The effect of reflective plastic foils on berry quality of Cabernet Sauvignon Slavica Todic 1, Zoran Beslic 1, Anita Vajic 1, Dejan Tesic 2 1 University of Belgrade, Faculty of Agriculture, Nemanjina 6, 11080 Zemun, Serbia 2 National Wine and Grape Industry Center, School of Wine and Food Sciences, Charles Sturt University, Locked Bag 588, Wagga Wagga NSW 2678, Australia E-mail: slavicat@agrifaculty.bg.ac.yu Key words: sunlight, reflective plastic foil, PAR, dry matter, phenols, anthocyanins. Abstract The sunlight condition in vineyard is fundamental factor to grape quality through its effect on photosynthesis. The elements of berry quality, as content of dry matter, phenols and anthocyanins are directly under the influence of light intensity and its penetration into the fruiting zone. The trial was established in vineyard with cv. Cabernet Sauvignon to determine the effect of silver, white and red colour plastic foil on dynamic of dry matter after veraison, and content of both total phenols and total anthocyanins in berries in compare to cultivated soil. The influence of different coloured foils on PAR into fruiting zone was determined after veraison up to harvest. The results showed that reflective plastic foils enhanced the PAR into the fruiting zone, increased total dry matter, total phenols and anthocyanins in berries depending of foils colour. Introduction Mulching of soil is an old practice aimed primarily to conserve moisture in soil and reduce the intensity of emergence of weed flora, thus increasing yield and quality of fruit in cultivated plants. In addition, mulching changes temperature conditions of the soil and of the air lying immediately above soil, facilitates the movement in the field, and reduces the level of soil erosion. Applying organic mulch (straw, leaves, compost, or similar), further benefits achieved are the increase of organic matter in soil and the stimulation of development of soil micro- and macro-flora. In addition to natural materials, plastic foil is used for mulching more and more often, because of their simple application, ease of manipulation and removal from the field. The application of plastic foil in viticulture becomes more common since the 1960s, primarily to prevent drying of soil and emergence of weeds in the grapevine nurseries and young vineyards (Branas, 1969). Originally the black polyethylene foil was used that had the added effect of increasing the soil temperature and enhancing the rooting ability of young plants. Since a more detailed investigation of the photoreceptive system in plants was conducted, and the positive effect of certain light spectra was determined (Quail et al. 1995, Kasperbauer, 2000), the application of the coloured foil (metallic, red, white, blue, and other colours) occurred first in vegetable production, and then in viticulture. Vegetative growth and yield increase can be achieved irrespective of species by selecting the appropriate coloured foil that will reflect light of the appropriate spectrum (Bunty and Rana, 2005). Coloured foil induces changes in the field microclimate, primarily affecting the light, temperature and air humidity conditions (Tarara, 2000). Field experiments in strawberries, apples, peaches and grapevines have shown a positive effect of the reflecting and coloured foils on earlier fruit maturity and improved colour (Gurnsey and Lawes, 1999; Zhiqiang et al. 1999; Kasperbauer, 2000) and fruit quality
