Effect of Potassium Solubilizing Biofertilizers Application Compared to Potassium Sulfate on Growth and Some Physiological Traits of Radish (Raphanus sativus L.) under Drought Stress

Plant growth promoting bacteria are beneficial microorganisms that produce plant resistance to a variety of biological and non-biological stresses, including drought, extreme temperatures, salinity, toxic metals, etc, and increase plant productivity and yield. The use of these microorganisms as biological agents in increasing soil fertility and improving agricultural productivity has been studied by many researchers, so a proper understanding of their effect on drought resistance can be effective in water resources management. Useful in field and reducing environmental effects of using chemical fertilizers. The purpose of this study was to investigate the effect of some bio-fertilizers on growth and some physiological and biochemical characteristics of red radish and in comparison with potassium sulfate application under drought stress.
In other to investigate the effect of application of bio-fertilizers containing potassium-soluble bacteria (Pseudomonas koreensis and Pseudomonas vancouverensis), phosphorus-solubilizing bacteria (Pseudomonas putida) and nitrogen-fixing bacteria (Pantoea agglomerans) on plant growth and function, this experiment was done with 10 treatments and three replications in the form of completely randomized design in greenhouse. Finally the statistical population consisted of 30 pots of 10 treatments and three replications for red radish. Drought stress was applied in such a way that the apparent symptoms of stress were seen in the plants and the amount of water used was the same for all plants. The experiment was carried out in greenhouses and nylon pots with a capacity of 6.5 kg were used. The soil was prepared using a calcareous soil of Zanjan University research field. Its absorption was less than critical. Organic matter content was 0.4% and lime equivalent was 14.1% pH of soil 7.57 and EC of abstract soil paste was 2.21. Pots were treated with municipal water for 25 days after planting. EC values of water was 400 µS / cm that irrigated the plants every three days. The desired bio-fertilizers were added to the pots with irrigation water. After 25 days, 15 pots of treatments 4 to 6 were subjected to drought stress. 40 days after planting before drying of the plants, weight, moisture content of plant tissue, leaf proline content, total free amino acid, and total soluble sugars in leaf extract were measured. Analysis of variance was performed using SAS software and LSD test at the 5% level was used to compare the means.
Results of analysis of variance showed that the effect of different treatments on aerial fresh weight was significant at 1% level. Fertilizer treatments under stress and non-stress conditions significantly increased aerial fresh weight. Among non-stress treatments, the highest fresh weight was obtained from treatment 2 (10.03 g / pot) and the lowest was in control treatment (6.55 g / pot). Among the drought stress treatments with application of different fertilizers used, treatment 8 (9.19 g / pot) had the highest and treatment 6 (7.04 g / pot) had the lowest fresh weight. Application of potassium sulfate fertilizer increased the fresh weight of aerial part both under stress and non-stress condition. Potassium soluble bio-fertilizer alone and in combination with other bio-fertilizers increased radish aerial fresh weight, which was not significantly different from potassium sulfate fertilizer. In radish, drought stress affected the tuber fresh weight more. The radish plant uses the water of the tuber reserve in drought stress so that the leaves are less susceptible to stress. In non-stress conditions, application of potassium sulfate fertilizer and bio-fertilizers in radish increased yield. Potassium sulfate effect was greater. In stress conditions, the effect of bio-fertilizers was more than potassium sulfate in stress condition. The effect of potassium soluble bio-fertilizer application was almost identical with the combined application of different biofertilizers. Drought stress increased the concentration of proline, amino acids and soluble sugars in leaves and tubers of radish. Increasing concentration of these compounds indicated that plants were resistant to drought. Application of potassium sulfate and bio-fertilizers decreased these concentration and the effect of bio-fertilizers was more than that of potassium sulfate. The amount of ion leakage also increased under drought stress but leakage decreased by using potassium sulfate and bio-fertilizers. Drought stress also reduced the starch concentration in leaves and tubers of radish, which is a consequence of drought stress.
In general, application of potassium sulfate and bio-fertilizers moderated the effects of drought stress and in some cases the effect of biofertilizers was greater. Integrated use of bio-fertilizers was not significantly different from the use of potassium soluble bio-fertilizer alone. So, the results of this study showed that the use of bio-fertilizers can be included in the plant nutrition program as a factor in reducing the negative effects of stress on plants.