Current of photosynthesis and remobilization of assimilate affected spraying growth regulator under drought stress condition on maize cultivar KSC 704

Drought is one of the major environmental conditions that adversely affects plant growth and crop yield. Drought is the most major restriction in maize production. The reduction in plant growth under drought stress conditions could be an outcome of altered hormonal balance and hence the exogenous application of growth regulators under stress conditions could be the possible means of reversing the effects of abiotic stress. Plant growth regulators such as auxin and cytokinin are known to be involved in the regulation of plant response to the adverse effects of stress conditions. Previous studies have shown that endogenous hormones are essential regulators for translocating and partitioning of photo-assimilates for grain filling in cereal crops (Yang, et al. 2003), and therefore could be involved in the regulation of grain weight and yield. This study was conducted to determine the effects of exogenous application of growth regulators on the current photosynthesis and remobilization of assimilates in maize cultivar KSC704 under drought stress conditions.
The experiment was carried out in three distinct environments at Seed and Plant Improvement Institute (SPII), Karaj, Iran, in 2013. The environments included non-drought stress (irrigation after soil moisture reached 75% of field capacity), drought stress at vegetative stage (irrigation after soil moisture reached 50% of field capacity from V4 to tasseling stage and irrigation after soil moisture reached 75% of field capacity from pollination to physiological maturity stage) and drought stress at reproductive stage (irrigation after soil moisture reached 75% of field capacity from V4 to tasseling stage and irrigation after soil moisture reached 50% of field capacity from pollination to physiological maturity stage). Cytokinin was applied at V5 –V6 and V8-V10 stages and auxin was sprayed at silk emergence stage and 15 days after that period. No usage of the growth regulators was served as control. The trial was laid out as a factorial scheme based on randomized complete block design with three replications. Auxin was used in the form of Indole-3-butyric acid and cytokinin was sprayed as N6-benzyladenin. Harvesting was done from 4.5 m2 at field maturity stage at 14 % grain moisture content and was used to estimate grain yield. Remobilization, efficiency of remobilization, contribution of remobilization, current photosynthesis, efficiency of current photosynthesis and contribution of current photosynthesis were measured by the equation of Uhart and Andrade (1995).
The effect of drought stress on current photosynthesis, efficiency of current photosynthesis, contribution of current photosynthesis and remobilization was significant (P Based on the results of this experiment, drought stress at vegetative stage (irrigation after decreasing soil moisture to 50% field capacity) can be effective in conserving irrigation water and increasing water use efficiency. Moreover, considering the fact that the higher rates of current photosynthesis and contribution of current photosynthesis to grain yield were achieved with cytokinin application at V8-V10 stage and spraying with auxin at silk emergence stage led to the increased rates of remobilization and contribution of remobilization to grain yield, the aforementioned growth periods were identified as the best application times for cytokinin and auxin, respectively.