Effect of Sea Weed Extracts and Selenium on Phenotypic and Biochemical Parameters of Okra Cultivars Under Drought Stress

Abstract

Drought stress is one of the most important constraint in crop production, particularly in arid and semi-arid regions of the world. A series of experiments were carried out in order to enhance growth and yield performance of okra under drought stress conditions. In the first year, eight commercially important okra cultivars (Arka Anamika, Punjab Selection, Posaswami, Tulsi, Sabzpari, Super Green, Local Multani, and Green Star) were tested against various drought levels to select the high yielding but drought-sensitive cultivar for further trials. All experiments were carried out in pots and water stress was applied 30 days after sowing (DAS). Irrigations at an interval of 3, 6 and 9 days were considered as control, mild stress and severe stress respectively. Based on the results of the first experiment, the most sensitive cultivar ‘Super Green’ was selected in order to assess its growth performance and yield under drought conditions with Selenium and Aschophym nodosum Extract (ANE) applications. In the second experiment, four levels of Selenium (0, 1, 2 and 3 mg L -1 ) were sprayed on okra plants, cultivar ‘Super Green’ that was irrigated at an intervals of 3, 6 and 9 days. Selenium application increased growth and biochemical parameters under control and under water deficit conditions. However, the effect was more pronounced with the foliar application of 3 mg L -1 . Okra plants treated with 3 mg L-1 of Selenium shown maximum Chlorophyll-a (30.01 μg ml-1 ), Chlorophyll-b (15.87 μg ml-1 ), Total Chlorophyll (45.88 μg ml-1 ), Carotenoids (11.36 μg ml-1 ), Anthocyanin (0.7712 mg g -1 ), Proline (25.08 u mole g-1 ), APX (18.52 u mg-1 protein), POD (27.78 u mg-1 protein) and Catalase (22.23 u mg-1 protein). In the third experiment, four levels of ANE (0%,0.1%,0.2% and 0.3%) were sprayed on okra drought susceptible cultivar Super Green, which were irrigated at intervals of 3, 6, 9 days, 30 DAS. ANE application enhanced growth and biochemical parameters under control and under water deficit conditions.Okra plants treated with 0.3% ANE shown maximum Chlorophyll-a (30.61 μg ml-1 ), Chlorophyll-b (16.35 μg ml-1 ), Total Chlorophyll (46.96 μg ml-1 ), Carotenoids (12.40 μg ml-1 ), Anthocyanin (0.7635 mg g-1 ), Proline (25.65 u mole g-1 ), APX (19.76 u mg-1 protein), POD (28.34 u mg-1 protein) and Catalase (22.89 u mg-1 protein). In experiment four, the combined effect of the optimized level of Selenium (3 mg L-1 ) and ANE (0.3%) on okra drought susceptible cultivar ‘Super Green’ was evaluated under drought stress. The okra plants were treated with optimized levels of Selenium (0, 3 mg L-1 ), ANE (0.3%) and their combination (3 mg L -1 Selenium + 0.3% ANE) under three irrigation 2 intervals (3, 6 and 9 days).The highest Chlorophyll-a (35.25 μg ml-1 ), Chlorophyll-b (17.66 μg ml-1 ), Total Chlorophyll (52.88 μg ml-1 ), Carotenoids (13.22 μg ml-1 ), Anthocyanin (0.717 mg g 1 ), Proline (25.90 u mole g-1 ) APX (20.91 u mg-1 protein), POD (27.57 u mg-1 protein) and Catalase (27.97 u mg-1 protein) in okra plants treated with 3 mg L-1 in combination with 0.3% ANE. It can be concluded from the overall results that Super Green and Arka Anamika are the most susceptible and most resistant cultivar to drought stress respectively, Moreover, the foliar application of Selenium at the rate of 3 mg L-1 in combination with 0.3% ANE alleviated the drastic effects of drought stress. Keywords: Abiotic stress, Cultivars, Micronutrient, Selenium, Okra (Abelmoschus esculentus L.), and Seaweed extracts.