Modelling the effects of leaf-to-fruit ratio on dry and fresh mass accumulation in ripening grape berries
Résumé
Process-based fruit growth models are useful frameworks to advance our understanding of fruit quality build-up in response to climate and management techniques. In the present study, we adapted a biophysical model originally designed for peach (Fishman and Génard, 1998) to grapevines, to simulate the effects of various leaf-to-fruit ratios on fresh and dry mass accumulation in a ripening berry. The model represents a virtual mean berry during the post-veraison developmental stage, which is assumed to behave as a single cell separated with a composite membrane from the parent vine and the outside environment. Water accumulation was calculated through the water balance between xylem and phloem water influx and transpirational water loss, controlled by water potential gradient between the berry and the parent vine. Meanwhile, dry mass accumulation was simulated with the balance between phloem sugar import and respiration carbon depletion. The inputs of the model included initial fresh and dry mass, phloem sugar concentration, xylem water potential, fruit temperature and air humidity. In 2006, experimental data were acquired on Vitis vinifera cv. Cabernet Sauvignon fruiting cuttings grown in greenhouse and submitted to three leaf-to-fruit ratios at veraison (control, low and recovery). The dataset of the control treatment was used to calibrate the model, while the dataset of low and recovery treatments were used to validate the model. The predictions of the model were in agreement with the observed data. The reduced berry fresh and dry mass caused by the low leaf-to-fruit ratio and the recovery growth corresponding to the alternation leaf-to-fruit ratio from low to control level could be accurately simulated with corresponding phloem sugar concentration. Furthermore, the within cluster variation in berry fresh and dry mass under the same treatment were also well simulated when the different initial fresh and dry masses were considered. Simulations of diurnal changes in fresh mass and berry water balance were also demonstrated and discussed.