Studies On The Cytology Mechanism Of The Elite Mandarin Accession From ’Ponkan’ Cultivars

Ponkan originated in China, is one of the most important cultivars in our country. Because of those fruits have excellent quality with flesh crap and nutrition, it is always popular among consumers. However the majority cultivars of ponkan-producing region in our country are seeded cultivars, which severely affect its commercial value and market competitiveness. So it has become one of the urgent problems of cultivation of seedless Ponkan varieties for citrus breeders.In this paper, we systematically investigated the mechanism of Jiangxi seedless Ponkan, compared with E-gan No.1Ponkan and Jiangxi seeded Ponkan. Male gamete fertility, self-incompatibility and embryo development were studied. The main results were as follows:1. Male gamete of Jiangxi seedless Ponkan developmental abnormality(1) Statistical results suggested that the pollen fertility of Jiangxi seedless Ponkan was low, which mean the pollen viability, pollen germination percentage and pollen quantity of Jiangxi Seedless Ponkan were significantly lower than the control group, meanwhile the abnormal meiosis percentage of pollen mother cell was severely higher than control.(2) Anatomic results shown that the male gamete of Jiangxi seedless Ponkan developed abnormally. The scanning electron micrographs of pollen grains indicated that the morphology structure of Jiangxi Seedless Ponkan was different from the control; The microstructure of microspore mother cell demonstrated that, in this stage, the anther dehisced and released the pollen graIn was the critical stage to observe the differences, In this stage, nucleus began to degenerat and eventually disappeared, and some of the microspore mother cells shown shrinking appearance.2. Self-incompatibility of Jiangxi seedless PonkanAlthough the pollen germination percentage of Jiangxi seedless Ponkan was lower than the control on the surface of the stigma, the germinated pollen tube could grow along the style and into the ovule through the micropyle to complete fertilization, which indicated that Jiangxi seedless Ponkan was self-compatibility.3. Embryo degeneration of Jiangxi seedless Ponkan (1) The results indicated that the embryo degeneration during early developmental stage caused the seedlessness of Jiangxi Seedless Ponkan. Both self-pollinated Jiangxi seedless Ponkan and cross-pollinated Jiangxi seedless Ponkan×Jiangxi seeded Ponkan existed Embryo degeneration.(2) The21st days after pollination was the critical stage to observe the embryo abortion. During this period, ovules began to degenerate and as time went on, protuberant juice sac appeared in the ovary until the ovules entirely degenerate in the empty ovary45days after pollination.In conclusion, male gamete of Jiangxi seedless Ponkan developmented abnormally, but embryo abortion is responsible for the seedless of Jiangxi Seedless Ponkan.