Submitted to: American Journal of Enology and Viticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 14, 2012
Publication Date: June 1, 2013
Citation: Shellie, K., King, B.A. 2013. Kaolin-based foliar reflectant and water deficit influence Malbec leaf and berry temperature, pigments, and photosynthesis. American Journal of Enology and Viticulture. 64:223-230. Interpretive Summary: Heat stress, high solar radiation and water deficit limit production of many horticultural crops in arid climates. Reflective foliar films have been used on many crops to provide thermal protection and to enhance water use efficiency. Warming trends in wine grape production regions have been associated with low color development in red wine grapes and delayed harvest for color development is often accompanied by undesirable high sugar content and high potential alcohol. The objective of this study was to relate the decrease in leaf and berry surface temperature provided by a kaolin-based foliar film to changes of commercial interest in the red-skinned wine grape cultivar Malbec. Vines of Malbec were either spayed with particle film or left untreated and irrigated with a standard or reduced amount of water over three growing seasons. Particle film increased the reflectance of UV-A and visible light from the surface of leaves by 2 to 10-fold and decreased leaf and berry surface temperatures. The decrease in temperature was greatest in vines under reduced irrigation. Particle film increased the ratio of color to sugar in the berry at harvest in two out of three years and did not affect yield components. Leaves with particle film had lower rates of photosynthesis and a change in leaf pigments that was similar to leaves maintained under shade conditions. Results demonstrated that foliar particle film can enhance the color of Malbec berries under warm, arid conditions with high solar radiation.
Technical Abstract: The effects of a kaolin-based foliar reflectant on traits of commercial interest in the red-skinned wine grape cultivar Malbec (Vitis vinifera L.) were evaluated over three growing seasons by measuring the surface temperatures of leaves and clusters, leaf-level assimilation, leaf and berry pigment composition and yield of vines grown under differing severities of water deficit with and without a foliar coating of particle film. Particle film increased the concentration of total monomeric anthocyanins in each year and the ratio of anthocyanins to soluble solids at harvest in two out of three years. The particle film did not alleviate differences in anthocyanin concentration between east and west-exposed clusters. Particle film decreased the surface temperature of leaves by a greater amount than of clusters, and decreases were greatest in vines under reduced irrigation. Leaves with particle film had lower mid-morning rates of assimilation, a lower chlorophyll-a to chlorophyll-b ratio, and a higher ratio of chlorophylls to carotenoids than leaves without particle film. Decreased assimilation was unrelated to the magnitude of leaf reflectance of visible light. Particle film did not affect yield components or fruit maturity, indicating that net primary productivity was sufficient to ripen fruit to maturity. These results demonstrate that foliar particle film can facilitate the accumulation of anthocyanins in deficit-irrigated Malbec under warm, arid conditions with high solar radiation.