Molecular approaches to improvement of biocontrol agents of plant diseases

Biological control holds out the prospect of an attractive proposition against plant diseases. Hitherto, a host of microorganisms have been identified as biocontrol agents while only a few have been able to be successfully commercialized. A major difficulty faced while translating the efficacious biocontrol agents into merchandise was that the efficacy of the developed strains was largely unstable under diverse environmental conditions in which the finished product of organismal origin was to tread before reaching the farmer's field. To add to the problem, desirable properties of a given biocontrol agent are not usually determined by a single attribute; on the contrary desirable biocontrol behavior of the agent is decided by its competitive ability, nature of antibiosis involved, lysis of the target pathogen and induced systemic resistance of the host plant, if any. Yet, a comprehensive understanding of the nature of genes encoding various observable biocontrol mechanisms of action and their putative role at molecular level is still elusive. A detailed characterization of gene(s) encoding biocontrol properties of a given biocontrol agent with respect to individual mechanism of action is a sine qua non for further improvement of biocontrol agents with a view to getting the most out of the individual biocontrol agent. With the advent of molecular biology, several approaches have been made towards achieving the following goals: i) Identification and characterization of genes encoding the specific biocontrol property against a given pathogen and ii) Designer biocontrol strains with potential genes responsible for superior biocontrol properties This review tries to focus on the recent developments on the above areas while bringing out a list of promising biocontrol agents so far worked upon with respect to individual target diseases of major crop plants.