Assessing the threat to resistant cultivars from public risk diseases and pests

A framework is developed on epidemiological criteria to classify the degree of public risk and the threat to resistant cultivars from a range of diseases within a region. A public risk disease or pest is one that is an external threat to the productivity of a field, posed by a plant pathogen or pest that originates elsewhere. Yield losses can occur in neighbouring crops when susceptible cultivars are grown and become diseased. There is also an increased risk of the emergence of new pathotypes. Costs arise directly from yield losses and from maintenance breeding that is necessary to counter the risk of new pathotypes or biotypes. The framework is based on the four components of the disease tetrahedron (host, pathogen, environment, management) and their interactions with the principal criteria and modifying factors that are identified. The principal criteria that influence public risk are inoculum dispersal and pathogen variability. These can be modified by the degree of pathogen variability, reproductive capacity, seasonal favourability, host non compensation, production system, and overseasoning location. The major threat arising from public risk diseases is their potential to reduce the effective life of resistant cultivars. As an illustration, the framework is applied to the wheat industry in southern New South Wales, Australia, to classify diseases into those with public risk that can result in high, medium, low and negligible threats to resistant cultivars. Measures for reducing the threats posed by public risk diseases are discussed.