Progression of molecular and phenotypic diversification in resynthesized Brassica juncea (L) gene pool with determinate inflorescence

Abstract

Indian mustard (Brassica juncea (L) Czern & Coss) is naturally indeterminate. Plants with determinate inflorescence were first discovered in the self progenies of B. juncea (AABB; 2n = 36), resynthesized by combining A-genome from B. napus (AACC; 2n = 38) and B-genome from B. carinata (BBCC; 2n = 34). In the determinate plants, apical meristems were transformed into pods. In contrast, the inflorescence in the indeterminate plants continues to grow indefinitely while producing peripheral flowers. Genotyping and morphological characterization of newly developed determinate gene pool (A8) showed a rapid emergence and progression of genetic and phenotypic alterations which continued even after seven generations of selfing. A large number of determinate genotypes (125) were evaluated to establish agronomic potential of determinate B. juncea. A high proportion of determinate genotypes outperformed the best indeterminate checks, suggesting that critical productivity related traits like pod number, seed size and oil content were not a function of indeterminacy. As the gene for determinacy has also been introgressed in B. napus and B. carinata, the stage is now set for future breeding to aim at crop architectural modifications through determinacy in all three types of oilseed Brassicas grown in the world. Our studies emphasized the role of polyploidy as a major force of differentiation at both genotypic and phenotypic level. Although, there was no direct correlation between evolution of genetic and phenotypic diversities following polyploidization. We suggest the use of polyploidy as a plant breeding tool to benefit from de novo variation rather than restricting its use as a method to overcome sterility following wide hybridization alone.