Akiyama Yukio, Goel Shailendra, Chen Zhenbang, Hanna Wayne W, Ozias-Akins Peggy
Department of Horticulture, University of Georgia Tifton Campus, Tifton, GA 31793-0748, USA.
J Hered. 2006 Sep-Oct;97(5):521-4. doi: 10.1093/jhered/esl005. Epub 2006 Jun 22.
Apomixis is a mode of asexual reproduction where maternal clones are produced through seeds. Consequently, genetic segregation is prevented in hybrid progenies. Pennisetum squamulatum has been used to transfer apomixis into the related sexual species Pennisetum glaucum by the introgression of an apospory-specific genomic region (ASGR)-carrier chromosome. Crosses between P. glaucum and P. squamulatum or Pennisetum purpureum have been relatively easy to make even though P. squamulatum has been reported to have a different basic chromosome number than the other 2 species (9 vs. 7) and to be hexaploid (2n = 6x = 54). Our extensive examination of one accession had shown a chromosome number of 2n = 56. In order to determine if there was a variation among accessions, we counted the number of chromosomes in 5 accessions of P. squamulatum using centromeric and 18S-5.8S-26S rDNA probes as molecular cytological markers. Our results showed that P. squamulatum is most likely octaploid with a basic chromosome number of 7 (2n = 8x = 56) and may belong to the secondary gene pool of Pennisetum. Moreover, a morphologically similar ASGR-carrier chromosome that confers apomixis was observed in all accessions.
无融合生殖是一种无性繁殖方式，通过种子产生母本克隆。因此，杂种后代中不会发生遗传分离。通过导入一个无孢子生殖特异性基因组区域（ASGR）携带染色体，已利用鳞状狼尾草将无融合生殖转移到相关的有性物种黍稷中。尽管据报道鳞状狼尾草的基本染色体数与其他两个物种不同（9对7）且为六倍体（2n = 6x = 54），但黍稷与鳞状狼尾草或紫狼尾草之间的杂交相对容易进行。我们对一个种质的广泛检查显示其染色体数为2n = 56。为了确定种质之间是否存在变异，我们使用着丝粒和18S - 5.8S - 26S rDNA探针作为分子细胞学标记，对5个鳞状狼尾草种质的染色体数进行了计数。我们的结果表明，鳞状狼尾草很可能是基本染色体数为7的八倍体（2n = 8x = 56），可能属于狼尾草的次生基因库。此外，在所有种质中都观察到了一条形态相似的赋予无融合生殖能力的ASGR携带染色体。
