Molecular markers have been used to study genetic diversity within a set of Lablab purpureus accessions collected from the southern states of India. Amplified fragment length polymorphism (AFLP) molecular marker studies using a total of 78 L. purpureus accessions with nine primer combinations showed there was very little genetic diversity within the L. purpureus accessions from the southern Indian germplasm collection as compared to a set of 15 accessions from other international germplasm collections that included African accessions. The set of 15 were selected from a random amplified length polymorphism (RAPD) marker study and chosen on the basis of widest genetic distance. Further molecular analysis with polymerase chain reaction (PCR) markers from 97 expressed sequence tag (EST) and gene-specific primer pairs, designed from a range of legume sequences, concurred with the AFLP analyses. Both of these approaches provide a wealth of markers for diversity and mapping studies. The 97 sequence-specific primer pairs tested in L. purpureus resulted in 70% amplification success, with 44% of primer pairs amplifying single bands and 10% double bands. Markers generated from these EST and genomic sequences provide useful cross-reference to comparative legume genomics that will potentially have long-term benefit to legume plant breeding.

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Association mapping (AM), an alternative method of quantitative trait loci (QTL) discovery, exploits historic linkage disequilibrium (LD) present in natural populations. AM is effective in self-pollinated crops such as Dolichos bean as LD extends over longer genomic distance driven-by low rate of recombination and thereby requiring fewer markers for exploring marker-traits associations. A core set of Dolichos bean germplasm consisting of 64 accessions was evaluated for nine quantitative traits (QTs) during 2014 and 2015 rainy seasons and genotyped using 234 simple sequence repeats (SSR) markers. Substantial diversity was observed among the core set accessions at loci controlling QTs and 95 of the 234 SSR markers were found polymorphic. The structure analysis and low magnitude of fixation indices suggested weak population structure, which in-turn indicated the low possibility of false discovery rates in the marker-QTs association. The marker allele's scores were regressed onto phenotypes at nine QTs following general linear model and mixed linear model for exploring marker-QTs associations. Significantly higher number of SSR markers was found associated with genomic regions controlling nine QTs. A few of the markers such as KT Dolichos (KTD) 200 for days to 50% flowering, KTD 273 for fresh pod yield per plant and KTD 130 for fresh pods per plant explained ≥10% of the trait variations. The study could also identify a few SSR markers such as KTD 273, KTD 271 and KTD 130 linked to multiple traits. These linked SSR markers are suggested for validation for their use in marker-assisted Dolichos bean improvement programmes.

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