S25 - Session P3 - The effect of phenological stages, pruning and harvesting time on vegetative growth (biomass yield) and antibacterial activity of Leucosidea sericea

Authors: Babalwa Matsiliza-Mlathi *, Maboka Mabusela, Riana Kleynhans, Hintsa Araya

Leucosidea sericea ('Oldwood') is a fast-growing evergreen tree used traditionally to treat various ailments in South Africa. Plant extracts of this plant have been reported to have the antibacterial activity against different types of bacteria, including Propionibacterium acnes (15.63 µg/ml), a gram-positive bacteria responsible for causing acne. Although wild harvesting can be used to collect material of L. sericea as the plant has been reported to be invasive, it is still advisable to have a ready source of good quality material with uniform activity available, for successful commercialization. The aim of the study, therefore, was to determine the effect of pruning and the time of harvest on vegetative growth (biomass) and biological activity of L. sericea . Five three-year-old L. sericea trees were used to characterise the phenological growth stages. A 4x4 latin square was used for the pruning trial with one tree as an experimental unit. Four pruning treatments were applied: pinching the apical tip below the 5 th leaf; pinching the apical tip and the tips of all the primary branches; pinching the apical tip and cutting the side branches leaving one node from the main stem and cutting the tree one meter from ground level. Leucosidea sericea leaves were first collected in September during the first pruning. Subsequently, harvests were made in December, March and June with the last harvest in August being the second pruning. For biological activity, leaf extracts of L. sericea were tested against Propionibacterium acnes . A micro-dilution method was used to determine the minimum inhibitory concentration (MIC) values. L. sericea trees grew throughout the year with defined peaks of growth flushes. Pruning the trees severely increased the amount of material harvested, reduced unwanted flowering; and resulted in higher antibacterial activity especially in plant material collected during the periods of slow growth.