Adaptability of Moringa oleifera Lam. (Horseradish) Tree Seedlings to Three Temperature Regimes

Abstract

Moringa oleifera trees are naturally found in tropical climates around the world and therefore the extent of their adaptability to cooler climates was the main objective of this study. A total of 264 trees, made up of an equal number hardened and non-hardened seedlings were randomly assigned to three temperature-controlled greenhouses each with a different fluctuating night/day temperature regime (TR) namely; 10/20°C ± 2°C, 15/25°C ± 2°C and 20/30°C ± 2°C. During the 32-week trial period, biweekly measurements of tree height, stem diameter and leaf area estimates of each individual tree within all three temperature regimes (TRS) were taken. The 20/30°C TR was the most favorable towards overall tree growth, as the highest values were obtained across most measured parameters. The increase in temperature resulted in growth rate increases of over 650% between the 10/20°C and 20/30°C and over 250% between the 10/20°C and 15/25°C night/day TRS. The hardening-off pre-treatment increased both final tree height and stem diameter, resulting in increases of 3.09X (10/20°C), 1.44X (15/25°C) and 1.23X (20/30°C) compared to their non-hardened off counterparts. The average tree leaf area increases followed a similar trend in both tree height and stem diameter, but expressed more volatility at the higher TRS. Although the average leaf area increased with the increase in TR and remained higher for the duration of the trial, cycles of regular leaf drop and renewed flushes were prevalent at both the 15/25°C and 20/30°C temperature treatments.