ROLF T. FOLKERTSMA1, BETTINA I.G. HAUSSMANN2, HEIKO K. PARZIES3, VOLKER HOFFMANN4, H. H. GEIGER3
1International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Kenya
2International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Niger
3University of Hohenheim, Population Genetics, Germany
4University of Hohenheim, Agricultural Communication and Extension, Germany
Sorghum is the staple food for millions of people in sub-Saharan Africa. The parasitic weed Striga hermonthica is a major constraint to sorghum production in this region with yield losses due to Striga reported up to 100%. Striga-resistant sorghums would be an important component of integrated Striga control if resistance was available in locally adapted farmer-participatory selected varieties. The application of marker-assisted selection in Striga resistance breeding will greatly accelerate progress since field screening is difficult, complex, and often unreliable; Striga seed is quarantined thus confining tests to areas where Striga is endemic; and because some Striga resistance genes are recessive, increasing the time required for conventional backcrossing. QTL mapping for resistance of sorghum to S. hermonthica was performed using a population of F3:5 lines developed from the cross N13 x E36-1, where the resistant sorghum line N13 is characterised by ``mechanical'' resistance (Hausmann et al., 2004). Composite interval mapping detected five QTL common across 5 environments over two years of Striga resistance evaluation, with the resistance alleles deriving from N13. Since their effects were validated across environments, years and independent genotype samples, these robust QTL are excellent candidates for marker-assisted selection. In a three year project, launched in April 2004, Striga resistance of farmer-preferred sorghum varieties in Eritrea, Kenya, Mali and Sudan will be enhanced through a combination of marker-assisted backcrossing and farmer-participatory selection. The impact of gene flow on the stability of the achieved Striga resistance will be investigated in a complementary study. Simultaneously, a socio-economic study of the sorghum seed supply systems in these countries will be undertaken to guide the design of effective seed interventions by partner institutions so that improved materials efficiently reach farmers. Linkage with technology exchange will boost promotion of the improved varieties as component of integrated Striga control.
Keywords: Farmer-participatory selection, Marker-assisted backcrossing, QTL, Sorghum bicolor, Striga