Sesbania sesban (L.) Merr. (sesbania) is a fast growing N 2 -fixing widely used as an improved fallow species by smallholder farmers in eastern and southern Africa to restore fertility of their N-deficient soils. In order to establish the need for inoculation, the population of sesbania rhizobia in soil collected from a site where the species is intended for introduction was assessed using the most probable number (MPN) plant infection assay. The MPN of sesbania rhizobia was low (21, 6-81 fiducial limits at P=0.05 g -1 soil) but with N 2 -fixation potential comparable to sesbania inoculant strain KFR 651. Evaluation of an indigenous sesbania rhizobial isolate GSS 1 from the MPN assay in potted field soil showed that it was more effective than strain KFR 651 in terms of plant growth and shoot dry matter (DM) accumulation at 9 and 12 weeks after planting, respectively. Total shoot N content was also higher for plants inoculated with isolate GSS 1 than inoculant strain KFR 651 and uninoculated control treatments 12 weeks after planting. These results demonstrate that it is better to inoculate with effective indigenous than exogenous rhizobia where the need for inoculation has been established.

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Osyris lanceolata Hochst. & Steud. is a multipurpose tree species widely spread in many of the sub-Saharan countries ranging from Algeria to Ethiopia all the way to South Africa. In Kenya, the species is endemic to the Arid and Semi-Arid Lands (ASALs). It is highly valued for its essential oils used in the cosmetic and pharmaceutical industries. Despite its endangered status and economic importance, little is known about its genetic diversity status and only few conservation strategies exist for the species. Overexploitation of the species has resulted in the decline of its population and reduced availability of its products. The mode of harvesting of sandalwood is destructive and unsustainable. This is because the whole tree is usually uprooted to get the heartwood from the stem, stump and roots. The exploitation of African sandalwood could soon drive the species to extinction unless proper control measures are put in place through regulation of its trade and development of conservation strategies. Despite its endangered status and economic importance, no genetic study has been carried out on the species to provide information vital for conservation strategies. This paper reports the development and characterization of a set of 12 polymorphic and five (5) monomorphic microsatellite markers isolated and characterized of O. lanceolata.One plant leaf sample was used as the source of DNA for genomic library construction. Total genomic DNA was extracted from silica gel dried leaf using DNeasy Plant Mini Kit (QIAGEN, Hilden, Germany). The DNA sample was then sent to The Gene Pool Institute of Evolutionary Biology, University of Edinburgh for sequencing. Simple sequence repeats (SSRs) were extracted through PAL Finder software version 0.02.04 (Castoe et al. 2012) and primer pairs developed. Identified microsatellites and designed primers were assembled using QDD (Meglécz et al. 2010) with parameters given in set_qdd_default.ini.file. The gaps emerging during the scaffolding process were closed using GapCloser (vs. 1.12). The contigs >1000 bp of the draft assembly were analyzed and functionally annotated using Blast2GO (Conesa et al. 2005). Based on this information, 48 primer pairs consisting of either di-or trinucleotide repeats were selected. After testing, 17 primer pairs were identified and used to characterize 84 samples of O. lanceolata from three natural populations, namely Mt. Elgon (28), Gachuthi (27) and Kitui (29). The PCR analysis was performed using Multiplex PCR Mater Mix (QIAGEN) and 10 ng of DNA as described by (Omondi et al. 2015). The PCR mix contained a fluorescently labelled M13 primer, M13-tailed forward primer and a reverse primer in the concentration ratio of 0.15:0.01:0.15 µM. For all loci, a touchdown thermal cycling program was used with annealing temperature ranging between 57-55°C. The cycling profile consisted of initial denaturation of 95°C for 15 min followed by 10 cycles at 94°C for 30 s, 57°C for 90 s and 72°C for 60 s (annealing temperature decreasing by 1°C per cycle); and 22 cycles...

SUMMARYNitrogen fixation by leguminous trees such as sesbania (Sesbania sesban) in acid soils is limited by aluminium (Al) toxicity and phosphorus (P) deficiency. We screened 214 East African sesbania accessions for Al toxicity tolerance, P use efficiency and sesbania–rhizobia symbiosis. Aluminium toxicity tolerance or sensitivity was measured by the relative root elongation index. Highly Al tolerant and sensitive accessions were screened for P use efficiency. Highly P use efficient and Al sensitive accessions were assessed for symbiotic effectiveness with acid tolerant rhizobia. Eighty-eight per cent of the accessions were Al toxicity tolerant. High Al levels reduced shoot P content by 88% and total dry matter (TDM) by 83%. P addition increased shoot P content and TDM. Rhizobia inoculation increased nodulation by 28–82%, shoot N content by 28–45% and TDM by 15–34% in the low rhizobia density acid soil of Bumala, Kenya. P use efficient accessions had higher nodulation, shoot N content and TDM in the ranges 32–70, 20–52 and 22–36%, respectively, compared to sensitive genotypes. The combination of sesbania accession (SSUG10) and rhizobia strain ASs48 was superior in shoot N accumulation. Inoculation of P use efficient germplasm with acid tolerant rhizobia can improve N-rich biomass accumulation suitable for N replenishment in acid soils.