Compatibility and crossbreeding barriers of hybridization in Primulina

In order to explore hybrid affinity and the causes of hybrid incompatibility within Primulina.

4 wild species and 2 cultivars were used as materials for conventional hybridization. After screening the parents for pollen vitality and stigma receptivity, hybridization work was carried out to preliminarily determine the affinity relationship of the hybrid combinations. The development of the ovary after pollination was tracked and observed, combined with experiments of pollen tube fluorescence observation, to explore the affinity and hybridization barriers of the interspecific hybridization in Primulina.

(1) Pollen viability and stigma receptivity within the Primulina was not absolutely causally related to hybrid affinity reaction. (2) The ovary swelled rate of all 16 hybrids was above 65.00%, and the seed setting rate was obviously different. When P. eburnea, P. pungentisepala, P. macrorhiza, and P. fimbrisepala were used as the female samples, the seed setting rates of each hybrid reached 75.55%, 78.44%, 46.67%, 57.78%, respectively, and showed high affinity, whereas the combination with P. ‘Spring of Beilin’, P. ‘Four Season’ as the female sample also showed the highest seed setting rate of only 6.67% and weaker affinity. (3) Fluorescence observations were conducted on the pollen tube behavior of five hybrid combinations with weak affinity. It was found that there was all combinations exhibited a certain degree of pre-fertilization barrier, which was manifested as pollen tube callus reaction, pollen tube tip swelling, twisting and rupture. However, all combinations eventually had pollen tubes extending into the embryo sac. Judging from the number of pollen tubes reaching the embryo sac, the amount of pollen from three native species such as P. eburnea was sufficient for fertilization, but the fruit set rate was still low.

Crosses within the genus Primulina show some affinity, but some combinations fail to produce seeds. This is not caused by limited pollen germination or pollen tube growth prior to fertilization, but may result in abortion due to metabolic disturbances occurring during the later development of zygotes or young embryos.