Meteorological Conditions: Influence on Yield, Sanitary Status and Grape Composition

The main climatic elements that explain variations in grapevine performance and oenological quality are sunlight, temperature and precipitation. Among these, temperature and precipitation have the most marked effect on yield components and berry composition, which are sensitive to their magnitude, variations and distribution over the crop cycle [1,2]. Bunch number per plant explains about 60-70 % in the interannual variation in grapevine yield [3]. Initiation – induction of inflorescences and floral diffe rentiation take place in the period of budbreak - fruit set, in two consecutive seasons, hence temperature and water availability during this phase are determinant factors for quality and yield in two harvests [4-6]. Water deficits in the season previoust o harvest produce yield declines by reduction in number of bunches per plant. For the harvest year, water deficit influences the differentiation of flowers, fruit set or abortion of flowers, fruit, and berry size, leadi ng to variations in yield [4, 7]. Vin e water requirements depend on phenological stage, being flowering - veraison (48.2 %) the most demanding period over a total of 750 mm required during the growing season [8]. Botrytis cinerea is a serious threat to grapevine and has a negative impact on grape and wine quality. Weather conditions during pre-harvest (frequent precipitations, high relative humidity, mild temperatures and low wind intensity) are key elements for the development of this disease [9,10]. Meteorological conditions accounted for 88 % of the total variability on grape composition, a higher percentage than that explained by variety or soil [11]. Wine grape quality between years depends on temperature variability that determines whether grape ripening would be completed, due to its imp act on sugar content, acidity degradation and berry anthocyanins balance [12]. The optimum diurnal temperature ranges from 25°C to 30°C. Values over 37°C inhibit sugar accumulation and induce a negative balance in anthocyanins; while the respiration of malic acid accelerates starting from 35°C [12, 13]. During maturation, optimal levels of acidity and a positive balance in anthocyanins require a temperature range night / day of 16 / 25°C; lower temperatures promote high levels of malic acid [13]. Meanwhile , thermal sum in that period, expressed as degree-day base 10ºC, is strongly associated with anthocyanin content [1]. In general, it is recognized that a progressive and moderate water stress from flowering to fruit set favors the accumulation of sugars an danthocyanins, and decreases the acidity associated with the reduction of vegetative growth in the fruit ripening stage [2,14]. Post veraison water stress is responsible for the largest increase in polyphenolic content. 

In this context, the current study aimed to establish which meteorological conditions have the strongest impact on grapevine yield, sanitary status and berry composition. An additional objective was to assess when and how weather interannual variability affects grapevine yield and berry qu ality, as well as checking its relative importance in relation to management practices and variety.