Marine vs. freshwater cyanobacteria as biostimulants for wheat under salt stress: morphophysiological, anatomical and phytochemical perspectives.

Salinity is a major abiotic stress that restricts global crop productivity, particularly in staple cereals such as wheat (Triticum aestivum). This study investigates the biostimulant potential of two cyanobacterial strains, Alkalinema pantanalense (freshwater origin) and Geminocystis sp. (marine origin), on the early growth of three wheat genotypes under varying salt stress conditions (0, 50, 100, and 200 mM NaCl). Algal extracts were applied to seeds and seedlings, and physiological, anatomical, and biochemical responses were assessed. Results revealed that A. pantanalense significantly improved seed germination and chlorophyll content under moderate salinity (50-100 mM), especially in genotype G2, with shoot length reaching up to 3.5 cm and chlorophyll levels maintained near control values. In contrast, Geminocystis sp. enhanced root dry weight even under high salinity (200 mM), suggesting improved osmotic adjustment, though it reduced root length and meristem size in some genotypes. Anatomical analysis revealed that A. pantanalense increased the number of root meristem cells and promoted vascular differentiation, thereby supporting structural resilience. Phytochemical profiling revealed that A. pantanalense was richer in flavonoids (130.7 µg/g naringin) and phenolic acids (ferulic and caffeic), while Geminocystis sp. had higher phytohormone levels, notably IAA (20.95 µg/g ) and BA. GC-MS analysis identified bioactive compounds such as lupeol and oleic acid in A. pantanalense, and phytol and methyl esters in Geminocystis sp. These findings demonstrate distinct yet complementary biostimulant profiles between the two cyanobacteria, underscoring their potential for sustainable wheat cultivation in saline soils.