ABSTRACT
A key application for plant pathology in agriculture, horticulture and forestry is the development and use of methods to rapidly and accurately diagnose disease. In human medicine, correct diagnosis of the causal agent can ensure that appropriate control methods are implemented and that unnecessary methods are avoided, and the same is true in plant pathology. Diagnostics are particularly important with the increase in global trade of plants and plant produce, and the associated risk of movement of pathogens and their vectors from one country to another. Tests that can reliably, quickly and cheaply detect the presence of plant pathogens are essential for preventing new outbreaks and potentially devastating crop diseases. Not only are diagnostics important for detection of organisms, but they are also important for identifying the isolate/race/pathotype/pathovar of the organism, so that pre-emptive breeding/control methods can be adopted based on predictions of likely future outbreaks. Annual surveys of rust populations in Australasia and the USA have been used to determine which resistance genes to deploy in wheat to reduce the likelihood of disease outbreaks, and surveys of antibiotic resistance in strains of bacteria, and of fungicide resistance in fungal populations have been used to improve the methods of deployment of chemical controls, such as use of mixtures and/ or alternating sprays. This chapter will discuss the molecular methods used for diagnosis of disease, and those used for identifying genetic variation within pathogen populations.
