Estimates of outcrossing rates in Moringa oleifera using Amplified fragment length polymorphism (AFLP)

The mating system in plant populations is influenced by genetic and environmental factors. Proper estimates of the outcrosing rates are often required for planning breeding programmes, conservation and management of tropical trees. However, although Moringa oleifera is adapted to a mixed mating system, the proportion of selfing has not been previously estimated. The current work therefore, shows the use of AFLP markers in a mating system study of M. oleifera seed orchard. Data revealed a mixed mating system with a multilocus outcrossing rate (tm) of 0.74. It further demonstrated that AFLP markers, though dominant with a lower information content than co-dominant markers are adequate for the study of the mating system in plant populations. The 26% selfing observed in M. oleifera can lead to overestimation of the proportion of additive genetic variance and appropriate adjustments are therefore required. However, the presence of selfing as well as early sexual maturity (6 months to 1 year) in M. oleifera provides an opportunity for developing inbred lines and hybridisation. Additionally, in designing M. oleifera seed orchards, randomisation and minimum distance between related individuals need to be worked out to maximise cross-fertilisation among unrelated clones and minimise selfing or mating among related ramets. Key words: Moringa oleifera, mating system, outcrossing rates, amplified fragment length polymorphism. African Journal of Biotechnology Vol.3(2) 2004: 146-15

Effects of lime, phosphorus and rhizobia on Sesbania sesban performance in a Western Kenyan acid soil

Aluminium (Al) toxicity, phosphorus (P) deficiency and low rhizobia populations limit Sesbania (Sesbania sesban) performance in tropical acid soils. The study determined the i) indigenous rhizobia populations that nodulate sesbania and ii) effects of lime (0 and 4 t/ha), P-fertilizer (0 and 60 kg/ha) and acid tolerant rhizobia (0 and inoculation) on soil and selected sesbania accessions performance in Western Kenya acid soil. Study site had acid soil, low available P, nitrogen (N) and rhizobia populations that nodulate Sesbania (146 cells/g soil). Lime increased soil pH, while both lime and P-fertilizer increased available P. Aluminium toxicity tolerant and P-efficient accessions (SSBSA004, SSUG3, SSUG4 and SSUG5) had faster growth, higher nodulation, shoot P, and shoot N and response to treatments than the sensitive one (SSBSA203). After 7 months of growth, SSUG3 had highest shoot length (306 cm) and dry matter (5.64 tons/ha), hence, most suitable for building poles and fuel wood. SSUG5 accumulated the highest shoot N (222 kg N/ha) and was therefore, most suitable soil N replenishment. Thus, in acid P deficient and low rhizobial population soils of Western Kenya, the use of lime, P-fertilizer, rhizobia inoculation and Al toxicity tolerant Sesbania are important for Sesbania establishment and growth. Key words: Rhizobia, Sesbania, soil acidity, aluminum toxicity, lime, phosphorus

Research into land atmosphere interactions supports the Sustainable Development agenda

Greenhouse gas emissions and land use change - from deforestation, forest degradation and agricultural intensification - are contributing to climate change and biodiversity loss. Important landbased strategies such as planting trees or growing bioenergy crops (with carbon capture and storage) are needed to achieve the goals of the Paris Climate Agreement and to enhance biodiversity. The integrated Land Ecosystems Atmospheric Processes Study (iLEAPS) is an international knowledge-exchange and capacity-building network, specialising in ecosystems and their role in controlling the exchange of water, energy and chemical compounds between the land surface and the atmosphere. We outline priority directions for land-atmosphere interaction research and its contribution to the sustainable development agenda

Full Length Research Paper - Nodulation and growth response of Sesbania sesban (L.) Merr. to increasing nitrogen (ammonium) supply under glasshouse conditions

A glasshouse experiment was carried out to study the effect of ammonium-N on the nodulation, growth and N-uptake of Sesbania sesban   (L.) Merr. inoculated with an effective Mesorhizobium   (S. sesban) strain. Ammonium-N was supplied twice weekly as 100 ml of nutrient solution at concentrations of 0, 100, 200, 400, 600 and 800 mg N/l. The seedlings were grown in pots with sterilized sand substrate and assessed at 5, 7 and 9 weeks after planting (WAP). Nitrogen supply significantly improved nodulation (number of nodules and nodule dry weight/plant) with treatment 100 mg N/l compared with 0 mg N/l at 5 and 7 WAP, thus indicating synergism for the N2-fixation symbiosis. However, with treatments ≥ 200 mg N/l nodulation was either depressed or inhibited. Seedlings treated with 100-400 mg N/l generally exhibited better growth (shoot and root dry weight/plant) and N-uptake than the other treatments (0, 600 and 800 mg N/l). This study has demonstrated that S. sesban seedlings are tolerant to relatively high levels of N, and that treatment with 100 mg N/l (20 mg N per week) is necessary to stimulate an early and effective N2-fixing symbiosis

Preliminary studies on mycorrhizal symbiosis in plant conservation, forestry and farming systems in Kenya

The paper presents studies on mycorrhizal symbiosis in plant conservation, agriculture and forestry in Kenya. Mycorrhizal studies in conservation of rare, threatened and endemic plant species of Kenya were undertaken with aim of establishing fungal species associated with the plant species. Mycorrhizal studies in farming system evaluated the impact of different farming practices on mycorrhizal symbiosis, while in forestry the mycorrhizal studies evaluated fungal species in exotic and indigenous forests. The four studies show affinities of plant species to specific mycorrhizal types. Association with plant species seems to be a heritable trait. Mycorrhizal species composition was affected by the habitat, moisture content, soil nutrients and root morphology. In forestry, indigenous plant communities maintained high species diversity than the exotic species and the species were specific to forest type. Farming systems affected the abundance of spores of Mycorrhizae with spore abundance higher in improved tree fallow than natural fallow and continuous cropping systems. Studies on orchids showed each orchid species to associate with specific Rhizoctonia isolate and taxonomic trends were observed in the association. The four studies show changes in host plant and soil conditions to greatly determine mycorrhizal symbiosis, species composition and abundance. Journal of Tropical Microbiology Vol.3 2004: 48-6