Oilseed Brassica represents an important group of oilseed crops with a long history of evolution and cultivation. To understand the origin and evolution of Brassica amphidiploids, simple sequence repeat (SSR) markers were used to unravel genetic variations in three diploids and three amphidiploid Brassica species of U’s triangle along with Eruca sativa as an outlier. Of 124 Brassica-derived SSR loci assayed, 100% cross-transferability was obtained for B. juncea and three subspecies of B. rapa, while lowest cross-transferability (91.93%) was obtained for Eruca sativa. The average % age of cross-transferability across all the seven species was 98.15%. The number of alleles detected at each locus ranged from one to six with an average of 3.41 alleles per primer pair. Neighbor-Joining-based dendrogram divided all the 40 accessions into two main groups composed of B. juncea/B. nigra/B. rapa and B. carinata/B. napus/B. oleracea. C-genome of oilseed Brassica species remained relatively more conserved than A- and B-genome. A- genome present in B. juncea and B. napus seems distinct from each other and hence provides great opportunity for generating diversity through synthesizing amphidiploids from different sources of A- genome. B. juncea had least intra-specific distance indicating narrow genetic base. B. rapa appears to be more primitive species from which other two diploid species might have evolved. The SSR marker set developed in this study will assist in DNA fingerprinting of various Brassica species cultivars, evaluating the genetic diversity in Brassica germplasm, genome mapping and construction of linkage maps, gene tagging and various other genomics-related studies in Brassica species. Further, the evolutionary relationship established among various Brassica species would assist in formulating suitable breeding strategies for widening the genetic base of Brassica amphidiploids by exploiting the genetic diversity present in diploid progenitor gene pools.

Brassica juncea (L.) Czern. & Coss. (Indian mustard) is an economically important edible oil crop. Over the years, plant breeders have developed many elite varieties of B. juncea with better yield traits, but research work on the introgression of stress resilience traits has largely been lagging due to scarcity of resistant donors. Crop wild relatives (CWRs) are the weedy relatives of domesticated plant species which are left unutilized in their natural habitat due to the presence of certain undesirable alleles which hamper their yield potential, and thus, their further domestication. CWRs of B. juncea namely include Sinapis alba L. (White mustard), B. tournefortii Gouan. (African mustard), B. fruticulosa Cirillo (Twiggy turnip), Camelina sativa L. (Gold-of-pleasure), Diplotaxis tenuisiliqua Delile (Wall rocket), D. erucoides L. (White wall rocket), D. muralis L. (Annual wall rocket), Crambe abyssinica R.E.Fr. (Abyssinian mustard), Erucastrum gallicum Willd. (Common dogmustard), E. cardaminoides Webb ex Christ (Dogmustard), Capsella bursa-pastoris L. (Shepherds purse), Lepidium sativum L. (Garden Cress) etc. These CWRs have withstood several regimes of biotic and abiotic stresses over the past thousands of years which led them to accumulate many useful alleles contributing in resistance against various environmental stresses. Thus, CWRs could serve as resourceful gene pools for introgression of stress resilience traits into Indian mustard. This review summarizes research work on the introgression of resistance against Sclerotinia stem rot (caused by Sclerotinia sclerotiorum), Alternaria blight (caused by Alternaria brassicae), white rust (caused by Albugo candida), aphid attack, drought and high temperature from CWRs into B. juncea. However, various pre- and post-fertilization barriers due to different ploidy levels are major stumbling blocks in the success of such programmes, therefore, we also insightfully discuss how the advances made in -omics technology could be helpful in assisting various breeding programmes aiming at improvisation of stress resilience traits in B. juncea.

In this study, we evaluated genetic diversity in a panel of 87 Indian mustard varieties using 200 genomic-SSR markers. A total of 189 SSRs resulted into positive amplification with 174 (92.06%) SSRs generating polymorphic products and 15 (7.94%) SSRs producing monomorphic amplicons. A total of 552 alleles were obtained and allele number varied from 2–6 with an average number of 3.17 alleles per SSR marker. The major allele frequency ranged from 0.29 (ENA23) to 0.92 (BrgMS841) with an average value of 0.58 per SSR locus. The polymorphic information content (PIC) value ranged from 0.10 (BrgMS841) to 0.68 (BrgMS519) with 0.39 as mean PIC value. The gene diversity per locus ranged from 0.13 (BrgMS841) to 0.72 (ENA23 & BrgMS519) with a mean value of 0.48 per SSR primer pair. Both Unweighted Neighbor Joining-based dendrogram and population structure analysis divided all the 87 varieties into two major groups/subpopulations. Analysis of molecular variance (AMOVA) inferred the presence of more genetic variation (98%) among individuals than among groups (2%). A total of 31 SSRs produced 36 unique alleles for 27 varieties which will serve as unique DNA-fingerprints for the identification and legal protection of these varieties. Further, the results obtained provided a deeper insight into the genetic structure of Indian mustard varieties in India and will assist in formulating future breeding strategies aimed at Indian mustard genetic improvement.