Study on low irrigation and growth-promoting bacteria effects on inulin content and morphological characteristics of different Tragopogon spp. genotypes root

Tragopogon spp. has many medicinal properties in addition to its edible consumption due to its many useful compounds. One of these identified compounds is inulin, which is present in the roots of this plant. To investigate the effects of low irrigation stress and growth-promoting rhizobacteria (Bacillus subtilis) on inulin content and root morphological traits in some genotypes of Tragopogon spp., a factorial experiment with three factors in a completely randomized design with three replications was conducted in the research greenhouse of Bu Ali Sina University in 2020. The factors included irrigation at two levels of without stress (100% of field capacity) and low irrigation stress (50% of field capacity) as the first factor, genotype at 15 levels (different genotypes of Tragopogon spp) as the second factor, and plant growth-enhancing rhizobacteria (PGPR) at two levels of inoculation with B. subtilis and without inoculation as the third factor. Length, area, volume, diameter, weight, and inulin content of the plant roots were measured. The results showed that the irrigation × genotype × bacteria interaction effect was significant on all studied traits. Low irrigation stress increased length, area, and volume of the plant roots in most genotypes, but decreased root weight and inulin content. Inoculation with B. subtilis affected genotypes differently. Iranian genotype No. 11 (Kaboudar Ahang) had the highest inulin content at different stress and B. subtilis levels, followed by Italian genotype No. 4 at both B. subtilis levels under non-stress conditions. Overall, stress reduced inulin content of the plant roots, but the effect of inoculation with B. subtilis depended on the genotype.