Reactions of Smooth Bromegrass Clones with Divergent Lignin or Etherified Ferulic Acid Concentration to Three Fungal Pathogens

over, the cell walls of some plants are modified by phenolic deposits in response to infection. Papillae or cell Increased digestibility of smooth bromegrass is associated with a wall apposition formation in epidermal cells of grasses, reduction in lignin concentration or etherified ferulic acid (EthFA) rich in lignin or lignin-like compounds, have been reconcentration, either of which may reduce host resistance to fungal diseases. The objective of this study was to determine the relationship lated to mechanisms for reduced fungal penetration and of lignin and EthFA concentration with disease reaction in smooth increased resistance to fungal organisms (Sherwood and bromegrass. Host clones, divergently selected for lignin and EthFA Vance, 1976, 1980; Vance and Sherwood, 1975). concentration, were challenged by three pathogenic fungi, one bioReductions in the concentration of lignin or ferulic troph (Puccinia coronata Corda) and two necrotrophs [Pyrenophora acid associated with increased forage digestibility may bromi (Died.) Drechs., anamorph Drechslera bromi (Died.) eliminate or impair the resistance mechanisms of plants Shoem., and Bipolaris sorokiniana (Sacc.) Shoem]. Significant posito stresses, herbivores, and parasitic organisms. This tive and negative associations were found between lignin or EthFA would be particularly true if selection acts upon the and host reaction to P. bromi or B. sorokiniana. The frequencies of these associations suggested that they arose by chance associations components responsible for these resistance mechabetween alleles, rather than tight linkages or pleiotropic (causal) efnisms and not on the components required for cell wall fects. Host reaction to P. coronata was consistently and negatively strength and structure per se (Buxton and Casler, 1993). associated with lignin, less so with EthFA. These associations, together Lower concentration of neutral and acid detergent fiber, with results from other species, suggest that lignin, and perhaps cellulose, and lignin in the stalk and leaf-sheath of maize EthFA, may be important components of rust resistance mechanisms (Zea mays L.) were related to increased feeding by in the Poaceae. If these mechanisms are real, they will cause considerthe second-generation European corn borer, Ostrinia able difficulty for breeders attempting to simultaneously improve both rust resistance and forage nutritional value. nubilalis (Hübner), regardless of the selection criterion (Buendgen et al.,1990; Ostrander and Coors, 1997). Little is known about the direct effects of lignin and C emphasis has been placed on improvferulic acid on the development of fungal diseases of ing forage quality of smooth bromegrass herbage, grasses. Sherwood and Vance (1980), studying epideron the basis of the concentration, composition, and dimal penetration in 12 species of 11 tribes of Poaceae to gestion of cell wall constituents (Vogel et al., 1996). three different leaf-infecting fungi, found that grasses Breeding for improved digestibility has resulted in large have both constitutive and inducible resistance mechareductions in lignin concentration, but highand lownisms associated with the epidermis, restricting fungal lignin populations did not differ in forage yield or lodgpenetration. Sherwood and Berg (1991), found that liging potential at several locations (Carpenter and Casler, nin was not related to resistance of orchardgrass (Dac1990; Casler and Ehlke, 1986; Ehlke et al., 1986). Phenotylis glomerata L.) to purple leaf spot caused by Stagolic components of the cell wall, such as etherified ferunospora arenaria Sacc. In two alfalfa (Medicago sativa lic acid, which acts as a ferulate bridge between lignin L.) populations, plants that represented a range of acid and hemicellulose, also regulate digestibility of smooth detergent lignin (ADL) concentration were inoculated bromegrass forage (Casler and Jung, 1999). with Uromyces striatus J. Schröt., the causal agent of The properties of lignin indicate a potential role in alfalfa rust. Although there were significant differences resistance to pathogens. An association between preamong clones for infection efficiency, latent period, and formed lignin and the limitation of fungal growth has sporulation capacity, there was little or no relationship been observed for some diseases (Ride,1983). In addibetween lignin concentration and components of alfalfa tion to preformed lignins, active lignification, by means rust resistance (Webb et al., 1996). of increases in the activity of enzymes involved in the Plant pathogens can be conveniently divided into two lignification pathway, has been observed in the response groups, depending on whether or not they can live in of plants to pathogen attack (Friend et al., 1973; Souththe absence of the living plant. Biotrophs depend on erton and Deverall, 1990). Inhibition of these enzymes the functional metabolism of their hosts for an adequate increased susceptibility to fungal infection (Moerschsupply of nutrients, whereas necrotrophs feed on the bacher et al., 1990; Tiburzy and Reisener, 1990). Morebreakdown products of host degradation (Heisteruber et al., 1994). Thus, the fundamental difference between necrotrophic and biotrophic parasitism is often reflected N.J. Delgado, Centro Nacional de Investigaciones Agropecuarias, APDO Postal 102, Acarigua 3301-A, Venezuela; M.D. Casler, Dep. in the extent of host cell-wall degradation (Cooper, of Agronomy, Univ. of Wisconsin, Madison 53706; C.R. Grau, Dep. 1983). Lignin and ferulic acid may have differential efof Plant Pathology, Univ. of Wisconsin, Madison 53706; H.G. Jung, fects on disease development, depending on the type of USDA-ARS, Dep. of Agronomy and Plant Genetics, 411 Borlaug pathogen that causes disease. Hall, 1991 Upper Buford Cir., Univ. of Minnesota, St. Paul, MN 55108. Received 28 Aug. 2001. Corresponding author (mdcasler@facstaff. wisc.edu). Abbreviations: EthFA, etherified ferulic acid; KL, Klason lignin; GPD, gametic phase disequilibrium. Published in Crop Sci. 42:1824–1831 (2002).