Effect of micronutrients foliar application on some physiological and agronomic traits of bread wheat (Triticum aestivum L.) under complete irrigation and terminal drought stress condition

Introduction Wheat (Triticum aestivum L.) is considered as the major cereal crop in the world in respect of the cultivated area and total production. Drought is a polygenic stress and is considered as one of the most important factors limiting crop yields around the world. Most of the Iranian soils, have a high pH and calcareous nature, and micronutrients solubility in these soils is low. Micronutrients plays a critical role in increasing plant resistance to environmental stresses. Iron as a micronutrient, is critical for chlorophyll formation and photosynthesis and is important in the enzyme systems and respiration of plants. Zinc is a ubiquitous micronutrient. It is required as a structural and functional component of many enzymes and proteins, and increases the yield and yield components of wheat. Manganese as a micronutrient, is necessary in photosynthesis, nitrogen metabolism and to form other compounds required for plant metabolism. Materials and methods To study the effect of micronutrients foliar application on some physiological and agronomic traits of bread wheat (Triticum aestivum L.) under complete irrigation and terminal drought stress condition, an experiment was conducted as split-plot based on randomized complete blocks design with four replications in Ramhormoz city located in south-western Iran. The experimental factors were included drought stress in two levels of complete irrigation (non-drought stress) and irrigation interruption from the beginning of flowering stage to the physiological ripening (terminal drought stress) as the main factor, and micronutrients foliar application in six levels of non-foliar application (control), foliar application by water, iron, zinc, manganese and iron + zinc + manganese (each 3 lit.h-1) as the sub factor. Solutions for foliar application were prepared by using Iron chelate (6%), Zinc chelate (7.5%) and Manganese chelate (7%). The measured traits included leaf chlorophyll index, leaf proline content, cell membrane stability index, grain yield, biological yield, harvest index and grain protein content. To determine the leaf chlorophyll index used of chlorophyll meter digital. To determine the leaf proline content, method of Bates et al. (1973) was used. To determine the cell membrane stability index used of method Lutts et al. (1996). The grain yield was determined at maturity stage and through the harvest of all spikes from the level of 1 m-2 per plot and after removing 0.5 m from the beginning and end respective planting rows (rows 5 and 6). To measure the biological yield at maturity stage, after removing 0.5 m from the beginning and end respective planting rows (rows 5 and 6) from the level of 1 m-2 per plot all the plants were harvested and weighted for each plot separately. The harvest index was determined by the equation GY/BY×100. The grain protein content was calculated as N% × 5.7 on a dry weight basis. N% in grain was determined by the Kjeldahl method according to A.A.C.C. (2000). Analysis of variance was performed using general linear model (GLM) procedure of statistical analysis system (SAS version: 9.3). The means were analyzed using the least significant difference (LSD) method at P=0.05 (LSD 0.05). Results and discussion Results showed that the terminal drought stress decreased significantly traits of leaf chlorophyll index, cell membrane stability index, grain yield, biological yield and harvest index except for leaf proline content and grain protein. However, micronutrients foliar application of iron, zinc and manganese increased significantly the measured traits in both non-stress and terminal drought stress condition. Meanwhile, application of zinc spray showed the greatest effect in reducing the damage caused by terminal drought stress on measured traits. Conclusions In general, the use of micronutrients, especially zinc, as foliar application, can reduce the harmful effects caused by terminal drought stress and improve the physiological, agronomic traits and grain protein content of bread wheat in Ramhormoz region.