Diseases and Management of Crops under Protected Cultivation

(Diseases and Management of Crops under Protected Cultivation)
Non target effect of BCAs- Non-target effects of bacterial biological control agents on soil
protozoa has been found recently. Negative effects of P. fluorescens DR54 were assessed on
growth of the amoebae Hartmanella vermiformis and Acanthamoeba sp. cultures and natural
assemblages of soil protozoans. The observed effects were larger than those of the P. fluorescens
type strain DSM50090 and Enterobacter aerogenes SC and were tentatively attributed to
viscosinamide, which is an antimicrobial compound with surfactant properties produced by P.
fluorescens DR54.
Possibility of Gene transfer in Biocontrol Agents: Transfer of agrocin plasmid p AgK84 to
pathogenic Agrobacteria. Pathogenic strains acquired resistance to Agrocin 84 and also produce
it. Mobilization of plasmid deleted by producing Tra - (transfer deleted) mutant of K84. A.
radiobacter K1026
Pathogen self defense: is mechanism to counter act Biocontrol Agents. Pathogen populations
are not evolutionary static entities. Pathogens have diverse responses to counteract antagonism
which can affect the efficacy of biocontrol.
• Pathogen defense against antibiosis -Natural diversity in sensitivity of pathogens to
antibiotics : Pseudomonas strains fail to control take-all caused by 2,4,-DAPG insensitive
G. graminis var. tritici. Resistance to Antibiotics : Agrobacterium tumefaciens – Agrocin 84 .
• Pathogen defense against competition - Altering the environment : A. tumefaciens
programms host plant to produce opines, that can not be utilized by other competitors.
Shutting out competitors: Pseudomonas syringae – phytotoxins – stomatal closing.
• Pathogen defense against mycoparasitism- Reverse Mycoparasitism : Pathogenic F.
oxysporum have the ability to parasitize T. hamatum, T. harzianum, T. longibrachiatum and
T. pseudokoningii
• Bacteriophage resistance : Erwinia amylovora – variations in sensitivity to bacteriophage.
Persistence and survival of biocontrol agents:
• Inadequate establishment and survival of biocontrol agents under field conditions.
• Microbial climax community resist invasion by introduced exogenous organism. Short time
persistence.
• Continued applications are necessary.
• Environmental factors influencing persistence of metabolites (toxins) produced by BCAs:
o Biotic – metabolites destroyed or exploited by plant/soil microbes
o Edaphic– metabolites adsorbed onto soil particles/inactivated due to soil chemistry
(e.g. pH)
o Climatic – metabolites inactivated by UV or heat, diluted by rain
Key elements for risk assessment of BCAs: The identity of the isolates- in particular their
relationships with human pathogens;
• The biological properties of the isolates- in particular their mode of action, the biotic and
abiotic factors determining the potential for persistence in the environment and for
reproduction, growth, or persistence in vertebrates;
• The quality assurance of the production process, specifically the control of the presence of
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