Photo courtesy of James Cook What is a Disease suppressive soil? “Take-all decline”:...
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Photo courtesy of James Cook What is a Disease suppressive soil? “Take-all decline”: well-characterized example Take-all of wheat caused by Gaeumanomyces
Photo courtesy of James Cook What is a Disease suppressive
soil? Take-all decline: well-characterized example Take-all of
wheat caused by Gaeumanomyces graminis var. tritici
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Photo courtesy of James Cook Fumigated Fumigation eliminates
soil microorganisms that suppress the take-all pathogen
Fumigated
Slide 4
Infestation of soil with the take all pathogen Gaeumannomyces
graminis var. tritici Fumigated Pathogen Fumigated
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Biological control by soil microflora Biological control:
natural ecological processes that promote plant health Biological
control destroyed by fumigation
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Suppressive soils develop in the presence of the pathogen
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Suppressive soil Heat-treated (50 C) suppressive soil Conducive
soil Conducive soil amended with 10% suppressive soil Heat-treated
(80 C) suppressive soil Rhizoctonia suppressive soil:
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More evidence for the biological basis of the Rhizoctonia
suppressive soil
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The PhyloChip assay is a microarray-based method that
identifies and measures the relative abundance of more than 59,000
individual microbial taxa in any sample. This approach relies on
the analysis of the entire 16S ribosomal RNA gene sequence which is
present in every bacterial genome but varies in a way that provides
a fingerprint for specific microbial types.
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Detected 33,346 Operational taxonomic Units (OTUs)
Acidobacteria: discovered in 1997 (Acidobacterium, Solibacter)
Fermicutes: low GC Gram+ (Bacillus, Staph, Lactobacillus) From
bottom to top: Actinobacteria: highGC Gram+ (Streptomyces,
Rhodococcus, Clavibacter) This somehow shows that different taxa
were most abundant in the six different treatments
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Comparisons between Operational Taxonomic Units: A= OTUs in
greater abundance in suppressive soil than in conducive soil C =
OTUs in greater abundance in conducive soil amended with
suppressive soil than in non-amended conducive soil F = OTUs in
greater abundance in suppressive soil inoculated with the pathogen
R. solani
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The Proteobacteria and Firmicutes differ between
treatments
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Background: Antibiotics produced by Pseudomonas spp. are key
factors in biological control
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Conclusions Pathogen Host Environment Microorganisms, whether
indigenous or introduced are an important component of the
environment that influence plant disease. Suppressive soils are
examples of natural biological control. Using new methods for
characterizing microbial communities, Mendes et al. (2011)
identified groups of microorganisms present in a soil suppressive
to Rhizoctonia root rot. From the suppressive soil, they identified
a strain of Pseudomonas that can suppress Rhizoctonia root rot and
an antibiotic that contributes to biological control.