<i>In situ</i> near-infrared non-destructive monitoring of sugar accumulation reveals that single berries ripening takes only 20 days

Understanding how climate change impacts berry ripening physiology is essential for selecting genotypes that balance sugars and acids under warming conditions. In this context, we used a portable near-infrared spectrometer in the vineyard, to monitor sugar and acid evolution in individual berries from 10 grapevine varieties over two years. Spectra were periodically acquired on the same berries all along ripening, and a subset of these berries was also collected for sugars and organic acids quantification by HPLC, to train partial least square regression models. Prediction models for glucose, fructose, and malic acid concentrations were characterized by validation R² of 0.71, 0.64, and 0.55, respectively. We further used these models to follow sugar accumulation in individual berries and observed that single berries ripen two times faster than found in samples composed of multiple berries. Our results pave avenues toward precise quantitative approaches on sugar and acid fluxes in berry ripening studies.