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F₄ Bulk Testing in Testcrosses of 27 Exotic Peanut Cultivars¹

Peanuts (Arachis hypogaea L.) are potentially a genetically vulnerable crop in the United States because of their narrow genetic base. To broaden the base, breeders must identify exotic parents for inclusion in programs of hybridization and selection. Parental, F₁, and/or F₂ performance could be used as indices to predict performance of inbred lines derived from crosses of adapted by exotic parents. Twenty-seven exotics representing five South American centers of diversity, Africa, and China were testcrossed to an adapted Virginia (ssp. hypogaea var. hypogaea) breeding line. The parents had been previously sorted into five morphological groups. Parents, F₁'S, and F₂'s were tested in 1979. Twenty F₂ families per cross were bulked in the F₄ and tested in 1981. Variation among bulks for pod and seed yield and other characters was due predominantly to differences among morphological groups. Exotics of ssp. hypogaea produced higher yielding bulks than those of ssp.fastigiata. Spanish (var. vulgaris Harz.) parents produced the hightest yielding fostigiata-derived bulks. Variation among bulks within morphological groups was significant for pod and seed size parameters and meat content, but not for yield. Performance of parents per se and F₂'s were the best indicators of F₄ bulk performance, based on product moment and rank correlations. F₁ performance, heterosis, inbreeding depression, and epistatic effects were largely unrelated to F₄ performance. It was proposed that exotics' performance per se could be used as a criterion for selection of parents for yield, although inclusion of F₂ yields in a multiple-variable index was more accurate in predicting F₄ bulk means. Selection should be practiced within morphological groups of parents in order to retain parents from ssp. fastigiata.

Key Words: Arachis hypogaea • Genetic vulnerability • Genetic diversity

² Former graduate assistant (now assistant professor, Dep. of Crop and Soil Sciences, Michigan State Univ., East Lansing, MI 48824) and associate professor, Dep. of Crop Science, North Carolina State Univ., Raleigh, NC 27650.

Received for publication June 17, 1982.