Effects of kaolin-based particle film and fruit zone netting on Cabernet Sauvignon grapevine physiology and fruit quality

摘要

Aims: Long exposure to high temperatures or UV-radiation may induce negative effects on vine physiology and grape composition. Here, the effects of two methods to moderate radiation and temperature in the fruit zone of a Cabernet Sauvignon vineyard were evaluated against a control.Methods and results: The treatments assessed were: (a) periodical spraying of kaolin on leaves and bunches and (b) fruit zone netting with a Raschell’s type mesh. The kaolin-based treatment increased the reflectance of light and moderately reduced fruit temperature (~1oC below the control), whilst the shading net caused a significant reduction in radiation and temperature in the fruit zone (~7oC below the control). The Net treatment showed lower (more negative) stem water potential values than the control, but did not persist until the end of the trial. Also, none of the treatments led to significant changes in stomatal conductance, transpiration or CO2 assimilation throughout the season. However, the incidence and severity of fruit dehydration was significantly lower in the treated plants compared to the control. Finally, no differences in fruit chemical composition were observed between the treatments and the control.Conclusion: Under the conditions of this trial, both treatments tested were sufficient in moderating the negative effects of excess radiation or high temperature on grape berries.Significance and impact of the study: Kaolin-based particle spraying and fruit zone netting were proved to be feasible practical alternatives to lessen the negative effects of excess radiation or high temperature on grape berries, under hot climate. IntroductionSolar radiation and temperature are essential for vine metabolism and are known to affect grape composition, yet can be harmful when in excess (Bergqvist et al., 2001; Spayd et al., 2002). Although difficult to assess independently from temperature, moderate amounts of photosynthetically active radiation (PAR) in the fruit zone (≤ 100 mmol m-2 s-1) have been correlated with increased soluble solids and phenolics, and reduced titratable acidity and malic acid (Bergqvist et al., 2001; Dokoozlian and Kliewer, 1996). Conversely, higher PAR values are linked with more transpiration and fruit dehydration, coupled with reductions in berry mass and size (Bergqvist et al., 2001). Furthermore, if either radiation or temperature is excessive, tissue damage could be observed (Dokoozlian and Kliewer, 1996; Spayd et al., 2002).To date, several practices have been used to moderate the effects of excessive radiation or temperature in wine grapes, including canopy management and the use of shading nets. These practices have also been reported to reduce plant temperature, soluble solids, anthocyanin accumulation, and stomatal conductance (Chorti et al., 2010; Iacono et al., 1995; Lobos et al., 2009 and 2012). As these practices can be labor consuming, the use of alternatives such as reflective particle films might be interesting. The most common material used for this purpose is kaolin, a white clay based on layered aluminum silicate, capable of leaving a thin deposit on the surface of the fruit, thus allowing an upsurge in light reflectance (Yazici and Kaynak, 2009). In apple trees, where fruit color development requires direct sunlight, the practice of spraying kaolin-based sunscreens has become a common way to reduce sunburn (Glenn et al., 2002). In grapes, however, the adoption of this technique has been slower. In fact, there are only a few papers in which this kind of product has been tested, focusing mainly on its protective effect against pests and diseases, and the combined effect with deficit irrigation on fruit composition (by Glenn et al., 2010; Ou et al., 2010; Shellie and Glenn, 2008; Song et al., 2012; Tubajika et al., 2007).Based on this knowledge gap, and considering that several studies have reported and projected rises in incident radiation and temperatures for various wine producing regions (Jones et al., 2005; Moriondo et al., 2013) as a consequence of climate change, the aim of this project was to evaluate and compare the effects of a kaolin-based sunscreen and a fruit zone netting on selected physiology and fruit quality variables of Cabernet Sauvignon grapevines.Materials and methods1. Plant material and experimental set upThe study was carried out during 2011/2012, in a Cabernet Sauvignon vineyard (35° 06' S, 71o 20' W, 230 m.a.s.l., Maule Region, Chile) established in 1994 under a 3x1.5 m frame, with a North-South orientation, trained in a vertical-shoot-positioned system and drip irrigated (drippers ~4 L h-1). The climate is Mediterranean, with an average rainfall of 676 mm per year, and diurnal temperatures during fruit ripening between 3.3 and 29.4oC. Meteorological data of season 2011–2012 is given in Table 1. The soil is sedimentary, dark brown, with texture ranging from loamy-sand to silty clay-loam soil, and a depth of root-growth of 0.6 m (CIREN-CORFO, 1997).Table 1.