Grassland Plant Diseases: Management and Control

Grasslands cover 40% of the earth’s surface and support animal-based industries; maintain soil cover, watersheds and biodiversity; sequester atmospheric carbon for storage in the soil; and provide tourism and leisure income. Diseases continue to decrease herbage and seed yield and reduce nutritive value and palatability of grasslands to impact on animal health and productivity but realistic data on loss are hard to find. Although principles of disease management remain the same, strategies used in crop protection can not be directly applied to grasslands due to differences in heterogeneity, population size, density and spatial distribution and population continuity. Low per hectare monetary return and the need to maintain disease control over a large area for a long time restrict the choice of control options. Genetic approaches are the most cost-effective and host resistance has been used mostly through selection. Molecular markers have improved efficiency of selection in species like Stylosanthes. Forms and mechanisms of resistance are important considerations. Quantitative multi-gene resistance is often longer-lasting than qualitative single-gene resistance, which is more prone to breakdown by new pathogen virulence. Grassland disease management has gained from new knowledge on the molecular basis of plant pathogen interaction and disease resistance. Many important forage grass and legume species have been genetically transformed as a first step towards introducing existing and novel disease resistance genes. At the same time, community concern over genetically modified organisms has grown and commercial exploitation of genetically modified grassland species will depend on environmental, economic and social imperatives. Rapid evolution of new pathogen races to devastate previously resistant varieties has been a consequence of host resistance. Strategic deployment of resistance genes is one way to combat pathogen variability. Genes can be deployed through heterogeneous cultivar mixtures relatively easily but this does not always provide long-term solution, and gene pyramiding may be more suitable. As threat of exotic pathogen incursion increase due to rising global trade and tourism, sharing knowledge of pathogen variation between trading countries through strong international collaboration becomes necessary to manage this risk. Pathogens interact with changing climate and biodiversity to impact on the sustainability of land and grassland ecosystems. Plant protection professionals will have to think beyond their disciplinary expertise to seek and invite concepts and frameworks at the appropriate spatial and temporal scales to manage grassland health.