Comparative karyotype analysis reveals evolutionary trends among cultivated and wild Brassica species of the Brassicaceae family

This study presents a comprehensive karyotype analysis of 14 Brassica species including six U’s Triangle species and eight Brassica wild relatives (BWRs). Chromosome slides were prepared using cytological techniques to determine chromosome numbers and analyze the karyotypes of all species. Evolutionary patterns were assessed, and cluster analysis was performed based on multiple karyotypic parameters, including chromosome length, arm ratio, centromeric index, relative length, karyotype type, asymmetry index, etc. The results revealed that the chromosome numbers of the eight wild relatives showed diploidy with 2n=2x=14, 16, 18, 20, 22, and 24, while among the U’s Triangle species, three species were diploid with 2n=2x=16, 18, and 20, and three species were amphidiploid having 2n=4x=34, 36, and 38. The karyotypes of these species comprised metacentric, submetacentric, and acrocentric chromosomes and were classified into types 2A, 2B, 3A, and 3B. Karyotype analysis indicated evolutionary trends from symmetrical to asymmetrical chromosome structures, supporting diversification and adaptation within the Brassicaceae family. Notably, Brassica fruticulosa and Brassica nigra exhibited comparatively higher karyotype asymmetry index values and average arm ratio values of (q/p). In contrast, Brassica oleracea and Brassica rapa showed the lowest karyotype asymmetry index values and average arm ratio of (q/p). Cluster analysis, based on karyotypic parameters, grouped these 14 species into four major groups. Interactome analysis highlighted strong positive and negative correlations among karyotypic parameters across the species. Overall, this study enhances the understanding of phylogenetic evolution, genetic relationships, and chromosomal diversification in Brassica species, providing valuable cytogenetic insights into the Brassicaceae family.