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a Dep. of Agronomy, Univ. of Missouri-Columbia, Columbia, MO 65211
b Univ. of Missouri-Columbia, the Southwest Research Center, Mt. Vernon, MO 65712
c USDA-ARS, Kimberly, ID 83341
d Univ. of Idaho, Twin Falls, ID 83303
* Corresponding author (sleperd{at}missouri.edu)
HiMag (Reg. no. GP-79, PI 615587) tall fescue (Festuca arundinacea Schreb.) was developed and released by the Missouri Agricultural Experiment Station and the USDA-ARS in 1997. HiMag has relatively high Mg and Ca concentrations and low tetany ratio [K/(Ca + Mg)] expressed as moles of charge.
Parental germplasm for the C0 cycle of selection for HiMag included 950 plants from ‘Kenhy’ (Buckner et al., 1977), 831 plants from ‘Kentucky-31’, and 688 plants from ‘Missouri-96’ (Asay et al., 1979). All plants were endophyte free [ Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon, and Hanlin comb. nov.]. Parental plants were transplanted to the field near Columbia, MO, in the fall of 1983. The soil was a Mexico silt loam (a fine, montmorillonitic, mesic Udollic Ochraqualf) with a pH of 6.4. Selection was applied against crown rust (caused by Puccinia coronata Corda. var. coronata), leaving 1011 plants which were harvested in the fall of 1984 and analyzed for elemental concentrations of Mg, Ca, K, and the tetany ratio. Sixty-five plants (11 from Kentucky-31, 54 from Missouri-96, and 0 from Kenhy) were chosen to generate the C1 cycle of selection. These 65 plants contained 5.0 to 7.0 g kg-1 Mg, 5.0 to 10.2 g kg-1 Ca, 20 to 33 g kg-1 K, and had K/(Ca + Mg) values of 0.61 to 0.99. These were allowed to open-pollinate in the greenhouse during the winter of 1985/86. Harvested seeds were germinated in the greenhouse and seedlings were transplanted to the field in the fall of 1986. During the fall of 1987 approximately 1000 plants were analyzed from the C1 cycle to determine elemental concentrations of Mg, Ca, K, and the tetany ratio. Forty-six plants chosen for the C2 contained 4.4 to 6.1 g kg-1 Mg, 5.5 to 8.1 g kg-1 Ca, 17.2 to 30.9 g kg-1 K, and had tetany ratios of 1.06 to 2.13. These were allowed to open-pollinate in the greenhouse in the winter of 1988–1989. Approximately 1000 seedlings were transplanted to the field having areas of Creldon silt loam (Mollic Fragiudalf) and Hobert silt loam (Umbric Fragiaqualf) at the Southwest Research Center, located near Mt. Vernon, MO, in the fall of 1989. In the summer of 1990, seed was harvested from these spaced plants and planted into an irrigated Portneuf silt loam soil (Durinodic Xeric Haplocalcid) to establish a seed increase block at Kimberly, ID, in April 1991. In 1992, seed from HiMag was harvested with the following characteristics: 1635 kg ha-1, 400 seeds g-1, 2.5 g 1000 seeds-1, and 302 kg m-3.
HiMag forage yields are similar to Missouri-96 and Kentucky-31, and it grows well on both calcareous alkaline and acid soils (Shewmaker et al., 1997; Wilkinson et al., 1997).
HiMag was developed for the purpose of minimizing the effects of grass tetany in cattle (Bos taurus) and sheep (Ovis aries). Grass tetany is characterized by hypomagnesemia resulting from low Mg concentrations in the herbage or reduced absorption of Mg by the grazing ruminant (Butler, 1963; Kemp et al., 1957; Martens et al., 1983). It has also been demonstrated that the K/(Ca + Mg) ratio should be kept below 2.2 in the herbage being grazed to reduce the hazards of grass tetany (Crawford et al., 1998; Kemp et al., 1957).
When HiMag was compared with ‘Au Triumph’ (Pedersen et al., 1983), Kentucky-31, ‘Martin’, and ‘Mozark’, it was found to have 22% more Mg, 18.5% more Ca, and 9% more P (Crawford et al., 1998). The mean tetany ratio was 1.34 for HiMag and 1.65 for the other three cultivars. Blood serum levels of Mg in grazing cattle were inconsistent (Crawford et al., 1998). Blood serum levels from steers grazing HiMag in the fall were 8% higher than the three check cultivars, but were not different compared to the checks in the spring. For grazing cows during the fall, blood serum Mg for HiMag was not different from the check cultivars, but approached significance (P = 0.09) during the spring calving season. For most grazing seasons, the check cultivars and HiMag consistently had tetany ratios below 2.2. Animal grazing preference for HiMag was less than for endophyte-free cultivars of Kenhy and Kentucky-31, similar to ‘Barcel’ and ‘Stargrazer’, and greater than Missouri-96 and Mozark (Shewmaker et al., 1997). Sheep and goat (Capra hircus) preference rankings for HiMag hay were similar to cattle rankings of grazed tall fescue cultivars (Burns et al., 2001). HiMag contains moderately high concentrations of soluble carbohydrates leading to its desirable palatability (Mayland et al., 2000). We conclude that HiMag is a good germplasm source for altering certain mineral concentrations in tall fescue.
Small quantities (100 g) of seed of HiMag are available to breeders and geneticists. Written requests should be addressed to the corresponding author. Recipients of the seed are asked to make appropriate recognition of the source of HiMag if it is used in the development of a new cultivar, germplasm, or genetic stock.
NOTES
REFERENCES
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