Submitted to: Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2012
Publication Date: 5/3/2013
Citation: Kwak, Y., Weller, D.M. 2013. Take-all of Wheat and Natural Disease Suppression: A Review. Journal of Plant Pathology. 29:125-135. Interpretive Summary: Biological control is the application or stimulation of antagonistic microorganisms for the control of plant pathogens. Some of the most effective biocontrol agents of soilborne pathogens are Pseudomonas bacteria that produce antifungal metabolites. Take-all is the most important root disease of wheat worldwide and there is no resistance in commercial varieties and chemical treatments are only effective during the seedling phase of the diseases. Biological control is the best alternative for controlling this disease. This review focuses on the biology of take-all and biological control of the disease by both naturally occurring introduced biocontrol agents. It reviews research that show how beneficial soil bacteria are enriched and recruited by roots under attack by soilborne pathogens in order to help the roots fend off the attack.
Technical Abstract: In agro-ecosystems worldwide, some of the most important and devastating diseases are caused by soil-borne necrotrophic fungal pathogens, against which crop plants generally lack genetic resistance. However, plants have evolved approaches to protect themselves against pathogens by stimulating and supporting specific groups of beneficial microorganisms that have the ability to protect either by direct inhibition of the pathogen or by inducing resistance mechanisms in the plant. One of the best examples of protection of plant roots by antagonistic microbes occurs in soils that are suppressive to take-all disease of wheat. Take-all, caused by Gaeumannomyces graminis var. tritici, is the most economically important root disease of wheat worldwide. Take-all decline (TAD) is the spontaneous decline in incidence and severity of disease after a severe outbreak of take-all during continuous wheat or barley monoculture. TAD occurs worldwide, and in the United States and The Netherlands it results from a build-up of populations of 2,4-diacetylphloroglucinol (2,4-DAPG)-producing fluorescent Pseudomonas spp. during wheat monoculture. The antibiotic 2,4-DAPG has a broad spectrum of activity and is especially active against the take-all pathogen. Based on genotype analysis by repetitive sequence-based-PCR analysis and restriction fragment length polymorphism of phlD, a key 2,4-DAPG biosynthesis gene, at least 22 genotypes of 2,4-DAPG producing fluorescent Pseudomonas spp. have been described worldwide. In this review, we provide an overview of G. graminis var. tritici, the take-all disease, Pseudomonas biocontrol agents, and mechanism of disease suppression.