ABSTRACT

The impact of crop diseases on quantitative and qualitative yields may vary, depending on the pathogen characteristics and responses of the host plant species to the pathogen(s) prevailing environment. Various aspects of host-pathogen interactions are investigated primarily to gather relevant information that will be useful for reducing infection by soilborne microbial pathogens and spread of the disease(s) induced by them. Strategies applicable against diseases caused by soilborne microbial pathogens may be of two types, acting either indirectly or directly on the pathogens. The strategies such as use of disease-free seeds and propagules, cultural practices and host resistance aim at preventing introduction of pathogens and/or build-up pathogen populations and their effects are not distinctly perceptible, but the beneficial effects may be realized over several years. By contrast, use of biocontrol agents (BCAs) and chemicals has direct adverse impact on the development of pathogens and consequently on the progress of disease symptoms. The effect of chemical application is highly recognizable and more effective against some pathogens, which may not be contained by other disease management strategies. However, there are certain limitations for universal application of chemicals, as the preferred method of disease control, necessitating the search for alternative and more economically feasible method(s). Application of chemicals against crop diseases will be acceptable, only if, the net profit for the growers can be increased. Generally, application of chemicals against diseases affecting cereals is limited. In contrast, high value crops such as fruits and vegetable crops are protected by frequent application of chemicals. Blemish-free market demands and economic value per unit of crops such as apples, citrus, grapes and potatoes may justify intensive use of chemicals against microbial plant pathogens. Such repeated applications at high doses of chemicals are, however, considered to be the primary reason for development of resistance in microbial pathogens to the chemicals. Host resistance and cultural practices are the tactics generally applicable for agronomic crops, keeping the use of chemicals to the minimum level, because of the lower net profit from these crops (Narayanasamy 2002, 2017).