Influence of varying concentrations of indole-3-acetic acid (IAA) on root growth characteristics of blackgram (Vigna mungo L.) varieties

Abstract

The present study investigated the influence of indole-3-acetic acid (IAA) on seed germination and seedling vigor in three pulse varieties, VBN-4, VBN-8, and VBN-11. Seeds were treated with varying concentrations of IAA (0, 10, 20, 50, and 100 ppm), and parameters such as germination percentage, lateral root formation, root and shoot length, fresh and dry root weight, and vigor index were recorded. The results revealed a clear dose-dependent response, with low concentrations of IAA (10–20 ppm) significantly enhancing germination and seedling growth, while higher concentrations (50–100 ppm) exerted inhibitory effects. Among the varieties, VBN-8 exhibited the most pronounced positive response at 10 ppm, recording the highest vigor index (963), longest roots (10.7 cm), and shoots (11.5 cm). VBN-11 showed enhanced lateral root branching at 20 ppm, while VBN-4 displayed moderate improvements in vigor at 10 ppm. In contrast, all varieties demonstrated reduced germination percentage, shorter roots and shoots, and lower vigor indices at 50–100 ppm, confirming the inhibitory nature of excess auxin. The findings highlight that IAA acts as a growth regulator with a narrow optimal window, where low concentrations stimulate seedling establishment and vigor, but supra-optimal levels suppress growth. Seed priming with IAA at 10 ppm emerges as the most effective treatment for improving early seedling performance, particularly in VBN-8. These results provide valuable insights for optimizing auxin application in pulse crops and suggest future research on varietal-specific responses and field-scale validation to enhance sustainable crop production.