Role of Selected Novel Growth promoting substances in enhancing cotton (Gossypium hirsutum L.) productivity under limited water conditions

Abstract

Water shortage is serious threat for food security. Harmful effects of water deficit can be mitigated by different approaches. Exogenous application of different plant growth promoting substances were used individually in the past to alleviate devastating effects of water deficit. Prime objectives of this research are to investigate and quantify the role of glycine betaine, salicylic acid and ascorbic acid as sole and in different combinations to alleviate the adversaries of water deficit in cotton. Foliar application of these plant growth promoting substances in different combinations is novel approach in this context. To assess the effect of exogenous application of glycine betaine, salicylic acid and ascorbic acid individually and in different combinations of two and three on growth, yield, physiological and biochemical attributes of cotton grown under normal irrigation and drought conditions, a study consisting of two pot and one field experiments was carried out in Department of Agronomy, College of Agriculture, University of Sargodha, Sargodha during year 2015 and 2016. Pot experiments were conducted in earthen pots of equal size with 8.5 kg soil capacity. These experiments were laid out in Completely Randomized Design with factorial arrangement. Two cotton cultivars viz. Lalazar and FH-142 reported as drought tolerant and moderately drought tolerant were used for study. Drought was imposed by maintaining 60% field capacity level while 100% field capacity level was kept as control. Field experiment was carried out in sandy loam soil. This experiment was laid out in Randomized Complete Block Design with split-split plot arrangement. Both cotton cultivars viz. Lalazar and FH-142 as used in pot experiments were utilized in field study. Drought under field conditions was imposed by skipping irrigation alternate to normal. Different plant growth promoting substances including; control (un-treated), distilled water spray, distilled water spray + Tween-20 (0.1%), glycine betaine @ 100 mg L-1 + Tween-20 (0.1%), salicylic acid @ 100 mg L-1 + Tween 20 (0.1%), ascorbic acid @ 100 mg L-1 + Tween-20 (0.1%), glycine betaine + salicylic acid @ 50 mg L-1 each + Tween-20 (0.1%), glycine betaine + ascorbic acid @ 50 mg L-1 each + Tween-20 (0.1%), salicylic acid + ascorbic acid @ 50 mg L-1 each + Tween-20 (0.1%), glycine betaine + salicylic acid + ascorbic acid @ 33 mg L-1 each + Tween-20 (0.1%) were applied 3, 6 and 9 weeks after sowing. Results of pot and field experiment showed that drought stress affected different agronomic and yield traits including number of monopodial branches per plant, number of sympodial branches per plant, plant height, number of main stem nodes per plant, number of open bolls per plant, average boll xxiii weight, seed cotton yield, cotton seed yield and lint yield. Different fiber quality characteristics including fiber length, fiber strength, fiber fineness, fiber uniformity were decreased under drought conditions. Different plant growth promoting substances improved these traits under water limited conditions. However, it was found that same combination of different plant growth promoting substances was not equally effective for both cultivars in mitigating the harmful effects of water deficit stress as each cultivar responded differentially to application of plant growth promoting substances under normal irrigation and drought conditions. Combinations of different plant growth promoting substances were superior as compared to individual plant growth promoting substances by improving growth, yield, yield components, physiological, biochemical and gas exchange characteristics. In pot and field experiments, cultivar FH-142 performed best under drought conditions with foliar application of combination of glycine betaine + ascorbic acid @ 50 mg L-1 each + Tween-20 (0.1%) while cultivar Lalazar showed improved performance under drought conditions with foliar application of salicylic acid and ascorbic acid @ 50 mg L-1 each + Tween 20 (0.1 %) by improving yield and related traits as compared to untreated control. Economic analysis showed that cultivar Lalazar can be grown economically with exogenous application of salicylic acid and ascorbic acid @ 50 mg L-1 each + Tween-20 (0.1%) while cultivar FH-142 can be gown economically with exogenous application of salicylic acid and ascorbic acid @ 50 mg L-1 each + Tween-20 (0.1%) as well as glycine betaine and ascorbic acid @ 50 mg L-1 each + Tween-20 (0.1%) at 3, 6 and 9 weeks after seedling emergence.