Heritability Estimates for Forage Yield, In Vitro Dry Matter Digestibility, Crude Protein, and Heading Date in Indiangrass

Space-planted populations derived from 'Holt' and 'Oto' indiangrass, Sorghastrum nutans (L.) Nash, were used to obtain heritability estimates for forage yield, in vitro dry matter digestibility (IVDMD), crude protein, and heading date and to determine their genotypic correlations. Heritability estimates were determined by variance component analyses and by parent-progeny regression. Average narrow sense heritability estimates for the two populations were 0.43, 0.42, and 0.50, for forage yield, IVDMD, and protein, respectively. Narrow sense heritability estimates for heading date were 0.90 or larger. Genotypic correlations of yield and IVDMD were negative for the Holt population but were positive, although low, for the Oto population in 1976. Protein and IVDMD had positive genotypic correlations for both populations. Heading date was positively correlated with yield but was negatively correlated with IVDMD and protein. Additional index words: Sorghastrum nutans, Forage quality, Quantitative genetics. I N DI AN G R ASS , Sorghastrum nutans (L.) Nash, is a warm-season cross-pollinated perennial grass that is native to the prairies and plains of the United States, where it is used for summer grazing and prairie hay. The chromosome number of indiangrass is 2n = 40, and its meiotic behavior is normally that of a diploid (Riley and Vogel, 1979). Although several cultivars of indiangrass have been released, there is little published information on the genetics of this species. The purpose of our research was to obtain heritability estimates for forage yield, in vitro dry matter digestibility (IVDMD), protein content, and heading date and to determine the relationship among these traits. Heritability estimates for forage yield and quality have been reported previously for several warm-season grasses. Ross et al. (1975) reported heritability estimates of 0.68 and 0.72, respectively, for forage yield and IVDMD in big bluestem, Andropogon gerardi Virm , Newell and Eberhart (1961) used several methods to determine the heritability of various traits in switchgrass, Panicum virgatum L. Their heritability estimates ranged from 0.05 to 0.74 for forage yield and from 0.27 to 0.90 for forage quality, which was estimated by a rating index. Heritabilities of I Contribution of the Dep. of Agronomy, Univ. of Nebraska, and AR-SEAUSDA. Published as Paper No. 5888, Journal Series, Nebraska Agric. Exp. Stn. Received 6 Feb. 1980. , Research agronomist, AR-SEA/USDA; supervisory research geneticist, AR-SEA/USDA; and George Holmes professor of agronomy, Univ. of Nebraska, Lincoln, NE 68583. 35 0,51 to 0.80 for leaf protein percentage in sand luestem, Andropogon hallii Hack, were reported by Kneebone (1958). Burton and Monson (1972) reported heritabilities ranging from 0.27 to 0.69 for dry matter digestibility of bermudagrass, Cynodon dactylon (L.) Pers. for seasonal averages of two to four clippings; and Quesenberry et al. (1978) reported broad sense heritabilities of in vitro organic matter digestibility in rhodesgrass, Chloris gayana Kunth, of 0.14 and 0.42 for 2and 6-weeks regrowth, respectively, MATERIALS AND METHODS The indiangrass population used in this study and the field plot procedures have been described previously (Vogel et aI., 1980a). In brief, two indiangrass populations derived from the cultivars 'Holt' and 'Oto' were used. Holt was developed by mass selection from ecotypes collected in northeast Nebraska, while Oro, which is 20 days later in maturity than Holt, was developed by mass and progeny selection from ecotypes collected in southeast Nebraska and northeast Kansas (Hanson, 1972). In 1973, space-planted populations of Holt and Oto were sampled at panicle emergence for IVDMD and for crude protein. Openpollinated seed was harvested from individual plants of the two isolated populations. In 1974, a twice-replicated, spaceplanted, half-sib progeny nursery was established at Mead, Nebr., from 41 Holt and 150 Oto parent plants. Within each cultivar, approximately one-sixth of these parent plants were selected for each of the following traits; high IVDMD, low IVDMD, high protein, low protein, early heading, and late heading. In this selection process, attention was given only to the trait being selected. For example, protein content or heading date was not considered when selecting plants for IVDMD. Consequently, we believe the selected parent plants approximate a random sample of the original cultivars. In 1975, two ramets of the parental clones, similar in size to the plants established the previous year, were transplanted into the same nursery. A family plot consisted of a parental ramet and four progeny plants. In 1976, data were collected on every plant in the nursery while in 1977 data were collected only from 30 Oto families that had high yields in 1976 for both parents and progenies. Complete data sets used in the statistical analyses were available from 36 Holt families, 147 sets of Oto parents and 146 sets of Oro progenies in 1976. On the heading date (the number of days after 30 June when five or more panicles had emerged from the boot), the tillers bearing the first five panicles were cut 5 em above the base of the plant. These tillers were used for IVDMD and protein analyses. The Tilley and Terry (1963) method was used to determine the IVDMD percentage and the Kjeldahl procedure was used to determine crude protein content (A.O.A.C., 1960). The parent and progeny data were analyzed using conventional analyses of variance and covariance procedures. The data for 19761977 were analyzed as a split plot in time. Individual progeny plants within a plot were analyzed as subsamples. The methods described by Gardner (1963) for separating variances into their genetic and environmental components were used. Published in Crop Science (January-February 1981) v. 21