Investigating Effective Factors in Improving Plant Growth by Native Phosphate-dissolving Bacteria Isolated from Wheat

Wheat is one of the most important strategic products in providing food security for the growing world population. The purpose of this research is to isolate and identify plant growth-promoting bacteria from the wheat rhizosphere and their inhibitory effect on the growth of the pathogenic fungus Fusarium sp. isolated from wheat. The initial screening of 100 bacterial strains isolated from wheat roots was done based on their ability to dissolve phosphate. The effective factors in plant growth and inhibition of fungal pathogens, such as the ability to produce IAA, siderophores, protease, biofilm, bacterial swarming motility, tolerance to salt, seed germination, and seed vigor tests, were investigated. In the initial screening, four bacterial isolates with the highest amount of phosphate dissolution were identified based on morphological and biochemical characteristics as well as the sequence of 16S rRNA region belonging to Curtobacterium sp., Arthrobacter sp., Acinetobacter calcoaceticus, and Cellulosimicrobium sp.; Curtobacterium sp. had the highest amount of IAA (6.14μg/ml), siderophore (2.25cm), protease (1.4cm), and the highest tolerance to salinity (20%) and phosphate dissolution (375.3mg/ml). In the swarming motility test, the highest values were related to Arthrobacter sp. and Curtobacterium sp. at 2.7 and 2.2cm, respectively. The highest amount of biofilm formation was associated with Acinetobacter calcoaceticus and Curtobacterium sp. with an average absorption coefficient of 0.153 and 0.139, respectively. The highest and lowest average values of percentage inhibition of pathogenic fungus colony growth were evaluated in Curtobacterium sp. isolate with a value of 57.3%, and Cellulosimicrobium sp. isolate with 33%, respectively.