Use of uv light for suppression of grapevine diseases

Abstract

Context and purpose of the study – Microbial pathogens of plant have evolved to sense, interpret, and use light to direct their development. One aspect of this evolved relationship is photolyase-mediated repair of UV-induced damage to pathogen DNA. Application of germicidal UV (UV-C) at night circumvents the blue light-driven repair of pathogen DNA and allows non-phytotoxic doses of UV-C to suppress a variety of pathogenic microbes and even certain arthropod pests without damage to vines or fruit. Lamps arrays have been designed specifically for the canopy architecture of grapevines and have been deployed on both tractor-drawn and robotic carriages for partial to near-complete suppression of powdery mildew (Erysiphe necator), sour rot (fungal, bacterial, and arthropod complex), and downy mildew (Plasmopara viticola).

Material and methods – Low-pressure discharge UV-C lamps (Osram HNS G13 55W UV-C, peak 253.7 nm, FWHM < 5nm) were used in both laboratory and vineyard studies over a 4-yr period in New York on Vitis vinifera ‘Chardonnay’ and the Vitis interspecific hybrid cultivar ‘Vignoles’. Detached leaves inoculated with conidia of E.necator or sporangia of P. viticola were exposed during darkness to UV-C at 25 to 200 J/m². In addition to laboratory studies, Chardonnay and Vignoles grapevines were exposed to weekly or twice-weekly nighttime applications of UV-C at 70 to 200 J/m². For vineyard applications, the lamps were borne in a hemicylindrical array backed by polished aluminum reflectors. The front and back of the array was fitted with reflectorized curtains to provide additional reflectance angles and improved canopy penetration.  Arrays were moved through the vineyards using either tractor-drawn or autonomous robotic carriages.  Several physiological and physical responses of the grapevines were monitored on UV-treated and non-UV-treated vines.

Results – Twice-weekly nighttime applications of UV-C at 200 J/m² provided consistent suppression of powdery mildew in high-inoculum Chardonnay research vineyards. In lower inoculum commercial Chardonnay vineyards, 200 J/m² applied weekly at night was sufficient to suppress powdery mildew to trace levels. No rate or frequency of UV-C provided significant suppression of downy mildew on Chardonnay (highly susceptible), but twice-weekly nighttime applications of UV-V at 200 J/m² suppressed downy mildew on Vignoles (moderately susceptible) by 75% compared to untreated control vines. Consistent suppression of sour rot was obtained by weekly to twice-weekly nighttime applications of UV-C at 200 J/m². UV-C applications produced no deleterious effects as indicated by 20 metabolic responses, as well as measurements of berry size, berry number per cluster, berry weight, cluster weight, yield per ha, fruit soluble solids, leaf size, leaves per shoot, and shoot length. Preliminary data indicate minimal persistent effects of nighttime UV-C applications on epiphytic microflora.