ALLELOPATHIC EFFECTS OF Grevillea banksii R. BR. LEAF EXTRACTS AND ITS RHIZOSPHERIC SOIL ON GERMINATION AND INITIAL GROWTH OF THREE AGRICULTURAL CROPS IN MADAGASCAR

G. banksii R. Br. is a widespread species forming dense populations in the Eastern part of Madagascar. The aim of this study was to investigate the allelopathic effects of G. banksii on seeds germination and initial growth of three agricultural crops: rice (Oriza sativa L.), maize (Zea mays L.) and bean (Phaseolus vulgaris L.). The effects of leaf (leaf powder and aqueous leaf extracts obtained after shaking during 24 and 48 h) and rhizospheric soil (soil powder and aqueous soil extract shaken during 72 h) of G. banksii on seeds germination, seedling length of each tested plant were described in vitro. Results showed that the rhizospheric soil of G. banksii activates the germination of bean and maize seeds as well as the seedling length development of all crop species but inhibit rice seeds germination. However, all aqueous leaf extract inhibit seeds germination and the shoot and root length development of the three crops species tested, especially for rice and maize roots length development. This investigation therefore comparatively reveals that the leaves extract of G. banksii has more allelopathy than rhizospheric soil in seed germination and initial growth of agricultural crops tested. The results suggest some cautions when using the shoots of G. banksii as plant cover in farming systems.