natural-products-in-plant-pest-management

12 Suppressive Effectsof Compost Teaon PhytopathogensMILA SANTOS, FERNANDO DIÁNEZAND FRANCISCO CARRETEROPlant Production Department, University of Almería, Almería, SpainAbstractSuppression of soilborne and airborne diseases of horticultural crops by compost hasbeen attributed to the activities of antagonistic microorganisms. A great diversity ofbiological control agents naturally colonize compost. The knowledge of mechanismsfor biological control through the action of compost or its water extracts (compost tea)is necessary in order to increase the efficiency of the suppressing power. Modes ofaction of biocontrol agents include: inhibition of the pathogen by antimicrobial compounds(antibiosis), competition for iron through production of siderophores, competitionfor colonization sites and nutrients supplied by seeds and roots, induction ofplant resistance mechanisms, inactivation of pathogen germination factors present inseed or root exudates, degradation of pathogenicity factors of the pathogen such astoxins, parasitism that may involve production of extracellular cell wall-degradingenzymes, for example, chitinase and β-1,3 glucanase that can cause lysis of pathogencell walls. None of the mechanisms are necessarily mutually exclusive and frequentlyseveral modes of action are exhibited by a single biocontrol agent. Indeed, for somebiocontrol agents, different mechanisms or combinations of mechanisms may beinvolved in the suppression of different plant diseases. The healthy development ofplants, as well as the biological control of soilborne fungi, originates from manymicroorganisms, partly due to the production of siderophores under iron-restrictingconditions. The siderophores are natural chelators that keep iron available for plantsin soil. Iron also plays a major role in nutrient competition among pathogens andbeneficial microorganisms in infection sites.12.1 IntroductionSuppressive soils or suppressive substrates are characterized by a very lowlevel of disease development even though a virulent pathogen and susceptiblehost are present. Biotic and abiotic elements of the soil environment contributeto suppressiveness; however, most defined systems have identified biologicalelements as primary factors in disease suppression. Many soils possess© CAB International 2011. Natural Products in Plant Pest Management242 (ed. N.K. Dubey)