Effect of PGPR inoculation on yield and nutrient uptake of corn (SC. 704)

Effect of Plant Growth Promoting Rhizobacteria on Growth and nutrient uptake of Corn (SC.704) Introduction: Maize (Zea mays) is one of the most important crops with high nutritive requirements. Due to the characteristics of its rooting system, maize develops a great deal of interaction with soil microorganisms and as a result, it is greatly influenced by soil microbial communities. Pseudomonas and Bacillus are the most important PGPRs that increase plant growth directly or indirectly via different mechanisms such as production of plant hormones (auxin, cytokinin, and gibberellic acid). This may result in increased plant root mass and root branching, ultimately contributing to the increased rates of nutrient uptake by roots. The inoculation of plants with Pseudomonas fluorescence increases plant growth through the production of growth stimulants such as indole acetic acid (IAA) and cytokinins (Vikram et al., 2007). PGPRs can also indirectly induce plant growth via protecting plants from pathogenic injuries. The aim of this study was to evaluate the effects of PGPR bacteria on growth and nutrient absorption of maize plant. Materials and Methods: In this experiment, of the 51 bacterial strains extracted from alfalfa rhizosphere, 8 superior isolates of Pseudomonas, Bacillus and Rhizobium (Pf54, Pf12, Pf39, Pf29, Bv1, Bv2, Rm42 and Rm43) were selected based on their growth parameters performance in the previous studies (Besharati et al., 2017). The experiment consisted of twelve treatments: 8 bacterial isolates, a mixture of Pseudomonas fluorescent, Rhizobium and Bacillus isolates, (T9), control without fertilization and inoculation (T10), low-input chemical treatment (50% fertilizer recommendation) (T11) and full application of chemical fertilizer (T12), which were arranged in a complete randomized block design with three replications.
Five maize seeds were sown in pots at 3 cm depth and one week after emergence, the number of plants per pot was reduced to 3. From planting till harvest, the phytotron chamber temperature was maintained at 25-28 ° C, relative humidity was from 50 to 70%, and a period of 12 hours of light 60,000 lux (day) and 12 hours of darkness were used. The measured traits included plant height, plant dry weight, root dry weight, root to shoot ratio, root length and the concentrations of N, P, Fe, Mn and Zn. Result and Discussion: The results showed that the greatest plant heights of 90.1, 89.9, 89.9 and 89.2 cm were respectively obtained from PF12, BV1, pf54 and T9 treatments. The highest nitrogen uptake occurred with RM43 and mixture of isolates treatments. The most effective treatment was found to be the mixture of all bacterial isolates (T9), which resulted in a 83 % increase in maize plant dry weight relative to control. Martin et al, (1982) reported that inoculation of maize seeds with azotobacter and pseudomonas bacteria respectively increased the plant dry weight by 17 and 21 % as compared to control (Zahir et al, 1998)
The Bacillus treatment increased phosphorus uptake by 3.5 times as compared to the control. PF54 treatment caused the highest Fe concentration in maize shoot. The mean absorption of phosphorus increased when the plant was treated with the mixture of Bacillus, Rhizobium and Pseudomonas (T9), which was 249% of the control. The highest (18.34 mg/kg) and the lowest (13.38 mg/kg) Mn shoot concentrations were respectively related to PF54 and control treatments.

Application of the bacteria strains significantly reduced the plant's need for nitrogen, iron, manganese and zinc elements, where the Bacillus was the most effective PGPR in this respect. The mixture of strains and the use of Rhizobium bacteria (RM42 and RM43) raised phosphorus absorption of maize shoot about 2.5 times of the mean value. All the Pseudomonas and Rhizobium strains used in seed inoculation have the ability to produce siderophore. The highest and lowest zinc concentrations in maize were observed under RM43 and PF540 treatments, respectively. Preparation of inoculum from two strains of Bacillus bacteria, two strains of Rhizobium bacteria and four strains of selected Pseudomonas bacteria and inoculation of maize seed before cultivation with these bacteria and using only one third of the recommended nitrogen and phosphorus fertilizers together with the bacterial treatments can compete chemical fertilizers and significantly increase the growth indices and shoot nutrient concentrations in maize as compared to the full application chemical fertilizers alone