Effectiveness of plant growth promoting rhizobacteria on Bromus tomentellus Boiss seed germination, growth and nutrients uptake under drought stress

The aim of the present study was to investigate the effect of growth-promoting bacteria on the germination, growth and nutrient uptake by rangeland species Bromus tomentellus Boiss under drought stress. The research was conducted as a factorial experiment in a completely randomized design. The first factor was bio-fertilizer (Azotobacter vinelandii = A, Pantoea agglomerans + P. putida = P, combined A + P and control (without bio-fertilizer). The second factor was drought stress, which was applied at three levels of field capacity (FC), 0.7 FC and 0.4 FC. The results showed, under drought stress, that both treatments A and P + A at 0.7 FC level increased the seed germination rate of B. tomentellus Boiss, while the control treatment at 0.7 FC level had the lowest germination rate. Germination percentage in the treatment P at FC level was the highest. In the control treatment at 0.4 FC level, the lowest germination percentage was measured. The results showed that both treatments A and A + P at FC level resulted in an increase in the root length. The P treatment at the level of 0.7 FC showed the lowest root length. Also, the highest and lowest shoot lengths were observed in treatments A + P and A at 0.4 FC level, respectively. In the control treatment, at FC level, the shoot dry weight was increased, but treatment P at FC level reduced the shoot dry weight. The highest and lowest root dry weights were observed in treatment A at 0.4 FC and FC levels, respectively. The results showed that treatment A absorbed potassium, iron, zinc and manganese. P treatment increased the uptake of nitrogen, phosphorus, and Fe, while treatment A + P increased K and Fe in the root and shoot. In general, the results showed that the use of bio-fertilizers could increase the germination and growth of B. tomentellus Boiss. In particular, the fertilizers in 0.7 FC and FC levels had increased traits and played no significant role in mitigating the effects of drought stress. The application of bio-fertilizers on B. tomentellus Boiss could be useful in the restoration and improvement of rangelands.