Foliage application of 5-aminolevulinic acid alleviates drought stress in sunflower (Helianthus annuus L.) through improving stay green and antioxidant enzymes activities

Drought stress hampers the yield of oilseed crops throughout the world. However, foliage application of plant growth regulators might be useful to reduce drought induced yield losses. In this study, the role of 5-aminolevulinic acid (5-ALA) in improving the performance of different sunflower hybrids under drought stress was evaluated. Five levels of 5-ALA viz., (i) control, (ii) 25, (iii) 50, (iv) 75 and (v) 100 mg L-1 were foliage applied on two sunflower hybrids (Parsun and Senji) under drought [40% water-holding capacity (WHC)] and well-watered (80% WHC) conditions. The results revealed that imposition of drought stress negatively impacted the performance of sunflower than well-watered conditions. However, foliage application of 5-ALA, at either rate, improved the performance of sunflower under drought stress by improving stay green and antioxidant enzyme activities which was translated to higher achene yield and better oil contents in both sunflower hybrids. Among the sunflower hybrids, the performance of sunflower hybrid 'Senji' was better in terms of morphological and yield related traits than 'Parsun'. Foliage application of 5-ALA at 75 mg L-1 was the most beneficial for improvement in sunflower performance which improved the achene yield, oil contents and stay green by 12.3, 9, 26%, respectively, than no 5-ALA application. Application of 5-ALA also enhanced the activities of catalase, ascorbate peroxidase and superoxide dismutase by 157.1, 90 and 80% under drought stress than no 5-ALA application. In conclusion, foliage application of 5-ALA at 75 mg L-1 in sunflower hybrid 'Senji' is useful to reduce drought induce yield losses and improve oil contents which is attributed to an improvement in stay green and activities of catalase, superoxide dismutase and ascorbate peroxidase.