Effect of xenia on fruit quality of Majiayou

Abstract：【Objective】Pollination of Majiayou with a local variety Xinmuyou and a tetraploid grapefruit was used to investigate xenia effect on the fruit quality of Majiayou. It was expected to improve the fruit quality of Majiayou by selecting pollen parent.【Methods】Mature 9- 10- year- old Majiayou trees were used as the seed parent. Xinmuyou and a tetraploid grapefruit were used as the pollen parents (pollination A group, Majiayou × Xinmuyou; pollination B group, Majiayou × tetraploid grapefruit), and natural open pollination was used as the control. After the fruit ripened, a fruits from different pollination groups were analyzed for fruit quality, primary metabolites in the pulp, and volatile substances in the pericarp.【Results】Pollen viability of Xinmuyou and the tetraploid grapefruit was 94.34% and 93.75%, respectively. Cross-pollination significantly increased the fruit set rate of Majiayou, and the effect of the tetraploid grapefruit was more significant compared to that of Xinmuyou. The average single fruit weight was 1 109.09 g in pollination A group, which was higher than pollination with the tetra-ploid grapefruit (pollination B group) and the control. Single fruit weight in pollination B was the lowest. Fruit diameter, pericarp weight and pericarp thickness (2.06 cm) in pollination B were significantly lower than the other groups. Pollination A significantly increased seed weight. Seed weight in pollination B group was the lowest, and most of the seeds were shrunken. The flesh recovery was highest in pollination B group, followed in descending order by the control and pollination A group. The difference between pollination B and pollination A was significant. In the control, total soluble solids (TSS) content and titratable acidity (TA) was higher than the other two pollination groups. However, TSS/TA ratio was 13.48 in the control, significantly lower than in pollination A and B groups. The primary metabolites included amino acids, organic acids, sugars, and alcohols. There were significant differences in the content of primary metabolites between different pollination groups, but there was no clear pattern in the contents of primary metabolites in fruits among pollen parents. Pollination B resulted in the highest citric acid content (2.35 mg·g^-1 ) and sucrose content (39.19 mg·g^-1 ), which were significantly higher than the control and pollination A. Glucose content in fruit of pollination A group was 43.52 mg·g^-1 , which was significantly higher than that of the other groups. In pollination A and B, the main amino acid in the fruit was proline, whose concentration was 0.32 mg·g^-1 in group B, which was significantly higher than the other two groups. A total of 85 volatile compounds were identified in fruits from different pollination groups and fruits from open pollination of the parents. They included 11 aldehydes, 28 terpenes, 16 esters, 14 alcohols, 14 ketones, 5 aliphatic hydrocarbons, 7 phenols, and 7 carboxylic acid compounds. 41 volatile compounds were detected in the fruit from open pollination, with limonene being the most abundant, accounting for 87.48% of the total content. In fruit from pollination A group, 36 volatile substances were found, with limonene accounting for 92.57% of the total content. In the fruit of Xinmuyou, 47 volatile substances were detected, with limonene making up 91.07% of the total content. In fruit from pollination B, 38 volatile substances were detected, with limonene representing 88.52% of the total content. In the fruit of the tetraploid grapefruit, 49 volatile substances were detected, with limonene constituting 88.65% of the total content. 21 volatile substances exhibited a significant xenia effect, including most of the terpene substances. Limonene content in fruit from open pollination was 25 822.76 μg·g^-1 , while it was 154 583.28 μg·g^-1 in Xinmuyou fruit. However, in fruit from pollination with Xinmuyou, limonene content reached 84 271.06 μg·g^-1 , which was more than three times higher than that under open pollination. This indicates that pollination with Xinmuyou pollen substantially increased the limonene content in the Majiayou fruit.【Conclusion】In conclusion, cross-pollination can increase the fruit set of Majiayou, and Majiayou fruit quality can be directly improved through the xenia effect. This research provides a theoretical basis and technical support for the practical production of Majiayou.