Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: May 4, 2009
Publication Date: August 1, 2009
Citation: Olanya, O.M., Honeycutt, C.W., Larkin, R.P., He, Z., Halloran, J.M. 2009. Fungicide effects on different spore types of Phytophthora infestans. (abstract) American Phytopathological Society annual meeting. p.741. Technical Abstract: Fungicide application is a widely used strategy for management of late blight of potato, caused by Phytophthora infestans. Assessment of pathogen sensitivity to fungicidal compounds is important for ensuring effective late blight control, long-term efficacy and low risk of resistance development. We assessed in-vitro growth of P. infestans isolates from divergent genotypes based on allozyme analysis on Rye-B media amended with chlorothalonil, mancozeb and cymoxanil at concentrations of 0, 10, 100 and 1000 ppm. Sporangia and zoospore germination, and oospore production potential of pathogen isolates were also determined. Significant differences (P<0.05) in hyphal growth were detected among pathogen isolates, and varied with fungicide treatments and concentrations. Mean colony growth of isolates on media ranged from 0.7-6.9 cm after 16 days of incubation at 18 C. Sporangia germination varied among pathogen isolates and fungicides, ranging from 0 to 30%. Zoospore germination and oospore production potential were greatly inhibited on fungicide amended media at concentrations exceeding 100 ppm. Laboratory studies indicate over 85% inhibition of P. infestans spore germination and growth with chlorothalonil regardless of fungicide concentration. These studies indicate that fungicidal compounds with multi-site modes of action are relatively effective on different spore types of P. infestans.