Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 14, 2006
Publication Date: February 1, 2007
Citation: Pratt, R.G., Brink, G.E. 2007. Forage Bermudagrass Cultivar Responses to Inoculations with Exserohilum rostratum and Bipolaris spicifera and Relationship to Field Persistence. Crop Science. 47:239-244. Interpretive Summary: Concentrated animal production facilities (swine, poultry, beef) are a common feature of American agriculture today. Disposal of waste materials generated by large numbers of animals each day in concentrated facilities without causing environmental pollution is a major challenge. The principal polluting substances in animal wastes are phosphorus and nitrogen; these can wash into surface waters to cause ecological deterioration and leach into ground waters to cause high nitrate levels in well water. In the southeastern USA, animal waste disposal is accomplished by applying wastes to bermudagrass. The grass absorbs phosphorus and nitrogen from wastes during its growth and enables them to be removed in hay without causing pollution. Diseases caused by fungal pathogens that weaken and kill bermudagrass may reduce nutrient removal on some animal waste application sites. In this study, seven cultivars of bermudagrass were compared for susceptibility and resistance to two of the major fungal pathogens individually, and also to natural infection by the whole array of fungal diseases in the field. None of the cultivars was found to possess sufficient resistance to the two pathogens individually to warrant its use for disease control. However, although all cultivars were basically susceptible to the fungal diseases, some did persist better than others in the field. The most persistent cultivars formed dense sods with numerous stolons and rhizomes that enabled them to compensate for disease damage better than those that formed loose sods. Results indicate that none of the cultivars of forage bermudagrass studied here are highly resistant to the fungal diseases, but that cultivars that form the most dense sods persist the best in the presence of these diseases in the field.
Technical Abstract: Environmental pollution caused by loss of nutrients derived from wastes from large-scale animal production facilities is a major environmental concern in the United States. In the southeastern USA, bermudagrass (Cynodon dactylon [L.] Pers.) is a major species to which animal wastes are applied for nutrient removal. Diseases caused by species of Exserohilum, Bipolaris, and Curvularia may reduce yield and persistence of bermudagrass and limit its use for this purpose. This study was undertaken to evaluate resistance and susceptibility of seven cultivars of forage bermudagrass to two major pathogens individually, E. rostratum (Drechs.) Leonard & Suggs and B. spicifera (Bain) Subram., and also to evaluate persistence of cultivars in the presence of natural infection by these and related pathogens in the field. All cultivars were susceptible to both pathogens when inoculum was applied to foliage, but significant differences in susceptibility were observed. 'Coastal' was least susceptible to the less virulent pathogen, B. spicifera, but no cultivar was consistently least susceptible to the more highly virulent E. rostratum. Persistence of cultivars for up to 1 year with natural infection in the field appears to be influenced by both susceptibility to pathogens and sod density. Dense sods appear to enable cultivars to generate more top growth and compensate for disease losses. Cultivars 'Common', 'Coastal', and 'Tifton-44' were most persistent during year-long experiments in the field; 'Tifton-85' and 'Alicia' were least persistent. Results indicate that greater resistance to these pathogens is needed in forage bermudagrass, and likely a strong sod-forming ability, to enable their persistence and effective use for nutrient removal on animal waste application sites.