Biofortification of New and Old Bread Wheat (Triticum aestivum L.) Cultivars through Foliar Application of Zinc and Iron Different Forms

Apart from inadequate soil N and P, soil zinc (Zn) and Iron (Fe) deficiencies also pose a serious threat to global crop production and food nutrition. Zn and Fe deficiencies affect more than half of the world’s population, especially women and preschool children. Micronutrient malnutrition in human in developing countries is derived from deficiencies of these elements in staple food. Many approaches have been chosen to increase the Zn and Fe content in wheat grains and ameliorate their malnutrition, including breeding, genetic engineering and agronomic approaches. Among them, fertilization, especially foliar Zn and Fe spray is considered as a rapid and efficient way to reach high Zn and Fe in grains. Foliar application is executable, sustainable, economically implementable, highly efficacious, and able to cover wide areas, especially in undeveloped regions worldwide.

In order to evaluate the effect of foliar application of zinc and iron in different forms on dry matter remobilization and grain quality of four bread wheat cultivars in two locations, an experiment in factorial conducted in randomized complete block design with three replications during 2015-16 cropping season. Experimental treatments were included: wheat cultivars Roshan, Roshan Back cross (old cultivars), Bam and Ofogh (new cultivars), zinc application in three levels of foliar application of water (control), zinc sulfate and chelated zinc and iron application in three levels of foliar application of water (control), iron sulfate and chelated iron (equivalent to 2.5 kg per hectare). The first experiment conducted at the Research Farm of Birjand University located in Amirabad region with sandy clay loam soil texture, and 8.1 pH. The second experiment conducted at the South Khorasan Agricultural and Natural Resources Research and Education Center located in Mohammadieh region with  loam soil texture, and 7.6 pH. Investigated traits were including the amount, efficiency and ratio of dry matter remobilization and current photosynthesis, Zn, Fe, P and N concentration in grain. Data analyses were performed using two-way analysis of variance with SAS 9.1. Means of treatments were compared according to protected least significance differences test at the 5% level.

According to the results, location had a significant effect on all traits. Grain Zn, Fe, P and N and also amount, efficiency and ratio of current photosynthesis were lower in Amirabad, perhaps because of its higher soil pH and EC. Grain Zn and Fe at Mohammadieh were 34.4 and 24 percent higher than Amirabad, respectively. Wheat cultivars were significantly different in their grain Zn, Fe and N. Older cultivars including Roshan and Roshan-Back cross had higher Zn and Fe contrasting with newer cultivars of Bam and Ofogh. The highest grain N with 1.94 percent was belonged to Roshan cultivar. The highest amount of remobilization and its efficiency were related to Ofogh and then Bam cultivars. In the present experiment it was observed that foliar application of zinc especially in the form of ZnSO4 significantly increased grain Zn (by 18%) and N (by 4.4%) but reduced grain P (by 15.2%). Wei et al., (2012) reported that foliar application of zinc forms with lower molecular weight such as ZnSO4 and Zn-AA were more effective contrasting their chelated and citrated forms. Grain Zn improved by 15.5% and 21.6% in Mohammadieh and Amirabad region via foliar application of ZnSO4, respectively. Furthermore, foliar application of iron especially in the form of FeSO4 significantly improved grain Fe concentration (by 12.9%) but reduced grain P (by 11%).

According to the results, it can be concluded that there is a significant genetic potential of grain nutrients between cultivars. Understanding these genetic properties and take advantage of them for wheat breeding could be helpful to reach cultivars with higher grain nutrients. The present study observed that the foliar application of Zn and Fe could improve their grain concentration, as well as N content, while decreased the P contents. The elevating effects of ZnSO4 and FeSO4 on the Zn and Fe concentration were better than those of Zn-EDTA and Fe-EDDHA, respectively especially in Amirabad region with higher pH and EC. In conclusion, foliar Zn and Fe fertilization is an effective agricultural approach for promoting grain Zn and Fe concentration.