interaction effects of phosphate solubilizing bacteria and mycorrhiza on the growth and phosphorus uptakeof sorghum

introduction: the most abundant of agricultural soils in iran, are calcareous. in calcareous soils, phosphorus fertilizers use efficiency is low. the usage of soil microorganisms is one of the effective ways to increment the uptake of phosphorus in calcareous soils. this microorganisms using various mechanisms, including the production of plant hormones or the production of organic and inorganic acids to dissolve the insoluble phosphorous compounds. mycorrhizal symbiosis is also one of the most recognized and important symbiosis relationship found in the world. in a mycorrhizal symbiosis,plants can be able to absorb more nutrients and water from soil and fungus plays a protective role as a growth enhancer and make the plants more tolerable to biotic (pathogens) and abiotic (drought, cold and salinity) stresses .this research conducted to study phosphate solubilizing bacteria and mycorrhiza roles on sorghum growth and phosphorus availability to this plant. materials and methods: to achieve the desired goals, a pot experiment was conducted as a factorial in completely randomized design with sixteen treatments in three replications. the treatments were combination of four p levels of zero, 25, 50, and 75 mg kg-1 p2o5 from triple super phosphate source, the two treatments of inoculation and without inoculation of phosphate solubilizing bacteria and the two treatments of inoculation and no inoculation of mycorrizal fungus. required fertilizers based on initial soil test results were supplied. accordingly, the same amount of nitrogen, 80 mg kg-1 (30 mg kg-1 before planting and 50 mg kg-1 after planting twice) as urea source, 10 mg zn kg-1 and 5 mg kg-1 cu per kg soil as the forms of zinc sulphate (znso4.7h2o) and copper sulphate (cuso4.h2o) were added to each soil sample. required phosphorus also was calculated based on treatments and added to potting soil. each pot size was 5 kg. every sample was thoroughly mixed and then were placed in pots. at the same time the seeds were inoculated. in harvesting time, some parameters such as plant height and diameter, wet and dry foliage yield, and phosphorous uptake were measured and analyzed statistically. after harvesting time also soils phosphorous content were measured and analyzed. results discussion: the results indicated that by utilizing the phosphate solubilizing bacteria, stem diameter, dry matter yield, phosphorous uptake, and soils phosphorous content after harvesting significantly increased. these findings indicated that the use of phosphate solubilizing bacteria affected plant growth. such results have been previously reported. ramezanian (31) reported that application of pgpr will be increase wheat stem height and diameter. li et al (18) and larsen et al (16) reported that soil microorganisms, including growth promoting bacteria through a variety of mechanisms such as acc deaminase production or an increase in available phosphorus can stimulate plant growth and increase height and diameter of the stem. glick et al (13) showed that plant growth promoting bacteria through the production of plants hormones increases plant height and stem diameter, and ultimately improve plants yield. increases yield of plants through the use of phosphate solubilizing bacteria previously has been reported by other studies. mycorrizal inoculation also had a significant effect (p<0.01) on increasing of stem diameter, dry matter yield, plant phosphorous concentration, plant phosphorous and zinc uptake and soils phosphorous content after harvesting. some earlier studies have also shown that the use of mycorrhizal fungi, especially in soils with low fertility, lead to an increase in crop yield. according to carlile and watkinson (8), due to the influence of mycorrhizal fungus mycelium in the soil, the root uptake enhances and thus the performance of plants will be improved. they stated that the production and secretion of organic acids, production of phosphatases and phosphorus transport from distant regions of the roots to close spaces near the root surface are some of the fungi efficient mechanisms. phosphorus application also had a significant effect on some indicators such as plants height, dry matter yield, shoot p and zn concentration, total uptake of phosphorus and zinc and soil phosphorous content after harvesting. combined use effect of phosphorus, bacteria and mycorrizal inoculation on stem diameter and dry matter yield also were significant. conclusion: the results showed that the combined application of phosphate solubilizing bacteria and mycorrhizal fungi can increase the efficiency of phosphorus fertilizer and improve growing conditions and yield of sorghum. based on the results, the combined use of 25 mg p2o5 per kg of soil, along with the use of phosphate solubilizing bacteria and mycorrhizal fungi produced the highest values of measured traits and can be recommended for the same conditions.