Wetlands in Nigeria face constant threat of destruction by urbanization, road construction and agricultural activities, but the floristic compositions of these fragmented communities are unknown. A comparative assessment study of the floral of three wetlands in a forest-savanna transition ecological zone, Ibadan (70261 N, 30541 E), Oyo State, Nigeria was conducted in the dry and wet seasons of 2002 to assess their species richness, density, community structure and diversity. Thirty-eight plant species from 19 families were enumerated in the three wetlands in two seasons. Nineteen species from 13 families were enumerated in the dry season, while 14 species belonging to nine families were enumerated in the wet season. Eight families were common to both seasons. Eleyele and Apete wetlands had relatively stable flora for both seasons, while Oba dam exhibited pronounced shift in flora between the dry and wet seasons. Continuous perturbation of the three wetlands encouraged proliferation and dominance of some invasive species at the expense of indigenous species populations, leading to subtle biodiversity erosion.

The natural fallow through which the fertility of tropical soils is restored and the weed pressure is alleviated can no longer be sustained. However, improved bush fallow using fast-growing, deep-rooting and good biomass-accumulating shrubby legumes provides a good alternative. The suitability of Senna obtusifolia in improved fallow management was investigated by studying its competitive ability relative to Chromolaena odorata (siam weed) and Euphorbia heterophylla (poinsettia weed) in replacement series studies at four total densities (29, 58, 115 and 230 plants m -2 ) in pure stands and at three total densities (58, 115 and 230 plants m -2 ) in equiproportion mixture. Replacement series diagrams were drawn and relative competitive ability indices (Relative Yield, RY; Relative Yield Total, RYT; Relative Replacement Rate, RRR) were determined from the plant dry weight (PDW). In the replacement series diagrams of Senna/Chromolaena combination, the curves of the PDW/pot and those of the RY were convex for the two species. The RY values were 0.64±0.12 and 0.59±0.05 for S. obtusifolia and C. odorata respectively. The RYT and RRR, averaged over all densities, were 1.23±0.08 and 1.27±0.17 respectively. However, in the Senna/Euphorbia combination, the curves were convex for S. obtusifolia and concave for E. heterophylla . The RY values were 0.81±0.06 for S. obtusifolia and 0.23±0.05 for E. heterophylla respectively. The RYT and RRR values for the combination were 1.05±0.07 and 11.07±2.40 respectively. The results indicated that though S. obtusifolia and C. odorata attained equilibrium growth with RYT significantly deviated from unity (RYT>1) when grown in mixture, S. obtusifolia exerted greater replacement pressure than C. odorata . Conversely, in the Senna/Euphorbia combination, there was a competitive relationship (RYT»1) in which S. obtusifolia was the aggressor and E. heterophylla the subordinate species. The study showed that while S. obtusifolia exhibited obvious competitive superiority in mixture with E. heterophylla , the superiority was less obvious in mixture with C. odorata . Key words : Competition; fallow management; helioplastic response; weed control DOI: 10.4038/tare.v11i0.1784 Tropical Agricultural Research and Extension Vol.11 2008 pp.25-30

Two pot trials were conducted in the crop garden of the Department of Crop Protection and Environmental Biology, University of Ibadan between March and June 2005, to evaluate the phytoremediating potential of Tithonia diversifolia in spent oil polluted soil to enhance the agricultural productivity. The study was a completely randomized design with three replicates. Varying pollution levels were created by administering spent lubricating oil at 0, 50, 100, 150 and 200 ml per 4-kg soil in pots. Two Tithonia seedlings were transplanted into each pot and were monitored for 12 weeks. At commencement of the two trials, lead concentrations in the soil averaged 3.78 mg/kg and 37.75 mg/kg in the control and in 200-ml treatment respectively, and cadmium concentrations averaged 0.73 mg/kg and 2.05 mg/kg in the control and 200-ml treatment respectively. At the end of the two trials, lead content was reduced to 0.00 and 11.88 mg/kg and cadmium content was reduced to 0.00 to 0.43 mg/kg in the control and 200-ml treatments respectively. Tithonia seedlings were able to absorb lead and cadmium in the polluted soils, and contents in the root were more than contents in the shoot. The lead and cadmium contents in the shoot compared to the root were about 54% and 30% respectively. The implication of the results for the quality of vegetable produced at urban and peri-urban roadside and wetland gardens is discussed.

