Genetic diversity and provenance integrity of Sesbania sesban germplasm used in dissemination activities on improved fallow technology in Kenya and Zambia

Background environmental problem: Soils on small scale farms in many parts of Kenya and Zambia have lost fertility due to continuous cropping and removal of biomass during harvesting of food crops. To restore the fertility of soil and realize good food crop yields, farmers may use artificial fertilizers or they can leave their land fallow (uncultivated) for sometime, normally 4 to 6 years, so that it can naturally regain its fertility. But farm sizes are reducing and farmers do not have the possibility of leaving land fallow for long periods of time. To reduce the fallow period and increase soil fertility, nitrogen fixing trees are planted on the plots for a period of 2 – 3 years after which they are removed and food crops are subsequently planted. The effect of the nitrogen fixing trees is dual via the roots and also by biomass transfer into the soil.Sesbania sesban is one of the most useful tree species for soil fertility improvement. The species is very fast growing, reaching a height of 2 – 2.5 m within 9 months of planting, and it produces a lot of leaf material that is easily decomposed in the soil. It also has an extensive root system that is closely associated with nitrogen fixing bacteria. Furthermore, its wood can also be used for various purposes on the farms and it protects the soil from erosion. Studies have shown that it also suppresses many weeds including the notorious Striga that reduce crop yields (particularly maize). Successful dissemination and adoption of agroforestry technologies depends largely on availability of high quality tree seed to participating farmers. The majority of the agroforestry technologies that are at the dissemination stage involve intensive management of the tree stands that precludes the possibility of using such stands as sources of seed. They include very close planting. Further, to have significant impact, large quantities of high quality germplasm are required at the start of a dissemination project.To supply seed needs, superior populations of Sesbania sesban have to be identified and multiplied in seed production stands, and seeds distributed to participating farmers. In the project under investigation, a number of seed stands of different provenances have been established. Seed distribution pathways are however not well understood, particularly possible exchange of provenancesn farmers, mixing different genetic backgrounds and possibly influencing the agronomic characteristics of subsequent generations. Further, interactions between introduced provenances and existing natural populations are not well understood. Since genetic differentiation in Sesbania sesban is known to be high, the implications of provenance interactions may be particularly significant. 1 To determine if there is genetic introgression among populations of Sesbania sesban use in dissemination of the ”improved fallow” agroforestry technology in Kenya and Zambia 2 Identify if there are inte-varietal crosses among populations of Sesbania sesban used in dissemination of the ”improved fallow” agroforestry technology in Kenya and Zambia 3 Determine if inte-varietal crossing should be promoted or not. This study will use a molecular genetics technique (Amplified Fragment Length Polymorphism – AFLP) to test the genetic diversity and integrity of provenances of Sesbania sesban seed used in dissemination of soil fertility replenishment using improved fallows. Seed from seed production stands, natural populations and of three provenances will be assessed in this study.Field trials will be established from seed collected from artificially crossed F1 and F2 generations of the original germplasm and characterized to develop auxiliary data for use in verifying molecular genetics data from laboratory studies and the agronomic implications of provenance hybridization. Indicators 1 Use of molecular marker information 2 Possible use of quantitative trait information generated from field trials