Submitted to: Journal of Plant Pathology
Publication Type: Abstract Only
Publication Acceptance Date: 6/20/2008
Publication Date: 8/20/2008
Citation: Thomashow, L.S., Mavrodi, D., Mavrodi, O., Bonsall, R., Paulitz, T.C., Okubara, P.A., Schroeder, K.L., Quak, Y., Weller, D.M. 2008. Biology, biological control and molecular genetics of root diseases of wheat and barley. Plant Pathology. S(2).18.
Technical Abstract: Root diseases cause billions of dollars annually in losses to cereal growers. Resistance to foliar diseases is common, but resistance to root diseases is rare. Soilborne pathogens of cereals are managed through crop rotation, tillage, and chemical seed treatments. However, plants also defend themselves by supporting rhizosphere microorganisms antagonistic to soilborne pathogens. One of the best examples of natural root defense is the spontaneous decline during monoculture of take-all of wheat or barley caused by Gaeumannomyces graminis var. tritici. Take-all decline results from the buildup of strains of Pseudomonas fluorescens that produce the antibiotic 2,4-diacetylphloroglucinol (DAPG). The robustness of this suppressiveness appears to be modulated by the genotype of the DAPG producer, the wheat variety, and the sensitivity of the pathogen to DAPG. Strains of Pseudomonas that produce phenazine antibiotics are abundant in the Pacific Northwest of the USA where cereals are grown under low rainfall, and these strains may be involved in the suppression of root diseases other than take-all. Pseudomonads involved in natural suppression are excellent biocontrol agents and the basis of recombinant strains with enhanced biocontrol activity. The introduction of genes encoding the phenazine biosynthetic pathway into the DAPG producer P. fluorescens Q8r1-96, a highly aggressive root colonizer of wheat and barley, resulted in enhanced control of Rhizoctonia root rot. Real-time PCR assays have made it possible to rapidly determine the inoculum density of soilborne pathogens and the population densities of natural microbial antagonists, giving growers new tools to manage root diseases.