Biological Control of Plant Pathogens PDF

BIOLOGICAL CONTROL OF PLANT PATHOGENS MECHANISMS OF BIOLOGICAL CONTROL Types of interspecies antagonism leading to biological control of plant pathogens: TYPE MECHANISM EXAMPLES Direct antagonism Hyperparasitism/ Lytic/some nonlytic...

BIOLOGICAL CONTROL OF PLANT PATHOGENS MECHANISMS OF BIOLOGICAL CONTROL Types of interspecies antagonism leading to biological control of plant pathogens: TYPE MECHANISM EXAMPLES Direct antagonism Hyperparasitism/ Lytic/some nonlytic predation mycoviruses Ampelomyces quisqualis Lysobacter enzymogenes Pasteuria penetrans Trichoderma virens Mixed-path Antibiotics 2,4-diacetylphloroglucinol antagonism Phenazines Cyclic lipopeptides Lytic enzymes Chitinases Glucanases Proteases Unregulated waste Ammonia products Carbon dioxide Hydrogen cyanide Types of interspecies antagonism leading to biological control of plant pathogens. TYPE MECHANISM EXAMPLES Mixed-path Physical/chemical Blockage of soil pores antagonism (cont.) interference Germination signals consumption Molecular cross-talk confused Indirect Competition Exudates/leachates antagonism consumption Siderophore scavenging Physical niche occupation Induction of host Contact with fungal cell walls resistance Detection of pathogen- associated, molecular patterns Phytohormone-mediated induction HYPERPARASITISM AND PREDATION  most direct form of antagonism  pathogen is directly attacked by a specific BCA that kills it or its propagules  4 Major Classes of Hyperparasites: 1. obligate bacterial pathogens (Pasteuria penetrans) 2. hypoviruses (dsRNA-mediated) 3. facultative parasites 4. predators HYPERPARASITISM AND PREDATION Pasteuria penetrans - a mycelial, endospore-forming, bacterial parasite that has shown great potential as a biological control agent of root-knot nematodes - spores adhere to the nematode cuticle (outer surface), infect the nematode and develop inside of the nematode body. HYPERPARASITISM AND PREDATION Hypoviruses - group of RNA viruses that infect the chestnut blight fungus Cryphonectria parasitica - reduce virulence (hypovirulence) of their pathogenic fungal host, providing the basis for their use as biological control agents ANTIBIOTIC-MEDIATED SUPPRESSION (mixed-path antagonism)  involves antibiotic secretion and the production of volatile antagonistic compounds  antibiotics are microbial toxins that can, at low concentrations, poison or kill other microorganisms A B  O OH O H 3C CH 3 HO OH Some of the antibiotics produced by BCAs ANTIBIOTIC SOURCE TARGET DISEASE PATHOGEN 2,4-diacetyl- Pseudomonas Pythium spp. Damping-off phloroglucinol fluorescens F113 Agrocin 84 Agrobacterium Agrobacterium Crown gall radiobacter tumefaciens Bacillomycin D Bacillus subtilis Aspergillus flavus Aflatoxin AU195 contamination Bacillomycin, Bacillus Fusarium Wilt fengycin amyloliquefaciens oxysporum FZB42 Xanthobaccin A Lysobacter sp. Aphanomyces Damping off cochlioides Gliotoxin Trichoderma virens Rhizoctonia solani Root rots Herbicolin Pantoea Erwinia Fire blight agglomerans C9-1 amylovora Some of the antibiotics produced by BCAs ANTIBIOTIC SOURCE TARGET PATHOGEN DISEASE Iturin A Bacillus subtilis Botrytis cinerea and Damping off QST713 Rhizoctonia solani Mycosubtilin Bacillus subtilis Pythium Damping off BBG100 aphanidermatum Phenazines Pseudomonas Gaeumannomyces Take-all fluorescens 2-79 graminis var. tritici and 30-84 Pyoluteorin, Pseudomonas Pythium ultimum and Damping off pyrrolnitrin fluorescens Pf-5 Rhizoctonia solani Pyrrolnitrin, Burkholderia Rhizoctonia solani and Damping off pseudane cepacia Pyricularia oryzae and rice blast Zwittermicin A Bacillus cereus Phytophthora Damping off UW85 medicaginis and Pythium aphanidermatum LYTIC ENZYMES AND OTHER BYPRODUCTS OF MICROBIAL LIFE  lytic enzymes can hydrolyze a wide variety of polymeric compounds, including chitin, proteins, cellulose, hemicellulose and DNA  Ex. Serratia marcescens produce chitinase which is effective against Sclerotium rolfsii COMPETITION  microorganism must effectively compete for available nutrients  production of siderophores is important for microorganisms which requires iron (an extremely limited micronutrient in the rhizosphere)  siderophores are iron-binding ligands with high affinity to sequester iron from the micro- environment  COMPETITION  Pseudomonas aeruginosa and P. fluorescens (from potato rhizosphere) – secrete hydroxamate siderophore, hydrocyanic acid, and IAA  against Fusarium oxysporum  INDUCTION OF HOST RESISTANCE  can be local and/or systemic in nature  induced resistance - physiological “state of enhanced defensive capacity” elicited by specific environmental stimuli, whereby the plant’s innate/basal defenses are potentiated against subsequent biotic challenges (van Loon et al., 1998)  elicitors stimulate the plant's active defenses before the pathogen is present… can also help strengthen passive defenses as well 2. SCREENING  ultimatesuccess of biocontrol depends on how well the searching and screening is done  “thereis no single, correct way to search or screen”  bothdepend on the target pathogen, the crop and the cropping system