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Title: Baseline Sensitivity to Fluopicolide in Phytophthora Capsici Isolates from the Eastern United States

Author
item KEINATH, A - Clemson University
item FILLIPPELI, E - Clemson University
item HAUSBECK, M - Michigan State University
item Kousik, Chandrasekar - Shaker

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 12/1/2009
Publication Date: 6/1/2010
Citation: Keinath, A.P., Fillippeli, E., Hausbeck, M.K., Kousik, C.S. 2010. Baseline Sensitivity to Fluopicolide in Phytophthora Capsici Isolates from the Eastern United States. Phytopathology. 100:S201.

Interpretive Summary: N/A

Technical Abstract: Fluopicolide was registered in 2007 to control diseases caused by Oomycete pathogens such as Phytophthora capsici on cucurbits and peppers. In this study, 69 isolates of P. capsici from Michigan (24 isolates), South Carolina (17), Georgia (14), Florida (11), and North Carolina (3) recovered from watermelon (22), pepper (11), bean (10), squash (9), cucumber (6), or unknown hosts (11) were tested to determine their sensitivities to fluopicolide. In three assays, isolates were grown on V8 agar amended with technical grade fluopicolide dissolved in DMSO. For the mycelial growth assay, concentrations were 0, 0.03, 0.10, 0.30 and 1.0 mg/l. For the sporangia production assay, concentrations were 0, 0.03, 0.10, and 0.30 mg/l with a few isolates also tested at 0.01 mg/l. For the zoospore germination assay, isolates were initially tested at 0.10, 1.0, and 10.0 mg/l; some isolates then were tested at 0.03 or 31.6 mg/l. Percentage colony diameter, zoospore germination, and sporangia production relative to the nonamended control was regressed against the logarithm of fungicide concentration to calculate EC50 values. All isolates of P. capsici tested were sensitive to fluopicolide in all three assays. EC50 values for each assay were non-normally distributed. The median concentration was 0.28 (range 0.11 to 1.56), 0.04 (<0.01 to 0.14), and 2.08 (0.14 to 13.74) mg/l in the mycelial growth, sporangia production, and zoospore germination assays, respectively. The ratio between the least and most sensitive isolates was 14 for mycelial growth and sporangia production. For zoospore germination, the ratio was 98 across all isolates but ranged from 3 to 44 for isolates within states. For mycelial growth and zoospore germination, isolates from Michigan had a higher mean EC50 value than isolates from other states (P<0.05). Zoospore germination was much less sensitive and sporangia production was much more sensitive to fluopicolide than mycelial growth was.