Location: Foreign Disease-weed Science ResearchTitle: Fungicide impact on in vitro germination of Basidiospores of Puccinia horiana, causal agent of Chrysanthemum white rust Author
Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2015
Publication Date: 4/7/2015
Citation: Palmer, C.L., Bonde, M.R., Nester, S.E., Revell, J.M., Luster, D.G. 2015. Fungicide impact on in vitro germination of Basidiospores of Puccinia horiana, causal agent of Chrysanthemum white rust. Plant Health Progress. 16(2):73-76. Interpretive Summary: Chrysanthemum White Rust (CWR) is a disease of Chrysanthemum that has caused economic hardship for growers in the U.S., particularly because the appearance of symptoms typically occurs during the peak fall season just as growers are preparing to ship their chrysanthemum crops. Diagnosis of CWR in a nursery triggers an eradication protocol combining destruction of symptomatic chrysanthemums and a strict fungicide regime for symptomless plants. Growers need additional fungicides to be identified and registered for use against CWR, and so we tested 14 fungicides for their ability to inhibit or kill CWR spores. We found several fungicides that were effective against spores of CWR, providing a baseline for future studies. Once further tests are conducted on live infected plants, and US regulatory agencies approve the most active fungicides for use against CWR, new fungicides will provide additional tools for growers in their efforts to manage the disease in their nurseries.
Technical Abstract: Puccinia horiana is an actionable pathogen, which upon diagnosis triggers an eradication protocol combining destruction of symptomatic chrysanthemums and a strict fungicide regime for symptomless plants. Appearance of symptoms typically occurs during the fall just as growers are preparing to ship their chrysanthemum crops. To expand the list of fungicide tools in the eradication protocol and develop fungicide sensitivity baselines, we screened in vitro germination of P. horiana basidiospores in 0.05 percent water agar solution amended with varying concentrations of 14 fungicides: azoxystrobin, boscalid + pyraclostrobin, fluoxastrobin, mancozeb, mandestrobin, metconazole, myclobutanil, propiconazole, tebuconazole, triadimefon, trifloxystrobin, trifloxystrobin + triadimefon, and triticonazole. Leaves with pustules ready to sporulate were affixed to petri plate lids over bases containing fungicide-amended agar. After 2 days in the dark, percent germination was assessed. Concentrations required for 50 percent germination (EC50) grouped according to fungicide mode of action class. Benzimidazole fungicides (FRAC 3) exhibited EC50s ranging from 9 to 244 ppm, while strobilurin fungicides (FRAC 11) ranged from 2 to 27 ppb. Mancozeb exhibited an EC50 of 7 ppm, and Daconil was 205 ppb. Combinations of FRAC 11 fungicides with other modes of action exhibited EC50s in the same range as the strobilurins. These data provide a baseline for monitoring resistance development to P. horiana over time.