Hardening-off Effects On Moringa oleifera Lam. Seedlings Prior to Cultivation At Three Temperature Regimes

Moringa oleifera Lam. is a fast growing, drought tolerant tree with numerous beneficial uses, such as for nutritious food, animal forage, green manure, water purification, traditional medicine and bio-fuel (Anwar et al., 2007). The effect of hardening-off tree seedlings and consequent cultivation at lower temperatures on growth and flowering of this tropical/subtropical tree was the main aim of the study. After germinating seed under favourable greenhouse conditions between 20/25°C, half the seedlings were left in the greenhouse, while the other half was hardened-off by placing them outside where the average minimum/maximum temperatures fluctuated between 15/30°C. Equal numbers of hardened-off (132) and non hardened-off (132) trees were randomly placed into three temperature controlled glasshouses at the Experimental Farm of the University of Pretoria, each with a different night/day temperature regime (TR) (10/20°C±2°C; 15/25°C±2°C; 20/30°C±2°C). During the 224-day trial period, bi-weekly measurements of individual tree heights were taken, while flower development was monitored throughout. After trial termination the fresh and dry mass of the roots, stems and leaves from each treatment were measured. Overall, tree height increased with temperature. At the 10/20°C, 15/25°C and 20/30°C TRS, the respective growth rates of the non hardened-off seedlings were 67.6%, 30.5% and 18.7% lower compared to their hardened-off counterparts. The increase in total tree biomass with the increase in TR was largely due to the above ground parts. Fresh and dry root mass did not differ significantly (P≤0.05) amongst the three temperature regimes (TRS), however the dry root mass in relation to the above growth decreased with an increase in TR. The root:shoot ratios were 0.2, 0.5 and 1.4 for the 10/20°C, 15/25°C and 20/30°C TRS, respectively. The highest instances of flowering trees (87.5%) were observed at the 15/25°C TR with noted instances of inflorescence reversion at the 20/30°C TR. The 10/20°C TR probably did favour floral induction, however the generally low temperatures hindered flower production. The 20/30°C TR was found to be the most favourable for vegetative tree growth, however the hardening-off of the seedlings prior to transplanting has proven to increase the tree growth rate across all three TRS and is therefore highly recommended for M. oleifera trees, especially if intended cultivation is at low temperature environments.  REFERENCES:  ANWAR, F., LATIF, S., ASHRAF, M. & GILANI, A.H., 2007. Moringa oleifera: A food plant with multiple medicinal uses. Phytother. Res., 21: 17–25.