WINE GRAPE RESPONSE TO KAOLIN PARTICLE FILM UNDER DEFICIT AND WELL-WATERED CONDITIONS

Abstract

Kaolin particle film was developed to reduce heat stress and improve water use efficiency in perennial fruit crops. A study was done to determine how the film impacts water relations of wine grape (I/ills vinijera L.) cultivars '%iognier' and Merlot' grown without rootstock in the high desert region of southwestern Idaho. Vines were either sprayed with kaolin or unsprayed (control) and either well- watered at 100% estimated crop evapotranspiration (ET,), or deficit-irrigated at 35% ET until veraison followed by 70% ET until harvest. As expected, kaolin reduced leaf temperature under both irrigation regimes. However, a reduction in stomatal conductance and less negative leaf water potential values for kaolin-treated vines were observed only under well-watered conditions. Lack of response to kaolin under deficit water conditions was probably due to a water-stress-induced increase in stomatal closure that was independent of leaf temperature. When leaf temperature difference between kaolin and non-kaolin sprayed leaves was at its daily maximum, deficit-irrigated vines had already reached their minimum or most negative values for stomatal conductance and leaf water potential, but values for well-watered vines had just begun to change. Kaolin had no effect on canopy total light interception, pruning weight, yield, berry titratable acidity or soluble solids concentration, though cluster weight of well-watered, kaolin-sprayed Viognier' was larger than well-watered non-kaolin 'Viognier' vines. The leaf water potential of 'Merlot' was more responsive to diurnal changes in vapor pressure deficit than 'Viognier' vet neither showed a response to foliar kaolin application under deficit irrigation. Better understanding of the mechanism by which kaolin film increases water use efficiency will provide insight as to the relative roles of plant hormones, evaporative demand, and plant water status on leaf gas exchange and facilitate determination of its potential for enhancing production efficiency of wine grapes in arid regions.