Impact of paclobutrazol on the initial growth of Tectona grandis clones under different water availability regimes

Plantations continually confront climatic challenges that may impede their initial establishment in the field, thereby adversely affecting their overall productivity. In order to establish protocols for forest plantations that address potential challenges arising from global climate variations, growth regulators play a significant role. The use of plant growth regulators in early forest species’ growth and establishment stages is limited. The present study assessed the morphophysiology of Tectona grandis clones in response to different water regimes and paclobutrazol concentrations applied to the soil. The experiment followed a randomized block design with four blocks and a 5x3 factorial scheme. This scheme included five concentrations of PBZ: 0.0 (control), 1.0, 2.0, 4.0, and 8.0 mg plant-1, and three levels of water availability: 40%, 70%, and 100% of field capacity. There was no interaction between PBZ concentration and water regime factors. Based on the analysis applied to each treatment, plants’ morphological and physiological variables did not respond to the use of different PBZ concentrations, although significant differences were observed in some morphological and physiological traits. The higher water availability provided by 100% field capacity led to the highest increase in stem diameter, root and total dry mass values. Tectona grandis clones presented increased carboxylation efficiency and water-use efficiency at 40% field capacity. Keywords: drought tolerance, field capacity, morphological changes, PBZ.