Phenotypic variation for agronomic characteristics in a groundnut core collection for Asia

The groundnut (Arachis hypogaea L.) core collection for Asia consists of 504 accessions of which 274 belong to subsp. fastigiata (var. fastigiata and vulgaris) and 230 to subsp. hypogaea (var. hypogaea). This core collection was evaluated for 20 agronomic characteristics in the 2000 rainy season and for 21 characteristics in the 2000/2001 post-rainy season at two locations, Raichur and Kawadimatti, India, to estimate phenotypic diversity and determine the importance of different descriptor traits. All traits, except leaflet length and width, pod length and width, and seed length and width showed genotype×location interactions. All traits except leaflet width, number of primary branches, nodes on main stem, nodes on cotyledonary branches, total and mature pods, and length of primary and cotyledonary branches, pod length and width, and seed length and width showed genotype×season interaction. The fastigiata and hypogaea groups differed significantly for all traits except one trait each in the rainy season at Raichur and post-rainy season at Kawadimatti and five traits in the post-rainy season at Raichur. The hypogaea group took longer to flower, had more primary branches, longer primary and cotyledonary branches, more nodes on cotyledonary branches, more total pods, mature pods and pegs per plant, longer and wider pods and heavier seeds than the fastigiata group. The range for most traits was different in the two groups. There were significant phenotypic correlations among the various characteristics. Three of these, between number of total pods and mature pods, number of total pods and pegs, and number of mature pods and pegs had values greater than 0.707 (r2=50%) in both the fastigiata and hypogaea groups and in the entire regional collection. Principal component analysis showed that 20 agronomic traits were important in explaining multivariate polymorphism. Pod yield per plant did not significantly account for variation in the first five principal components of fastigiata and hypogaea types as well as for the entire regional collection in either season or location, indicating its relatively low importance as a descriptor. Average phenotypic diversity index was similar in both groups. The Shannon–Weaver diversity index varied among traits between the two groups, and the diversity within a group depended on location, season, and traits recorded.