Strains Induce Resistance to f. sp. Race 3 in Tomato Through Different Molecular Mechanisms.

Plant growth promoting rhizobacteria (PGPR) are potential natural alternatives to chemical fungicides in greenhouse production via inducing plant immune system against biotic stresses. In this research, 126 isolates were recovered from rhizosphere soils of 13 different commercial vegetable greenhouses in Iran. isolates were screened for Plant growth promoting (PGP) traits and ability to antagonize f. sp. race 3 (), the causal agent of Fusarium wilt of tomato (FWT). Six isolates with the highest antagonistic activity and at least three PGP traits were selected and compared with chemical fungicide Carbendazim in a greenhouse experiment. All bacterial treatments mitigated FWT disease symptoms like chlorosis, stunting and wilting at the same level or better than Carbendazim. Strains IC10 and Y28 increased shoot length and shoot fresh and dry weight compared to not inoculated control plants. Phenotypic characterization and 16S rRNA gene sequencing showed, strains IC10 and Y28 were closely related to and , respectively. The ability of the superior biocontrol strains to induce antioxidant enzymes activity and systemic resistance (ISR) was investigated. Increased activity of catalase (CAT) in plant treated with both strains as well as an increase in peroxidase (POX) activity in plants treated with Y28 pointed to a strain specific-induced systemic resistance (ss-ISR) in tomato against . The differential induced expression of and (two transcription factors involved in plant defense) and and by the analyzed strains, especially after inoculation with , suggests that ss-ISR is triggered at the molecular level.