Molecular Biology Laboratory-1, Central Sericultural Research and Training Institute, Mysuru, Karnataka, India.
Mulberry Tissue Culture Lab, Central Sericultural Germplasm Resources Centre, Hosur, Tamil Nadu, India.
PLoS One. 2023 Aug 11;18(8):e0289766. doi: 10.1371/journal.pone.0289766. eCollection 2023.
Elucidation of genome size (GS), genetic and phenotypic variation is the fundamental aspect of crop improvement programs. Mulberry is a cross-pollinated, highly heterozygous tree eudicot, and comprised of huge ploidy variation with great adaptability across the world. However, because of inadequate information on GS, ploidy-associated traits, as well as the correlation between genetic and phenotypic variation hinder the further improvement of mulberry. In this present research, a core set of 157 germplasm accessions belonging to eight accepted species of Morus including promising functional varieties were chosen to represent the genetic spectrum from the whole germplasm collection. To estimate the GS, accessions were subjected to flow cytometry (FCM) analysis and the result suggested that four different ploidies (2n = 2x, 3x, 4x, and 6x) with GS ranging from 0.72±0.005pg (S-30) to 2.89±0.015pg (M. serrata), accounting~4.01 fold difference. The predicted polyploidy was further confirmed with metaphase chromosome count. In addition, the genetic variation was estimated by selecting a representative morphologically, diverse population of 82 accessions comprised of all ploidy variations using simple sequence repeats (SSR). The estimated average Polymorphism Information Content (PIC) and expected heterozygosity showed high levels of genetic diversity. Additionally, three populations were identified by the model-based population structure (k = 3) with a moderate level of correlation between the populations and different species of mulberry, which imply the effect of genetic variation instead of ploidy on trait plasticity that could be a consequence of the high level of heterozygosity imposed by natural cross-pollination. Further, the correlation between ploidies, especially diploid and triploid with selected phenotypic traits was identified, however, consistency could not be defined with higher ploidy levels (>3x). Moreover, incite gained here can serve as a platform for future omics approaches to the improvement of mulberry traits.
阐明基因组大小（GS）、遗传和表型变异是作物改良计划的基础。桑树是一种异花授粉、高度杂合的被子植物，具有巨大的倍性变异，在世界各地都有很强的适应性。然而，由于对 GS、倍性相关性状以及遗传和表型变异之间的相关性的信息不足，阻碍了桑树的进一步改良。在本研究中，选择了来自整个种质资源收集的 157 个种质资源，这些资源属于八个公认的桑属物种，包括有前途的功能品种，以代表遗传谱。为了估计 GS，对材料进行了流式细胞术（FCM）分析，结果表明，有四个不同的倍性（2n = 2x、3x、4x 和 6x），GS 范围从 0.72±0.005pg（S-30）到 2.89±0.015pg（M. serrata），差异约为 4.01 倍。预测的多倍体进一步通过中期染色体计数得到证实。此外，通过选择具有所有倍性变异的 82 个材料的代表形态多样性群体，使用简单序列重复（SSR）来估计遗传变异。估计的平均多态性信息含量（PIC）和预期杂合度显示出高水平的遗传多样性。此外，通过基于模型的群体结构（k = 3）鉴定了三个群体，群体之间以及不同桑树物种之间的相关性中等，这意味着遗传变异而不是倍性对表型可塑性的影响可能是自然异花授粉引起的高水平杂合性的结果。此外，还确定了倍性之间的相关性，特别是二倍体和三倍体与选定的表型性状之间的相关性，然而，随着倍性水平的提高（>3x），一致性无法定义。此外，这里获得的启示可以作为未来通过组学方法改良桑树性状的平台。
