Evaluation of morphophysiological traits of Ocimum basilicum L. in response to foliar application of putrescine and 24-epibrassinolide under drought stress

To investigate the role of putrescine and 24-epibrassinolide on the morphophysiological changes of Ocimum basilicum L. in the water deficiency tolerance, an experiment was conducted as a factorial split plot in a randomized complete block design with three replications in the research farm of Agriculture Faculty, Ilam University during 2017-19 crop years. The experimental treatments included the drought stress at three levels (40, 80, and 120 mm evaporation from Class A evaporation pan) in the main plots and putrescine foliar application at three levels (Put0: 0, Put1: 0.5, and Put2: 2 mM) and 24-epibrassinolide foliar application at three levels (Br0: 0, Br1: 0.5, and Br2: 2 μM) factorially in the subplots. The results showed that the multiple interaction of year, drought stress, putrescine, and 24-epibrassinolide had a significant effect on the traits including chlorophyll a, chlorophyll b, and basil essential oil percentage, so that the foliar application of 2 mM putrescine and 2 μM 24-epibrassinolide at all levels of drought stress, especially 80 mm evaporation from the evaporation pan, caused a further increase in these traits in both years of the experiment, which was higher in the first year than the second one. The optimal irrigation treatment (40 mm evaporation from evaporation pan) with application of 2 mM putrescine and 0.5 μM 24-epibrassinolide and drought stress treatments (80 and 120 mm evaporation from evaporation pan) with application of 2 mM putrescine and 2 μM 24-epibrassinolide had more leaves and secondary branches. The results of this study showed that the drought stress had an important role in reducing the basic factors in basil growth. In general, according to the results obtained, the foliar application of 2 mM putrescine with 2 μM 24-epibrassinolide to improve the physiological activities and increase the essential oil content, and 2 mM putrescine with 0.5 μM 24-epibrassinolide to increase the seed yield could be recommended in basil under drought stress conditions.