SSR and morphological trait based population structure analysis of 130 diverse flax (Linum usitatissimum L.) accessions.

A total of 130 flax accessions of diverse morphotypes and worldwide origin were assessed for genetic diversity and population structure using 11 morphological traits and microsatellite markers (15 gSSRs and 7 EST-SSRs). Analysis performed after classifying these accessions on the basis of plant height, branching pattern, seed size, Indian/foreign origin into six categories called sub-populations viz. fibre type exotic, fibre type indigenous, intermediate type exotic, intermediate type indigenous, linseed type exotic and linseed type indigenous. The study assessed different diversity indices, AMOVA, population structure and included a principal coordinate analysis based on different marker systems. The highest diversity was exhibited by gSSR markers (SI=0.46; He=0.31; P=85.11). AMOVA based on all markers explained significant difference among fibre type, intermediate type and linseed type populations of flax. In terms of variation explained by different markers, EST-SSR markers (12%) better differentiated flax populations compared to morphological (9%) and gSSR (6%) markers at P=0.01. The maximum Nei's unbiased genetic distance (D=0.11) was observed between fibre type and linseed type exotic sub-populations based on EST-SSR markers. The combined structure analysis by using all markers grouped Indian fibre type accessions (63.4%) in a separate cluster along with the Indian intermediate type (48.7%), whereas Indian accessions (82.16%) of linseed type constituted an independent cluster. These findings were supported by the results of the principal coordinate analysis. Morphological markers employed in the study found complementary with microsatellite based markers in deciphering genetic diversity and population structure of the flax germplasm.