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Research Project: Identification, Characterization, and Biology of Foreign and Emerging Viral and Bacterial Plant Pathogens

Location: Foreign Disease-weed Science Research

Title: Rathayibacter toxicus and bacterial head blight diseases of grasses

Author
item Murray, Timothy - Washington State University
item Schroeder, Brenda - University Of Idaho
item Schneider, William
item Luster, Douglas - Doug
item Sechler, Aaron
item Rogers, Elizabeth
item Subbotin, Sergei - University Of California

Submitted to: Phytopathology
Publication Type: Review Article
Publication Acceptance Date: 4/13/2017
Publication Date: 6/26/2017
Citation: Murray, T.D., Schroeder, B.K., Schneider, W.L., Luster, D.G., Sechler, A.J., Rogers, E.E., Subbotin, S.A. 2017. Rathayibacter toxicus and bacterial head blight diseases of grasses. Phytopathology. 107:804-815.

Interpretive Summary: Rathayibacter toxicus, a Select Agent in the United States, is one of six recognized species in the genus Rathayibacter. The Rathayibacter species are unusual among plant pathogenic bacteria in that they are transmitted by nematodes and produce yellow extracellular polysaccharide “slime” in infected plants, resulting in diseases with common names such as yellow slime and bacterial head blight. R. toxicus is distinguished from the other species by producing toxins in infected plants. These toxins cause grazing animals feeding on infected plants to develop ‘staggers,’ which often results in death and led to naming of the syndrome Annual Ryegrass Toxicity, which occurs only in parts of Australia. Rathayibacter toxicus is the only recognized Rathayibacter species to produce toxin, although anecdotal reports of livestock deaths in the USA suggest a closely related species that also produces a toxin may be present. A closely related but undescribed species in South Africa is also suspected of producing toxin. Many of the diseases caused by Rathayibacter species occur in arid areas and the slime they produce is believed to aid in their survival between crops. Similarly, the nematode associated with these bacteria form seed galls in infected plants and are capable of surviving for very long periods of time.

Technical Abstract: Rathayibacter toxicus, a Select Agent in the United States, is one of six currently recognized species in the genus Rathayibacter and the best known due to its association with Annual Ryegrass Toxicity (ARGT), which occurs only in parts of Australia. The Rathayibacter species are unusual among phytopathogenic bacteria in that they are transmitted by anguinid seed gall nematodes in the genera Anguina or Afrina and produce extracellular polysaccharides in infected plants resulting in bacteriosis diseases with common names such as yellow slime disease and bacterial head blight. R. toxicus is distinguished from the other species by producing corynetoxins in infected plants. These are neurotoxins causing grazing animals that feed on infected plants to develop ‘staggers’ that often result in death and led to naming of the syndrome ARGT. R. toxicus is the only recognized Rathayibacter species to produce toxin, although anecdotal reports of livestock deaths in the U.S. suggest a closely related toxigenic species may be present. Furthermore, a closely related but undescribed species, ‘R. woodi’, isolated from Ehrhata villosa var. villosa in South Africa, produces toxin in culture. Toxin production by R. toxicus is associated with infection by a bacteriophage and is lost when the bacterium is cultured in vitro. Many of the diseases caused by these Rathayibacter species occur in arid areas and the extracellular polysaccharide they produce is believed to aid in their survival between crops. Indeed, ‘R. agropyri’ was isolated from infected plant material after being stored for 50 years in a herbarium. Similarly, the anguinid vectors associated with these bacteria form seed galls in infected plants and are capable of surviving for very long periods of time.