Effect of growth regulators on some of growth parameters and secondary metabolites in two wheat cultivars under different moisture regimes

Wheat is one of the most important plant sources for humans and drought is one of the most important abiotic limiting factors that affects the growth and development of wheat. Exogenous applications of plant growth regulators (PGRs) may be useful for decreasing the harmful effects of drought stress on wheat, therefore, this research was laid out to investigate the effect of foliar sprays of gibberellin, cytokinin and cycocel on root and shoot characteristics, secondry metabolites and yield of two wheat cultivars under different moisture regimes.

The present study was conducted as two separate designs each with three replications in hydroponic and field conditions in the University of Kurdistan, in 2015-2016. Hydroponics experiment was conducted as factorial based on randomized complete block design. The factors were the moisture levels (control, -4, -8 bar), two wheat cultivar (Sirvan and Homa) and four levels PGR foliar application including water as control, gibberellin (100 µm), cytokinin (100 µm) and cycocel (3 grlit-1). Field experiment was carried out as split-split based on randomized complete block design. The irrigation treatment at four levels (dryland, one time irrigation, two times irrigation and three times irrigation) as the main plots, two wheat cultivars (Sirvan and Homa) as sub-plots and the plant growth regulators foliar application listed above as the sub-sub plots were considered. Root and shoot dry weight and root to shoot dry weight ratio, root volume, root length, Plant height, total phenol, flavonoids, anthocyanins content and yield were determined.

In the hydroponics experiment, root traits increased in the -4 bar as compared with the control while plant weight and height were decreased in the -4 and -8 bar. In most treatments, the highest ratio of root to shoot weight was obtained in drought stress. Homa cultivar was superior to Sirvan cultivar in terms of all traits. Foliar application treatments hadn't a significant influence on root length and plant height, but the application of PGRs especially cycocel, increased the root and seedling weight and root volume. In field experiments, the results showed that the amount of phenol, flavonoids, and anthocyanins in dryland conditions was higher than other irrigation treatments. Among growth regulators, gibberellin increased flavonoids (13.2%), and cycocel increased anthocyanins content (17.3%) Compared to the control. The results also showed that, the highest grain yield in both cultivar was obtained under three times irrigation condition and cytokinin and cycocel consumption.

It seems that cycocel can increase the resistance of wheat to drought stress by improving the root characteristics and increasing anthocyanin content. In both cultivars, irrigation increased grain yield compared to rainfed conditions and the use of growth regulators, especially cytokinin and cycocel, increased yield compared to the control. Therefore, based on the results of this experiment, applying even one stage of irrigation in water limitation conditions and the use of cytokinin and cycocel in water availability conditions could be recommended to enhance grain yield under the region climatic condition.