Berry weight loss in Vitis vinifera (L.) cultivars during ripening

Abstract

Abstract: Context and purpose of the study – Berry shriveling (BS) in vineyards are caused by numerous factors such as sunburn, dehydration, stem necrosis. Climate change results in an increase in day and night temperatures, rainfall throughout the year, changes in the timing and quantities, long dry summers and a combination of climatic variability such as floods, droughts and heatwaves). Grape development and its composition at harvest is influenced by the latter as grape metabolites are sensitive to the environmental conditions. The grape berry experiences water loss and an increase in flavour development as a result of the BS. An increased sugar content in grapes will result in higher alcohol wines and concentration of grape aromas which may be detrimental to the final wine quality. More so, crop estimations are negatively impacted as a result of BS which results in lower compensation for grape producers. This pilot study seeked to investigate the berry weight loss in twelve Vitis vinifera (L.) cultivars in WashingtonState.

Material and methods – This study was conducted during the 2018 growing seasons at the Washington State University (WSU) Irrigated Agriculture Research and Extension Center (IAREC) in Prosser, Washington, USA (46°17’N; 119°44’W; 365 m a.s.l.). The vineyard contained 30 wine grape cultivars (Vitis vinifera) separated into 16 main blocks of 13 row seach along with border sections of 5 vines each. All vines were planted at a spacing of m × 2.7 m (2058 vines/hectare). Grape cultivars were separated into groups of either white or red, with all vines planted in a north-south orientation using the Vertical Shoot Positioned (VSP) training system.Each of the 16 main blocks was dedicated too neoffour main cultivars;Merlot,CabernetSauvignon,Chardonnay, orRiesling. Border sections containing the additional 26 cultivars were located on the southern, eastern, and western portionsofthevineyard.Eachborder cultivar sectionconsistedofthreeorfourrepetitionsoffivevineseach.All weather data was gathered from the Roza automated weather station and the WSU AgWeatherNet system (AgWeatherNet2018).Berry fresh weight and total soluble solids were determined just after véraison throughout berry development.

Results – In this study on weight loss in ripening white (Chardonnay, Weisser Riesling, Gewurztraminer, Alvarinho, Muscat blanc and Sémillon) and red grape cultivars (Cabernet Sauvignon, Merlot noir, Grenache, Lemberger, Malbec, Cabernet franc) ripening curves of non-solutes per berry (mostly water) were similar to the berry weight curves. Solutes per berry (mostly sugar) increased to a maximum berry weight for most of the cultivars. Prior to véraison phloem sap is the only source for water and solutes that enter grape berries until maximum berry weight followed by a decrease in the solutes per berry. Later during the ripening stage berry shrinking occurred due to elevated transpiration, which resulted in an increase in ˚Brix (solutes). Grape cultivar, environmental and cultivation practices have an impact on the concentration of berry of solutes, which dictates the composition and will have an impact on the wine quality. However, this study needs to be repeated and the wine quality should be assessed.