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Abstract

Plant growth-promoting rhizobacteria (PGPR) have emerged as sustainable alternatives to synthetic fertilizers for improving crop productivity and fruit quality; however, comparative field evaluations of commercial and locally developed multi-strain formulations remain limited. Therefore, this study evaluated the comparative effects of two commercial (TB1 and TB2) and four non-commercial (BS1, BS2, BS3 and BS4) PGPR combinations, together with a mineral fertilizer treatment (G) and an untreated control (O), on the yield, vegetative growth, and fruit quality of 'Gülpembe' tomato (Solanum lycopersicum L.). The trial was established under field conditions in a randomized complete block design (RCBD) with three replications and fifteen plants per replicate. The bacterial combinations contained strains of Bacillus megaterium, Bacillus licheniformis, Bacillus subtilis, Pseudomonas fluorescens and Pantoea agglomerans, selected on the basis of complementary plant growth-promoting traits, including phosphate solubilization, indole-3-acetic acid (IAA) production, siderophore production, biological nitrogen fixation and induction of systemic resistance. The parameters evaluated included total fruit yield, plant height, stem (collar) diameter, average fruit weight, fruit chroma and hue angle, fruit firmness, titratable acidity, total soluble solids (°Brix), lycopene content, total phenolic content and antioxidant capacity. Combined application of PGPR significantly improved vegetative growth, yield, and quality as compared with the control. Notably, the performance of non-commercial four-strain combinations BS3 and BS4 was equal or better than the commercially available PGPR and conventional mineral fertilizers for all traits like lycopene content, total phenolic content (TPC), antioxidant capacity and total soluble solids (TSS). These results suggest that locally characterized multi-strain PGPR combinations are effective biofertilizers for sustainable tomato production. Moreover, these biofertilizers were cost-effective and environment friendly alternatives to conventional chemical fertilizers

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