Differential response of photosynthetic activity, leaf nutrient content and yield to long-term drought in cacao clones

Abstract

Cacao (Theobroma cacao L.) is not frequently cropped in water limited environments, however it is cultivated in several drought-prone regions, where soil water is gradually depleted on an annual cycle. In regions where cacao is subjected to long periods without precipitation, the physiological responses under field conditions may differ between cacao clones. Evaluation of these responses are required to select potential clones that could be used for breeding programs in the context of future climatic scenarios. In order to identify physiological and yield responses to drought of 10 Ecuadorian cacao clones, relative leaf water content (RWC), CO2 assimilation rate (A), transpiration (E), stomatal conductance (gs), water use efficiency (WUE), relative quantum yield of photosystems II (ΦPSII), non-photochemical quenching (NPQ), leaf nutrient content (N, P K, Ca, and Mg) and yield were assessed during the dry (DS) and rainy seasons (RS). On average, A and E decreased by 33 and 22 %, respectively under drought, whereas WUE was higher during RS. Clones exhibited an increase in NPQ during DS, suggesting greater energy dissipation. Clones showed differences in macronutrient content and in most cases drought caused a reduction in Ca and Mg content. Two groups were established according to yield: one which maintained higher yields during RS, while the other had higher yields during drought. This offers strategic alternative in order to maintain a relatively high yield throughout the year with combination of clones in the plantations.