective】In order to investigate the genetic variation characteristics of fruit sugar and acid in the triploid jujube offsprings, we determined the sugar and acid contents of triploid hybrids and their parents by HPLC. Jujube is a characteristic economic fruit tree species native to China. With the increasing diversification of consumer preferences for fruit flavor, polyploid breeding has become an important approach for creating new varieties. In previous studies, the tetraploid cultivar Chenguang was used as the male parent and diploid Dongzao as the female parent to generate a triploid hybrid progeny population through interspecific hybridization. However, the genetic patterns of sugar and acid components in triploid jujube have not yet been reported. Therefore, this study aimed to elucidate the inheritance mechanisms of fruit sugar and acid contents in triploid jujube offsprings and provide a theoretical basis for ploidy hybridization in jujube breeding programs.【Methods】The tetraploid Chenguang (CG, 2n=48) was used as the male parent and diploid Dongzao (DZ, 2n=24) as the female parent. A total of 41 trip-loid progeny populations were generated through controlled hybridization under net- covered conditions, along with fruits from both parents serving as test materials. In 2023, 30 fruits were collected from each tree for sugar and acid composition analysis. The samples were freeze-dried for 48 hours using a vacuum freeze dryer, weighed, and ground into powder using a grinder. Each sample was then thoroughly mixed to form three technical replicates and stored in a -80 ℃ freezer for subsequent experiments. Sugar and acid components were quantified using high- performance liquid chromatography (HPLC). Genetic variation in fruit traits was assessed based on the coefficient of variation (CV), transgressive segregation, and genetic transmission rates. Pie charts and box plots were employed to illustrate the distribution and content levels among the progeny, while normal distribution plots were used to depict the overall genetic trends. Data analysis was conducted using Excel 2016, and graphing was performed using Origin 2024.【Results】The sugar composition in the triploid hybrids fruit primarily consisted of sucrose, fructose, and glucose. Among these components, sucrose exhibited the highest content, accounting for 67.18% of total sugars, with a range from 98.76 mg·g-1 to 222.60 mg·g-1 and an average of 153.62 mg · g-1 . Fructose and glucose followed, representing 16.09% and 16.73%, respectively. The average contents of fructose, glucose, and total sugar were higher than those observed in the midparents. The variation coefficients among sugar components in the hybrid progeny ranged from 18.40% to 52.45%. The genetic transmission rates of fructose, glucose, and sucrose in the triploid hybrids were 174.96%, 193.25%, and 94.83%, respectively, indicating that the variation in sugar components was predominantly influenced by genetic factors. Furthermore, the proportions of total sugar, fructose, and glucose were 78.05%, 80.49%, and 78.05%, respectively. However, the sucrose content in the hybrid progeny fruits was lower than that of the parents, with only 65.85% similarity to the low parent, suggesting a tendency for fructose and glucose levels to increase while sucrose levels tend to decrease in the progeny. The acid composition in the fruit of triploid hybrids was ranked as follows: citric acid＞ascorbic acid＞malic acid＞quinic acid＞tartaric acid＞oxalic acid＞fumaric acid. Citric acid (1.41-5.98 mg · g- 1 ) and ascorbic acid (0.93-5.68 mg · g- 1 ) were the predominant organic acids, accounting for 36.62% and 29.28%, with average contents of 3.32 mg·g-1 and 2.54 mg·g-1 , respectively. The total organic acid contents ranged from 3.84 to 15.78 mg·g-1 , with an average of 9.07 mg·g-1 . Citric acid, ascorbic acid, malic acid, fumaric acid, and total acid exhibited a normal distribution, whereas the frequency distributions of oxalic acid, quinic acid, and tartaric acid showed skewed patterns. The coefficient of variation among acid components ranged from 34.04% to 67.57%. On average, the acid content of triploid-hybrid fruits was higher than that of the midparent value. The midparent heterosis rate varied between 31.94% and 166.78%, with the heterosis rate for total acid being 67.68%. The proportion of individuals exhibiting superior performance over the high parent was 87.80%. The results indicated a genetic predisposition toward the accumulation of organic acids beyond that observed in the parental lines. Fructose and glucose showed an extremely significant positive correlation with each other; fructose and glucose showed an extremely significant positive correlation with total sugar; both fructose and glucose showed an extremely significant negative correlation with sucrose. Citric acid was positively correlated with oxalic acid, quinic acid, and malic acid. Quinic acid demonstrated positive correlations with malic acid, citric acid, ascorbic acid, and total sugar, while showing a negative correlation with tartaric acid. Total acidity was positively associated with quinic acid, malic acid, citric acid, and ascorbic acid. The total sugar content across the tested samples ranged from 268.03 mg · g-1 to 282.00 mg · g-1 . Among the four high-acid genotypes, the total acid contents ranged from 12.10 to 15.78 mg · g- 1 . Two genotypes with total sugar content ≥ 274.95 mg · g-1 and total acid content ≥ 12.72 mg · g-1 were identified as superior germplasm resources with high sugar and acid content.【Conclusion】Sucrose, fructose, and glucose were identified as the primary components of soluble sugars, whereas citric acid and ascorbic acid were the main organic acids present in the triploid hybrid progeny. Fructose, glucose, sucrose, citric acid, and ascorbic acid are quantitative traits that are regulated by polygenes. The contents of fructose, glucose and acid components show a tendency of high heredity, while the content of sucrose shows a tendency of low heredity. Four superior lines exhibiting high sugar content, four lines with high acidity, and two lines characterized by both high sugar and acid contents were successfully selected within the triploid hybrid progeny.