Use of genetic resistance is the most practical and economic way to manage major diseases of yams. In a search for sources of resistance, 40 water yam (Dioscorea alata L.) accessions from Benin, Ghana, Nigeria and Puerto Rico were screened under natural disease infection conditions in Ibadan, Nigeria. The accessions were evaluated at 1, 3 and 6 months after planting (MAP) for severity of yam anthracnose and viral diseases. The effect of the pathogens on yield was also evaluated at harvest 9 MAP. There were significant differences (P < 0.001) between accessions for severities of anthracnose and viral diseases. Eight (20%) of them had lower anthracnose area under disease progress curves (AUDPC) values than the resistant check while 10 (25%) had AUDPC values below the trial mean. There were significant variations (P < 0.001) in yield components among the accessions. There was significant negative correlation of anthracnose severity with fresh tuber yield (r = -0.51) and with number of tubers per plot (r = -0.40). Similarly, significant negative correlations were observed of virus disease severity with fresh tuber yield (r = -0.78) and number of tubers per plot (r = -0.65). Linear regression models also showed that the fresh yield had significant negative relationships with anthracnose (R-2 = 0.26) and viral (R-2 = 0.62) diseases. The accessions identified as resistant constitute a valuable resource for breeding of resistant germplasm.

Environmental pollution associated with the exploitation of minerals (oil, columbite and coal) in Nigeria had led to the destruction of farm lands while rivers and ponds which served as both source of drinkable water and fishing grounds are severally polluted, killing most of the aquatic life. Field experiments were conducted in the early rainy season and mid rainy season in the year 2000 at Umunarukwu village in Oguta LGA of Imo State, Nigeria (5 degrees 22'N, 6 degrees 46'E) to investigate the effects of crude oil pollution, gas flaring and exhaust fumes of tankers ( which transport these petroleum products to the urban areas) on the growth and performance of three different varieties of maize, namely, DMR ESR.W (VI), DMR ESR.Y M) and Oguta Local M), the local variety. These maize varieties were also chemically analyzed for their absorption of heavy metals along with the soil samples collected before and after planting. The amounts of lead (Pb) and Cadmium (Cd) absorbed by the local variety were significantly Pb = 9.83ppm, and Cd =0.93ppm. This local variety also exhibited an appreciable increase in plant height (in PI) despite the high accumulation of cadmium and lead in its tissue. The result of this study suggests that the local variety can be cultivated on a large scale and be used to clean up or remediate a polluted land provided the produce is destroyed and not consumed.

Field studies were conducted in Oyo, Nigeria, to determine the effect of level and source of shade (polyethylene plastic fabric and velvetbean canopy) on the dry matter of speargrass (Imperata cylindrical (L.) Raeuschel). Shade levels provided by the plastic fabric were 0 (full solar radiation), 50, 75 and 88% of the incident solar radiation. Velvetbean shade levels of 40.5 to 97% were provided by densities of 4, 8, and 16 plants m-1. In 1999, the velvetbean canopy intercepted 40.5% of solar radiation at 3 weeks after treatment (WAT) and 82% between 5 and 11 WAT. At 11 WAT, velvetbean shading reduced the speargrass biomass by 48% and shade from plastic fabric by 41%. In 2000, radiation interception by the velvetbean canopy was 86.7-97.2% between 3 and 11 WAT. Shade from the velvetbean canopy reduced speargrass biomass by 90% and shade from plastic fabric by 44% at 11 WAT. Velvetbean biomass and LA1 were negatively correlated with speargrass biomass (r = -0.85 to -0.91, P<0.05) and incident solar radiation (r = 0.46 to 0.79, P = 0.05). The similarity of the effects on speargrass biomass of shading by plastic fabric and velvetbean indicated that shading was the principal mechanism by which velvetbean suppresses speargrass.

Abstract Amplified fragment length polymorphism (AFLP) markers were employed to assess intraspecific variability in water yam (Dioscorea alata L.). Fifty-three accessions of diverse geographic origins in West and Central Africa (Benin, Côte d'Ivoire, Ghana, Nigeria and Chad) and Puerto Rico were analysed using three AFLP primer combinations. Of the 342 amplification products generated, a mean of 53.4% were polymorphic. Genetic similarity coefficients ranged from 0.29 to 0.95. The accessions could be clustered into three major genetic groups with one outlier. Each group was a mixture of accessions of different geographical origin indicating that geography has not played a major role in the differentiation of the species. A few accessions clustered very tightly suggesting that there may be duplicate accessions in the collection. The wide genetic variation observed constitutes a good basis for genetic improvement of yam.

Tropical Agricultural Research and Extension is a peer-reviewed international scientific journal covering a wide range of subject areas in tropical and subtropical agriculture published quarterly by the Faculty of Agriculture, University of Ruhuna, Sri Lanka. The journal is also available on the Faculty of Agriculture, University of Ruhuna website https://www.agri.ruh.ac.lk/tare/index.htm .