The allelopathic effect of Aloe ferox, Aloe marlothii, Anthocleista grandiflora and Pollichia campestris extracts on the germination of selected plants.

• All four extracts had a negative effect on the germination of species tested. • The A. grandiflora extract inhibited the germination more effectively in all species except V. unguiculata. • A 50 % dilution of the A. grandiflora extract made it less potent. • Extracts had a stronger effect when used to irrigate the seeds rather than a pre-germination soak. Many unpopular species are useful for medicinal and food security use. However, their extracts can be used to improve seed germination and can remove unwanted vegetation by acting as herbicides. Often, such use is based on a history of traditional practices. For example, Vhavenda villages in the Limpopo province (South Africa) use Anthocleista grandiflora leaves to cover maize and millet grains during malting to stimulate germination, but few studies have tested their efficacy or even formulated extracts out of them. This study tested the allelopathic effect of aqueous leaf extracts of Aloe ferox, Aloe marlothii, Anthocleista grandiflora and shoot extracts of Pollichia campestris. The extracts were applied at a 100 or 50 % concentration through irrigating or soaking seeds of Strychnos spinosa and common vegetable seeds of Pisum sativum, Vigna unguiculata and Zea mays were used as benchmark species. The results showed that the extracts had a significant effect (P < 0.001, P < 0.002 and P < 0.010) on the germination of three species and suppressed germination instead of enhancing it. The exception was Vigna unguiculata , where extracts had a non-significant effect (P = 0.784). The highest inhibition was observed in the crude extract of Anthocleista grandiflora (100 %), which inhibited Pisum sativum germination with a percentage inhibition of 76 %. All extracts inhibited the seed germination of Zea mays and the highest germination of 52 % was achieved compared to 87 % germination in the control (no extracts applied). None of the different extract concentrations (100 or 50 %) or application methods (irrigation and soaking) improved the seed germination of species. These results suggest the tested extracts could be useful as growth suppressors (especially Anthocleista grandiflora) of Strychnos spinosa but more research is required. [ABSTRACT FROM AUTHOR]