Effect of cross-pollination on fruit set, growth and quality of pomelo with red flesh and green peel

【Objective】Poor fruit set rate, unstable yield, and variable quality are the significant challenges in cultivating the green peel and red flesh pomelo [Citrus maxima (Burm.) Merr.]. This study examined the effects of pollen source on fruit set, growth, and quality, with regard to xenia (pollen direct effect on fruit and seed traits) and metaxenia (its influence on maternal tissue development) The aim was to identify optimal pollinizer varieties to enhance yield and fruit quality.【Methods】Mature 10- year-old red-flesh, green-peel pomelo trees served as seed parents. Artificial cross-pollination was performed using pollen from three pomelo varieties: Hongbaoshi, Dongshizao, and Vietnam Red Pummelo. Fruit set rate, fruit growth, and quality parameters (single fruit mass, longitudinal diameter, transverse diameter, peel thickness, total soluble solids (TSS), titratable acid (TA), vitamin C (Vc) content, seed number, edible rate, flesh segment number, and flesh color) were measured. Self-pollination served as the control. Data analysis included correlation analysis and comprehensive analysis and evaluation of the impact of pollinizers on the fruit set rate, growth and development, and quality of the green peel red flesh pomelo.【Results】Cross-pollination significantly increased fruit set rate compared with self-pollination. Metaxenia effects were evident, resulting in a more uniform, nearly spherical fruit shape (fruit shape index closer to 1). Cross- pollinated fruits exhibited significantly higher levels of gibberellin (GA3) and cytokinin (CTK) compared to self- pollinated fruits. Auxin (IAA) significantly increased in fruits pollinated with Hongbaoshi Pomelo and Vietnamese Red Pomelo. TSS was 1%-2% higher than self-pollination, with Hongbaoshi achieving the highest (10.97% ). Flesh redness, potentially linked to higher sugar accumulation, was enhanced. Vc content was also increased (40-50 mg · 100 g- 1 vs 30- 40 mg·100 g-1 in self-pollinated fruit). Peel thickness was reduced but seed number increased (95-112 vs average 71 in natural pollination). Hybrid seeds were cuneiform, flattened, with fin-like ribbed surfaces. While fruits from pollination with Vietnamese red pomelo had the thinnest peel and smaller fruit size. Correlation analysis revealed that fruit weight had a highly significant positive correlation with both fruit length and width (P＜0.01); fruit length exhibited a highly significant positive correlation with both fruit width and shape index (P＜0.01). Flesh recovery had a highly significant negative correlation with peel thickness (P＜0.01) and a significant positive correlation with seed number (P＜0.05). TSS exhibited a significant positive correlation while titratable acid content demonstrated a highly significant negative correlation with the solids-to-acid ratio (P＜0.05). Metaxenia and xenia effects varied significantly among pollinizer varieties. Based on comprehensive evaluation, the Hongbaoshi Pomelo as pollen source yielded the best fruit quality.【Conclusion】Cross-pollination significantly improved fruit set rate and enhanced multiple fruit quality attributes in red- flesh, green-peel pomelo, displaying pronounced Xenia and metaxenia effects. Hongbaoshi pomelo was identified as the most effective pollinizer variety. Rational selection of pollinizer varieties in production is recommended to boost fruit set, yield stability, and fruit quality. This study provided practical guidance for improving the cultivation of red-flesh, green-peel pomelo.