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Submitted to: Frontiers in Veterinary Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 1/12/2016 Publication Date: 1/27/2016 Citation: Kagan, I. 2016. Blackpatch of clover, cause of slobbers syndrome: A review of the disease and the pathogen, Rhizoctonia leguminicola. Frontiers in Veterinary Science. doi: 10.3389/fvets.2016.0003. Interpretive Summary: Rhizoctonia leguminicola is the current name for the causal agent of blackpatch disease of red clover. This article reviews current knowledge about the host range, symptomology, taxonomy, and pathogenicity of blackpatch, caused by the fungal pathogen Rhizoctonia leguminicola. An overview is provided of the alkaloids produced by the pathogen, and the effects on animals consuming the alkaloids. Past and future methods of disease management are discussed as well. R. leguminicola produces alkaloids (slaframine and swainsonine). Slaframine causes livestock to salivate profusely, and swainsonine may contribute to some of the nervous behaviors exhibited in livestock after ingestion of infected forage. The fungal pathogen, which also infects other legumes, is difficult to identify in the field because its mycelium resembles normal red clover pubescence. Symptoms include dark circular lesions on leaves and stems. Although the blackpatch fungus was classified as a Rhizoctonia species, sequencing data have indicated that it may be an Ascomycete, and morphological studies indicate that it is Botrytis fabae Sardina. The fungus has been grown on many different kinds of media. Plants have to be inoculated with mycelium because no spores are produced. Past methods of disease management have included seed treatments and fungicides, which have been relatively ineffective. Searches for resistant cultivars have been limited but have shown variation in susceptibility. Future disease management efforts should include studies of resistance in a greater number of cultivars, with quantification of inoculum density. Gathering data on environmental conditions at the time of outbreaks may enable modeling of conditions most likely to lead to outbreaks, which could enable livestock and forage producers to know when to look out for the disease. Technical Abstract: Rhizoctonia leguminicola Gough and E.S. Elliott is a widely used name for the causal agent of blackpatch disease of red clover (Trifolium pratense L.), which infects other legumes as well. This fungal pathogen produces alkaloids (slaframine and swainsonine) that affect grazing mammals. Slaframine causes livestock to salivate profusely, and swainsonine causes neurological problems. Although the blackpatch fungus was classified as a Rhizoctonia species (phylum Basidiomycota), morphological studies have indicated that it is in the phylum Ascomycota, and sequencing data have indicated that it is a new genus of ascomycete. The effects of the alkaloids on grazing mammals, and their biosynthetic pathways, have been extensively studied. Less work has been done on management of blackpatch disease, which requires a greater understanding of the pathogen. Methods of disease management have included seed treatments and fungicides, but these have not been investigated since the 1950s. Searches for resistant cultivars have been limited. This review summarizes the biological effects and biosynthetic precursors of slaframine and swainsonine. Emphasis is placed on current knowledge about the epidemiology of blackpatch disease and the ecology and taxonomy of the pathogen. Possibilities for future research and blackpatch disease management efforts are suggested. |
