Effect of plant growth promoting rhizobia on seed germination, growth promotion and suppression of Fusarium wilt of fenugreek (Trigonella foenum-graecum L.)

Five bacterial strains (TR1 to TR5) isolated from root nodules of fenugreek (Trigonella foenum-graecum) were tested for their plant growth promotory traits and biocontrol potential against Fusarium oxysporum. On the basis of morphological, physiological, biochemical and molecular characteristics, strains TR1 and TR3 - TR5 were identified as Ensifer meliloti, and TR2 as Rhizobium leguminosarum. All bacterial isolates utilized phosphate in vitro. Except TR5, all isolates produced IAA and none of them showed volatile cyanogens production. Except TR3, all isolates produced in vitro siderophore. Isolate TR1 and TR4 showed chitinase production while only TR2 showed β-1,3-glucanase activity. Isolates TR1, TR2 and TR5 exhibited ACC deaminase activity. Isolates TR1, TR2 and TR4 inhibited the growth of F. oxysporum, causing loss of structural integrity of the mycelium, hyphal perforation, lysis, fragmentation and degradation. The potential for nodulation and nitrogen fixation of the strains were confirmed by amplification of 500 bp nodC and 781 bp nifH fragments. The application of the TR1 + TR2 combination resulted in increased grain yield by 35% and 36% of fenugreek in two consecutive field trials, respectively as compared to control. Maximum increments in vigour index, nodule number and root and shoot biomass were recorded with seed inoculated with consortium (TR1 + TR2) followed by single inoculation as compared to control. The antibiotic resistant marker strain of E. meliloti TR1^strep+ and R. leguminosarum TR2^tet+ confirmed the efficient colonization of fenugreek roots. This study showed that these rhizobial isolates have properties of biocontrol agents and may be applied to promote the growth of fenugreek.