Wavelength dependent recovery of UV-mediated damage: Tying up the loose ends of optical based powdery mildew management

Controlled environment chamber experiments at Petri dish level were conducted to examine the wavelength and dose dependent efficacy of ultraviolet (UV) radiation, the recovery action potential of optical radiation applied concomitantly/subsequently to effective UV treatment, and the lapse time between UV treatment and subsequent exposure to recovery wavelength on germination efficiency of Oidium neolycopersici conidia. Conidia of eight- to nine-day-old colonies were dusted on water agar surface in Petri dishes and exposed to UV treatments (without lid). Immediately after UV treatments, Petri dishes were sealed and incubated in darkness or differing optical environments generated using seven different radiation sources (range 290 nm to 780 nm). Twenty-four hours after UV treatment, fifty conidia from each sample were assessed for germination. Compared to non-UV controls, < 10% of the conidia germinated after 30 s of exposure to 254 nm or 283 nm UV and subsequent dark incubation. Conidia germination was almost negligible if the exposure duration increased to 4 min. Germination was about 60% with broad spectrum UV after 1 min of exposure, and about 35% after 2 to 4 min of exposure. There was no reduction of conidia germination with the exposure of ≤ 4 min with 310 nm. With the tested wavelength and dose ranges, germination recovery was effective in the 350 nm to 500 nm range. Germination efficiency of conidia treated with effective UV was significantly higher (> 73%) if incubated subsequently in the 350 nm to 500 nm range (germination recovery). Furthermore, germination recovery depends on the characteristics of UV treatment (wavelength, and duration of exposure) and the lapse time between UV treatment and subsequent exposure to optical radiation in the recovery range. The findings of this study provide key criteria for wavelength selection, combination and application time in the optical radiation range, enabling improved design of optical based management strategies against powdery mildews.