COMPOSITIONAL AND STRUCTURAL ASPECTS OF SUNBURN INGRAPE BERRIESASPECTS COMPOSITIONNELS ET STRUCTURELS DU SOLEIL EN BOIS DERAISINS
BONDADA, Bhaskar*; FORD, Melanie; XIE, Zhaosen Wine Science Center, Washington State University, 2710 Crimson Way, Richland, WA 99354, USA. *Corresponding author: bbondada@wsu.edu Abstract In recent years, sunburn has become a major concern to viticulture throughout the world. Given that grapevines differ in heat tolerance, the incidence of sunburn is likely to vary among different cultivars. Therefore, the objective of this study was to determine if grapevine cultivars varied in tolerating overexposure of sunlight and temperature by analyzing skin characteristics and fruit composition among red (Merlot, Syrah, Cabernet Sauvignon, Grenache, Sangiovese, and Cabernet Franc) and white (Riesling, Chardonnay, and Gewurztraminer) cultivars. Study showed that the symptomatology of sunburn between red and white cultivars varied; in red cultivars, color development was poor whereas brown lesions appeared on the skins of white cultivars. In all cultivars, the exposed surfaces lost their crystalline structure of epicuticular wax resulting in a shiny surface. The wax platelets were transitioned into amorphous masses with rough surface morphology. The flesh cells incurred losses in cell viability. With respect to composition, generally sunburned berries in all cultivars dehydrated, consequently Brix increased, on the other hand, the acids were lost to respiration. The study revealed that the degree of quality deterioration due to sunburn varied and was a function of berry structure and physiology. Keywords: Anthocyanins, organic acids, sugars, tannins, Vitis vinifera Resumé Au cours des dernières années, les coups de soleil sont devenus une préoccupation majeure pour la viticulture dans le monde entier. Étant donné que les vignes diffèrent par la tolérance à la chaleur, l'incidence des coups de soleil est susceptible de varier selon les différents cultivars. Par conséquent, l'objectif de cette étude était de déterminer si les cultivars de vigne variaient en tolérant la surexposition de la lumière du soleil et de la température en analysant les caractéristiques de la peau et la composition des fruits Parmi les cultivars rouges (Merlot, Syrah, Cabernet Sauvignon, Grenache, Sangiovese et Cabernet Franc) et blanc (Riesling, Chardonnay et Gewurztraminer). L'étude a montré que la symptomatologie des coups de soleil entre les cultivars rouge et blanc variait; Dans les cultivars rouges, le développement de la couleur était médiocre alors que les lésions brunes apparaissaient sur les peaux des cultivars blancs. Dans tous les cultivars, les surfaces exposées ont perdu leur structure cristalline de cire épicuticulaire, ce qui entraîne une surface brillante. Les plaquettes de cire ont été transformées en masses amorphes avec une morphologie de surface rugueuse. Les cellules de la chair ont subi des pertes de viabilité cellulaire. En ce qui concerne la composition, généralement les baies brûlées par le soleil dans tous les cultivars déshydratés, par conséquent, Brix a augmenté, d'autre part, les acides ont été perdus pour la respiration. L'étude a révélé que le degré de détérioration de la qualité due aux coups de soleil variait et était fonction de la structure des baies et de la physiologie. Mots-clés: Anthocyanines, acides organiques, sucres, tanins, Vitis vinifera 1. Introduction Ripening process persists as the prime topic of discussion among grape growers and wine makers as it determines fruit composition, yield, and ultimately the time of harvest. Among the many factors that affect ripening, temperature is the central environmental cue with a far-reaching impact on ripening (Greer and Weedon, 2014). The recent warming trends and erratic weather patterns in WA associated with wide fluctuations in daily and seasonal temperatures have resulted in an increased frequency, extent and intensity of hot temperatures (heat waves). The manifestations of such events are generally marked by high incidence of sunburn injury to grapes. Sunburn is economically detrimental to fruit quality as it renders afflicted clusters unusable for making wine imposing a serious concern to grape growers and winemakers worldwide (Bondada and Keller, 2012). Furthermore, hot seasons hasten the ripening process with reduced sugars and acids (Greer and Weedon, 2013). In the context of climate change scenarios, the incidence of sunburn may exacerbate in the foreseeable future and with no known clues, the vexation will escalate among grape growers and viticulturists. Hence, there is an urgent need to keep a curb on its incidences by employing practical cultural operations. One way to go about is to understand cultivar differences in resisting sunburn and plant resistant cultivars in hot AVA’s. Hence, the objective of this study was to determine cultivar differences in sunburn resistance by analyzing the physical and fruit compositional attributes between healthy and sunburned clusters. Materials and Methods A commercial vineyard with mature own-rooted Vitis vinifera cultivars of red and white wine grapes located in Red Mountain and HHH AVA’s were chosen for determining the effects of sunburn on various fruit quality attributes desired for making wine. All cultivars were trained to VSP system and spur-pruned to equate the shoot density to 20 shoots/m. The vineyard with north-south oriented rows had vine by row spacing of 6 x 9 feet on a uniformly deep loamy fine sand. All vines were drip-irrigated and standard cultural practices were performed to maintain healthy vines. Healthy and sunburned clusters were harvested on the same day and various fruit quality attributes were analyzed. Microscopy technique was used to examine cell viability of flesh cells in healthy and sunburned berries. Cell viability was determined by the method suggested by Bondada et al. (2017). Results and Discussion The study showed that the symptomatology of sunburn between red and white cultivars varied; in red cultivars, color development was poor whereas brown lesions appeared on the skins of white cultivars (Figure 1). In all cultivars, the exposed surfaces lost their crystalline structure of epicuticular wax resulting in a shiny surface. The wax platelets were degraded and transitioned into amorphous masses creating a rough surface morphology (Bondada and Keller, 2012). The flesh cells incurred losses in cell viability in the sunburned berries whereas the healthy berries showed viable cells (Figure 2). With respect to composition, generally sunburned berries in all cultivars dehydrated, consequently Brix increased, on the other hand, the acids were lost to respiration. Both the total anthocyanins and amount of individual anthocyanins were significantly reduced in sunburned berries. On a per whole berry basis, quercetin levels were low in the healthy berries (Figure3) whereas at a single berry level, the exposed half showed higher levels than the shaded surface. In conclusion, the study revealed that the degree of quality deterioration due to sunburn varied and was a function of cultivar. References BONDADA, B., HARBERTOSN, E., SHRESTHA P.M., KELLER M., 2017. Temporal extension of ripening beyond its physiological limits imposes physical and osmotic challenges perturbing metabolism in grape (Vitis vinifera L.) berries. Scientia Horticulturae, 219 135-143. BONDADA B., KELLER M., 2012. Not all shrivels are created equal – morpho-anatomical and compositional characteristics vary among different shrivel forms that develop during ripening of grape (Vitis vinifera L.) berries. American Journal of Plant Science, 3 879-898. GREER D.H., WEEDON M.M., 2013. The impact of high temperatures on Vitis vinifera cv. Semillon grapevine performance and berry ripening. Frontiers in Plant Science, 4 Article 491 GREER D.H., WEEDON M.M., 2014. Temperature-dependent responses of the berry development processes of three grapevines (Vitis vinifera) cultivars. New Zealand Journal of Crop and Horticultural Science, 42 233-246. Figure 1. Sunburned affected clusters of (A) Cabernet Sauvignon and (B) Riesling. Figure 2. Healthy berries with no sunburn showing viable mesocarp cells in Cabernet Sauvignon. Figure 3. Quercetin levels in healthy and sunburned berries.
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