Effect of Phosphate Solubilizing Bacteria and Mycorrhizal Fungi on Growth Parameters of Isabgol in Saline Conditions

Some beneficial soil microorganisms can reduce salt stress in many crops. Two experiments were carried outto study the effect of salinity and microorganisms on the growth characteristics of Plantago ovata Forsk. In the first experiment, tolerant species of phosphate-soluble bacteria screened in a salinity stress condition, a number of bacteria were subjected to semi-quantitative phosphate solubility test. The superior isolate was identified as Pseudomonas fluorescens based on the sequence 16S rRNA gene and other phylogenetic analysis. The second experiment was a factorial experiment in randomized complete block design with three replications. The first factor was three levels of salinity (2.5, 5 and 10 dS/m), the second factor was mycorrhizal fungus including Funneliformis mosseae, Rhizophagus intraradices and Glomus fasciculatum, and the third factor consisted of two levels of non-bacterial and bacterial application. Shoot and root dry weight, root to shoot dry weight ratio, mycorrhizal growth response and root colonization percentage were measured. Analysis of variance showed that interaction of salinity stress and mycorrhizal fungus on shoot dry weight was significant at level 1% probability. The interaction of salinity stress and bacteria on the ratio of root dry weight to shoot was significant at 5% probability level. The highest root dry weight and root/shoot ratio (1.7 and 0.9 respectively) were obtained at 2.5 dS/m + Glomus fasciculatum treatment. The highest mycorrhizal growth response percentage was 76.7% at 10 dS/m + Rhizophagus intraradice treatment.  Comparison of the mean interactions between salinity stress and bacteria showed that the highest mycorrhizal growth response percentage was obtained in the 10 dS/m salinity + Pseudomonas fluorescens treatment (45.6%). The results also showed that salinity decreased the yield of Isabgol, but the simultaneous application of PSB and AMF could compensate the negative effects of salinity stress. According to the results, it is possible to use the simultaneous application of Pseudomonas fluorescens and Rhizophagus intraradices to maximize the production of Plantago ovata Forsk.