Optimisation of auxin concentration and exposure duration for enhanced adventitious rooting and survival in Nerium oleander L. stem cuttings

Nerium oleander L. is an important ornamental and medicinal shrub widely propagated through stem cuttings; however, successful rooting and survival are often limited by endogenous physiological constraints. Optimisation of auxin concentration and exposure duration is therefore critical for enhancing adventitious root formation and establishment. The present study evaluated the effects of different concentrations and dipping durations of indole-3-butyric acid (IBA) and naphthaleneacetic acid (NAA) on sprouting, rooting, root quality and survival of semi-hardwood stem cuttings of N. oleander. The experiment was conducted under controlled polyhouse conditions using a completely randomised design with 15 treatments, including IBA and NAA at 60, 80 and 100 ppm for 12 and 24 hr, along with water-soaked and untreated controls. Observations on days to sprouting, days to rooting, rooting percentage, root length, root number, root diameter and survival percentage were recorded and statistically analysed. Auxin-treated cuttings significantly outperformed controls for all parameters studied. Among the treatments, IBA at 100 ppm for 24 hr resulted in the earliest sprouting (22.1 days) and rooting (26.9 days), highest rooting percentage (98.2 %), superior root length (18.6 cm) and maximum survival (93.7 %). Although NAA treatments enhanced root number, they were comparatively less effective in producing a vigorous and stable root system. The results demonstrate that both auxin concentration and exposure duration play a decisive role in adventitious rooting. Based on overall performance, IBA at 100 ppm for 24 hr is recommended as an optimal protocol for efficient and commercial propagation of N. oleander.