ABSTRACT
Investigations on various aspects of soilborne microbial plant pathogens and the diseases induced by them in different crops aim at providing information for the development of methods to eradicate or restrict the incidence and/or severity and also spread of the diseases within and outside the geographical location/field. As the first step, highly sensitive and reliable methods are employed to establish the identity of the pathogen(s) involved in the disease(s) and quantify their populations precisely along with their pathogenic potential (virulence). Studies on the biology of the pathogens provide information on the nature of survival structures formed by the pathogens during the life cycle, genetic diversity and differential sensitivity of strains/isolates to environmental conditions and chemicals, and availability of various sources of infection, in addition to the primary (crop) host to determine the extent of protective cover needed for crop cultivars that may vary in the levels of susceptibility/resistance to the target pathogen(s). Short-term and long-term strategies have been developed, the effectiveness of which differ based on the cultural practices adopted in different locations primarily for improving yield levels of cultivars. It has been necessary to continue the search for new disease management strategies, as the predominance of one pathogen(s) changed as new cultivars with improvement in yield and quality of produce were released for large-scale cultivation, without much concern for the level of resistance to disease(s). Prior to the 19th century, cultural methods were essentially applied for the management of diseases. From the latter half of the 20th century, chemicals with pathogen-suppressive activity were used increasingly either in conjunction with or instead of cultural practices. Development of cultivars with built-in resistance to major disease(s) was given more importance because of growing awareness of harmful effects of excessive use of chemicals on the environment and chemical residue accumulation in harvested produce. However, limitations of the approach of disease management through breeding for disease-resistant cultivars was realized when pathogen races/strains capable of overcoming the effects of resistance gene(s) introgressed into the susceptible cultivars emerged over wide areas. Effectiveness of biological control agents – biotic and abiotic – was demonstrated in due course and this approach has become acceptable because of its ecofriendly nature, receiving the attention of researchers and growers involved in the production and supply of agricultural and horticultural produce free of residues (Narayanasamy 2002, 2017).
