Biochemical and microbial interactions of Sargassum wightii extract and plant growth-promoting rhizobacteria consortia enhance growth and yield of tomato (Solanum lycopersicum L.)

Abstract

The increasing need for sustainable agricultural practices has intensified interest in seaweed-based biostimulants and plant growth-promoting rhizobacteria (PGPR) as eco-friendly alternatives to chemical fertilisers. This study examined the individual and combined effects of Sargassum wightii extract and PGPR strains (Azospirillum lipoferum TSA-6 and Bacillus megaterium TSB-3) on the growth and yield of tomato (PKM-1) under pot culture conditions. Seaweed extracts obtained through hot-water and solvent extraction were screened for phytochemicals and endogenous growth hormones (IAA, GA₃ and cytokinin). Among the six species analysed, S. wightii exhibited the highest levels of auxin (3.7 mg L-1) and cytokinin (4.9 mg L-1). Preliminary screening using crude extract showed that a 2.5 % concentration significantly enhanced germination, seedling vigour, root and shoot length and leaf area index. In the pot experiment, the integrated treatment comprising 75 % recommended dose of fertilisers (RDF) + 2.5 % S. wightii extract + A. lipoferum + B. megaterium (T8) recorded superior growth and yield attributes, including increased dry matter production, fruit number, fruit weight and total fruit yield, comparable to 100 % RDF. The results demonstrate that the combined application of  S. wightii extract and PGPR can effectively enhance tomato productivity while reducing fertiliser usage by 25 %. This integrated biostimulant strategy offers a sustainable approach to improving crop performance and reducing chemical fertiliser dependence.