Abstract

Nonapomictic citrus tetraploids are desirable in citrus breeding for the production of triploid, seedless varieties, and polyploid rootstocks. However, only a few lines have been reported, and they were all generated using chemical methods. A 2x + 4 × cytochimera of the nonapomictic citrus variety ‘Orah’ mandarin, which developed from a bud mutant, was found due to its morphology differing from that of diploid plants and characterised via ploidy analysis combining flow cytometry and chromosome observation. The chimaera was stable, and there were 1.86–1.90 times as tetraploid cells as diploid cells. Anatomical structure observation revealed that the ‘Orah’ chimaera may be a periclinal chimaera with diploid cells in the L1 layer and tetraploid cells in the L2 and L3 layers. The chimaera showed some typical traits of polyploid plants, including thicker shoots, wider and thicker leaves, larger flowers and fruits, and fewer but larger seeds in fruits than in diploid plants. Almost all the seeds of the chimaera were monoembryonic. Most of the self-pollinated progenies of the chimaera were identified as tetraploids, and some triploid, pentaploid, and hexaploid plants were found. As a female, the chimaera produced allotriploids when crossed with Australian finger lime. In addition, 6 plants developed from polyembryonic seeds of the chimaera were identified as sexual tetraploid progenies with low-level recombinant genomes. Therefore, the ‘Orah’ 2x + 4 × chimaera can be used as a female parent to produce hybrid triploid and tetraploid citrus plants with high efficiency. Identification of the chimaera demonstrated that tetraploid citrus plants, especially nonapomictic varieties, can be generated from shoot bud mutants.

中文翻译：

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由非无融合生殖柑橘品种“Orah”的天然芽突变体开发的四倍体主导的细胞嵌合体

摘要

非无融合生殖柑橘四倍体在用于生产三倍体、无核品种和多倍体砧木的柑橘育种中是理想的。然而，仅报道了少数几行，并且它们都是使用化学方法产生的。由芽突变体发育而来的非无融合生殖柑橘品种“Orah”柑橘的 2x + 4 × 细胞嵌合体，由于其形态与二倍体植物不同而被发现，并通过流式细胞术和染色体观察相结合的倍性分析进行了表征。嵌合体稳定，四倍体细胞数量是二倍体细胞的1.86~1.90倍。解剖结构观察表明，“奥拉”嵌合体可能是周生嵌合体，其L1层为二倍体细胞，L2、L3层为四倍体细胞。嵌合体表现出多倍体植物的一些典型特征，包括比二倍体植物更粗的枝条、更宽更厚的叶子、更大的花和果实、以及果实中种子更少但更大的特征。几乎所有嵌合体的种子都是单胚的。嵌合体的自花授粉后代大部分被鉴定为四倍体，也发现了一些三倍体、五倍体和六倍体植物。作为雌性，嵌合体与澳大利亚指柠檬杂交后产生了异源三倍体。此外，从嵌合体多胚种子发育而来的6株植物被鉴定为具有低水平重组基因组的有性四倍体后代。因此，‘Orah’2x+4×嵌合体可以作为母本高效生产杂种三倍体和四倍体柑橘植株。嵌合体的鉴定表明，四倍体柑橘植物，特别是非无融合生殖品种，可以从芽芽突变体产生。