Potassium Nutritional Status Affects Physiological Response of Tamarillo Plants (Cyphomandra betacea Cav.) to Drought Stress

Cyphomandra betacea (Cav.) is a native species from South America that is cultivated because its fruits have a high content of vitamins. In Colombia, it is common to find periods of drought between the rainy seasons or during ENSO events such as El Niño. An adequate nutritional status of K+ in plants helps to increase the chance of tolerating the negative effects of drought stress. Regarding this situation, a study was conducted to determine the effect of the interaction between the nutritional status of potassium (K+) and the levels of water availability in the soil. Twenty-week-old Tamarillo seedlings were transplanted into 1 L plastic pots containing peat as substrate. Fifteen Days After Transplanting (DAT), the plants were irrigated with nutrient solutions with two different concentrations of K+ (0.05 and 2.5 mM KCl) until the end of the experiment. When differences in growth due to the two levels of K+ were observed, drought stress treatments were established during two drought periods of two weeks. The results showed that plants under drought stress and/or a lack of K+ had a lower growth rate, total plant dry weight, transpiration (E), and stomatal conductance (gs). Plants grown with an optimal nutritional status of K+ showed a better performance under drought conditions, as their Water Use Efficiency (WUE) did not fall sharply despite having low E and gs. These results suggest that a good supply of K+ can improve the acclimation of plants of C. betacea during periods of drought stress.