Recurrent Half-Sib Selection with Testcross Evaluation for Increased Oil Content in Soybean

and a decreasing supply (Golbitz, 1999), suggest that oil productivity of soybean should be improved. Previous Protein meal and oil are the two commodities produced from research indicated that seed oil concentration is consoybean [Glycine max (L.) Merr.] that give the crop its value. Increasing seed concentrations of either or both may add value. Objectives trolled by multiple genes with additive inheritance of this study were to investigate the effectiveness of recurrent half(Brim, 1973). Broad sense heritability estimates (plot sib selection for increased seed oil, to evaluate the effect of tester oil mean basis) for oil content are relatively high (Burton, content on selection response, and to investigate testcross heterosis 1987) and range from 0.47 to 0.89. (Johnson et al., 1955; and inbreeding depression for seed oil content. A recurrent half–sib Kwon and Torrie, 1964; Shorter et al., 1976; Smith and selection system was devised for soybean and selection for increased Weber, 1968). Because of this high heritability, Burton oil content was conducted in a population for seven and three cycles and Brim (1981) developed a recurrent selection proceusing a high and a low-oil tester, respectively. The base population was dure for the rapid increase in oil content using a populaa high-oil composite with gray pubescence (tt) that was segregating for tion segregating for a male-sterile gene, ms1. Using this nuclear genetic ms1 male sterility. In summer, the base population was planted in single plant hills and bordered with the tester (Ms1Ms1TT) in method, they showed that three cycles of recurrent sea random mating block in North Carolina. About 100 to 200 random lection increased seed oil content 11 g kg 1 seed and male-sterile plants with hybrid seeds were harvested. Half-sib families found realized heritability estimates for within-family derived from each male-sterile plant were then grown in Puerto Rico and mass selection to be 0.2 and 0.28, respectively. in winter. At maturity, seeds from tawny plants (tester hybrid) were In two populations derived from a base population used to identify half-sib families with high-oil content. Corresponding segregating for ms1 male sterility, Priadi (1993) comgray plant hybrids from sib matings within the population were bulked pared half-sib family and single selfed-plant recurrent to start the next cycle of selection. Random progenies from the base selection for oil content. Six cycles of recurrent selection populations and selected progenies from each cycle of selection were resulted in a per cycle linear increase of 1.1 0.3 g kg 1 evaluated in a replicated field experiment at three locations in North Carolina. Cycle tester hybrids and cycle cycle sib hybrids were for single-plant and 0.5 0.2 g kg 1 for half-sib family also included in the tests. The results showed that oil content was selection. No correlation was seen between oil and other significantly increased at a rate of 1.1 0.2 g kg 1 cycle 1 in the highagronomic traits, although there was a nonsignificant oil tester populations but not in the low-oil tester populations. The linear decrease in protein content. realized heritability estimate for the high-oil tester population was Recurrent selection, as practiced above, is rapid in 0.12 0.03. Evidence of heterosis indicated that some dominance terms of cycles per year. That the mean oil concentration effects on oil content existed. Dominance effects may affect the evaluaincreased indicates that the frequency of genes affecting tion accuracy of the genotypes being tested. A high-oil tester and that trait increased in the population. The problem with high-oil populations may have many common alleles resulting in less selection for seed composition alone is that agronomic dominance and more additive effects in their hybrids. Consequently, a high-oil tester can lead to better evaluation and selection precision, quality of the population may decline as the seed compocompared with a low-oil tester which could mask additive effects and nent increases (Brim and Burton, 1979). A possible way reduce selection precision. to prevent this would be to use half-sib recurrent selection and employ a good agronomic cultivar as the tester. At the very least, the improved trait would be expressed P meal and oil are the two commodities that in a more agronomic genetic background, i.e., the popugive soybean its value. Increasing the seed concenlation tester cross. Possible advantage could be made tration of both as a way to add value to the soybean of this with additional breeding. crop has been the subject of numerous studies. Of the Testcross evaluation of unadapted germplasm in soytwo, oil concentration has received less attention. It is bean was proposed by Kenworthy (1980) as a way to often considered a byproduct of protein meal producdetermine the combining ability of plant introductions. tion. Yet about half of the soybean value is derived Several studies of testcross evaluation of germplasm from oil and an increasing world demand for edible oils have been conducted using the F1 generation (Lewers et al., 1998) or advanced generations (Reese et al., 1988; L. Feng, Pioneer Hi-Bred International, Inc., P.O. Box 1004, Johnston, St. Martin and Aslam, 1986). Results on the importance IA, 50131-1004; J.W. Burton and T.E. Carter, Jr., USDA-ARS and of choice of tester, however, were mixed. Lewers et al. Dep. of Crop Science, North Carolina State Univ., Raleigh, NC 27695(1998) conducted F1 generation testcross evaluation of 7631; V.R. Pantalone, Dep. of Plant and Soil Sciences., Univ. of soybean germplasm using male sterility (ms6ms6) and Tennessee, Knoxville, TN 37901-1071. Part of a thesis submitted by L. Feng in partial fulfillment of the requirements for an M.S. degree seedling marker W1. Significant F1 and F2 midparent at North Carolina State Univ. Received 21 Jan. 2003. *Corresponding heterosis and inbreeding depression for oil content were author ([email protected]). observed. Hence, there may have been some dominance Published in Crop Sci. 44:63–69 (2004).  Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: HOT, high-oil tester; LOT, low-oil tester.