Suppression of Cucumber Powdery Mildew by Supplemental UV-B Radiation in Greenhouses Can be Augmented or Reduced by Background Radiation Quality

A Suthaparan; A Stensvand; K A Solhaug; S Torre; K H Telfer; A K Ruud; L M Mortensen; D M Gadoury; R C Seem; H R Gislerød

doi:10.1094/PDIS-03-13-0222-RE

Suppression of Cucumber Powdery Mildew by Supplemental UV-B Radiation in Greenhouses Can be Augmented or Reduced by Background Radiation Quality

Plant Dis. 2014 Oct;98(10):1349-1357. doi: 10.1094/PDIS-03-13-0222-RE.

Authors

A Suthaparan¹, A Stensvand², K A Solhaug³, S Torre⁴, K H Telfer⁴, A K Ruud⁴, L M Mortensen⁴, D M Gadoury⁴, R C Seem⁵, H R Gislerød⁴

Affiliations

¹ Department of Plant Sciences, Norwegian University of Life Sciences, 1432 Ås, Norway.
² Norwegian Institute for Agricultural and Environmental Research, Høgskoleveien 7, 1432 Ås, Norway.
³ Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, 1432 Ås, Norway.
⁴ Department of Plant Sciences, Norwegian University of Life Sciences.
⁵ Department of Plant Pathology and Plant-Microbe Biology, Cornell University, New York State Agricultural Experiment Station, Geneva, NY 14456.

PMID: 30703932
DOI: 10.1094/PDIS-03-13-0222-RE

Abstract

This study demonstrates that the spectral quality of radiation sources applied with ultraviolet-B (UV-B; background radiation) affects the suppression of cucumber powdery mildew (Podosphaera xanthii) by UV-B. Suppression provided by daily UV-B exposure of 1 W/m² for 10 min was greatest in the presence of red light or by a complete lack of background light, and powdery mildew suppression was least in the presence of ultraviolet-A (UV-A) or blue radiation compared with plants exposed only to 16 h of daily natural light supplemented with high-pressure sodium lamps that supply broad-spectrum radiation with peaks in the yellow-orange region. Exposure of powdery mildew-inoculated plants to supplemental red light without UV-B, beginning at the end of the daylight period, also reduced disease severity; however, supplemental blue light applied in the same fashion had no effect. Daily application of UV-B at 1 W/m² beginning on the day of inoculation significantly reduced the severity of powdery mildew to 15% compared with 100% severity on control plants. Maximum suppression of powdery mildew was observed following 15 min of exposure to UV-B (1.1% severity compared with 100% severity on control plants) but exposure time had to be limited to 5 to 10 min to reduce phytotoxicity. There was no additional disease suppression when plants were exposed to UV-B beginning 2 days prior to inoculation compared with plants exposed to UV-B beginning on the day of inoculation. UV-B inhibited germination, infection, colony expansion, and sporulation of P. xanthii. The results suggest that efficacy of UV-B treatments, alone or in combination with red light, against P. xanthii can be enhanced by exposure of inoculated plants to these wavelengths of radiation during the night, thereby circumventing the counteracting effects of blue light and UV-A radiation. The effect of UV-B on powdery mildew seemed to be directly upon the pathogen, rather than induced resistance of the host. Night exposure of plants to 5 to 10 min of UV-B at 1 W/m² and inexpensive, spectral-specific, light-emitting diodes may provide additional tools to suppress powdery mildews of diverse greenhouse crops.