Mitotic chromosomal variation in Dioscorea spp. from Parents to F₂ progenies

Abstract

ABSTRACT

Yam (Dioscorea spp.) is an important staple crop in West Africa, and genetic diversity plays a crucial role in its improvement. The complexity of ploidy levels and chromosomal instability in yam species presents a significant challenge to breeding efforts. Therefore, this study aimed to investigate chromosomal variation in Dioscorea spp. from parental lines to F₂ progenies to provide crucial information for optimising yam breeding programs and improving hybrid selection processes. A total of 67 accessions, including parental lines (Dioscorea praehensilis, D. abyssinica, and D. rotundata), their F₁ and F₂ progenies, were assessed. Chromosome counts were conducted on mitotic cells using the squash technique and FLP orcein staining. The number of chromosomes and abnormalities was recorded, and data were analysed using descriptive statistics. Among the 15 parental lines (D. praehensilis, D. abyssinica, and D. rotundata) assessed, 12 had diploid chromosome counts of 2n=2x=40, indicating chromosomal stability. Chromosomal abnormalities, including aneuploidy (2n=2x=34, 2n=2x=37, and 2n=2x=35), were observed in three parental accessions, accounting for a 19.05% abnormality. Interestingly, out of the 30 F₁ hybrids, 10 exhibited haploid chromosomes (2n=2x=20), while the others showed high chromosomal variation, with chromosome counts ranging from 2n=2x=18 to 2n=2x=33, resulting in a 66.67% abnormality rate. In contrast, 14 of 22 F₂ progenies displayed increased chromosomal stability, with a higher proportion of diploid counts (2n=2x=40) aligning with the parental lines. The abnormality rate dropped to 33.52% in F₂ progenies, indicating restored chromosomal balance through selfing and backcrossing. This study demonstrates that while interspecific hybridisation induces chromosomal instability in F₁ yam hybrids, subsequent selfing and backcrossing with D. rotundata can restore diploid stability in F₂ progenies. The findings offer cytogenetic insights vital for optimising hybrid selection and developing genetically stable yam cultivars for breeding programmes.