Biological Management of Diseases of Crops

With growing concern for environmental pollution and presence of chemical residues in grains, vegetables, fruits and other food materials, biological disease management tactics have emerged as potential alternative to chemical application for containing crop diseases. Biological control agents (BCAs) - biotic and abiotic agents - have been demonstrated to be effective against diseases caused by microbial plant pathogens. Biological management of diseases of crops involves utilization of biotic and abiotic agents that act through one or more mechanisms to reduce the potential of the pathogen directly or indirectly by activating the host defense systems to reduce the disease incidence and/or intensity. Biotic biological control agents include living oomycetes, fungi, bacteria and viruses that have inhibitory effects on the microbial pathogens through various mechanisms of action such as antagonism, competition for nutrients and niches, prevention of colonization of host tissues by the pathogen and induction resistance in plants against the diseases. It is essential to assay the biocontrol potential of all species/isolates of fungal, bacterial and viral BCAs in in vitro, greenhouse, and under field and storage conditions, in addition to their precise identification by biological, immunological and nucleic acid-based assays. Abiotic biological control agents include solarization, physical and chemical agents and those derived from diverse organic and inorganic sources. Organic amendments such as composts, green manures, vegetable wastes, plant extracts and secondary metabolites like essential oils have been shown to have high level of disease-suppressive activity. Chitosan derived from the crab shell, synthetic organic compounds such as SA, ASM, BTH and BABA have been used for treating seeds and plants. Combination of biotic and abiotic agents leads to synergism and consequent improvement in the effectiveness of disease control.  Some of the biotic abiotic agents have provided effective disease suppression, when tested under in vitro and field and storage conditions. Protocols for isolation, identification and assessing the biocontrol activities of biotic and abiotic biocontrol agents provided in relevant chapters will be useful for researchers and teachers.