To Study the response of grain yield and some agronomical traits of foxtail millet (Setaria italica L.) to foliar application of growth regulators under drought stress condition

Abiotic stresses are major constraints for many crop plants in specific areas over the globe which limits crop production. Drought, the occurrence of a substantial water deficit in the soil, is an alarming constraint to crop productivity and yield stability worldwide. Drought is the leading environmental stress in world agriculture, causing losses in crop yield. Drought stress adversely affects a variety of vital physiological and biochemical processes in plants, leading to reduced growth and final crop yield. One quick strategy to promote plant drought tolerance is exogenous application of various compounds, including organic solutes (organic osmolytes and plant growth regulators) and mineral nutrients. Recently, this strategy has gained considerable attention because of its efficiency, feasibility, and cost- and labor-effectiveness. In this experiment, we studied the roles of some plant growth regulators foliar application including putrescine, humic acid, salisylic acid and methanol, in foxtail millet response to drought stress in enhancing millet drought tolerance and alleviating the damaging effects of drought stress.

In order to evaluate the effect of plant growth regulators on yield and morpho-phenological traits of foxtail millet under drought stress condition an experiment in split plot arranged in randomized complete block design with three replications conducted in two years of 2017 and 2018 at the Agricultural Research Center of Birjand branch, Islamic Azad University, Birjand. Experimental factors included drought stress as main factor in three levels (irrigation in 30, 70 and 100 percent of plant water requirement) and foliar application of plant growth regulators as sub plot in five levels (control and foliar application of putrescine, humic acid, salisylic acid and methanol). The water requirement was determined by FAO method using evaporation data from Class A pan with 80% efficiency for field water distribution (Hellen et al., 1998). In this method, FAO guidelines were used to determine the vegetative coefficient at different stages of growth. Foliar application of 1 mM salicylic acid, 1 mM putrescine, 1.5 kg.ha-1 humic acid, and 25% volumetric methanol were used in two stages (early stem elongation and early flowering). The averages of data statistically analyzed using analysis of variance (ANOVA) by using the SAS system for windows, version 9.1 (SAS Inst., 2001) and means were compared using Duncan Multiple Range Test at 0.05% probability.

Results showed that drought stress led to significant reduction in plant height, peduncle length, number of panicle per meter square, number of grain per panicle, 1000 grain weight, grain yield and biomass while foliar application of plant growth regulators improved morphological traits, yield components and finally grain yield. The highest biomass and grain yield were obtained at 100% water requirement with 704.5 and 267.7 g.m-2, respectively. At 70% of water requirement these traits decreased by 20.2 and 25.2 percent and in 30% of water requirement they reduced by 51.2% and 58.4%, respectively. Foliar application of putrescine, humic acid, salisylic acid and methanol enhanced millet grain yield by 8.3, 23.9, 17.1 and 19.6 percent, respectively in contrast to control treatment. Investigation the interaction of year in irrigation on biomass and grain yield revealed that in both studied years, the highest values of these traits were obtained from 100% water requirement treatment and with increasing of stress intensity they reduced significantly.

Generally, results revealed that application of plant growth regulators improved foxtail millet grain yield under water stress. Application of humic acid under optimal irrigation condition and application of methanol in severe drought stress had the highest impact in improving grain yield.