Plant growth promoting rhizobacteria (PGPR) associate with roots of plants and improve plant growth by utilizing diverse mechanisms like nitrogen fixation, phosphorus solubilization and phytohormone production. Current study was conducted to isolate, characterize, and identify the wheat associated PGPR and investigate the inoculation effect of selected strains for growth promotion of wheat in combination with different levels of chemical fertilizer at two different ecological locations (Multan and Layyah, Pakistan). Among the total 22 bacterial isolates, 11 were positive for acetylene reduction assay (ARA), 9 isolates exhibited P solubilization activity and 19 bacterial isolates produced growth hormone indole-3-acetic acid (IAA) in culture medium. From these, two bacterial isolates with maximum potential to fix nitrogen, solubilize phosphorous and to produce IAA were identified through 16S rRNA gene sequence analysis as Pseudomonas sp. LYT-1 (accession no. KT933231) and Bacillus sp. . Their performance as PGPR along with different levels of nitrogen (N) and phosphorous (P) chemical fertilizers (0-0, 105-75 and 150-100 NP kg ha -1 ) was evaluated under field conditions at two different locations (Multan and Layyah) in 2014-15. The experiments were laid out in Randomize Complete Block Design (RCBD). Results indicated that bacterial strain Pseudomonas sp. LYT-1 (with maximum in vitro nitrogenase activity), increased the growth parameters like plant height, chlorophyll contents, productive tillers, spike length and straw yield of wheat at both the locations. The inoculation of Bacillus strain MWT-14 (with highest in vitro phosphate solubilization and IAA production) in combination with 0-0, 105-75 and 150-100 kg ha -1 N-P fertilizer improved the 1000-grain weight by 9.8%, 5.4%, 4.6% and 2.1%, 6.6%, 4%, respectively at Multan and Layyah, and grain yield by 16.3%, 12.3%, 4.7% and 17.1%, 14.2%, 8.5%, respectively at Multan and Layyah over their respective non-inoculated control treatments. These results concluded that plant growth promoting strains Pseudomonas sp. LYT-1 and Bacillus sp. MWT-14 enhance the growth, productivity and net returns of wheat when used as bio-inoculant along with 30% reduced of the recommended NP fertilizer dose.
