Estimation of the seedbank of Striga spp (Scrophulariaceae) in Malian fields and the implications for a model of biocontrol of Striga hermonthica

Striga seeds were extracted from soils collected in Mall and the viability of these seeds was estimated. Striga seeds were found in 45 of 46 samples taken from 23 fields. Striga hermonthica (Del.) Benth., growing on the host crop millet, was present at all 46 sites sampled. The average size of the Striga seedbank measured to a depth of 15 cm was estimated to be 38 800 m(-2) of surface area (geometric;mean 11 500). The average number of S. hermonthica plants observed per millet hill was 8.83 (geometric mean 3.89) or 13.98 m(-2) (geometric mean 5.69 m(-2)). Higher crop hill densities tended to result in higher densities of emerged S. hermonthica per hill. The relationship between seeds m(-2) and S. hermonthica plants m(-2) was fitted to a rectangular hyperbola and used to reassess an existing model of S. hermonthica control.