Growth Promotion and Disease Suppression of Tomato by Root-Colonizing Bacteria in Saline Soil

Abstract

Soil salinity and soil-borne fungal pathogens severely limit tomato production worldwide, necessitating sustainable management strategies. This study evaluated the potential of five plant growth–promoting rhizobacterial (PGPR) strains—Pseudomonas putida 1T1, Stenotrophomonas rhizophila ep-17, S. rhizophila e-p10, Serratia plymuthica RR2510, and Pseudomonas trivialis 3Re27—for suppressing tomato Fusarium root rot (TFRR) caused by Fusarium solani and for their ability to colonize tomato roots under saline conditions. Disease suppression assays revealed that pathogen inoculation significantly increased TFRR incidence, while bacterial inoculation markedly reduced disease severity in most treatments. Among the tested strains, P. putida 1T1 exhibited the strongest biocontrol activity against F. solani. Rifampicin-resistant mutants of all strains successfully colonized tomato roots and persisted under salt stress, with population densities ranging from 3.8 to 4.2 log₁₀ CFU g⁻¹ root. Higher bacterial inoculum densities further enhanced plant performance under saline conditions. Overall, the results demonstrate that salt-tolerant PGPR can effectively suppress TFRR while maintaining stable root colonization under salinity stress, highlighting their potential as sustainable bioinoculants for improving tomato resilience in saline soils.