Pruning intensity influences growth, flower and fruit development of Moringa oleifera Lam. under sub-optimal growing conditions in Gauteng, South Africa

• Pruning influences growth, flowering and fruit development of Moringa oleifera Lam. under sub-optimal growing conditions in Gauteng, South Africa. • Moderate pruning (2 m pollarding above ground level) improved flower and fruit number on trees after 124 days. • Pruning synchronize and promote earlier flowering. • Moderate pruning significantly increased fresh- and dry biomass, and leaf area index over time. • Moderate pruning resulted in increased stem circumference of trees. Moringa oleifera Lam. is becoming increasingly popular as an industrial crop due to its multitude of useful attributes as a water purifier, nutritional supplement and biofuel feedstock. Horticultural practices such as pruning that encourage improved production of M. oleifera in terms of flowers and fruits have been given little attention especially in sub-Sahara Africa. This study therefore aimed to establish an ideal pruning intensity level on ±5 year old M. oleifera trees. A trial was conducted at the University of Pretoria Experimental Farm of the Hillcrest Campus on trees of an established orchard with four treatments namely severe (1 m), moderate (2 m), light (3 m) pruning above the ground level (pollarding), and no pruning (control). These were applied once in September for two consecutive years. Individual inflorescences from each treatment were tagged during floral initiation and monitored throughout until fruiting stage. Records for Leaf Area Index (LAI), fresh and dry biomass, chlorophyll content, as well as tree stem circumference were taken over a period time at around 81, 98 and 124 days after pruning (DAP). Results showed that light pruning (3 m from the ground) resulted in the highest quantity of flower buds at 124 DAP, and of flowers at 98 DAP in both years. In addition, moderate pruning (2 m from the ground) increased flower number on trees at 124 DAP. Highest quantity of fruits were recorded from the moderate pruning treatment. Measurements done on total leaf area, fresh and dry biomass showed that although plants pruned at 1 m above the ground (severe pruning) received better initial penetration of light into the plant canopy, not enough plant vigor could out-perform plants pruned at 2 m above the ground level. Moderately pruned trees also recorded a substantial increase in stem circumference in comparison to the control and lightly pruned trees at 124 DAP in the first year. Moderate pruning promoted significantly higher total chlorophyll accumulations in mature leaves. Although the onset of low temperatures in both years may have led to increased flower abortion resulting in lower fruit numbers across treatments, results suggest that pruning a M. oleifera tree at 3 m (light) and 2 m (moderate) above ground level under sub-optimal growing conditions in Gauteng, South Africa once a year, will result in maximum flower and fruit harvest. The moderately, but also the severely pruned trees produced more than double the amount of fresh biomass in comparison to the control and lightly pruned trees. This study therefore concludes that M. oleifera crop production for the sole purpose of fruit production may not be optimal in Pretoria, Gauteng, however, leaf production is promising due to the higher plant biomass recorded with the moderate pruning treatment.