Abstract:【Objective】Pollen viability and stigma pollinability are important indicators for assessing the quality of parental gametes. Understanding the changing law of kumquat pollen viability and stigma pollination rate and finding the best pollination period can effectively improve the quality and success rate of hybrid breeding. At the same time, the growth of kumquat pollen tubes under self-pollination and heterogametic pollination was studied to find out the biological characteristics and laws of kumquat heterogametic pollination to provide a theoretical basis for kumquat promiscuity. By studying the fruiting rate under different treatment conditions, we can provide some practical basis for kumquat promiscuity. 【Methods】Embryo types of 23 Fortunella germplasm resources were statistically analyzed. Materials with different embryo numbers were selected to analyze pollen viability and stigma receptivity at four different stages (Small bud stage, Big bud stage, Early florescence stage, and Full bloom stage) by using TTC staining and benzidine-peroxidase methods, respectively. Subsequently, three treatments, including emasculation without pollination, artificial self-pollination, and hybrid pollination. The growth of pollen tubes was compared under both artificial self-pollination and hybrid pollination. Finally, fruit setting rates under the three treatments were statistically analyzed and compared. 【Results】F. japonica (Thunb) Swingle have the fewest embryos, making them suitable as female parents, followed by F. hindsii (Champ) Swingle, F. crassifolia Swingle, and F. margarita (Lour.) Swingle. F. obovata Tanaka have the most embryos. Pollen viability of all tested Kumquat materials at all four stages followed the same trend increase first and then decrease and the peak was reached at the early florescence stage. The highest pollen viability was found in the Lanshanjingan (F. crassifolia Swingle), which was significantly different from other species, and Liuyangjingan CQ (F. crassifolia Swingle) is the lowest pollen viability. Stigma receptivity followed an increasing-decreasing trend at all four stages, with maximum receptivity observed at the early florescence stage. Lanshanjingan exhibited the highest pistil receptivity, while Liuyangjingan CQ showed the lowest. There were no significant differences in pistil receptivity among other kumquat varieties, therefore they can all serve as female parents for hybridization. Analysis of pollen activity and stigma receptivity revealed that kumquats exhibit synchronous maturation of male and female reproductive organs, reaching peak values at the early florescence stage. Pollen tubes of both self-pollination and hybridization treatments began germination approximately 2 hours after pollination. Hybrid pollen tubes showed a faster elongation rate compared with self-pollination pollen tubes. After 12 to 24 hours of pollination, most hybrid pollen tubes reached the base of the style as a result of fast elongation, whereas some self-pollination pollen tubes had already ceased elongation at 2/3 of the style length. After 48 hours of pollination, all hybrid pollen tubes and a few self-pollination pollen tubes penetrated the base of the style and entered the ovary. Under the condition of emasculation without pollination, all 7 kumquat germplasm obtained fruits, Lanshanjingan had the highest fruiting rate and showed significant difference with other kumquat germplasm. The kumquat flowers can develop into fruits without pollination, demonstrating the characteristic of parthenocarpy; Under conditions of artificial self-pollination, Lanshanjingan have the highest fruit setting rate, showing significant differences from other kumquat germplasms. Under the condition of hybridization pollination treatment, the fruiting rate of Liuyangjingan CQ is the highest, followed by Lanshanjingan. However, there is no significant difference in fruit set rate between these two kumquat varieties, but there is a significant difference between them and the other 5 kumquat varieties; Except for Ningboluowen CS (F. japonica (Thunb) Swingle), the fruit setting rates of the other 6 kumquat from cross-pollination treatments are higher than those from artificial self-pollination; among the 7 kumquat varieties, only Ningbojindan (F. crassifolia Swingle) shows no significant difference in fruit setting rates under both artificial self-pollination and cross-pollination treatments. The difference in fruit set rate indicates that the cross-compatibility of kumquats is stronger than self-compatibility, which is more conducive to the hybrid breeding of kumquats. When the hybrid paternal parent was the same, the higher the stigma pollinability of the female parent, the higher the fruit setting rate, and The fruit setting rate of intraspecific hybridization was higher than that of interspecific hybridization, and there was a significant difference.【Conclusion】The female parent with single embryo should be selected in kumquat hybridization; kumquat belongs to hermaphroditism, and the best time for pollen collection and pollination is the early florescence stage; kumquat cross-compatibility is stronger than self-compatibility, which is beneficial to kumquat cross breeding.
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