Study on embryo abortion regularity and immature embryo rescue technique in distant hybridization of apricot, plumcot and peach

To explore the critical periods and occurrence patterns of embryo abortion during distant hybridization among apricot, plumcot, and peach, and to provide a theoretical basis and practical guidance for embryo rescue methods in Rosaceae stone fruit trees.

Twelve distant hybrid combinations were designed using apricot, plumcot, and peach as female parents. Following controlled artificial pollination, the developmental progression of young fruits was monitored, fruit size and fruit set rates at different developmental stages were recorded. The survival time of immature embryos was assessed using fluorescent staining. Viable immature embryos were subjected to bud induction, proliferation, and rooting cultures. Different plant growth regulator combinations were evaluated to establish an effective immature embryo rescue system for Rosaceae stone fruit trees.

Fruit development and immature embryo survival time in distant hybridization of Rosaceae stone fruit trees were significantly influenced by the female parent species. In hybrid combinations with common apricot or kernel apricot, plumcot, and peach, common almond, or almond as female parents, fruit growth ceased at 12, 6, and 31 days after pollination, respectively, and fruit drop began at 21, 18, and 38 days after pollination. Distant hybrid young fruits of Rosaceae stone fruit trees commonly exhibited prevented transverse diameter growth, occurring in 48.3%-69.0% of cases compared with compatible pollination controls. In addition, prevented vertical diameter growth was observed in young fruits of four combinations such as ‘Fengweimeigui’ × ‘Xiaobaixing’, with an incidence of 52.8%-55.9%, while prevented side diameter growth was noted in young fruits of ten combinations such as ‘Zhongren 3’ × ‘Jinbian 1’, occurring in 47.2%-74.3% of cases relative to controls. Seven hybrid combinations, with ‘Longwangmao’, ‘Fengweimeigui’, ‘Zhongyoutao 4’, and ‘Shantao 1’ as female parents, showed fertilization timing similar to that of compatible controls, whereas the remaining combinations exhibited delayed fertilization. The optimal embryo rescue medium consisted of MS basal medium supplemented with 2,4-D or IAA (2.0 mg/L), 6-BA (0.5 mg/L), sucrose (30 g/L), and agar (7 g/L), with 40.0% of the rescue rate of immature embryos. The proliferation medium comprised MS basal medium supplemented with 6-BA (1.0 mg/L), sucrose (30 g/L), and agar (7 g/L), with 30.5 of the average of new buds. The rooting medium consisted of WPM basal medium supplemented with NAA (0.5 mg/L), sucrose (20 g/L), and agar (7 g/L), with 25.5 of the average of roots.

The female parent genotypes significantly affect the time when young fruits stop growing and drop, as well as the survival time of immature embryos in distant hybridization of Rosaceae stone fruit trees. The optimal periods for immature embryo rescue, when apricot, plumcot, and peach are used as female parents, are 12-18, 6-15, and 12-30 days after pollination, respectively. Among these, combinations using ‘Longwangmao’, ‘Fengweimeigui’, and ‘Zhongyoutao 4’ as female parents show relatively higher success rates in embryo rescue. Plant growth regulators such as 2,4-D, IAA, 6-BA, and NAA serve as critical additives during embryo rescue.