Juan Hu

Fruit cracking affects both the yield and economic efficiency of citrus; however, the underlying mechanism remains unclear. Therefore, this study focused on resistant and susceptible cultivars to identify the mechanisms underlying fruit cracking. The results showed that in ‘Mingrijian’, pectin morphological transformation and hemicellulose and lignin degradation in the pericarp were important contributing factors. During the critical fruit-cracking period (115–150 days after flowering), the water-soluble pectin, protopectin, and lignin contents in the pericarp of ‘Daya’ presented inverse changes relative to those in ‘Mingrijian’, thus enhancing the mechanical properties and resistance of pericarp. From 115 to 150 days after flowering, the soluble sugar content in the pulp of ‘Mingrijian’ increased rapidly by 97.35%, aiding in pulp water absorption and expansion. Moreover, the soluble protein content in the pericarp of ‘Mingrijian’ exhibited a declining trend and was lower than that of ‘Daya’, thus affecting the overall metabolism. The superoxide dismutase (SOD) activity in the pericarp of ‘Mingrijian’ gradually decreased from 115 to 180 days after flowering, while the peroxidase (POD) activity remained at a low level, resulting in weaker antioxidant capacity and lower environmental resistance. This study provides valuable insights into the mechanisms of citrus fruit cracking, laying the foundation for preventive and control strategies.

Adequate yield and fruit quality are required in commercial plum production. The pollen source has been shown to influence fruit set and fruit characteristics. In this study, ‘Siyueli’, ‘Fenghuangli’ and ‘Yinhongli’ were used as pollinizers of ‘Fengtangli’ plum. Additionally, self-pollination, mixed pollination, and open pollination were performed. We characterized the differences in pollen tube growth, fruit set and fruit quality among pollination combinations. ‘Fengtangli’ flowers pollinated by ‘Fenghuangli’ had more pistils with pollen tubes penetrating the ovary and the highest fruit set rate, while the lowest fruit set rate was obtained from self-pollination. In self-pollinated flowers, 33% of pistils had at least one pollen tube reaching the ovary, implying that ‘Fengtangli’ is partially self-compatible. Pollen sources affected ‘Fengtangli’ fruit size, weight, pulp thickness, soluble solids, and sugar content. Transcriptome analysis of ‘Siyueli’-pollinated and ‘Yinhongli’-pollinated fruits revealed 2762 and 1018 differentially expressed genes (DEGs) involved in the response to different pollen sources. DEGs were enriched in plant hormone signal transduction, starch and sucrose metabolism, and MAPK signaling pathways. Our findings provide a reference for the selection of suitable pollinizers for ‘Fengtangli’ plum and promote future research on the metaxenia effect at the molecular level.