Resistance to Striga hermonthica in wild accessions of the primary gene pool of Pennisetum glaucum

Resistance to Striga hermonthica in 274 wild Pennisetum glaucum subsp. mono dii and stenostachyum accessions was evaluated at Samanko, Mali in 1997 and 1998, and at Cinzana, Mall and Sadore, Niger in 1998. Data recorded includ ed number of striga plants per plot at least three times during the season, date of striga emergence, number of Pennisetum plants, Pennisetum anthesis date, and downy mildew incidence (caused by Sclerospora graminicola). Acro ss trials, the average maximum number of striga per host plant ranged from 0.9 to 8.3. Average days to striga emergence ranged from 54 to 68 days acro ss trials, and was negatively correlated (P < 0.01) with maximum striga wit hin trials. Days to Pennisetum flowering ranged from 54 to 74 days across t rials. Host flowering was correlated (P less than or equal to 0.05) positiv ely with maximum striga at Samanko in 1997 and 1998, but negatively at Cinz ana. Downy mildew incidence ranged from 10 to 32% across trials, and was ne gatively correlated with maximum striga in three trials. Days to striga eme rgence and Pennisetum flowering were significant covariates affecting maxim um striga values, but downy mildew incidence was not. Least squares means o f maximum striga across trials averaged 5.7, and ranged from -0.2 to 19.1 s triga per host plant. Broad-sense heritability of observed maximum striga w as estimated to be 0.55. Agar-gel assays conducted in the laboratory were i neffective in identifying differences in stimulating striga seed germinatio n among se selected accessions. Variables not directly related to genetic r esistance can affect maximum striga emergence in the field, and their ident ification may allow more effective resistance screening.