assessed via dry matter content, total anthocyanins and phenolic compounds (Coventry et al. 2005). Material and methods The trials were conducted during the 2005-2006 period in a Cabernet Sauvignon (Vitis vinifera L.) vineyard, which is a part of the experimental farm «Radmilovac» (University of Belgrade, Faculty of Agriculture). This location is in the Sumadija Velika Morava wine region, and it has a temperate - continental climate with the annual mean air temperature of 10.8 C, and the seasonal mean temperature of 16.6 C. Total annual rainfall averages 660 mm, with 410 mm of rainfall during the growing season. The vineyard soil type is a lessive cambisol that has favourable physical characteristics. The vineyard was planted in 2002, at a spacing of 3 m between rows and 1 m between vines. The training system is a double Guyot with a trunk height of 90 cm, pruned to a mix of canes and spurs. The vineyard soil management consisted of repeated cultivation to prevent the development of weeds or larger soil aggregates that would hinder placement of the plastic foil. The plastic foils were placed six weeks before harvest in form of tracks across the inter-row. White, red and silver foils, all 1.5m-wide were used. The experiment was set in three blocks with three replicates and a control in each block. A space of 20m was left between adjacent foils as a buffer zone. Each replicate consisted of 30 homogeneous vines. The content of solids in berry juice was determined every 8-10 days using a hand-held refractometer Bellingham & Stanley Ltd, in the period from veraison to harvest. The photosynthetically active radiation (PAR) was measured using a line quantum sensor LI-190SA; LI-COR, Inc.) around noon (11:00-13:00 h) on completely clear days only. Total anthocyanin and phenolic content in berry skin was determined by spectrophotometry. Each sample consisted of 200 berries from which the skins were removed and then homogenised. Extraction was performed using acidified ethanol. Total anthocyanin content was determined at 530 nm and total phenolic content at 740 nm, after a reaction with a Folin-Ciocalteu reagent. Results and Discussion Measurement of the amount of light expressed as PAR determined a significant difference between the means for different coloured foils as well as the non-mulched soil (Tab. 1). Other research has unarguably demonstrated the increase of PAR when reflective foils were applied. Green et al. (1995) found a total increase of up to 40% in the absorbed PAR where reflective foils were applied. Layne and Rushing (1999) have measured an increase in PAR from 68 µmol m -2 s -2 to 646 µmol m -2 s -2 when they applied metallic reflective foils. Tab.1. The amount of PAR determined for different coloured plastic foils and nonmulched soil (control) Control White Red Silver PAR (µmol m -2 s -2 ) 105 d 302 b 128,7 c 323,7 a Lsd 0,95 = 13,09 Over a six-week period during fruit ripening it was observed that there was a significant effect of coloured foils on the concentration of solids in berries (Fig. 1). In the beginning of the observed period, this concentration was about 1% higher in the white coloured foil treatment, while at harvest all coloured foil treatments had a 0.6% higher
concentration of solids compared to control. In the first stage of the observed period, the largest effect was observed in the red colour foil treatment. In the last third of September the effect of foils was reduced due to the occurrence of cloudy and rainy weather conditions, Fig.1. Just before harvest, the marked effect of foils was observed again. A gradual reduction in the effect of foils is caused by a reduction in their ability to reflect light, which is a result of the accumulation of dust and dirt on their surface (Coventry et al. 2005, Layne and Rushing, 1999). 800 700 Solar radiation 600 500 400 300 200 100 0 Precipitation Aug. Sept. Oct. Fig.1. The level of average solar radiation Wm -2 and precipitation (mm) from Aug. to Oct. in 2007. obtained from automatic meteorological station on Experimental Station Radmilovac, Belgrade 24 Soluble solids content (%) 23 22 21 20 19 19.6* 19.45 18.6 21* 20.6 20.2 21.5 21 22.8* 22.8* 22.6 22 21.9 Silver White Red Control 18 Aug. 23 Sept. 13. Sept. 19 Sept. 26. Oct. 3. Oct. 10. Fig. 2. Soluble solid accumulation in grape berries after veraison up to harvest depending of coloured plastic foils.
