Microbial bioagents in agriculture: Current status and prospects

Abstract

Bioagents are widely used in agri-horticultural ecosystem as plant protectants which have profound impact on plant community through enhancing plant growth, biotic and abiotic tolerance to host. Biological control is the way of controlling of plant disease by the application of fungi, bacteria, actinomycetes, and viruses (bacteriophages). It has been estimated that rupees 60,000 crores worth of crop are lost each year due to plant diseases. The degree of plant disease control/ disease suppression achieved with biological agents can be comparable to that achieved with chemicals. In India, the maximum crop protectants used are insecticides (65%), herbicides (15%), fungicides (15%), and rodenticides or nematocides (4%) but at global level herbicides (45%) are used more followed by fungicides (27%), insecticides (15%), and other chemicals (7%). India is one of the fourth largest producers of pesticides (1,39,000 tonnes/annum) in the world after the USA, Japan, and China. As per estimates, Indian bioagents market is equivalent to 2.5% of total pesticides market with worth of rupees 690 crores. Indiscriminate and non-judicious use of synthetic pesticide for preventing and controlling crop diseases adversely affects the environment, microbiome, development of resistance, and hormoligosis in several plant pathogens and also acts as serious non-tariff barrier to trade of farm commodities. Among agriculturally important microbes Trichoderma viride, T. harzianum, Pseudomonas fluorescens, and Bacillus subtilis are most efficient antagonistic bioagents of plant diseases, producers of biologically active metabolites, elicitors and inducers of systemic resistance. Better understanding of the application of genomics and genetic modification techniques opened new doors for multifaceted traits enhancement in strain of bioagents. The knowledge of the diversity spectrum and genetic structure of microbial population has direct implication in development of formulations of potential bioagents. Formulations of bioagents are commercially available in the form of 1-5% WP followed by 5-10% G and 10-20% EC for agricultural applications. Trichoderma and Pseudomonas based generic plant protection products are commercially available in India, but very few of them are label claimed for use in various crops by Central Insecticide Board and Registration Committee. No doubt, biocontrol production technology has promising and gained good success but still there are key researchable gaps on understanding of taxonomy, isolation, and screening strategies of effective biocontrol agents, mechanistic basis of colonization, tripertite interactions with plant/crop and/or pathogen, and ecological implementation of biocontrol strategies and how they work need to be addressed. In conclusion, the farmers interested on healthy crop yield rather than diseases in this context should better focus on bioagents mediated improved performance on plant health management. In this chapter, we would attempt to present an overview of the "Current status-strengths, weaknesses, opportunities, and threats of bioagents" controlling of plant diseases.