Changes in physiological parameters of boldo plants under water deficit conditions1

Water deficit is one of the main factors affecting the growth and development of boldo plants. This study aimed to evaluate the effects of water deficit on the growth and physiological parameters of Plectranthus barbatus. The experiment was conducted in pots, and the treatments were arranged in a completely randomized design, with five irrigation intervals (1 to 5 days) and four replicates. Plant height, leaf area, number of leaves, transpiration rate (E), stomatal conductance (gs), net photosynthetic rate (A), water- use efficiency (WUE), intrinsic water-use efficiency (iWUE), and leaf water potential (Ψw) were evaluated. Thermal time was also computed. The thermal requirement of the species was 3,253 ºC degree-days. Increasing the irrigation interval reduced the plant height, leaf area, number of leaves, and biomass production of both shoots and roots. Reductions in E, gs, A, WUE, and iWUE were also observed, along with a decrease in relative water content at the turgor loss point, as the irrigation interval was prolonged. No significant effect of irrigation interval was observed on the osmotic potential at full turgor, at turgor loss point, or on Ψw; however, the cell wall rigidity increased, as indicated by a higher volumetric elastic modulus. Water deficit induces water stress in boldo plants, impairing vegetative growth and gas exchange, with consequent changes in plant water status.