Centro de Protección Vegetal y Biotecnología, Instituto Valenciano de Investigaciones Agrarias, Ctra. Moncada-Náquera km 4·5, 46113 Moncada, Valencia, Spain.
Ann Bot. 2011 Jul;108(1):37-50. doi: 10.1093/aob/mcr099. Epub 2011 May 17.
Polyploidy is a major component of plant evolution. The citrus gene pool is essentially diploid but tetraploid plants are frequently encountered in seedlings of diploid apomictic genotypes. The main objectives of the present study were to establish the origin of these tetraploid plants and to ascertain the importance of genotypic and environmental factors on tetraploid formation.
Tetraploid seedlings from 30 diploid apomictic genotypes were selected by flow cytometry and genotyped with 24 single sequence repeat (SSR) markers to analyse their genetic origin. Embryo rescue was used to grow all embryos contained in polyembryonic seeds of 'Tardivo di Ciaculli' mandarin, followed by characterization of the plantlets obtained by flow cytometry and SSR markers to accurately establish the rate of tetraploidization events and their potential tissue location. Inter-annual variations in tetraploid seedling rates were analysed for seven genotypes. Variation in tetraploid plantlet rates was analysed between different seedlings of the same genotype ('Carrizo' citrange; Citrus sinensis × Poncirus trifoliata) from seeds collected in different tropical, subtropical and Mediterranean countries.
Tetraploid plants were obtained for all the studied diploid genotypes, except for four mandarins. All tetraploid plants were identical to their diploid maternal line for SSR markers and were not cytochimeric. Significant genotypic and environmental effects were observed, as well as negative correlation between mean temperature during the flowering period and tetraploidy seedling rates. The higher frequencies (20 %) of tetraploids were observed for citranges cultivated in the Mediterranean area.
Tetraploidization by chromosome doubling of nucellar cells are frequent events in apomictic citrus, and are affected by both genotypic and environmental factors. Colder conditions in marginal climatic areas appear to favour the expression of tetraploidization. Tetraploid genotypes arising from chromosome doubling of apomictic citrus are extensively being used as parents in breeding programmes to develop seedless triploid cultivars and have potential direct use as new rootstocks.
多倍体是植物进化的主要组成部分。柑橘基因库本质上是二倍体，但在二倍体无融合生殖基因型的幼苗中经常发现四倍体植物。本研究的主要目的是确定这些四倍体植物的起源，并确定基因型和环境因素对四倍体形成的重要性。
通过流式细胞术从 30 个二倍体无融合生殖基因型中选择四倍体幼苗，并使用 24 个单序列重复（SSR）标记对其进行基因型分析，以分析其遗传起源。利用胚胎拯救技术培养‘Tardivo di Ciaculli’橘柚多胚种子中的所有胚胎，然后通过流式细胞术和 SSR 标记对获得的植株进行特征描述，以准确确定四倍体化事件的发生率及其潜在的组织位置。分析了 7 个基因型的四倍体幼苗率的年际变化。分析了来自不同热带、亚热带和地中海国家采集的种子中同一基因型（‘Carrizo’克里曼丁橘柚；甜橙×枳）不同幼苗之间的四倍体植株率的变化。
除了 4 个蜜柑外，所有研究的二倍体基因型都获得了四倍体植物。所有四倍体植物与它们的二倍体母系在 SSR 标记上完全相同，并且不是细胞嵌合体。观察到显著的基因型和环境效应，以及开花期平均温度与四倍体幼苗率之间的负相关。在地中海地区种植的克里曼丁橘柚中观察到更高的四倍体频率（20%）。
无融合生殖柑橘中核细胞染色体加倍的四倍体化是频繁发生的事件，受基因型和环境因素的影响。在边缘气候区较冷的条件下，似乎有利于四倍体化的表达。无融合生殖柑橘染色体加倍产生的四倍体基因型被广泛用作杂交育种计划的亲本，以开发无核三倍体品种，并具有作为新砧木的直接潜力。
