Phytotoxicity evaluation of six fast-growing tree species in South Africa
South African Journal of Botany
Research Centre for Plant Growth and Development, School of Life Sciences, University of KwaZulu-Natal Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa
Vachellia sieberiana, Albizia adianthifolia, Buddleja saligna, Combretum kraussii, Halleria lucida and Rapanea melanophloeos are fast-growing, indigenous tree species in South Africa. They are usually found growing alongside other plants in agricultural systems. In this study, the comparative phytotoxic activity of aqueous leaf extracts of these tree species at different concentrations was investigated using lettuce seeds (Lactuca sativa L.) in a laboratory bioassay. To simulate natural situations, seeds were germinated under 16. h light/8. h darkness in a growth chamber using distilled water as control. The results showed that germination, chlorophyll accumulation and growth indices (plumule and radicle lengths) were significantly inhibited with increasing concentration of plant extracts. The treated lettuce seedlings experienced lipid peroxidation at high extract concentrations (1.0% and 2.0%) as evidenced by increased concentration of malondialdehyde (MDA). In response to this, the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) increased at low extract concentration but significantly dropped as concentration increased. These results suggest that aqueous extracts of the studied tree species may produce growth inhibitory substances. Thus, our study revealed that these trees possess phytotoxic activity which could be exploited in the management of weeds in agroforestry systems. © 2013 South African Association of Botanists.
agroforestry; aldehyde; allelochemical; antioxidant; bioassay; chlorophyll; comparative study; enzyme activity; evergreen tree; germination; growth regulator; inhibitor; leafy vegetable; legume; lipid; native species; phytotoxicity; plant extract; potential biocontrol agent; seed; weed control; South Africa; Acacia; Albizia; Albizia adianthifolia; Buddleja; Buddleja saligna; Combretum; Halleria lucida; Lactuca; Lactuca sativa; Rapanea melanophloeos