Chemical root-pruning of Moringa oleifera for improved seedling growth

Abstract

Low survival rates in greenhouse raised Moringa oleifera seedlings after transplanting had been ascribed to rapid growth rates and poorly formed and etiolated stems. The objective of the study was to determine the effect of indole acetic acid (IAA) on above-ground vegetative growth of M. oleifera seedling when used as root pruning agent. Hardened-off uniform one-month-old M. oleifera seedlings were transplanted in 20-cm-diameter plastic pots containing pasteurised loam soil and Hygromix at 3:1 (v/v) ratio. A week after transplanting, IAA concentrations of 0.0, 0.2, 0.4, 0.8, 1.6, 3.2, 6.4, 12.8, 25.6 and 51.2 mg mL−1 distilled water with G49 wetting agent and sticker were applied weekly to the respective plants. The effects of IAA concentrations were highly significant (P ≤ .01) on plant height, leaf number, dry root mass and significant (P ≤ .05) on stem diameter, which were further subjected to the lines of the best fit. Leaf number, plant height and stem diameter over increasing IAA concentrations exhibited positive quadratic relations, with the relationships being explained by 99, 98 and 98%, respectively. However, dry root mass and increasing concentrations of IAA exhibited negative quadratic relations, with the relationship being explained by 98%. At low concentrations, IAA increased plant height, number of leaves and stem diameter, whereas, at high concentration, the material reduced plant variables. However, all concentrations used reduced dry root mass. In conclusion, IAA was able to reduce root growth and promote shoot growth, with optimum for M. oleifera seedling growth established at a concentration level of 1.98 mg mL−1.