Biostimulant potential of biomass-free supernatant from extracellular biopolymer-producing cyanobacteria in the germination of white corn, Agave, and huacle chilli seeds

Cyanobacteria biomass is a promising source of biomolecules with biostimulant and biofertilizer potential in sustainable agriculture. The biomass-free supernatant from extracellular biopolymer-producing microalgae has been unexplored for agricultural applications. This study assessed the biostimulant potential of biomass-free supernatant (BFS) from Nostoc sp. and Synechocystis sp. PCC 6803 in seed germination of native seeds such as white corn, Agave, and huacle chilli from various municipalities in Oaxaca-Mexico. Nostoc sp. and Synechocystis sp. PCC 6803 produced the highest extracellular biopolymer production of 191.37 mg D-glucose L⁻¹ at 40 days and 142.93 mg D-glucose L⁻¹ at 61 days, respectively, measured by carbohydrate quantity. The BFS from both strains contained 43 metabolites, as identified by mass analysis. Biostimulant activity was assessed by seed germination assay; it was conducted by soaking seeds in the BFS of Nostoc sp., BFS of Synechocystis sp., Stimulate® (a commercial stimulant), and tri-distilled water. The germination response of the treatments was similar to the Stimulate® in the three kinds of seeds. All samples of corn had a germination percentage between 94 ± 3.8% and 100 ± 0.6% after 48 h. The Agave marmorata (ATE) seeds had the best response with germination percentages between 89.7 ± 2.5% and 96% at seven to twelve days. Huacle chilli seeds showed germination percentages between 76.0 ± 1.0% and 93.7 ± 1.2% at eight to nine days. Seed surface analysis showed a uniform coating on the corn seeds and a coating-like crust on the Agave seeds, both treated with BFS of Nostoc sp. These findings provide a way to understand the potential of BFS in agricultural applications from extracellular biopolymer-producing cyanobacteria.