Peach is one of the most economically valuable fruit trees. Haploid peach trees occur spontaneously at very low frequencies and they are usually highly sterile. Therefore, the haploid with partial fertility is extremely rare germplasm, which is highly valuable to genetic research and breeding programmes. In this study, we investigated the cytological mechanism underlying the fertility of a peach haploid mutant ‘9-D’ derived from a spontaneous mutation. Cytologic evaluation and flow cytometry analysis demonstrated that ‘9-D’ is a pure haploid. Scanning electron microscope analysis revealed a considerable proportion of abnormal pollen grains in ‘9-D’. Pollen viability assay by Alexander staining showed that 50.4% of pollen grains from ‘9-D’ were viable. However, the pollen germination assay showed that only 7.6% of the pollen grains could germinate normally. Investigation of the chromosomal behavior of pollen mother cells at different stages of meiosis showed that pollen mother cells of ‘9-D’ lacked the process between anaphase I and prophase II of meiosis. Various types of sporophyte morphology were observed in haploid pollen mother cells at the tetrad stage. Measurement of the diameter of pollen grains indicated the presence of pollen with 2x ploidy in ‘9-D’. The offspring of ‘9-D’ were predominantly triploid or triploid aneuploid. The triploid offspring were more likely derived from the 2x male gametophyte combined with the haploid female gametophyte, which may explain the reason why ‘9-D’ has fertility. This study not only expands our understanding of haploid fertility mechanisms, but is also useful for ploid breeding programs in peach.

中文翻译：

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产生桃单倍体三倍体后代的细胞学机制


桃子是最具经济价值的果树之一。单倍体桃树以非常低的频率自发出现，并且它们通常是高度不育的。因此，部分生育的单倍体是极其稀有的种质，对遗传研究和育种计划非常有价值。在这项研究中，我们研究了源自自发突变的桃单倍体突变体 '9-D' 生育能力的细胞学机制。细胞学评估和流式细胞术分析表明，'9-D' 是一种纯单倍体。扫描电镜分析显示 '9-D' 中存在相当大比例的异常花粉粒。亚历山大染色花粉活力测定显示，来自 '9-D' 的花粉粒中有 50.4% 是活的。然而，花粉发芽试验表明，只有 7.6% 的花粉粒可以正常发芽。对减数分裂不同阶段花粉母细胞染色体行为的研究表明，“9-D”的花粉母细胞缺乏减数分裂后期 I 和前期 II 之间的过程。在 tetrad 阶段的单倍体花粉母细胞中观察到各种类型的孢子体形态。花粉粒直径的测量表明，在“9-D”中存在具有 2 倍倍性的花粉。'9-D' 的后代主要是三倍体或三倍体非整倍体。三倍体后代更可能来源于 2x 雄配子体与单倍体雌配子体的组合，这可能解释了 '9-D' 具有生育能力的原因。这项研究不仅扩展了我们对单倍体生育机制的理解，而且对桃子的倍性育种计划也有用。