Use of a continuous vine water deficit index and link with fruit composition

Abstract

Authors have reported that water deficit impact on fruit composition can be modulated according to its timing, severity or grape varietal sensitivity to drought. However, until recently, measurement methods were lacking to characterize continuously the dynamic variations of vine water deficit. Consequently, it was difficult to analyze the effect of contrasted levels of water deficit on fruit composition according to plant development stage. Today, thanks to the development of new sensing technologies, it is possible to monitor vine water deficit continuously by combining sap flow and climatic data. Then, by monitoring fruit ripening along continuous vine water deficit variations, new insights can be gained to better understand the relationship between vine water status and fruit composition. To evaluate the potential of this new approach a study was set in French vineyards to achieve three objectives. First, we wanted to analyze the relationship between discontinuous and continuous measurements of vine water deficit. Second, we wanted to characterize how effective is irrigation at creating different vine water deficit profiles within the same block. Third, we wanted to investigate the link between different vine water deficit profiles and fruit composition. Contrasted conditions of vine water supply were obtained by imposing differential irrigation treatments across multiple vineyard locations. We tracked irrigation effect on vine water status variations by using 3 different measurement methods. We combined sap flow and climatic data into a framework to automatically compute a daily water deficit index, Ks, and compared with discontinuous measurements of water deficit using reference methods. Then, we used advanced analytical methods to investigate the link between fruit composition and vine water status variations. Our conclusions show that water deficit was low to moderate in 2012 and in 2013, as expected considering the climatic context, regardless of the measurement method. We tested the relationship between delta C13, predawn leaf water potential and Ks for both years and analyzed the results. Our study reveals that under low to moderate water deficit, we observe no correlation between irrigation treatments and fruit composition. However, using continuous vine water deficit measurement, we found the existence of relationships between small variations of vine water deficit and fruit composition, particularly thiol aroma precursors.