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Photo courtesy of James Cook

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

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  1. Photo courtesy of James Cook What is a Disease suppressive soil? “Take-all decline”: well-characterized example Take-allof wheat caused by Gaeumanomycesgraminisvar. tritici

  2. Photo courtesy of James Cook Fumigation eliminates soil microorganisms that suppress the take-all pathogen Fumigated Fumigated Fumigated

  3. Infestation of soil with the take all pathogen Gaeumannomycesgraminisvar.tritici Fumigated Fumigated Pathogen Fumigated

  4. Biological control: natural ecological processes that promote plant health Biological control by soil microflora Biological control destroyed by fumigation

  5. Suppressive soils develop in the presence of the pathogen

  6. 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

  7. More evidence for the “biological basis” of the Rhizoctonia suppressive soil

  8. “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.”

  9. 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

  10. 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

  11. The Proteobacteria and Firmicutes differ between treatments

  12. Background: Antibiotics produced by Pseudomonas spp. are key factors in biological control

  13. Pathogen Host Environment Conclusions • 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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