Combining Ability Effects for Mineral Elements in Forage Sorghum Hybrids

The concentrations of minerals in forages are important in satisfying animal requirements, but little attention has been given to determining these concentrations in forage sorghum (Sorghum bicolor (L.) Moench.) breeding programs. In this 2-yr study, the objectives were to determine the contents, genetic variability, combining ability effects, and correlations for 12 mineral elements in 49 experimental hybrids of forage sorghum. Mineral elements studied were N, Mg, Si, P, S, CI, K, Ca, Mn, Fe, Cu, and Zn. General combining ability (GCA) effects exceeded specific combining ability (SCA) effects for all elements except P, CI, and Fe in females, and Sand CI in males. The GCA and SCA effects in females were low for both Fe and Cu. Genetic ratios. resembling heritability, were higher for GCA than SCA except for Cl and Fe in females, and S and CI in males. Thirty phenotypic correlations among the 12 elements were statistically significant. Some of the highest values were from the relationships of N with P, S, Cu, and Zn; Mg with Si and Cu; Si with Ca; P with Cu and Zn; S with K; and Cu with Zn. Some of the highest phenotypic correlations calculated among the mineral elements and 12 agronomic and quality traits were the positive association of protein with P, and the negative relationship of height with Nand P, Brix of stem juice with K, and neutral detergent fiber with P. Data obtained in these studies show the feasibility of altering the mineral content of forage sorghum by breeding. Additio1Ul1 index words: Sorghum bieolor (L.) Moench, Heritability, Forage quality, Mineral nutrition, Mineral accumulation, Animal nutrition. FORAGE sorghum hybrids [Sorghum bieolor (L.) Moench] are commonly grown in areas where rainfall is insufficient for corn (Zea mays L.) production and may be utilized as silage, greenchop, pasture, or dry hay or fodder. Little attention has been given to mineral concentration of the forage in sorghum breeding programs because the attributes normally emphasized are agronomic performance, adaptation, , Contribution from the USDA-ARS, and the Nebraska Agric. Res. Div., Lincoln, NE 68583. Published as Paper no. 8064, Journal Series, Nebraska Agric. Res. Div. Research was conducted under Project 12-114. Received 23 May 1986. 2 Supervisory research geneticist, USDA-ARS, Lincoln, NE; George Holmes professor of agronomy, Univ. of Nebraska, Lincoln, NE; assistant professor of agronomy, Auburn Univ., Auburn, AL 36849, and research geneticist, USDA-ARS, Lincoln, NE 68583, respectively. J Experimental forage sorghum line. Published in Crop Sci. 27:216-219 (1987). pest resistance, and quality factors such as protein and digestibility. Nevertheless, the concentrations of var· ious minerals in forages are often important in satisfying animal requirements because forages supply the great majority of the feed units consumed by beef and dairy cattle (Bos taurus) (3). Unfortunately, the mineral composition of plants does not always fulfill the requirements of consuming animals (12). Breeding improved cultivars with higher concentrations of nor. mally deficient elements, or lower concentrations of normally excessive elements, would significantly reo duce deviations from animal needs and provide an economical means for improving animal performance. Previous work with several plant species other than sorghum suggested that mineral concentration was at least partially under genetic control and that considerable progress was possible by selecting for either high or low mineral accumulation (1,2,7). The objectives of our study were to determine the contents, genetic variability, combining ability effects, and correlations. for 12 mineral elements in 49 experimental hybrids of forage sorghum. MATERIALS AND METHODS The 49 F, hybrids used, growing conditions, and har· vesting and sampling procedures were described in an earlier paper (10). Pertinent information relative to this study is repeated here. The 49 hybrids were produced by crossing each of seven females ('Redlan', N35, N38, N48, N4692, KS5, N50133) with each of seven males [Early Hegari-Sart (EH-Sart)J, Early Hegari-White Sourless (EH-WSP, Early Hegari-Rox (EH-Rox)3, N6229, 'Rox', 'White Collier' (WC), and H60-293]. The 49 hybrids were grown in a randomized complete block design with three replications at the University ofNebraska Agricultural Research and Development Center, Mead, in 1979 and 1980 using standard agricultural practices for that area. The plots were established on Sharpsburg silty clay loam (Typic Argiudoll-fine montmorillonitic mesic) for which detailed chemical and physical characterization has been reported (5). The forage sorghum nursery was adjacent to an area where extensive soil fertility studies have shown that the only fertilizer element producing a positive effect on yield was N. Plots were three 9.1-m rows spaced 0.76 m apart with plants hand-thinned to a spacing of approximately GORZ ET AL.: COMBINING ABILITY EFFECTS IN SORGHUM HYBRIDS 217 Table 1. The GCA effects, significant GCA values, and experimental means and ranges for 12 mineral elements of 49 forage sorghum hybrids grouped by female and male parents, grown at Mead, NE, 1979 and 1980.