بهبود جوانه زنی و شاخص های رشدی بذر گیاه Astragalus cyclophyllon در اثر تیمار بذر با باکتری Peribacillus frigoritolerans

Commercial cultivation and propagation of Astragalus cyclophyllon despite its valuable forage features, due to its hard seed, weak germination and poor seedling establishment, has not been developed. Probiotic bacteria can promote plant growth and increase successful establishment of plant. The present study, investigated the characteristics of the plant growth–promoting Prebacillus sp. Strain (Rh18) which was isolated from the rhizosphere of A. cyclophyllon. Based on the results of the 16S rDNA sequence and its alignment with known sequences, it showed more than 99.89% similarity to Peribacillus frigoritolerans species. The effect of bacterial treatment on the seeds quality characteristics and the seedling vigor were investigated. Based on the results of previous research, all the seeds were pre-treated with 98% sulfuric acid and then washed to remove part of the seed hardness. After washing and disinfection, the seeds were placed in the bacterial suspension (108 CFU/gr) for one hour, and the planted seeds were kept at 25-27 °C. Germination percentage was checked and recorded daily, and after 15 days, seedling vigor, plant length, root length, and dry weight of seedlings were calculated. This experiment was conducted as a completely randomized design with three replications based on the guidelines of the International Seed Testing Association. The growth promoting characteristics of the P. frigoritolerans isolate, were studied and its ability to produce indole acetic acid hormone, nitrogen fixation, and phytase enzyme production were identified as some prominent characteristics of this isolate. The results of treatment of A. cyclophyllon seeds with P. frigoritolerans (Rh18) showed that the bacterial treatment increased the germination rate from 45% to 73.3% (about 1.63 times). Also, it caused an increase of 1.32, 1.19, and 1.48 cm in the length of seedling, stem, and root, respectively, compared to the control plant. The seedling vigor index of the treated plants increased more than twice and also the dry weight was recorded with an increase of 1.1 times compared to the control plant. It seems auxin production by P. frigoritolerans isolate has been effective in increasing the length and weight of roots and the development of hairy roots. The nitrogen-fixing ability of the isolate improved seedling growth via enhancing nitrogen uptake as an essential nutrient which required in growth and development of plants. According to the presented results, using of plant probiotic bacteria can be considered as one of the promising solutions for improving germination, growth and effective establishment of A. cyclophyllon seeds in the pastures of the country.