Effects of Seed Priming with Ginger (Zingiber officinale) and Neem (Azadirachta indica) Extracts on Germination Kinetics, and Water Relations of Bambara Groundnut (Vigna subterranea) under Moisture Deficit Conditions

Seed priming with botanical extracts is a sustainable strategy to enhance crop establishment under water-limited conditions. This study evaluated the effects of ginger (Zingiber officinale) and neem (Azadirachta indica) extracts on the germination kinetics and early vegetative development of two Bambara groundnut (Vigna subterranea L.) genotypes (ZM 1856 and ZM 2656) subjected to moisture stress. A factorial experiment was conducted using varying concentrations of ginger (0–20% w/v) and neem (0–4% w/v). Results revealed highly significant main treatment effects (p < 0.001) for germination index, total dry matter (TDM), and root nodulation. Effect size analysis (η²)) established that botanical treatments exerted the largest functional effects on root nodulation (η²) = 0.55), germination rate (η²= 0.44), and seedling vigour index (SVI; η²= 0.44). Pearson correlation analysis further elucidated these relationships, showing a near-perfect positive correlation between germination rate and SVI (r = 0.97, p < 0.001), and significant positive associations between TDM and both root nodulation (r = 0.52) and leaf efficiency (r = 0.52). However, a notable negative correlation between TDM and germination rate (r = -0.44, p < 0.05) suggests a physiological trade-off between rapid emergence and long-term biomass accumulation under stress. While ginger priming at 10–15% was the most effective for enhancing kinetics, higher neem concentrations (4%) significantly delayed germination. These findings demonstrate that botanical priming, particularly with ginger, triggers a holistic developmental shift that balances rapid establishment with enhanced resource partitioning for drought resilience.