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Protein hydrolysate-based biostimulants have been increasingly investigated due to their potential to improve seedling growth and physiological responses; however, integrated interpretations of dose-dependent morphophysiological and photochemical responses in Theobroma cacao L. during nursery production remain limited. This study evaluated the effects of increasing concentrations of Terrativa®, an organomineral biostimulant formulated with animal-derived protein hydrolysate, on growth, chlorophyll indices, and photosystem II performance in cacao seedlings of the Catongo and TSH1188 genotypes. The experiment was conducted in a randomized block design in a 2 × 6 factorial arrangement, corresponding to two genotypes and six Terrativa® concentrations (0, 1, 2, 3, 4, and 6 mL L−1). Most morphological and physiological variables exhibited quadratic responses. Intermediate concentrations promoted greater vegetative growth and improved photochemical responses, with maximum values observed for number of leaves (13.98 at 2.50 mL L−1), leaf area (994.10 cm2 at 2.91 mL L−1), stem length (42.79 cm at 3.44 mL L−1), root volume (9.21 cm3 at 3.70 mL L−1), and total chlorophyll (34.58 at 3.08 mL L−1). Catongo seedlings showed greater chlorophyll accumulation, whereas TSH1188 exhibited higher ABS/RC, TRO/RC, and PIabs values, indicating genotype-dependent differences in photochemical energy utilization. Higher concentrations were associated with reduced performance in several variables, suggesting lower physiological efficiency under elevated biostimulant doses. Overall, Terrativa® concentrations between 2.50 and 3.70 mL L−1 were the most effective for promoting balanced seedling development in both cacao genotypes, with Catongo responding more strongly in chlorophyll accumulation and TSH1188 showing greater photochemical responsiveness.
Hoste et al. (Fri,) studied this question.