Genetic Diversity and Structure of Pea (Pisum sativum L.) Germplasm Based on Morphological and SSR Markers

The pea (Pisum sativum L.) is one of the oldest domesticated, highly valued and extensively cultivated pulse crops throughout the world. We studied genetic structure, diversity and inter-relationships in a worldwide collection of 151 pea accessions using 21 morphological descriptors and 20 simple sequence repeat (SSR) primers. Among quantitative traits, seed yield per plant followed by seed weight and pod length have shown significant variation. SSR primers showed a high level of diversity and amplified a total of 179 alleles with an average of 8.95 alleles per primer in a size range of 95-510 bp. Primer AA-122 amplified the maximum (21) alleles while primer AB-64 amplified the minimum (4) alleles. Mean polymorphism information content (PIC) was 0.72. Observed heterozygosity (H-o) varied from 0.10 to 0.99 in primers AB-64 and AD-160, respectively, with a mean value of 0.46. Expected heterozygosity (H-e) ranged from 0.47 to 0.94 in primers C-20 and AA-122, with a mean of 0.75. Genetic relationships inferred from a neighbour-joining tree separated accessions into 3 groups. Bayesian model-based STRUCTURE analysis detected 3 gene pools for the analysed pea germplasm and showed a high admixture within individual accessions. Furthermore, STRUCTURE analysis showed that these 3 gene pools co-existed in accessions belonging to different geographic regions indicating frequent transference and exchange of pea germplasm during its domestication history. The results of the present study will be useful in understanding the pea's genetic structure and in the selection of suitable diverse accessions for future improvement programmes in the pea.