Development and Evaluation of a Mini Core Collection for the U.S. Peanut Germplasm Collection

examining all accessions in the core collection for a desired characteristic. This information is then used to A core collection (831 accessions) has been developed to represent determine which clusters of accessions in the entire germthe U.S. Arachis hypogaea L. germplasm collection. This core collection has been shown to be effective in improving the efficiency of plasm collection should be examined during the secidentifying genes of interest in the entire germplasm collection. Howond stage of screening. Theoretically, the probability of ever, an even smaller subset of germplasm is needed for traits which finding additional accessions with a desired characterisare difficult and/or expensive to measure. The objectives of this study tic would be highest in these clusters. Holbrook and were to select a core of the core collection and to evaluate the useAnderson (1995) used data on resistance to late leaf fulness of this subset of germplasm to identify genes of interest in spot that was available for the entire peanut germplasm peanut. Data for eight above ground and eight below ground morphocollection to determine retrospectively how effective logical characteristics were measured for each accession in the core the use of a core collection approach would have been collection. Cluster analysis was used on these data to partition the core for identifying sources of resistance in the entire collecaccessions into groups which, theoretically, are genetically similar. tion. Holbrook et al. (2000b) evaluated the effectiveness Random sampling was then used to select a 10% sample from each group. The result was a core of the core collection (mini core) conof a two-stage core screening approach in identifying sisting of 112 accessions. Examination of morphological data indicated resistance to the peanut root-knot nematode [Meloidothat the majority of genetic variation expressed in the core collection gyne arenaria (Neal) Chitwood race 1] in the U.S. germhas been preserved in this core of the core collection. Data on disease plasm collection of peanut. Results from both of these resistances for accessions in the core collection were collected and studies demonstrated that the peanut core collection can used to determine retrospectively how effective the use of a mini core be used to improve the efficiency of identifying genes collection would have been in identifying sources of resistance in the of interest in the entire germplasm collection. core collection. Results indicated that the mini core collection can be The peanut core collection has been very effective in used to improve the efficiency of identifying desirable traits in the enhancing the utilization of peanut genetic resources core collection. For resistance to late leaf spot (Cercosporidium perso(Holbrook, 1999). However, an even smaller subset of natum (Berk. & M. A. Curtis), the use of a mini core collection would have improved the efficiency of identifying resistant accessions in the germplasm is needed for traits which are difficult and/or entire collection. The core of the core approach should be particularly expensive to measure. Upadhyaya and Ortiz (2001) suguseful for traits which are difficult and/or expensive to measure. gested a strategy for sampling the entire and core collections for developing a mini core subset which contains about 1% of total accessions in the entire collection but M efficient methods for evaluating and maincaptures most of the useful variation of the crop. A taining genetic diversity in germplasm collections peanut mini core collection has been selected (Upadare needed. One possible method is the development hyaya et al., 2002) from the ICRISAT core collection and use of core collections (Frankel, 1984; Frankel and (Upadhyaya et al., 2003). The objectives of this study Brown, 1984). A core collection has been developed for were to develop a core of the core collection (mini the U.S. peanut germplasm collection (Holbrook et al., core) for the U.S. peanut core collection and to use 1993). Data on peanut in the Germplasm Resource Ininformation on resistances to leaf spot, Tomato spotted formation Network (GRIN) were used to select this core wilt virus (TSWV), aflatoxin, and root-knot nematode collection. The U.S. germplasm collection was first stratifor the core collection accessions to evaluate the core fied by country of origin and then divided into nine sets of core concept. based on the amount of additional information available for accessions and on the number of accessions per MATERIALS AND METHODS country of origin. This procedure resulted in the selecSelection of a Core of the Core Collection tion of 831 accessions from the U.S. A hypogaea germplasm collection. Data for eight above-ground and eight below-ground morThe core collection approach to germplasm evaluaphological characteristics (Pittman, 1995) were measured for each accession in the core collection. The eight above-ground tion is a two-stage approach. The first stage involves descriptors were growth habit, plant size, prominence of main stem at mid season, prominence of main stem at harvest, C.C. Holbrook, USDA-ARS, Coastal Plain Exp. Stn., P.O. Box 748, presence of flowers on the main axis, leaf color, stem pigmentaTifton, GA 31793; W. Dong, Visiting Scientist, Univ. of Georgia, Coastal Plain Exp. Stn., P.O. Box 748, Tifton, GA 31793. Received 17 June tion, and maturity. The below-ground descriptors were mea2004. *Corresponding author ([email protected]). sured post harvest and included pod shape, pod constriction, pod reticulation, seed per pod, 100-pod weight, U.S. pod marPublished in Crop Sci. 45:1540–1544 (2005). ket type, seed coat color, and 100-seed weight. Plant Genetic Resources doi:10.2135/cropsci2004.0368 © Crop Science Society of America Abbreviations: GRIN, germplasm resources information network; TSWV, Tomato spotted wilt virus. 677 S. Segoe Rd., Madison, WI 53711 USA 1540 Published online June 24, 2005