A significant increase in the content of total anthocyanins was determined in the white colour foil treatment when compared to other foils and control (Tab. 2). The marked effect of white foil can be attributed not only to reflection of light, but also to a well-known effect of white foil on air temperature (which were not determined) immediately above the foil, which could have contributed to the synthesis of anthocyanins (Layne and Rushing,1999;Yamane et al. 2006). Red and silver foils had no effect on anthocyanins compared to control. Applying coloured foils as mulch did not affect the total phenolic content in berry skins. Other research has shown varied effects of reflective foils on the total anthocyanin and phenolic content in berry skins. Merwin et al. (2005) have shown that there was no effect of reflective foils on anthocyanin and berry solids content, although their study determined an increase in the amount of light reflected from the foils. Other studies have found no increase in anthocyanin content in berry skins of several grape varieties exposed to full light when compared to shaded berries (Hannah et al. 2004; Price et al. 1995). Opposite results were reported by Coventry et al. (2005) who found that application of reflective foil caused an increase in total anthocyanin and phenolic content in cv Cabernet Sauvignon. Tab.2. Total anthocyanin and phenolic content in berry skins of cv. Cabernet Sauvignon when mulched with different coloured plastic foils. Colour of the foils Content of total anthocyanins (mg/g) Content of total phenols (mg/g) White Red Silver Control 5.15333 a 3.78333 b 3.84333 b 3.50333 b 564.6 559.7 561.8 588.0 Lsd (0,95) 0,822243 31,112 Conclusion In addition to an already established effect of reduction in soil evaporation and the prevention of weed emergence, the application of coloured plastic foils as a mulching material appears to alter the microclimatic conditions of the vineyard. In addition to an expected change in soil temperature, as well as the air temperature in immediately above the foil, possibly the most important effect is achieved by improving the quality and the amount of light reaching the canopy, depending on the colour of the foil. The application of white, red and silver foil increased the concentration of solids in the grape juice compared to control (non-mulched soil). The prolonged exposure of foils to the environment appeared to have reduced their reflective capacity due to accumulation of dust and dirt. A significant increase in total anthocyanin content in berry skins was determined in the white coloured foil treatment compared to other foils and control, while there was no effect of mulching on the content of total phenolics. Acknowledgements We thank the Ministry of Science and Environmental Protection of the Republic of Serbia who funded this research project.
Literature Branas, J. 1969. Concerning the use of plastics. Progr.Agric.Viticole 86:63-73. Bunty, S., Rana, R. 2005. Coloured plastic mulches on Horticulture crops. Science Tech Entreprenteur. Dec. 2005. Coventry, J.M., Fisher, K.H., Strommer, J.N., Reynolds, A.G. 2005. Acta Hort. (ISHS) 689: 95-102. Green, S.R., McNaughton, K.G., Greer, D.H., McLeod, D.J. 1995 Measurement of the increased PAR and net all-wave radiation absorption by an apple tree caused by applaying a reflective ground covering. Agr.For.Meteor. 76: 163-183. Gurnsey,S., Lawes, G.S. 1999. Reflective mulches in improving apple color. Tree Fruits Tasmania. 3. Hannah, R., Downey, M., Hogg, A., Krstic, M. 2004. The effect of bunch exposure on anthocyanin accumulation in different grape cultivars. Poster abstract in 12th Wine Industry Technical Conference information and abstracts, 24-29 July, Melbourne p.73. Kasperbauer, M.J. 2000. Strawberry yield over red versus black plastic mulch. Crop Sci. 40: 171-174. Layne, D.R. and Rushing, J.W. 1999. Color sells: reflective film may improve color and quality in your peaches and apples. American Fruit Grower. May: 18-19. Merwin, I., Hostetleri, Martinson, T. 2005. Managing vine vigor and improving red winegrape quality with reflective or black geotextiles, and bark mulch. http://www.nysaes.cornell.edu/pubs/vitcon/06pdf/merwin01.pdf Price, S.F., Breen, P.J., Valladao, M., Watson, B.T. 1995. Cluster sun exposure and quercetin in Pinot noir grapes and wine. Am. J. Enol. Vitic. 46: 2: 187-194. Quail, P.H., Boylan, M.T., Parks, B.M., Short, T.W., Xu, Y., Wagner, D. 1995. Phytochromes: photosensory perception and signal transduction. Science 268: 675-680. Tarara, J.M. 2000. Microclimate modification with plastic mulches. HortScience 35: 169-180. Yamane, T., Jeong, S.T., Yamamoto, N.G., Koshita, Y., Kobayashi, S. 2006. Effects of temperature on anthocyanin biosynthesis in grape berry skins. Am. J. Enol. Vitic. 57:1: 54-59. Zhiqiang, J., Yousheng, D., Zhiguo, J. 1999. Effects of covering the orchard floor with reflecting films on pigment accumulation and fruit coloration in Fuji apples. Sci.hortic. 82: 1-2: 47-56.