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Photo courtesy of James Cook. What is a Disease suppressive soil? “T ake-all decline”: well-characterized example Take-all of wheat caused by Gaeumanomyces graminis var. tritici. Photo courtesy of James Cook. Fumigation eliminates soil microorganisms that

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Photo courtesy

of James Cook

What is a Disease suppressive soil?

“Take-all decline”: well-characterized example

Take-allof wheat caused by Gaeumanomycesgraminisvar. tritici

Photo courtesy

of James Cook

Fumigation eliminates soil microorganisms that

suppress the take-all pathogen




Infestation of soil with the take all pathogen






Biological control: natural ecological processes

that promote plant health

Biological control

by soil microflora

Biological control

destroyed by


Suppressive soils develop in the presence of the pathogen

Rhizoctonia suppressive soil:

Heat-treated (80 C) suppressive soil

Conducive soil

Conducive soil amended with 10% suppressive soil

Heat-treated (50 C) suppressive soil

Suppressive soil

More evidence for the “biological basis” of the

Rhizoctonia suppressive soil

“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.”

Detected 33,346

“Operational taxonomic

Units” (OTUs)

Fermicutes: low GC Gram+

(Bacillus, Staph, Lactobacillus)

Actinobacteria: highGC Gram+

(Streptomyces, Rhodococcus, Clavibacter)

Acidobacteria: discovered in 1997

(Acidobacterium , Solibacter)

From bottom to top:

This somehow shows that

different taxa were most abundant

in the six different treatments

Comparisons between Operational Taxonomic Units:

A= OTUs in greater abundance in suppressive soil than in conducive soil

F = OTUs in greater abundance in suppressive soil inoculated with the pathogen R. solani

C = OTUs in greater abundance in conducive soil amended with suppressive soil than in non-amended conducive soil

The Proteobacteria and Firmicutes differ between treatments


Antibiotics produced by Pseudomonas spp.

are key factors in biological control





  • 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.

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