Fall 2024 Plant Pathology (PLP894) Seminar Series

November 25, 2024 1:30PM - 2:30PM

PSSB A271 Conference Room

River Dean (Hausbeck lab) Effects of Light Quality on Impatiens Downy Mildew: Strategies for Disease Suppression

Roberto G. Lopez, Jan M. Byrne and Mary K. Hausbeck

Downy mildew (DM) of Impatiens walleriana, caused by Plasmopara destructor, leads to chlorosis, defoliation, and significant crop losses. Current control includes fungicides and genetic resistance. We tested photoperiodic light treatments to limit DM and enhance plant quality in ‘Accent Premium White’ impatiens from seed sowing to flowering. The greenhouse was set to 23 °C with a daily light integral of 12 mol·m–2·d–1, and a 9-hour short-day (SD) photoperiod was created using blackout cloth. Nine treatments included the 9-hour SD control or SD extended by 7 hours of continuous LED light emitting blue (405 and 445 nm), green (525 nm), red (660 nm), far-red (730 nm), white (18:38:41:3 blue:green:red:far-red ratio), screw-in LED flowering lamps provided 100-nm waveband ratio (%) of 7.6:15:72.4:5, and UV-A (385 nm) was applied intermittently. The total photon flux density was adjusted to 20 µmol·m–2·s–1 at plant height. Impatiens were inoculated with P. destructor (2.6 to 3 x 104 sporangia·mL–1) at 70 days, and disease incidence was measured 9–11 days post inoculation. Across four trials (Dec 2023–May 2024), monochromatic lights suppressed disease incidence to 0% in some treatments while SD and white light showed minimal suppression.

In a parallel study, we plan to evaluate biological, reduced-risk, and OMRI-certified pesticides against P. destructor. Seeds will be sown in a greenhouse with temperature setpoints at 18 °C/21 °C, transplanted, and treated with conventional (Oxathiopiprolin or mono- and dibasic sodium, potassium, and ammonium phosphites) or OMRI-certified (cinnamon oil with garlic, potassium bicarbonate, hydrogen peroxide with peroxyacetic acid, Pseudomonas aeruginosa rhamnolipid biosurfactant, Bacillus mycoides isolate J, Bacillus amyloliquefaciens strain F727) products at 7- and 14-day intervals beginning 10 days prior to inoculation with P. destructor (2.5 to 3 x 104 sporangia·mL–1). Disease incidence will be rated 10 days post-inoculation.

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