Genome downsize insight into plant biodiversity conservation: a case study of polyploid Morus spp.

Biotechnological involvement in gene pool conservation is limited, particularly among natural polyploid tree species such as mulberry (Morus spp.), due to the diversity in genome sizes and the additional complexity imposed by heterozygosity. Plant performance may be greatly influenced by variations in the number, size, and structure of chromosomes. The current work has devised a step-by-step, cost-effective procedure for the chromosomal analysis of Morus spp. shoot tips. We identified various cytotypes of Morus spp. available at Central Sericultural Germplasm Resources Centre (CSGRC), Hosur, Tamil Nadu, India, including diploid (2n=2x=28), aneuploid (2n=2x=30), triploids (2n=3x=42), tetraploids (2n=4x=56), hexaploidy (2n=6x=84), and decasoploidy (2n=22x=308). Flow cytometry (FCM) analysis was performed to confirm the genome size of highly polyploid species such as M. tiliaefolia Makino. (2n=6x=84; ~1188.83 Mbp), M. serrata Roxb. (2n=6x=84; ~1386.32 Mbp), and slow-growing phenotype M. nigra L. (2n=22x=308; ~4239.86 Mbp). This study identified considerable genome downsize in decosaploid M. nigra L. (1Cx, ~353.25±07.23). Furthermore, morpho-anatomical, physiological, and biochemical traits were estimated for the selected 50 accessions, considering all cytotypes. Overall, current research suggests that over episodes of polyploidization and selection pressure, factors like the growth rate, genome size, and nutritional constraints enforced not only reduce the genome size but also restrict the growth (slow-growing) of polyploid mulberry. As a consequence, immediate attention is necessary to understand the structural and functional implications for polyploid conservation, particularly in tree species of wild origin. [The present research was supported by the Central Silk Board, MoT, and GoI funded projects PIG06004SI and POG06010SIC.]