Griffin A R, Vuong T D, Vaillancourt R E, Harbard J L, Harwood C E, Nghiem C Q, Thinh H H
School of Plant Science, University of Tasmania, Private Bag 55, Hobart, TAS 7001, Australia.
Sex Plant Reprod. 2012 Dec;25(4):257-65. doi: 10.1007/s00497-012-0195-2. Epub 2012 Aug 4.
Colchicine-induced neoautotetraploid genotypes of Acacia mangium were cloned and planted in mixture with a set of diploid clones in an orchard in southern Vietnam. Following good general flowering, open-pollinated seed was collected from trees of both cytotypes and microsatellite markers were used to determine the breeding system as characterised by the proportion of outcrosses in young seedling progeny. As predicted from the literature, the progeny of diploid clones were predominantly outcrossed (t(m) = 0.97). In contrast, the progeny of the tetraploid clones were almost entirely selfs (t(m) = 0.02; 3 of 161 seedlings assayed were tetraploid outcrosses and there were no triploids). Segregation at loci heterozygous in the tetraploid mothers followed expected ratios, indicating sexual reproduction rather than apomixis. Post-zygotic factors are primarily responsible for divergence of the breeding systems. Commonly, less than 1 % of Acacia flowers mature as a pod, and after mixed pollination, diploid outcrossed seed normally develops at the expense of selfs. Selfs of the tetraploid trees appear to express less genetic load and have a higher probability of maturing. However, this does not fully explain the observed deficiency of outcross tetraploid progeny. Presumably, there are cytogenetic reasons which remain to be investigated. In nature, selfing would increase the probability of establishment of neotetraploids irrespective of cytotype frequency in the population. Breeders need to review their open-pollinated breeding and seed production strategies. It remains to be seen whether this is an ephemeral problem, with strong fertility selection restoring potential for outcrossing over generations.
将秋水仙碱诱导的马占相思新同源四倍体基因型进行克隆，并与一组二倍体克隆混合种植在越南南部的一个果园中。在普遍良好开花之后，从两种细胞型的树上收集开放授粉的种子，并使用微卫星标记来确定育种系统，其特征是幼苗后代中外交的比例。正如文献所预测的那样，二倍体克隆的后代主要是杂交的（t(m)=0.97）。相比之下，四倍体克隆的后代几乎全是自交的（t(m)=0.02；在检测的161株幼苗中，有3株是四倍体杂交后代，没有三倍体）。四倍体母本中杂合位点的分离遵循预期比例，表明是有性繁殖而非无融合生殖。合子后因素是育种系统差异的主要原因。通常，马占相思不到1%的花能发育成果荚，混合授粉后，二倍体杂交种子通常以自交种子为代价发育。四倍体树的自交后代似乎表现出较低的遗传负荷，成熟的概率更高。然而，这并不能完全解释所观察到的四倍体杂交后代的缺乏。据推测，存在一些细胞遗传学原因尚待研究。在自然界中，自交将增加新四倍体建立的概率，而与种群中的细胞型频率无关。育种者需要重新审视他们的开放授粉育种和种子生产策略。这是否是一个短暂的问题，强大的育性选择是否能恢复几代人杂交的潜力，还有待观察。
