Plant Biostimulant Based on Biomass of Chlorella sorokiniana Treated with SL-6 Strigolactone Mimic

This study aimed to evaluate the impact on Chlorella sorokiniana NIVA-CHL 176 growth and the plant biostimulant functions of the microalgal extract of the strigolactone mimic SL-6, in com-parison with the strigolactone analog GR24. Three molar SL-6 concentrations were tested: 10-7 M, 10-8 M, and 10-9 M, respectively. Five parameters of the microalgal growth were assessed: optical density, turbidity, biomass production, chlorophyll fluorescence, and pigment concentration. Results after 15 days of culturing revealed that the SL-6 treatments significantly enhanced bio-mass production, chlorophyll synthesis, and photosystem II activity. Treatment with SL-6 c3 (10-9 M) exhibited significant increases in chlorophyll a (27.55%), chlorophyll b (24.81%), carotenoids (12.31%), and total pigments (24.00%) compared to the solvent control (DMSO). Experimental treatment SL-6 c2 (10-8 M) followed next and recorded notable enhancements in chlorophyll a (25.80%), carotenoids (9.77%), and total pigments (20.08%). Conversely, higher doses of GR24 and SL-6 (10-7 M) inhibited the microalgal growth, reducing cell density, biomass production, and pigment synthesis. The microalgal extracts acted as a plant biostimulant stimulating root and shoot elongation and proton pump functioning in the presence and absence of salt stress. The extracts from SL-6 bio-stimulated C. sorokiniana NIVA-CHL 176 are more active as plant biostimulants.