The effect of humic acidic and cycocel on yield, yield components, and photosynthetic material remobilization of wheat (Triticum aestivum L.) under end-of-the-season drought stress conditions

In order to investigate the effect of humic acidic and cycocel on yield, yield components, and remobilization of wheat photosynthetic materials under end-of-the-season drought stress conditions, a split factorial experiment was conducted based on a randomized complete block design with three replications in field in Ahvaz during two years (2017-19). The main factor of drought stress at the end of the season with two levels of normal irrigation and cessation of irrigation in the post-pollination stage, cycocel with three levels of water as a control, 1.5 g/l, and 3 g/l, and humic acid with three levels of non-foliar application (water as control), 2 liters per hectare, and 4 liters per hectare were factorial sub-factors. Results showed that the interaction of end-of-the-season drought stress and cycocel on grain yield and number of grains per spike was significant. The highest grain yield (4840.5 kg ha-1) was obtained by applying 3 g/l cycocel under normal irrigation conditions, which did not show a statistically significant difference from the application of 3 g/l cycocel under drought stress at the end of the season. Application of humic acid had a positive and significant effect on all test traits. The highest grain yield, number of grains per spike, and 1000-grain weight were obtained from the application of 3 liters per hectare of humic acid under normal irrigation conditions. Under end-of-the season drought stress, the current photosynthesis and the share of current photosynthesis decreased by 29% and 10%, respectively while remobilization and contribution of remobilization increased by 16% and 34%, respectively. In general, to increase the rate of grain yield under optimal conditions and reduce the drop in stress conditions, growth regulators such as cycocel by a concentration of 3 g/l and organic acid fertilizer by the concentration of 4 liters per hectare are recommended.