Quantification of airborne spinach and lettuce downy mildew at three different ranches in California

Authors: Liu, Samuel; Anchieta, Amy; Clark, Kelley; CORRELL, JIM - University Of Arkansas; PLACELLA, SARAH - Root Applied Sciences; Klosterman, Steven

Submitted to: American Phytopathological Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/15/2023
Publication Date: 8/12/2023
Citation: Liu, S.S., Anchieta, A.G., Clark, K.J., Correll, J., Placella, S., Klosterman, S.J. 2023. Quantification of airborne spinach and lettuce downy mildew at three different ranches in California. American Phytopathological Society Annual Meeting, August 12-16, 2023, Denver, Colorado.

Interpretive Summary:

Technical Abstract: California accounts for about 70% of the nation's fresh spinach and lettuce production. Spinach and lettuce downy mildew are caused by obligate oomycete pathogens Peronospora effusa and Bremia lactucae, respectively, which are major diseases that severely reduce the market value of spinach and lettuce. Downy mildew is managed primarily by a combination of disease-resistant plant varieties and repeated applications of fungicides. In addition to the direct increase in economic costs caused by the frequent use of fungicides, these downy mildew pathogens can develop fungicide resistance and overcome plant-based resistance, which remains a great challenge to lettuce and spinach production. The purpose of this project is to increase our knowledge of the epidemiology of P. effusa and B. lactucae, and thus contribute to the improvement of integrated disease management strategies that do not mainly rely on repeated use of fungicides. Both P. effusa and B. lactucae are spread primarily by airborne sporangia. During this project, we deployed 8 cyclone spore traps initially in 2022 and 12 cyclone spore traps in 2023 in the spinach and lettuce fields of the Salinas valley to simultaneously detect sporangia of P. effusa and B. lactucae. Quantitative polymerase chain reaction (qPCR)-based assays were performed using conserved primers derived from the mitochondrial DNA to simultaneously detect P. effusa and B. lactucae spores. In ongoing work, spore load quantities are correlated with environmental conditions of precipitation, temperature, relative humidity and/or wind speed and direction. The findings, which will be discussed, are useful to forecast inoculum loads of these airborne pathogens to enable more judicious timing of fungicide application.