Genetic Variability for Mineral Element Concentration of Crested Wheatgrass Forage

Grass tetany is a complex metabolic disorder that causes substantial livestock production losses and deaths in temperate r gions of the world. It is caused by low levels of Mg or an imbalance of K, Ca, and Mg in forage consumed by animals. Development of grasses with improved mineral balance would be an economical means of minimizing losses from this malady. This study was conducted to determine if genetic variability exists among crested wheatgrasses, Agropyron cristatum (L.) Gaertner and A. desertorum (Fisher ex Link) Schultes, for forage Mg, Ca, K, Fe, Zn, Mn, Cu, Na, and concentrations. Forage of spaced plants of 10 diverse crested wheatgrass strains was harvested from replicated plots at Lincoln and Alliance, NE, which differ markedly in climate, and analyzed for these minerals. There were genetic differences among strains over locations for Ca, Mg, and Fe concentration i the forage. There were differences among strains within locations but not over locations for K. Strain differences in Zn, Mn, Cu, Na, and P concentrations of the forage were not significant (P > 0.05) when averaged over locations. Calcium and Mg were positively correlated (r = 0.40). These results indicate that it should be possible to breed crested wheatgrass with increased Mg and Ca concentrations in its forage, thus reducing rass tetany potential. C WHEATGRASS is a genetic complex comprised of several species. The most important species in North America are A. cristaturn and A. desertorum, which are diploids and tetraploids, respectively (Asay and Dewey, 1983; Barkworth and Dewey, 1985). In this paper, these two species will be referred to as crested wheatgrass, as they are in commerce. Crested wheatgrass, which is utilized primarily by ruminants, does not contain significant amounts of any antiquality factor or toxic compounds except for occasionally high levels of nitrates (Mayland, 1986). Ruminant livestock grazing crested wheatgrass in the spring, however, can be severely affected by grass tetany (hypomagnesemic tetany), which can result livestock deaths and production losses (Mayland, 1986). Thirty percent of all livestock losses attributed to grass tetany in the USA are thought to occur in animals grazing crested wheatgrass (Mayland, 1986). Grass tetany is a nutritional ruminant disease caused by a deficiency of Mg. It is a complex disease because of interactions of Ca, K, inorganic P, vitamin D, and parathyroid hormone in the ruminant (Littledike and Cox, 1979; Littledike and Goff, 1987). High K levels in the diet reduce Mg absorption (Littledike and Cox, 1979). Milk fever (parturient hypocalcemia), which is due primarily to low availability of Ca to the ruminant, particularly during the initial stages of lactation, is often associated with grass tetany in lactating animals (Littledike and Cox, 1979; Littledike and K.P. Vogel, USDA-ARS andDep. of Agronomy, Univ. of Nebraska, Lincoln, NE 68583; H.F. Mayland, USDA-ARS, Snake River Conservation Res. Ctr., Route 1, Kimberly, ID 83341; P.E. Reece, Panhandle Res. and Extension Ct., Univ. of Nebraska, 4502 Ave. I, Scottsbluff, NE 69361; and J.F.S. Lamb, 1219 Front, Crookston, MI Received 17 Oct. 1988. *Corresponding author. Published in Crop Sci. 29:1146-1150 (1989). Goff, 1987). Calcium, Mg, and K levels and the ratio K/(Mg + Ca), in which elements are expressed equivalents kg-1, are used to estimate the grass tetany potential of grass herbage. Genetic variability for the concentration of these mineral elements and the K/(Ca + Mg) ratio in grass forage has been reported for tall fescue (Festuca arundinaceae Schreber) (Nguyen and Sleper, 1981), reed canarygrass (Phalaris arundinaceae L.) (Hovin et al., 1978), and perennial ryegrass (Lolium perenne L.) (Sleper, 1979). Hides and Thomas (1981) demonstrated that it was possible to alter the Mg content of Italian ryegrass (Lolium multiflorum Lam.) by breeding. Mayland and Asay (1989) demonstrated the existence of genetic variability among 12 clones of A. desertorum and among 16 of the 18 original clones of ’Hycrest’ crested wheatgrass for Mg, Ca, K, and K/ (Ca ÷ Mg) in a study at Logan, UT. Broad-sense heritability estimates were determined from the replicated clones. The objectives of this study were to: (i) determine if genetic variability exists among crested wheatgrass strains for the concentration of K, Ca, Mg, Fe, Zn, Mn, Cu, Na, and P in their forage, (ii) obtain preliminary estimates of the magnitude of genotype × environment interaction effects, and (iii) determine the correlation of mineral element concentrations with other important agronomic traits. MATERIALS AND METHODS The crested wheatgrass and the field cultural procedures used in this study were described previously (Lamb et al., 1984; Vogel et al., 1984.) In brief, 42 crested wheatgrass strains representative of the array ofgermplasm available to breeders were grown in space-planted nurseries at Lincoln and Alliance, NE during the period 1979 to 1981. The Lincoln and Alliance experiments were located on a Kennebec soil (fine-silty, mixed, mesic, Cumulic Hapludoll) and Keith soil (fine-silty, mixed, mesic, Aridic Arguistoll), respectively. Alliance is located 540 km west of Lincoln at about the same latitude. Its growing season is 40 d shorter than at Lincoln (120 vs. 160 d) and its annual precipitation is half that of Lincoln (400 vs. 740 mm). The specific climatic conditions at both locations during the study were described by Lamb et al. (1984). Plots were single rows of 10 spaced plants with plants and rows spaced 1 m apart. The experimental design at both locations was a randomized complete block with four replicates. Plants in both nurseries were harvested for forage yield and sampled for forage quality in 1980 and 1981 after anthesis. Ten of the strains were harvested on an individual plant basis to obtain estimates of within-strain variation while the remaining strains were harvested on a plot basis. The strains harvested on an individual plant basis were used in this study. They included the released cultivars Nordan (tetraploid) and Ruff (diploid), six plant introduction li-~es (two tetraploids and four diploids), and two experimental lines (tetraploids). PI 370645 and PI 401003 are tetraploids and PIs 314596, 325180, 369167 and 369170 are diploids. One of the experimental lines, NE 10b-l, is a clonal line that was vegetatively propagated from a single plant of