Faculty of Food Technology and Biotechnology, University of Zagreb
Abstract
The efficacy of strains of Pseudomonas fluorescens, Bacillus megaterium and Azospirillum spp. in in vitro solubilization of Ca3PO4 was studied. Pseudomonas fluorescens and Bacillus megaterium strains were the most powerful phosphate solubilizers on Pikovskaya (PVK) plates and liquid medium. Azospirillum lipoferum strains showed weak zones of solubilization on the PVK plates. Phosphate solubilization by the tested organisms was accompanied with pH reduction of the culture medium. Maximum pH reduction was 2.8, 1.2 and 0.5 units for Pseudomonas fluorescens, Bacillus megaterium and Azospirillum lipoferum strain 137, respectively. Alginate and agar immobilization of the tested bacteria or coimmobilization of A. lipoferum 137 and B. megaterium significantly enhanced phosphorus solubilization for four consecutive 4-day cycles. In a pot experiment, phosphorus mobilization in wheat (Triticum aestivum L. cv. Beni Swif 1) inoculated with B. megaterium or A. lipoferum 137 as single or mixed inocula (as free or alginate immobilized beads) was studied in presence of Ca3PO4. Wheat inoculated with mixed inocula exhibited high shoot dry weight, total nitrogen (N) yield and the shoot phosphorus content increased by 37 and 53 % compared to the plants inoculated with A. lipoferum and uninoculated ones, used as control, respectively. Maximum nitrogenase activity (measured by acetylene reduction assay) was observed in mixed inoculum treatment, and was increased by 500 and 32 % compared to uninoculated and A. lipoferum inoculated plants. Results demonstrate the beneficial influence of coinoculation of A. lipoferum and B. megaterium for providing balanced N and P nutrition of wheat plants
