平邑甜茶无融合生殖基因型分析及雌配子发育模式研究

Analysis of apomictic genotypes and the developmental mode of female gametes of 'Pingyi Tiancha'(Malus hupehensis var.pingyiensis)

【目的】为探明平邑甜茶的无融合生殖遗传与发育机制，【方法】以平邑甜茶与B，、M。M。为亲本杂交，并筛选杂种实生苗；用去雄套袋法鉴定杂种的无融合生殖率，用流式细胞仪鉴定杂种的染色体倍性。【结果】获得种子3101粒，培育实生苗2388株。从中筛选出杂种实生苗73株，其中58株开始开花结果。经无融合生殖率鉴定，有25株为84．00％～95．06％，8株为10．00％～48．00％，25株为O。5．00％；倍性鉴定表明，10株四倍体皆为无融合生殖型，4株二倍体皆为有性生殖型，三倍体植株中无融合生殖型加上中间型与有性生殖型数量比接近1：1。【结论】验证了平邑甜茶的无融合生殖以显性单基因质量性状为主，也有数量性状效应；初步认为平邑甜茶无融合生殖核基因型为“Aaa”（“A”代表无融合生殖基因，显性；“a”代表有性生殖基因，隐性）；平邑甜茶胚囊多数情况下由未减数的2n=3x配子直接发育成与母株基因相同的胚，部分2n配子与雄配子结合，形成2n＋n=4x型后代，少量胚囊经减数分裂产生n=x、n=2x两种配子．无融合生殖基因随n=2x配子分离。

[Objective] The objective of the study is to elucidate the mechanism of inheritance and development of apomixis in ＇Pingyi Tiancha＇ （Malus hupehensis var. pingyiensis）. [Method] The crosses between ‘Pingyi Tiancha＇, ‘B9＇ , ‘M27＇ and ‘M9＇ were made, the seedlings were fostered and then selected. The bagging pollination was made to identify the apomictic ratio and the flow cytometry was used to identify the ploidy of seedlings. [Result] There were 73 sexual hybrids among the 2 388 seedlings derived from 3 101 seeds. Identification of apomictic ratio showed that, among the 58 hybrids which had started bearing, 25 hybrids were 84.00% to 95.06%, 8 hybrids were 10.00% to 48.00%, and 25 hybrids were 0 to 5.00%. The results of the hybrids＇ ploidy revealed that： All of 10 tetraploids were apomictic seedlings and all of 4 diploids were sexual seedlings, the ratio of the apomictic plus the intermediate type to the sexual type was nearly 1：1 in the triploids. [Conclusion] The studies suggested the apomixis could be controlled mainly by major genes, and also could be controlled by some minor genes, We primarily considered that the genotype of amomixis of ‘Pingyi Tiancha＇ might be Aaa A represents a dominant type controlling apomixes and a represents a recessive type controlling sexual reproduction）. Most megaspores could directly developed into an embryo by a 2n=3x gamete without a meiosis process resulting in the genotype of the offsprings, the same with their mother tree. Some of the 2n gametes could combined with a male gamete and formed a 4x genotype （2n＋n=4x）. Few megaspores might segregate into two types of gametes, that is n=x and n=2x, and the apomixis gene could separate freely with the 2n gametes.