Executive Summary : | Polyploidy is the presence of more than two complete sets of chromosomes within an organism. It is reported to occur in many animals, plants, and crops, with 30-80% of all extant flowering plants having experienced at least one round of whole genome duplication. The timing of ancient polyploidization events in the Brassicaceae (Cruciferae) family suggests associations with major environmental disruptions. The process of cytological diploidization, which is necessary to form a fertile and competitive allopolyploid embryo, is accompanied by the selection of favourable structural and functional genome variants that frequently arise from interchanges between homeologous chromosomes. Homeologous exchanges (HE) and other segmental exchanges during homeologous chromosome pairing are essential to genome restructuring, gene conversion, and adaptive variation. Brassica juncea (genome AABB, 2n = 4x = 36), an important allopolyploid crop that originated from interspecific hybridizations between the diploid parental species Brassica rapa L. (AA, 2n = 20) and Brassica nigra L. (BB, 2n = 16), is a potential subject to study of allopolyploidization. Cytogenetic studies provided the earliest observations for genomic shock and meiotic instabilities inherent to newly formed hybrids and polyploids. In the last decade, molecular data from resynthesized and natural allopolyploids indicate that genetic and epigenetic changes are expected consequences of polyploidization across various species. Till now, very little of the mechanisms that lead to these changes and know even less about their directed or random nature. This project aims to investigate the evolution of polyploids, species formation, intergenomic interactions, and diversification in resynthesized amphidiploid B. juncea. The objective will be achieved by characterizing a set of resynthesized B. juncea lines in different generations (F1-S1, S2,…..S8) produced earlier at ICAR-NIPB using specific accessions of B. rapa and B. nigra. These populations represent a unique and valuable resource for studying the evolution of Brassica juncea and its speciation. The project also aims to explore how homoeologous recombination generates novel gene combinations and phenotypes and how natural selection contributes to establishing and maintaining fertile and stable natural allopolyploids over the generation exhibiting stable chromosome inheritance and a few advantageous chromosomal rearrangements. |