1. Suppression of cucumber powdery mildew by UV-B is affected by background light quality
A. Suthaparan, A. Stensvand, K. A. Solhaug, S. Torre, K. H. Telfer, A. K. Ruud, L. Cadle-Davidson, L. M. Mortensen, D. M. Gadoury, R. C. Seem, H. R. Gislerød

2. Light & ultraviolet Light
Visible part of the electromagnetic spectrum to human eye
From 400 nm to 790 nm
Ultraviolet
Short wavelength part of the electromagnetic spectrum
Divided into
UV-A ( nm)
UV-B ( nm)
UV-C ( nm)
Vacuum UV ( nm)
200
Wavelength (nm)
400
600
800

3. Why light & ultraviolet?
Norway is situated in Northern Europe
Very low solar irradiance during winter months
Supplemental lighting is common practice
Photo - Unknown

4. Effect of red light on conidial release of rose powdery mildew (Plant Dis 94:1105-1110)

5. Effect of 5 min with UV-B applied in the dark period on severity of rose powdery mildew 9 d after inoculation (Plant Dis doi: RE)

6. Effect of UV-B if the short wavelength part was filtered out by cellulose diacetate (remove wavelengths below 295 nm)
Rose powdery mildew 9 d after inoculation (Plant Dis doi: RE)

7. Powdery mildew in cucumber
Three different pathogens can cause powdery mildew
Podosphaera xanthii (syn. Sphaerotheca fuliginea)
Golovinomyces cichoracearum (syn. Erysiphe cichoracearum)
Leveillula taurica

8. Spectral quality of radiation sources used in the experiments
Spectral width (nm)
Peak (nm)
UV-B
313
UV-A
340
Blue
450
Red
635

9. Effect of UV-B on cucumber powdery mildew

10. Effect of UV-B on severity of powdery mildew 9 d after inoculation

11. 0 min
5 min
15 min
10 min
Effect of UV-B on development of P. xanthii 6 d after inoculation

12. Effect of background light on efficiency of UV-B

13. 16 h W
16 h W +
UV-B
UV-A
UV-B +
Blue
UV-B + Blue
Red
UV-B +Red
Effect of background light on the efficiency of UV-B on cucumber powdery mildew; assessed at 3 d intervals over 12 d (bars = AUDPC)

14. Mechanisms of red light and UV-B
Indirectly via induced resistance
Directly upon the pathogen
Systemic induced resistance
Locally induced resistance
Presence of photoreceptors
UV-B induced DNA damage and its light dependent repair X X

15. Photoreceptor genes in powdery mildew fungi among classes of photoreceptors
UVR8
Phototropins
ZEITHLUPE
White collar
VIVID
Cryptochromes
Cry-DASH
Photolyase
Phy A-E
FPH 1, 2 and E
BPH
CBPH
BRh
BovR
Tryptophan
FAD/FMN
FAD
Retinal
Bilin

16. Increasing wavelength (nm)
Conclusion
The shortest wavelength part of UV-B ( nm) inhibits all developmental stages of powdery mildew
Orange red light ( nm) at low intensity reduces sporulation, at high intensity it also reduces colony growth
UV-A
Blue
Far-red
Increasing wavelength (nm)
400
600
200
800