There is considerable evidence to increase diosgenin and other medicinally useful compounds production in fenugreek with microbial inoculations. Fenugreek (Trigonella foenum-graecum L.), as an annual medicinal plant, is extensively cultivated in most regions of the world. In the present study we evaluate the role of plant growth-promoting rhizobacteria (PGPR) inocula (Pseudomonas putida and Bradyrhizobium japonicum) alone or in combination with an arbuscular mycorrhizal fungus(AMF) (Glomus intraradices) on diosgenin content, some biochemical characteristics and phosphorus accumulation of fenugreek plants subjected to drought stress. ACC deaminase activity was detected in both bacteria and it was 2.1 fold higher in B. japonicum than the P. putida. Results showed that diosgenin content was commonly higher in leaves under non-stress vs drought stress condition. In non-stress, plants with dual inoculation (G. intraradices and B. japonicum) resulted in highest diosgenin content significantly different with other treatments. The leaf proline content was the highest in plant subjected to drought stress with dual inoculation (G. intraradices and P. Putida), whereas the highest total soluble proteins was belonged to plants with triple inoculation(P. putida, B. japonicum and G. intraradices). Bacterial and fungal inoculation decreased peroxidase activity both in stress and non-stress condition. The highest amount of phosphorous in the roots was assigned to single inoculation with P. putida in stress and with G. intraradices in non-stress condition. The present study provides a good insight on the effect of PGPR and AMF on diosgenin content as a major bioactive constituent.

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