Evaluation of the effect of urea foliar application on polyamine content, grain protein content, and the agronomic traits of bread wheat cultivars under dryland and supplemental irrigation conditions

The purpose of the experiment was to investigate the relationship between the accumulation of polyamines during the filling period of wheat grain with yield and grain protein under dryland and supplemental irrigation (SI) conditions and also the effect of foliar spraying of urea on the amount of polyamines in grain a factorial experiment was conducted based on randomized complete block design with three replications during two cropping seasons. The examined treatments included water availability (dryland and SI), wheat cultivars (Homa, Sardari, Rijaw, Ouhadi, and Azar2), and foliar application of urea (control and 4% urea foliar application). The results demonstrated that SI (10%) reduced and urea foliar (12%) application increased the percent of grain protein. SI reduced the contents of three PAs by 24%: spermine, spermidine, and putrescine. But urea foliar application increased the three PAs in the first and second years by 31% and 27% in dryland conditions and 12% and 4% in SI conditions, respectively. These results indicated that there is less need for PAs in SI conditions, and they thus exhibit poorer accumulation in the grain; in dryland conditions, however, their content increases with greater access to foliar nitrogen. Older cultivars Sardari and Azar 2 had more polyamines. According to the observed positive correlation between 1000-grain weight and the three PAs under stress conditions, PAs are probably involved in the improvement of grain filling, and urea foliar application can affect drought tolerance by increasing PA accumulation. Moreover, cadaverine exhibited a different function from the other PAs.