Phenotypic diversity in groundnut (Arachis hypogaea L.) core collection assessed by morphological and agronomical evaluations

The groundnut (Arachis hypogaea L.) core collection consists of 1704 accessions of which 910 belong to subsp. fastigiata (var. fastigiata, vulgaris, aequatoriana, peruviana) and 794 to subsp. hypogaea (var. hypogaea, hirsuta). This core collection was evaluated for 16 morphological descriptors and for 32 agronomic characteristics, 15 in the 1999 rainy season and 17 in the 1999/2000 postrainy season, to estimate phenotypic diversity and determine importance of different descriptor traits. The two groups differed significantly for all the traits except leaflet surface and oil content. The hypogaea group showed significantly greater mean pod length, pod width, seed length, seed width, yield per plant, and 100-seed weight than the fastigiata group in both seasons whereas it is opposite for plant height, leaflet length, leaflet width and shelling percentage. There were significant phenotypic correlations among the various characteristics. Four of these, days to 50% flowering (r = 0.752), leaflet length (r = 0.743), pod length (r = 0.758), and seed length (r = 0.759) in the rainy explained more than 50% variation in the postrainy season. Principal coordinate and principal component analyses showed that 12 morphological descriptors and 15 agronomic traits, respectively, were important in explaining multivariate polymorphism. Leaflet shape and surface, colour of standard petal markings, seed colour pattern, seed width, and protein content did not significantly account for variation in the first five principal coordinates or components of fastigiata and hypogaea types as well as for the entire core collection. This indicates their relatively low importance as groundnut descriptors. The average phenotypic diversity index was similar in both subspecies groups. The Shannon-Weaver diversity index varied among traits between the two groups, and the diversity within a group depended upon the season and traits recorded.