Biostimulant Effects of Plant-Growth-Promoting Bacteria (PGPB) Consortia in Zea mays, Brassica oleracea, and Solanum lycopersicum

Abstract

The overuse of chemical fertilizers highlights the need for sustainable alternatives, such as plant-growth-promoting bacteria (PGPB). However, bacterial inoculant performance may vary with plant species and growth conditions. This study evaluated the effects of microbial consortia combining Azospirillum brasilense, Pseudomonas putida, Bacillus sp., and Mycobacterium sp. on blue maize, broccoli, and tomato grown in commercial substrate and greenhouse soil. Consortium effects on early plant growth varied according to bacterial combination, plant species and substrate conditions. Pseudomonas putida + Bacillus sp. increased blue maize main root length by 28.45% in greenhouse soil and stem length by 44.70% in commercial substrate, while increasing tomato shoot dry weight by over 500% in greenhouse soil. Azospirillum brasilense + Bacillus sp. increased shoot dry weight by 154.06% in broccoli and 274.87% in tomato, both in commercial substrate. Results obtained with consortia containing Mycobacterium sp. provide exploratory evidence strictly under laboratory conditions. Due to the potential health risk associated with opportunistic and pathogenic species within this genus, these strains cannot be considered for agricultural applications or biofertilizer development, serving exclusively as a model for studies. Overall, these findings emphasize that PGPB consortium performance was context-dependent, emphasizing the importance of plant species, substrate conditions, and microbial composition when evaluating bacterial inoculants.