Control of Common Bunt in Organic Wheat

Common bunt, caused by the seedborne and soilborne pathogens Tilletia caries and T. laevis, has re-emerged as a major disease in organic wheat. In conventional agriculture, common bunt is routinely managed with the use of synthetic chemical seed treatments. For this reason, common bunt is a relatively unimportant disease in conventional agriculture. However, since synthetic chemical inputs are prohibited in organic agriculture, common bunt is a major threat once more in organic wheat and seed production. The challenge today is to manage the disease without the use of chemical seed treatments. This review reports on the management of common bunt under organic farming systems, mainly through host resistance and organic seed treatments. We report the history of screening wheat germplasm for bunt resistance, the search for new sources of resistance, and identification and mapping of bunt resistance genes. Since the pathogen has a gene-for-gene relationship with the host, this review also includes a summary of work on pathogen race identification and virulence patterns of field isolates. Also included are studies on the physiological and molecular basis of host resistance. Alternative seed treatments are discussed, including physical seed treatments, and microbial-based and plant-based treatments acceptable in organic systems. The article concludes with a brief discussion on the current gaps in research on the management of common bunt in organic wheat.