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

Increased digestibility of smooth bromegrass is associated with a reduction in lignin concentration or etherified ferulic add (EthFA) concentration, either of which may reduce host resistance to fungal diseases. The objective of this study was to determine the relationship of lignin and EthFA concentration with disease reaction in smooth bromegrass. Host clones, divergently selected for lignin and EthFA concentration, were challenged by three pathogenic fungi, one biotroph (Puccinia coronata Corda) and two necrotrophs [Pyrenophora bromi (Died.) Drechs., anamorph = Drechslera bromi (Died.) Shoem., and Bipolaris sorokiniana (Sacc.) Shoem]. Significant positive and negative associations were found between lignin or EthFA and host reaction to P. bromi or B. sorokiniana. The frequencies of these associations suggested that they arose by chance associations between alleles, rather than tight linkages or pleiotropic (causal) effects. Host reaction to P. coronata was consistently and negatively associated with lignin, less so with EthFA. These associations, together with results from other species, suggest that lignin, and perhaps EthFA, may be important components of rust resistance mechanisms in the Poaceae. If these mechanisms are real, they will cause considerable difficulty for breeders attempting to simultaneously improve both rust resistance and forage nutritional value.