Abstract
Arbuscular mycorrhizal fungal (AMF) species, Glomus fasciculatum, PGPR strains Pseudomonas putida (Pp) and Bacillus sp. (Bac) were studied for their effect on plant growth parameters and induction of systemic resistance against Fusarium oxysporum f. sp. carthami (Path) in safflower (Carthamus tinctorius L.), both singly and in combination with or without pathogen. All the tested microorganisms showed a stimulatory effect in the form of significant increase in shoot and root length, plant (shoot+root) fresh and dry weight, and seed yield at two intervals of crop growth over control. Combined inoculation with AMF+Pp+Bac enhanced growth parameters, in addition to significant reduction in percentage disease incidence. AMF+Path treated plants recorded the least disease incidence (13.33%), followed by P. putida (17.00%) and Bacillus sp. (22.67%) when compared to only pathogen inoculated plants (75.33%). Disease incidence in co-inoculation with AMF+Pp+Bac+Path further reduced and turned out to be the least (8.67%). Increase in the activity of defence-related enzymes such as L-phenylalanine ammonia lyase, peroxidase, and polyphenol oxidase were recorded in the individual bio-inoculant treatments in pathogen-infested soil. Even higher levels increase in the activity of defence-related enzymes were detected in the plants inoculated with the combination: AMF+Pp+Bac+Path. An increase in phenol content was also recorded in bio-inoculant (single)-treated plants and maximum levels were detected in combination inoculated plants. The tested bio-inoculants—G. fasciculatum, P. putida, and Bacillus sp.—showed promising results in reduction of disease incidence and were effective in inducing defence responses, and triggering resistance against Fusarium wilt pathogen (Fusarium oxysporum f. sp. carthami) in safflower.