Effects of sunlight exposure on grapevine powdery mildew development

Phytopathology. 2012 Sep;102(9):857-66. doi: 10.1094/PHYTO-07-11-0205.

Abstract

Natural and artificially induced shade increased grapevine powdery mildew (Erysiphe necator) severity in the vineyard, with foliar disease severity 49 to 75% higher relative to leaves in full sun, depending on the level of natural shading experienced and the individual experiment. Cluster disease severities increased by 20 to 40% relative to those on check vines when ultraviolet (UV) radiation was filtered from sunlight reaching vines in artificial shading experiments. Surface temperatures of leaves in full sunlight averaged 5 to 8°C higher than those in natural shade, and in one experiment, filtering 80% of all wavelengths of solar radiation, including longer wavelengths responsible for heating irradiated tissues, increased disease more than filtering UV alone. In controlled environment experiments, UV-B radiation reduced germination of E. necator conidia and inhibited both colony establishment (hyphal formation and elongation) and maturity (latent period). Inhibitory effects of UV-B radiation were significantly greater at 30°C than at 20 or 25°C. Thus, sunlight appears to inhibit powdery mildew development through at least two mechanisms, i.e., (i) UV radiation's damaging effects on exposed conidia and thalli of the pathogen; and (ii) elevating temperatures of irradiated tissues to a level supraoptimal or inhibitory for pathogen development. Furthermore, these effects are synergistic at temperatures near the upper threshold for disease development.

MeSH terms

  • Ascomycota / drug effects*
  • Ascomycota / physiology*
  • Plant Diseases / microbiology*
  • Plant Leaves / microbiology
  • Plant Leaves / radiation effects
  • Sunlight*
  • Time Factors
  • Ultraviolet Rays
  • Vitis / microbiology*