Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/19/2016
Publication Date: 12/22/2016
Citation: Janisiewicz, W.J., Takeda, F., Jurick II, W.M., Evans, B.E., Glenn, D.M., Camp, M.J. 2016. Use of low-dose UV-C irradiation to control powdery mildew caused by Podosphaera aphanis on strawberry plants. Canadian Journal of Plant Pathology. 38:430-439.
Interpretive Summary: Powdery mildew of strawberry plants is a fungal disease that can cause severe losses by reducing fruit yield and quality, and predisposing fruit to other diseases. Fungicides have been routinely used to control this disease. However, limitations mainly related to their effectiveness and a time required before re-entry of the field after application necessitate the development of alternative approaches, especially for protective culture and organic production. We have developed a strategy that combines treating strawberry plants with a low dose of ultraviolet light followed by a dark-period incubation. Darkness prevents light-induced repair of the fungal DNA that was damaged by the exposure to ultraviolet light, thus greatly increasing the lethality of this ultraviolet treatment. Treating plants with ultraviolet light twice a week for three weeks resulted in more than a four-fold reduction in fungus biomass on leaf surfaces. Leaf photosynthesis was not affected and fruit yield and quality increased. This approach may be a valuable alternative to synthetic fungicides.
Technical Abstract: Powdery mildew of strawberry plants, caused by Podoshaera aphanis, can cause severe losses by reducing fruit yield, quality and predisposing fruit to other diseases. Fungicides have been routinely used to control this disease. However, limitations mainly related to their effectiveness, re-entry period after application, and harmful effects on human health and the environment necessitate the development of alternative approaches, especially for protective culture and organic production. We have developed a strategy that combines treating strawberry plants with a low dose of UV-C (low dose/short duration) followed by a defined dark-period incubation. Darkness prevents activation of the light-induced DNA repair mechanism in fungal pathogens after damage from UV-C exposure and greatly increases the lethality of UV-C. A leaf disc assay was developed to quantitate the effectiveness of the UV-C treatment. Irradiation for only 15 sec by UV-C lamps with an output of 20.6 µW/cm2 followed by four hours of a dark period resulted in a significant decrease in P. aphanis viability as determined by infection incidence on the leaf discs. An increase in irradiation exposure to 60 sec resulted in complete killing of the fungus in most cases. Treating plants with this dose twice a week for three weeks resulted in more than a four-fold reduction of conidia on leaf surfaces exposed to the UV-C irradiation and did not affect leaf photosynthesis. The UV-C treatment of plants over 15 weeks reduced the amount of diseased fruit and increased fruit yield and quality. We demonstrated that UV-C treatment can greatly reduce strawberry powdery mildew even at low doses if irradiation treatment is followed by several hours on darkness. The control could be further improved by optimizing the positioning of lamps and/or using reflecting surfaces to irradiate the abaxial surface of the leaves simultaneously.