Variation among and within Smooth Bromegrass Collections from Rural Cemeteries

Development of new tillers in smooth bromegrass is largely determinant, with synchronized elevation and Smooth bromegrass (Bromus inermis Leyss.) is poorly adapted to elongation of new apical meristems above the soil surmanagement-intensive rotational grazing because of slow and limited regrowth potential. In an effort to find existing germplasm with tolerface (Krause and Moser, 1977). Cutting or grazing beance to frequent cutting, smooth bromegrass germplasm was collected fore new tillers have developed sufficiently reduces refrom fence and sod habitats of 30 rural cemeteries in Iowa, Minnesota, growth and persistence (Eastin et al., 1964; Reynolds and Wisconsin. Ramets of 25 clones from each habitat of each cemeand Smith, 1962). During reproductive development, tery were transplanted into a replicated and randomized experiment this critical time occurs from culm elongation to late at Arlington, WI, and evaluated from 1999 to 2002. Within-population heading. Cutting before culm elongation (to avoid regenotypic variance was greater in sod populations for plant height moval of apical meristems) or well after heading (when and diameter. Across cemeteries, genotypic variances for regrowth new tillers have begun to emerge) leads to increased forage vigor of sod and fence populations were positively correlated. These yields and persistence (McElgunn et al., 1972; Paulsen two results suggest that a large amount of genotypic variability is being and Smith, 1968). Apical dominance in smooth bromemaintained at some cemeteries by migration into sod populations and disruptive selection favoring different genotypes in the two habitats. grass is strong until anthesis, when auxin activity declines Fence populations averaged 7.6% higher in reproductive forage yield, and tillering is normally resumed (Eastin et al., 1964). 9.5% higher in vegetative forage yield, 6.0% taller, 8.4% wider plant Because smooth bromegrass produces true culms with diameter, 4.7% higher regrowth vigor, and 6.9% higher frequentelevated apical meristems upon regrowth, timing of subharvest forage yield than sod populations. Sod populations tended to sequent harvests may also be critical for smooth bromebe more variable among cemeteries than fence populations, suggesting grass regrowth and persistence. Regrowth of smooth greater adaptive responses to selection pressure. Two sod populations bromegrass is not closely related to carbohydrate rewere highly unusual, one with unusually fast regrowth arising from serves in roots and crowns (Eastin et al., 1964; Paulsen tillers that initiated obvious growth within 24 h after apical dominance and Smith, 1969; Raese and Decker, 1966; Reynolds was removed, the other with extremely high reproductive forage yield, and Smith, 1962). but low regrowth vigor. This germplasm may have value in the development of smooth bromegrass germplasm with improved tolerance Use of smooth bromegrass in grass–legume mixtures to frequent cutting or grazing. is limited by its synchronized tiller development. First harvest in smooth bromegrass–alfalfa (Medicago sativa L.) mixtures typically occurs during the critical latejointing phase. This suppression of smooth bromegrass S bromegrass is an important forage grass in regrowth potential, combined with shading from the much of temperate North America. It is preferenrapidly recovering alfalfa canopy leads to rapid smooth tially adapted to hay management and favored by infrebromegrass stand losses (Casler, 1988; Smith et al., quent cutting, relatively high cutting heights, and high 1973). Breeding and selection for persistence of smooth nitrogen fertility (Casler and Carlson, 1995). Conversely, bromegrass in mixture with alfalfa under a threeor smooth bromegrass is not well adapted to frequent defofour-cut management system has been somewhat sucliation, whether by cutting (Smith et al., 1973) or by cessful. Populations selected for persistence had 40% grazing (Casler et al., 1998), or to low defoliation heights greater ground cover and 42% faster recovery after (Lawrence and Ashford, 1969; Raese and Decker, 1966; cutting than unselected cultivars (Casler, 1988). The Smith et al., 1973). Unlike many other cool-season forcultivar Alpha, a product of this program, had 10% age grasses, forage production of smooth bromegrass is greater survival after 2 yr in mixture with alfalfa across not stimulated by defoliation, regardless of the growth five locations than the second-ranked cultivar (Casler, stage (Harrison and Romo, 1994; Lawrence and Ash1988; Casler and Walgenbach, 1990). Despite these sucford, 1969). Smooth bromegrass stands decline under cesses, smooth bromegrass cultivars, including Alpha, rotational grazing, an effect that is magnified by increashave relatively low persistence under management-inteningly intensive grazing (Bittman and McCartney, 1994). sive rotational grazing systems (Casler et al., 1998). Smooth bromegrass is used primarily for infrequent hay In June 1995, while visiting my maternal grandparharvests, soil conservation, or other situations that are ents’ gravesite, I discovered a thick and vigorous stand characterized by relatively low levels of management. of smooth bromegrass growing in a sod dominated by Regrowth and persistence of smooth bromegrass is Kentucky bluegrass (Poa pratensis L.). The turf was limited largely by the timing of new tiller development. well-managed and frequently mowed to maintain its USDA-ARS, U.S. Dairy Forage Research Center, Madison, WI 53706visual appearance, suggesting that this smooth brome1108. This research was supported by the College of Agricultural and grass population may have adaptive traits allowing it Life Sciences, Univ. of Wisconsin. Received 19 Feb. 2003. *Correto survive and vegetatively reproduce under frequent sponding author ([email protected]). defoliation. Subsequent investigations identified numerPublished in Crop Sci. 44:978–987 (2004).  Crop Science Society of America Abbreviations: NPD, normalized phenotypic distance; PD, Euclidean phenotypic distance. 677 S. Segoe Rd., Madison, WI 53711 USA