A Biostimulant from Kappaphycus alvarezii Enhances the Growth and Development of Basil (Ocimum basilicum L.) Plants

This study evaluated the efficacy and optimal concentrations of Kappaphycus alvarezii biostimulant from São Paulo (Kal-SP) and Santa Catarina (Kal-SC) for the hydroponic cultivation of basil (Ocimum basilicum). Basil plants were grown with 1%, 3%, 5%, and 7% concentrations of each extract using distilled water as a control. The extracts were applied via weekly foliar sprays. Morphological and biochemical parameters, in addition to the biogenic amine profile, were evaluated. Morphologically, 3% Kal-SP increased plant height by 17.1% and length of the roots by 54.8%, while 3% and 5% Kal-SC enhanced node number by 95.2% and 120.2%, respectively. Biochemically, 5% Kal-SP and 1% and 7% Kal-SC maximized chlorophyll and carotenoid content, 5% Kal-SP and 5–7% Kal-SC increased soluble sugars, and 7% Kal-SP and 3–7% Kal-SC elevated starch. Amino acid levels were the highest with 7% Kal-SP and 5% Kal-SC. The biogenic amine profile was also modulated by the K. alvarezii extracts, demonstrating their ability to influence compounds of interest. The results suggest that 3% or higher concentrations of these extracts can be beneficially applied to basil cultivation, with potential variations depending on the seaweed’s geographic origin.