Bioactive Compounds/Metabolites from Extremophiles for Biocontrol and Plant Disease Management

Extremophiles refer to organisms that live and thrive in severe conditions, like extreme pH, high temperature, salinity, pressure, and aridity. The majority of extremophiles belong to unicellular bacteria or archaea. These organisms develop some adaptive traits to thrive in one or more extreme conditions. Only a few reports cite the exploitation of extremophiles as biocontrol agents and for controlling plant diseases alongside improving crop productivity. Few strains isolated from varied high-temperature environments like hot springs, compost and soil in arid regions have been reported to function as a biocontrol against various types of plant pathogens. Plant-associated extremophilic microbes are being effectively used for maintaining plant and soil health as well as soil fertility and are cost-efficient, thereby contributing to sustainable agricultural practices. Burkholderia gladioli KRS027 is an effective microbe for biocontrol and biofertilizer agents used against plant diseases caused by Botrytis cinerea. These strains belong to various microbial species and work by competing with pathogens, producing lytic enzymes and secondary metabolites capable of neutralizing them. Volatile organic compounds (VOCs) produced by certain extremophilic bacteria, like Bacillus atrophaeus L193, Bacillus velezensis XT1 and Psychrobacillus vulpis Z8, show antagonistic activity against certain fungal plant pathogens, thereby making these bacterial strains good candidates for controlling post-harvest diseases. Polyamines (putrescine and spermidine) and lytic enzymes secreted from extremophilic bacteria from Andean soil are being used as potential biocontrol agents as they restrict the growth of Macrophomina phaseolina, further reducing the disease severity in soybean seedlings. In this chapter, we have briefly discussed the bioactive metabolites such as non-ribosomal peptides, polyketides, siderophores and VOCs for biocontrol of plant pathogens. The chapter also highlights their mode of action and management of plant disease.