Enhancing growth and physiological performance of Theobroma cacao plantlets with biostimulant extracts from Acanthophora spicifera and Ulva sp

Abstract

The establishment of Theobroma cacao L. plantlets in the field is a critical stage in the cultivation process for ensuring successful crop development. Perennial crops such as cacao may benefit from biostimulants that enhance early establishment and support long-term growth and productivity. The objective of this study was to investigate the effects of algal-based biostimulant extracts derived from Acanthophora spicifera and Ulva sp. on the growth and physiological performance of T. cacao plantlets. A grafted CCN-51 plantlets from approximately 2 to 3 months old before acclimatation period for two weeks, were used for transplantation and later treatment initiation. The extracts of seaweeds were obtained using water, 25% of aqueous ethanol and 50% aqueous ethanol were applied at concentrations of 2.5%, 5% and 7.5% (V/V). The treatments were applied for eight consecutive weeks, where plants physiological traits were evaluated at 15-day intervals. Treatment effects depended on the algal species, extraction medium, and mainly application concentration. Selected Ulva sp. extracts, particularly the 50% ethanol extract applied at a low concentration (doses at 2.5%), increased the Chlorophyll Content Index compared with other treatments up to 43.1 ± 1.19 CCI. Leaf number also varied among treatments across assay, whereas plant height and leaf length were not significantly affected. These findings indicate that selected seaweed extracts can modulate the early physiological performance of cacao plantlets, although their effects are dose and time dependent.