Abstract
The rhizosphere microorganisms of rubber plants (Hevea brasiliensis) were determined using the soil dilution plate method, while the rhizoplane was determined by serial washing of root lengths and plating on PDA plates. Fungi belonging to the genera Aspergillus, Trichoderma, Penicillium, Botryodiplodia and Mucor were isolated from both the rhizoplane and rhizosphere of rubber, at both Iyanomo and Akwete rubber plantations. Staphylococcus sp., Bacillus sp. were the only bacteria isolated from the rhizoplane and rhizosphere, together with Bacillus cereus var mycoides, which occurred only on the rhizoplane. A. niger, together with species of Trichoderma, constituted by far the dominant mycoflora in the rhizoplane, at both Iyanomo and Akwete, while A. niger, Penicillium spp. together with Trichoderma spp. dominated at the rhizosphere. In vitro interactions showed that the occurrence of antagonists of R. lignosus: Trichoderma spp., Penicillium spp., and Botryodiplodia theobromae, isolated from the root zone of rubber plants were significantly higher at Akwete, than at Iyanomo plantations (P=0.05).
Highlights
Much of the rubber latex in world commerce is tapped from the rubber plant, H. brasiliensis Mullarg, which is grown in many tropical regions of the world [1]
Microbial counts of the rhizosphere soil of rubber showed that while the bacterial population increased from Microbial Iyanomo (May) to September at Iyanomo, and June to October at Akwete (p=0.05), the fungal population decreased on both sites (Table 1)
While the bacteria counts increased significantly with time at the rhizosphere of the rubber plants at both Iyanomo and Akwete, during the period of study from May to October, 2004, the fungal counts decreased on the both sites
Summary
Much of the rubber latex in world commerce is tapped from the rubber plant, H. brasiliensis Mullarg, which is grown in many tropical regions of the world [1]. R. lignosus, the causal agent of white root rot disease of rubber, is the pathogen most feared by planters throughout the rubber growing regions of the world [4]. The Rubber Research Institute of Nigeria (RRIN), which maintains two groups of plantations of rubber, one in Iyanomo near Benin, Midwestern Nigeria, and the other in Akwete in Abia State, eastern Nigeria, reported that the white root rot disease continued to be the most serious problem of rubber on the plantations in Iyanomo, where it accounts for 99% of diseased trees representing nearly 47% of trees inspected, despite the regular round of inspections and treatments [5,6]. Esekahade, both of the RRIN regard the disease as of no serious concern in the Akwete plantations (Personal Communication). The scenario suggests that the soil at Iyanomo is conducive, while that at Akwete is suppressive to R. lignosus, the causal agent of the disease
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