Seasonal variation in gas exchange and water status of cocoa clones (Theobroma cacao L.) from contrasting agroecological conditions

Background: Esmeraldas province has distinct agroecological zones with a natural rainfall gradient, with higher rainfall in the north-than-south. Hypotheses: Due to the high genetic variability in cocoa, clones from the south will be less affected by drought than those from the north. Plant material: Nine cocoa clones belonging to the National × Criollo complex: five from the north and four from the south, all grown in the field. Site and years of study: Esmeraldas province, Ecuador, during 2022. Methods: Seasonal variation was evaluated for: water potential (Y), hydraulic conductance (KL), photosynthetic rate (A), transpiration rate (E), stomatal conductance (gs), intercellular CO2 concentration (Ci), water use efficiency (WUE), leaf area index (LAI) and chlorophyll content (SPAD). Results: There were significant differences in Y, KL, A, E, gs, WUE, LAI and SPAD among clones, between seasons and the interaction clone × season. Drought caused a reduction in Y, which was associated with a differential reduction of 40 % in A and WUE, depending on the clone. No correlation was found between A and gs, suggesting that the reduction in A in drought was not due to the reduction in gs but to metabolic factors. Southern clones, showed drought had a smaller effect on Y, did not affect gs, E, LAI and SPAD and plants were more efficient in water transport due to higher rainfall KL. Conclusions: A differential physiological response to drought was found depending on the clone, supporting that genetic variability in the clones differently influenced physiological performance in drought.