Modeling dormancy in grapevines (Vitis vinifera L.)

Hector Andres Camargo Alvarez

Dormancy in plants is an evolutionary strategy to overcome the adverse climatic conditions during winter through the detention of growth and the decrease in the metabolism. This period is defined in greater depth as endodormancy when the growth is inhibited by internal signs in the buds, and ecodormancy when the adverse environmental conditions inhibit the growth. When conditions are suitable again, ecodormancy ends, growth resumes, and bud break occurs. Nevertheless, the transitions between stages during dormancy do not have visual symptoms, obstructing the decision-making process and the associated timing of management activities in the vineyard. Therefore, the goal of this study was to develop a model to predict the occurrence of the phenological stages during dormancy and bud break in grapevines ‘Cabernet Sauvignon’ and ‘Chardonnay.' In the first part of this study, the effect of photoperiod and temperature on endodormancy induction were evaluated. In the second part, the dates of the onset and release of endodormancy for an experimental vineyard were estimated for four years. In the final part of this study, an integrated phenological model was developed. The model assumes that the shortening of the photoperiod induces the onset of endodormancy when a critical day length (CDL) specific for each cultivar is reached. Then, a period of exposure to chilling temperatures leads the transition from endodormancy to ecodormancy, and finally, a period of warm temperatures forces bud break. The model showed that ‘Cabernet Sauvignon’ has a longer endodormancy period caused by the cultivar-specific sensitivity to CDL, as well as a faster completion of the chilling requirement in ‘Chardonnay.’ While the forcing effect of different temperatures and the length of the ecodormancy period were similar in both cultivars, resulting in an earlier bud break for ‘Chardonnay.’ Predicted dates of bud break were compared against 31 observed dates, showing a correlation of 0.95, an RMSE of 3.9 days and a MBE of -0.97 days was found, meaning that bud break estimations tend to occur earlier than the observed bud break. The accuracy of the model could be improved including an interaction effect between temperature and CDL for the endodormancy onset.

Modeling dormancy in grapevines (Vitis vinifera L.)

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