The effect of salinity stress and soil microorganisms on quantity and quality characteristics of isabgol (Plantago ovata Forsk)

Isabgol (Plantago ovata Forsk.) is a plant from (Plantaginaceae) family. Isabgol mucilage is valuable compounds that have valuable properties such as stability, suspension and emulsion and has been widely used in pharmaceutical and industrial. In arid and semi-arid area, soil salinity and water shortage is the most important factors in crop growth limitation. In water shortage usage of salinity water is unavoidable Most of the scientists believe that biofertilizers and microorganisms application can improve plant nutrition’s availability in stress condition. To find out the effect of salinity stress, arbuscular mycorrhizal fungi, Mineral phosphate-solubilizing bacteria on morphophysiological characteristics of Isabgol (Plantago ovata Forsk.), this experiment designed and implemented.
The field experiment was conducted at the research farm national salinity research center in 2015. A split-factorial experiment based on randomized complete block with three replications. Three levels of salinity 2.5 (control), 5 and 10 dS.m-1 were as the main plot and mycorrhizal fungi and PSB were as sub plots. Arbuscular mycorrhizal fungi include two levels (Glomus intraradices and control) and PSB also includes two levels (Pseudomonas fluorescens bacteria control). To determine the morphological traits, five plants of each plot were selected randomize. And plots harvested at end to extract seed mucilage and determine yield traits and quality. Chlorophyll index measured every 20 days by SPAD. Statistical analysis was performed with SAS software. Comparison of mean also was conducted by protected LSD test at five percent probability level.
Analysis of variance showed salinity, arbuscular mycorrhizal fungi and Mineral phosphate-solubilizing bacteria had a significant effect at 1% level on plant height, mucilage percentage, mucilage yield, inflation factor, inflation rate per gram mucilage. Interaction between salinity and arbuscular mycorrhizal fungi had a significant effect at 1% level on mucilage yield and inflation factor and had significant effect at 5% level on inflation rate per gram mucilage. Comparison of means showed that the maximum spike height and mucilage yield was 2.21 cm and 176.7 kg.h-1 respectively at 2.5 dS.m-1 salinity and minimum spike height and mucilage yield was 1.99 cm and 91.6 kg.h-1 respectively at 10 dS.m-1 .The maximum mucilage percentage, inflation factor and inflation rate per gram mucilage was 28.8%, 16.2 and 119.3 ml respectively at 10 dS.m-1 salinity. The minimum mucilage percentage, inflation factor and inflation rate per gram mucilage was 24.1%, 12.4 and 49.4 ml respectively at 2.5 dS.m-1 salinity. Comparison of means among Mineral phosphate-solubilizing bacteria levels showed that the maximum spike height, mucilage percentage, mucilage yield and inflation factor was respectively 2.2 cm, 26.8%, 146.7 kg.h-1 and 14.2 ml at Pseudomonas fluorescens usage. The interaction effect of salinity and arbuscular mycorrhizal fungi showed, the maximum mucilage yield was 215 kg.h-1 at 2.5 dS.m-1 salinity and Glomus intraradices application. Research showed that biofertilizer can increase mucilage yield of Isabgol. The maximum inflation factor was 17 ml at 10 dS.m-1 salinity and Glomus intraradices application. The minimum inflation factor was 12.2 at 2.5 dS.m-1 salinity and no mychorrhiza usage. The interaction effect salinity, arbuscular mycorrhizal fungi and Mineral phosphate-solubilizing bacteria showed, the maximum plant height was 28.9 cm at 2.5 dS.m-1 salinity, Glomus intraradices and Pseudomonas fluorescens. The minimum plant height was 17 cm at 10 dS.m-1 salinity and no mychorrhiza and bacteria usage. Variation of SPAD showed that salinity decreased chlorophyll index but mycorrhizal fungi and Mineral phosphate-solubilizing bacteria increased chlorophyll index. The maximum chlorophyll index was 45.6 at 2.5 dS.m-1 salinity 65 days after planting and minimum chlorophyll index was 17.1 at 10 dS.m-1 salinity 105 days after planting.
Totally the results of this study showed that water salinity can have negative effect on morphological characteristic and mucilage yield of Isabgol, but utilizing of some soil microorganisms can compensate these negative effects. In other hand, in high degree of water salinity and no utilizing of bio-fertilizers condition, mucilage quality improved. But according to the international pharmacopeias standard mucilage quality was acceptable at all treatments. therefore biofertilizer application can improve mucilage yield in salinity stress.