effects of phosphorus solubilizing bacteria and nitrogen on the qualitative and quantitative properties of tuberose (polianthes tuberosa)

introduction: in iran, tuberose is ranked the forth after gladiolus, rose and carnation. these flowers are known as high quality products among which maximum exportation belongs to tuberose and gladiolus. in plant cultivation and development, adequate provision of nutrients is of crucial importance. tuberose needs plenty of nutrients to obtain the desirable quality and flowering. hence, tuberose balanced nutrition can play an important role in increasing the yield and quality of its flowers. nitrogen is a deciding factor for the plant growth and physiology. this nutritional element contributes to the formation of amino acids, proteins, nucleic acids and other cellular components that are required for the construction of new cells. bio fertilizers containing phosphate solubilizing bacteria (bacillus and pseudomonas) have microorganisms which are beneficial to the soil; these bacteria are conducive to the production of biological materials and as a consequence to plant development. according to a report by rawia eid et al., (2009) the application of phosphate solubilizing bacteria increased the growth rate of matthiola cut flower and improved its quality. in another study on soybean, it was observed that the application of phosphate solubilizing bacteria led to a rise in the plant dry matter content. considering the contributory role of nitrogen and phosphorous in increasing the yield and quality of ornamental plants, the aim of this research was to examine the impact of different nitrogen levels and phosphate solubilizing bacteria on the yield and qualitative properties of tuberose cut flower. materials and methods: this research was carried out in a greenhouse in the city of zanjan in iran in 2011 through a factorial-form experiment based on a randomized complete block design with three replications and twelve treatments performed on tuberose double cultivar. the treatments included bio fertilizer containing phosphate solubilizing bacteria at three levels (0, 5 and 10 kg ha-1) and nitrogen at four levels (0, 50, 100 and 200 kg ha-1) taken from urea source. before cultivation, the bulbs, which were supposed to be inoculated with the mentioned bacteria, were placed in dense suspension (4gl-1) containing phosphate solubilizing bacteria for some minutes. after germination of the bulbs and formation of the actual leaves, the first stage of nitrogen consumption was performed during the growing season. the second stage of n consumption began 20 days after the first stage. at the end of the experiment, such parameters as flower vase life, leaf area per plant, percentage of simultaneous opening of the florets, relative water content percentage, leaf chlorophyll index, plant biomass, dry matter percentage and leaf nitrogen and phosphorous percentages were measured. for means comparison, data variance analysis was carried out by sas software and duncan’s multiple-range test. results and discussion: according to data variance analysis, different levels of nitrogen had a significant impact on all properties except for flower vase life and leaf p percentage at the probability level of 1℅. also, phosphate solubilizing bacteria left a significant effect on all properties except for flower vase life and leaf n and p percentages at p=1℅. the interactive effect of nitrogen and the bacteria on such traits as percentage of simultaneous opening of the florets, flower vase life, dry matter percentage and plant biomass was significant at p=1℅. also, with rise in n levels and in bio fertilizer containing phosphate solubilizing bacteria, there occurred an increase in leaf area, relative water percentage, leaf chlorophyll index, leaf n percentage, dry matter content and plant biomass as well. the results showed that a rise in the application of nitrogen up to 200 kg ha-1 led to an increase in leaf area in bush, relative water percentage, leaf chlorophyll index, leaf n and p percentages, biomass per plant and the percentage of bulb dry matter as well. in contrast, it led to a decline in flower vase life, percentage of simultaneous opening of the florets and leaf p percentage. maximum values for these properties were obtained when nitrogen was consumed at the level of 50 kg ha-1. the treatment of bio fertilizer containing phosphate solubilizing bacteria at the level of 10 kg ha-1 resulted in an increase in leaf area, relative water percentage, leaf chlorophyll index, leaf p percentage, plant biomass in bush and plant dry matter percentage. according to the results from this work, a consumption of 200 kg ha-1 nitrogen accompanied by 10 kg ha-1 bio fertilizer containing phosphate solubilizing bacteria is recommended. in their study on matthiola cut flower, rawia eid et al., (2009) showed that a rise in nitrogen level caused a reduction in the percentage of simultaneous opening of the florets, which is in accordance with our results. after examining the effects of n and p levels on tuberose single cultivar, patel et al., (2006) reported that an application of 200 kg ha-1 p2o5 fertilizer and 400 kg ha-1 nitrogen resulted in a maximum production of plant biomass. the presence of nitrogen and phosphate solubilizing bacteria in bio fertilizers is crucial for the production of a desirable biomass and for the attainment of maximum economic yield. sirvastava et al., (2005) conducted a research on the impact of phosphate solubilizing bacteria on gladiolus cut flower and showed that high concentration levels of the bacteria reduced the percentage of simultaneous opening of the florets