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ARS Home » Pacific West Area » Davis, California » Crops Pathology and Genetics Research » Research » Publications at this Location » Publication #327527
Title: A faster infection assay for Armillaria using Herbaceous plants

Author
item FORD, KATHRYN - University Of Bristol
item HENRICOT, BEATRICE - Royal Horticultural Society
item Baumgartner, Kendra
item BAILEY, ANDREW - University Of Bristol
item FOSTER, GARY - University Of Bristol

Submitted to: Journal of Horticultural Science and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2016
Publication Date: 8/31/2016
Citation: Ford, K.L., Henricot, B., Baumgartner, K., Bailey, A.M., Foster, G.D. 2016. A faster infection assay for Armillaria using Herbaceous plants. Journal of Horticultural Science and Biotechnology. Doi:10.1080/14620316.2016.1223528.

Interpretive Summary: Armillaria (commonly known as the honey fungus) causes Armillaria root disease, which rots away the woody roots and ultimately kills the infected plant (aka host). In the laboratory, when testing which plants are most resistant to infection, there are frequent problems with the inoculum dying before a plant becomes infected or with infection progressing so slowly that symptoms of the disease do not appear. We have developed and evaluated a faster inoculation assay for Armillaria that uses herbaceous plants as hosts, is carried out in controlled conditions and reduces experimental durations to three months. Plant species of known susceptibility to Armillaria and comparisons between a very aggressive Armillaria species (A. mellea) and a weak species (A. gallica) were used to validate the assay. The percentage of dead plants and sypmtomatic plants were used to assess levels of infection. We also attempted to reduce assay preparation time by substituting woody inocula with agar inocula, but typical symptoms of Armillaria root disease were only observed on plants infected with woody inocula. Through our assay, we identified five new potential herbaceous hosts of Armillaria: Torchlily (Kniphofia hirsuta), Barley (Hordeum vulgare), Cardinal flower (Lobelia cardinalis), Tobacco (Nicotiana tabacum), and Orange helenium (Helenium hoopesii) – further expanding the extensive list of plants with susceptibility to Armillaria and suggesting infection of herbaceous species may be more widespread than currently acknowledged.

Technical Abstract: Armillaria (honey fungus) is a virulent necrotrophic pathogen that causes Armillaria root disease. Conventional Armillaria inoculation assays use young saplings as hosts and consequently are cumbersome, frequently conducted outdoors and take many years from establishment to analysis of infection. We have developed and evaluated a faster inoculation assay for Armillaria that uses herbaceous plants as hosts, is carried out in controlled conditions and reduces experimental durations to three months. Plant species of known susceptibility to Armillaria and comparisons between virulent A. mellea and opportunistic A. gallica were used to validate the assay. Mortality and diagnostic symptoms of Armillaria root disease such as epiphytic rhizomorphs and mycelial fans were used to assess levels of infection. We also attempted to reduce assay preparation time by substituting woody inocula with agar inocula, but typical symptoms of Armillaria root disease were only observed on plants infected with woody inocula. Through our assay, we identified five new potential herbaceous hosts of Armillaria: Kniphofia hirsuta, Hordeum vulgare, Lobelia cardinalis, Nicotiana tabacum and Helenium hoopesii – further expanding the extensive list of plants with susceptibility to Armillaria and suggesting infection of herbaceous species may be more widespread than currently acknowledged.