Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: March 30, 2006
Publication Date: June 5, 2006
Citation: Locke, J.C., Omer, M.A., Widrig, A.K., Krause, C.R. 2006. Delay of expression of powdery mildew on zinnia grown hydroponically in Hoagland's solution fortified with silicon [abstract]. Phytopathology. 96(6):S70. Technical Abstract: Powdery mildew, caused by the fungus Erysiphe cichoracearum, is one of the most common foliar diseases that occur in greenhouse bedding plant production. Although powdery mildews are somewhat host specific, E. cichoracearum is reported to have a wide host range which includes the commonly grown bedding plants begonia, phlox, saliva, sunflower, verbena, and zinnia. Among these hosts, we have reported that begonia, verbena, and zinnia can accumulate silicon when grown in silicon-fortified hydroponic solution (1). Inoculation of zinnia (Z. elegans cv. ‘Oklahoma White’) grown hydroponically, with and without silicon, initially resulted in typical white, fuzzy powdery mildew growth on the upper leaf surfaces of silicon (-) plants. After an additional two days, minute colonies began developing on the silicon (+) plants. Disease progression occurred on plants of both treatments but the silicon (+) treatment never developed symptoms to the same degree as the silicon (-) treatment. This delayed expression of powdery mildew supports the report of reduced (delayed) black spot disease on rose (2) and supports a role for silicon in an active mechanism of defense within the host plant (3). Better understanding of the mechanism(s) involved in delayed expression could lead to new approaches for controlling this widespread greenhouse production problem.