Characterization of genetic diversity and its association with heterosis in an oleiferous Brassica rapa germplasm assemblage

Germplasm collection of oleiferous Brassica rapa ecotypes was assessed for genetic diversity. Initially 144 genotypes were field evaluated for important morphological traits, of which 51 diverse genotypes were assayed for molecular diversity using 44 polymorphic SSR primers. Neighbor-joining analysis classified the germplasm into six clusters. Grouping was fairly consistent with botanical classification of Brassica rapa as similar ecotypes were generally grouped together. Thus cluster II, V and VI had only brown sarson types whereas cluster IV had predominantly cultivated Indian toria cultivars only. Grouping was, however, not always coherent with the geographic origins, apparently due to gene flow and parallel variation. Brown sarson genotypes as a whole showed maximum divergence. Varied levels of heterosis were recorded in hand bred intervarietal hybrids (74). For seed yield, hybrid yield advantage ranged from -103.2 to 132.4 per cent over mid parent (RMPH) and -102.1 to 71.6 per cent over high parent (RHPH). No correlation was observed between heterosis and genetic/geographic diversity of the parents. Heterosis for biomass yield was also not reflected in seed yield.