Among soil microorganisms, bacteria and fungi and to a lesser extent actinomycetes, have received considerable attention as
biocontrol agents of soil-borne fungal plant pathogens and as plant growth promoters. Within actinomycetes, Streptomyces spp. have
been investigated predominantly, mainly because of their dominance on, and the ease of isolation from, dilution plates and because of the
commercial interest shown on the antibiotics produced by certain Streptomyces spp. Many of non-streptomycete actinomycetes (NSA)
taxa are therefore rarely reported in literature dealing with routine isolations of biocontrol agents and/or plant growth promoters from
plant and soil. It is clear that special isolation methods need to be employed in routine isolations to selectively isolate NSA. Some
interesting information exists, albeit in relatively few reports compared to that on other microorganisms, on the biological activities of
NSA, especially in relation to their mechanisms of action in the biological control of soil-borne fungal plant pathogens and plant growth
promotion. This review presents an overview of this information and seeks to encourage further investigations into what may be
considered a relatively unexplored area of research. Certain soil environmental factors, especially in horticultural systems, could be
manipulated to render the soil conducive for the biological activities of NSA. A variety of NSA isolated by selective methods have not
only shown to be rhizosphere competent but also adapted for an endophytic life in root cortices. Some of the NSA, including endophytic
strains that have shown potential to suppress soil-borne fungal plant pathogens, are able to employ one or more mechanisms of
antagonism including antibiosis, hyperparasitism and the production of cell-wall degrading enzymes. Strains of NSA promote plant
growth by producing plant growth regulators. Enhancement of plant growth by the antagonists are considered to help the host by
producing compensatory roots that mask the impact of root diseases.
Among soil microorganisms, bacteria and fungi and to a lesser extent actinomycetes, have received considerable attention asbiocontrol agents of soil-borne fungal plant pathogens and as plant growth promoters. Within actinomycetes, Streptomyces spp. havebeen investigated predominantly, mainly because of their dominance on, and the ease of isolation from, dilution plates and because of thecommercial interest shown on the antibiotics produced by certain Streptomyces spp. Many of non-streptomycete actinomycetes (NSA)taxa are therefore rarely reported in literature dealing with routine isolations of biocontrol agents and/or plant growth promoters fromplant and soil. It is clear that special isolation methods need to be employed in routine isolations to selectively isolate NSA. Someinteresting information exists, albeit in relatively few reports compared to that on other microorganisms, on the biological activities ofNSA, especially in relation to their mechanisms of action in the biological control of soil-borne fungal plant pathogens and plant growthpromotion. This review presents an overview of this information and seeks to encourage further investigations into what may beconsidered a relatively unexplored area of research. Certain soil environmental factors, especially in horticultural systems, could bemanipulated to render the soil conducive for the biological activities of NSA. A variety of NSA isolated by selective methods have notonly shown to be rhizosphere competent but also adapted for an endophytic life in root cortices. Some of the NSA, including endophyticstrains that have shown potential to suppress soil-borne fungal plant pathogens, are able to employ one or more mechanisms ofantagonism including antibiosis, hyperparasitism and the production of cell-wall degrading enzymes. Strains of NSA promote plantgrowth by producing plant growth regulators. Enhancement of plant growth by the antagonists are considered to help the host byproducing compensatory roots that mask the impact of root diseases.
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