Wheat (Triticum aestivum L.) is considered as the major cereal crop in the world in respect of the cultivated area and total production. High temperature resulting from delay in planting is one major environmental factor limiting growth and production of wheat, especially in tropical regions. 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.
To study the effect of iron, zinc and manganese foliar application on the physiological, agronomic traits and protein of wheat under late season heat stress, 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 planting date in two levels (5 November and 20 December) 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 showed that the delay in planting due to terminal heat 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, iron, zinc and manganese foliar application could increase significantly the measured traits in optimum and late planting date. Meanwhile, application of zinc spray showed the greatest effect in reducing the damage caused by terminal heat stress on measured traits.
In general, planting on 5 November and the use of micronutrients, especially zinc, as foliar application, can reduce the harmful effects caused by terminal heat stress and improve the physiological, agronomic traits and grain protein content of bread wheat in the region.
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