Genetic Variation in Dry Matter Production and Nutritional Characteristics of Meadow Bromegrass under Repeated Defoliation

Meadow bromegrass (Bromus riparius Rehm.) has gained interest as a highly productive pasture grass that can be used under management intensive grazing with limited irrigation. In 1999, 28 cloned parents and half-sib families of meadow bromegrass were each planted in a randomized complete block design to evaluate genetic variation of meadow bromegrass for dry matter yield (DMY) (Harvests 1 to 6), forage quality under repeated defoliation (Harvests 1, 3, and 5), and investigate intercharacter correlations. Narrow-sense heritability estimates and their standard errors for DMYat Harvests 2, 3, and 4 were 0.89 6 0.32, 0.59 6 0.28, and 0.53 6 0.29, respectively. However, at Harvest 1 and 5, standard errors of the heritability estimates for DMY were equal to or greater than the estimates. All heritability estimates for crude protein (CP) were at least twice their standard errors at Harvests 1, 3, and 5. High narrow-sense heritabilities at Harvest 5 for acid detergent fiber (ADF) suggest that selection on forage harvested later in the growing season might be more efficient than forage harvested earlier in the season. Combined across years and within harvests, narrow-sense heritability estimates and standard errors for neutral detergent fiber (NDF) were 0.66 6 0.29, 0.47 6 0.30, and 0.716 0.28, respectively. Based on correlations, it seems reasonable to assume that when selecting for increased DMY that ADF and NDF will increase and that CP and IVTD will decrease in this population. INTEREST in utilizing less productive agricultural land, often associated with periods of reduced irrigation, soil salinity, and low fertility, is gaining greater interest as an alternative source of forage to public grazing. Productivity of these lands can be increased through genetically improved plant materials selected for more intensive management practices under abiotic and biotic stresses. One such species is meadow bromegrass due to its early seasonal forage production and rapid regrowth after defoliation. Meadow bromegrass is a moderately creeping perennial grass, native to southeastern Europe, the Caucasus, Turkey, and Central Asia (Knowles et al., 1993), that was first introduced to North America in 1957. Meadow bromegrass is predominantly cross-pollinating, however, it does have the ability to produce seed under selfpollination (Knowles et al., 1993).Meadowbromegrass cultivars are decaploids (2n5 10x5 70) compared to smooth bromegrass, which is an autoallooctaploid (2n 5 8x 5 56) (Tzvelev, 1976, Armstrong, 1987,Armstrong, 1991). Unlike its counterpart smooth bromegrass [B. inermis Leyss.], which regrows slower after defoliation, meadow bromegrass is known for its rapid regrowth of tillers after defoliation (Jensen et al., 2001). Due to meadow bromegrass’s short rhizomes, it is less aggressive than smooth bromegrass in perennial grass–legume mixtures (Ferdinandez and Coulman, 2000). In the central Great Plains, meadow bromegrass is not as productive as smooth bromegrass (Vogel et al., 1996). Under a fourcut system in Canada, meadow bromegrass had lower initial yields than smooth bromegrass but had higher regrowth yields (Knowles et al., 1993). Under a sixharvest management and multiple irrigation levels in Northern Utah, meadow bromegrass significantly out yielded smooth bromegrass on total DMY by 28% (Jensen et al., 2001). Estimates of heritability have varied among traits in grasses, with lower estimates reported for traits under complex genetic control, such as forage yield (Tan et al., 1978; Casler 1998) and fiber concentration (Tan et al., 1978), compared to high estimates for more simply inherited characters, such as plant height (Ross et al., 1970). Under a single harvest management system and open-pollination, narrow-sense heritability estimates and standard errors in 48 half-sib families of meadow bromegrass were 0.33 6 0.21, 0.08 6 0.29, and 0.21 6 0.26, for DMY, CP, and NDF, respectively (De Araujo and Coulman, 2002). The relationships between DMY and CP have generally been negative (Asay et al., 1968; Vogel et al., 1981; Berg and Hill, 1983) in perennial grasses. De Araujo and Coulman (2002) reported a nonsignificant relationship between DMY and CP, ADF, or NDF in meadow bromegrass, but did find a negative correlation between CP and ADF and NDF concentrations. In Timothy (Phleum pratense L.), Berg and Hill (1983) concluded that simulataneous selection for increased DMY, in vitro dry matter disappearance, and CP would probably lead to undesirable correlated responses. Van Soest (1965), proposed that NDF best estimated cell wall constituents (CWC), which are comprised of partially digestible cellulose, hemicellulose, and indigestible residue which includes lignin. Mertens and Van Soest (1973) reported a correlation (r 5 0.73) between CWC and DMY intake in grass samples. The majority of the selection efforts in meadow bromegrass have been restricted to combining genotypes with increased seed yield (Alderson and Sharp, 1994). The initial breeding work on meadow bromegrass in North America began with the development of a 15 clone synthetic cultivar Regar (Foster et al., 1966) originating from PI 173290. Two cultivar releases, Fleet and K.B. Jensen, J.G. Robins, B.L. Waldron, and M.D. Peel, USDA-ARS, Forage and Range Research Lab., 695 North 1100 East., Logan, UT 84322-6300. Joint contribution of the USDA-ARS and the Utah Agric. Exp. Stn. Utah Agric. Exp. Stn. Journal Paper No. 7798. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the USDA or Utah State University. Received 15 Mar. 2006. *Corresponding author ([email protected]). Published in Crop Sci. 46:1948–1954 (2006). Crop Breeding & Genetics doi:10.2135/cropsci2005.12-0511 a Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA R e p ro d u c e d fr o m C ro p S c ie n c e . P u b lis h e d b y C ro p S c ie n c e S o c ie ty o f A m e ri c a . A ll c o p y ri g h ts re s e rv e d . 1948 Published online July 25, 2006