Response of safflower genotypes to different nitrogen sources under non-stress and terminal water stress

Safflower is an oilseed plant tolerant to water deficit, and have an important role in oil production. Drought stress is the most important factor limiting crop yields in many parts of the world, including Iran. Nitrogen plays a key role in plant growth and this role is highly related to the amount of water and how it is distributed. Bacteria of the genus Azotobacter are one of the most important growth-promoting bacteria in plants due to their abundance and extent of spread, which is able to improve the availability of nitrogen. In areas where most rainfall occurs in winter and early spring, crops will face water constraints at the end of the growing season. In such conditions, finding cultivars and lines that have good performance in non-stress and drought stress conditions and have a suitable response to Azotobacter and nitrogen fertilizer is of special importance.The aim of this experiment was to evaluate the response of safflower genotypes to the application of Azotobacter and nitrogen fertilizer under different moisture conditions.

This experiment was carried out during two growing seasons (2015/2016 and 2016/2017), in Sarableh Agricultural Research Station, Ilam Province. The factorial scheme 4 × 6 experiment was performed in both years in a randomized complete block design with three replications under terminal drought stress and non-stress conditions. The distance between these two environments was considered to be 10 meters so that the humidity of the two adjacent environments did not affect each other. Experimental factors included seed inoculation with A. chroococcum using urea chemical fertilizer at four levels [without using any N fertilizer source (control), seed inoculation with A. chroococcumalso without use N fertilizer, seed inoculation with A. chroococcum + 50% N of urea fertilizer source, and 100% N of urea fertilizer source], and six safflower genotypes (312-S6-697, PI-401478, PI-253895, PI-306974, Padideh, and Sina).After harvesting and determining grain yield in both experimental conditions, stress tolerance indices including stress sensitivity index (SSI), mean productivity (MP), tolerance (TOL), geometric mean yield (GMP), stress tolerance index (STI) and Modified stress tolerance indices (MSTI) were calculated. Statistical calculations of analysis of variance and mean comparisons were performed using SAS 9.1 software. STATGRAPH software was used to principal component analysis and drawing biplot diagrams.

The results showed that among the nitrogen source treatments, the highest percentage of grain yield reduction with 48% in drought stress conditions compared to non-stress conditions was related to the application of 100% nitrogen chemical fertilizer. This result shows that in drought stress conditions, the application of 100% nitrogen fertilizer due to the increase of biological substances, causes an imbalance between the roots and plant aerial parts in water absorption and water loss through transpiration by aerial organs, which in Extremely serious damage to the economic sector of the plant.Azotobacter inoculation + 50% nitrogen fertilizer application had the highest mean productivity index and the lowest stress sensitivity index among nitrogen source treatments, although it was not significantly different from other nitrogen source treatments. These results indicate that the use of Azotobacter in combination with the application of 50% nitrogen fertilizer reduces the damage caused by drought stress in safflower. Sina cultivar was the most tolerant genotype under drought stress under Azotobacter inoculation and 100% nitrogen fertilizer application. In conditions of inoculation with Azotobacter + 50% of nitrogen fertilizer application, Sina and Padideh cultivars are located in the area of high production potential and low drought sensitivity in the vicinity of vectors related to drought tolerance indices

Sina cultivar in inoculation treatment with Azotobacter and consumption of 100% nitrogen fertilizer, Padideh cultivar in addition to Sina cultivar in combined application of Azotobacter + 50% nitrogen fertilizer had the highest tolerance to terminal drought stress; Therefore, in selecting drought tolerant genotypes, special attention should be paid to nitrogen source factor.