Optimization of Gibberellic Acid (GA₃) and Kinetin Seed Priming for Improving Germination and Seedling Vigour of Soybean

Abstract

Soybean (Glycine max (L.) Merr.) is one of the most important oilseed crops, and its successful cultivation depends on rapid germination, uniform emergence, and vigorous seedling establishment. Hormonal seed priming has been recognised as an effective technique for improving seed physiological performance; however, the appropriate concentration and soaking duration of plant growth regulators must be optimised before their practical application. The present investigation was undertaken to optimise the concentration and soaking duration of gibberellic acid (GA3) and kinetin for soybean seed priming under laboratory conditions. The experiment was conducted at the Seed Testing Laboratory, Department of Seed Science and Technology, Bidhan Chandra Krishi Viswavidyalaya (BCKV), Mohanpur, West Bengal, India, using a completely randomised design with three replications. Seeds of the soybean cultivar BRAGG were exposed to nine treatment combinations for each hormone, including an unprimed control. Germination percentage, root length, shoot length, and Seedling Vigour Index-I were assessed according to ISTA procedures. Hormonal priming significantly improved all the evaluated seed quality parameters compared with the control. Among the GA3 treatments, priming with 100 ppm GA₃ for 2 h proved most effective, resulting in the highest germination (91.3%), root length (15.747 cm), shoot length (19.800 cm), and Seedling Vigour Index-I (3246.660). Likewise, priming with 200 ppm kinetin for 2 h produced the best response among the kinetin treatments, recording a germination percentage of 88.3%, root length of 14.100 cm, shoot length of 18.567 cm, and Seedling Vigour Index-I of 2885.533. Increasing the concentration of either hormone beyond the optimum level did not produce further improvement, emphasising the importance of optimising both hormone concentration and priming duration. Comparative evaluation indicated that GA₃ was more effective than kinetin in enhancing seed germination and seedling vigour under laboratory conditions. Therefore, priming soybean seeds with 100 ppm GA₃ for 2 h can be recommended as the optimum treatment, while 200 ppm kinetin for 2 h may serve as a suitable alternative. Nevertheless, field studies are required to validate these findings under diverse environmental conditions.