Chapter 6 - Pseudomonas and Bacillus: A biological tool for crop protection

Abstract

The problems caused by soil-borne pathogens in crop production worldwide include reduced crop performance, decreased yield, and higher production costs. The threats of soil-borne disease epidemics in crop production, high cost of chemical fungicides and development of fungicide resistance, climate change, new disease outbreaks and increasing concerns regarding environmental as well as soil health are becoming increasingly evident. Research in the past few years has clearly shown that selected strains of bacteria (Pseudomonas spp. and Bacillus spp.) provide an eco-friendly well balanced plant health management system through systemic resistance to diseases of biotic and a biotic nature. Pseudomonas can also synthesize enzymes which may modulate the plant hormone levels, limit the available iron by production of siderophores and can also kill the pathogen by producing antibiotics such as Phenazine, 2,4-diacetylphloroglucinol (DAPG), Phenazine carboximide, Pyoluteorin and Pyrrolnitrin, volatile compounds such as hydrogen cyanide (HCN), siderophores and biofilms mainly responsible for the inhibition of pathogens. Pseudomonas might have stimulated the plant growth by improving uptake of minerals into the host plants particularly phosphate production of IAA, production of cytokinin, regulating ethylene production in roots and solubilizing nutrients such as phosphorus. Likewise, Bacillus produced several kinds of antimicrobial peptide substances such as subtilin, bacilysin, mycobacillisyn, iturin, oligomycin A, kanosamine and zwittermicin A, which may be responsible for the inhibition of pathogen. It also play an important role in plant growth promotion by production of GA3 and IAA, production of cytokinin, synthesize various types of lipopeptides and zinc solubilization. Both powder and liquid formulations of Pseudomonas and Bacillus have been successfully used for the control of foliar and soil-borne diseases. Bio-fungicidal association also stimulated plant defensive mechanisms induction of resistance metabolism similar to the hypersensitive response, systemic acquired resistance and induced systemic resistance in plants. Nowadays, there is a growing demand for biologically based soil-borne pathogen management practices.