<p class="MsoNormal" style="margin-bottom: 12.0pt; text-align: left; mso-line-height-alt: 14.0pt; layout-grid-mode: char; mso-layout-grid-align: none; border: none; mso-padding-alt: 31.0pt 31.0pt 31.0pt 31.0pt; mso-border-shadow: yes;" align="left">Dose-Dependent Effects of a Protein Hydrolysate Biostimulant on the Growth, Performance, and Quality of <em>Theobroma cacao</em> L. Seedlings

Protein hydrolysate-based biostimulants have been widely investigated for their potential to enhance seedling growth; however, integrated interpretations of dose-dependent morphophysiological and photochemical responses remain limited for Theobroma cacao L., particularly during the nursery phase. This study aimed to evaluate dose-dependent physiological modulation in cacao seedlings of the Catongo and TSH 1188 genotypes under increasing concentrations of a protein hydrolysate-based biostimulant. The experiment was conducted in a randomized block design arranged in a 2 × 6 factorial scheme, corresponding to two genotypes and six biostimulant concentrations. Morphological traits, biomass accumulation, morphophysiological indices, chlorophyll indices, and chlorophyll a fluorescence parameters were assessed. The results revealed clear dose- and genotype-dependent responses, with predominantly quadratic patterns across most variables. Intermediate concentrations were associated with coordinated improvements in vegetative growth, root development, and photosystem II (PSII) functional performance, whereas higher concentrations were linked to reduced physiological balance. Overall, the findings indicate that protein hydrolysate-based formulations modulate cacao seedling performance through dose-dependent physiological adjustment, contributing to a more integrated understanding of biostimulant action during the nursery phase.