Investigating Heteromorphic Self-incompatibility In Primula Forbesii Using Pollination Experiment

Primula species are widely, naturally distributed and have a long history of cultivation, some of which have become famous potted and bedding plants. Most species in genus Primula have two types of pistil, and are basically self-incompatible. There were plenty of researches on self-incompatibility of Primula, involving about at least50species. Primula forbesii is newly cultivated in China, with abundant flowers and a long flowering period, however there was no research on its reproduction system. In this paper, we investigated the self-incompatibility of P. forbesii by crossing with fluorescent and electronic microscope observation. The main results are shown as follows:(1) For P. forbesii’Red Star’,’Purple Cloud’and’Fragrant Luolan’, the fruiting rate and seed-set per capsule were different significantly among different crosses (p=0.01), and in a descending order were legitimate crosses (T×P and P×T)> within-pin cross and pin selfing> within-thrum cross and thrum selfing. The fruiting rates of all legitimate crosses reached100%and the mean number of seeds per capsule obtained ranged from44to181, which were significantly higher than that of illegitimate crosses. By using intermorph pollens without vitality as mentor in intramorph combinations, fruiting rate and seeds per capsule of T×T crosses were improved. However, mentor pollination had no unambiguous effect on P×P crosses.18combinations were designed in’Red Star’to get further research, the data of which also shows that the pins produced more seeds than the thrums when used as maternal plants, either in legitimate crosses or illegitimate crosses. The self-compatible indexes of pin and thrum plants are0, which indicated seriously self-incompatible. Selfings and intra-morph pollinations with thrum plants as maternal plants produced few seeds (0-0.6), and there were no significant difference among those combinations. Illegitimate crosses with pin plants as maternal plants produced more seeds (0.1-22.2), and there were significant difference among those combinations. Compared with pollination during flower opening, bud pollination, post pollination and mentor pollination produced more seeds. In addition, the fruiting rate and seed-set per capsule in intra-morph crossing combinations were higher than selfings normally.(2) The results of fluorescent microscope observation suggested that pollens germinated easily and pollen tubes penetrated directly into the stigma surface in intermorph crosses (T×P and P×T), and pollen tubes grew nearly to the style base and began to insert into the ovary after pollination for144hours. In PxP and TxT crosses, pollens began to germinate after pollination for12hours, however, pollen tubes were blocked and didnot penetrate the stigma surface after pollination for144hours, and the pollen tubes were distorted. In pin and thrum selfings, pollens did not germinate on the stigma surface after pollination for144hours. The consequences of fluorescent and electronic microscope observations indicated that:compared with the pins, the thrums had larger pollen grains and shorter stigmatic papillae. Pollen grains had three weak points and pollen tube grew from one of them. In T×P and illegitimate combinations in pin plants, pollen germinated after pollination for24h while pollen tubes in illegitimate combinations of pins grew randomly, distortedly or inflatedly, with only a few tubes elongating in style. However, tubes grew better in post pollinations. In P×T cross pollen began to germinate after pollination for48h. No pollen grain germinated on the stigmatic surface in illegitimate crosses of the thrums; furthermore, in all cases the grains fluoresce highly and cause neighbouring stigmatic papillae to fluoresce.The results in this research demonstrated that self-incompatibility worked mainly by prohibiting pollens from germinating in thrum plants, however, it took effect mainly by preventing pollen tubes penetrating in stigma and elongating in style in pin plants. All the results layed foundation for further study on self-incompatibility of P. forbesii.