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Resistance to Striga hermonthica in Wild Accessions of the Primary Gene Pool of Pennisetum glaucum

First and third authors: U.S. Department of Agriculture-Agricultural Research Service Crop Genetics and Breeding Research Unit, University of Georgia Coastal Plain Experiment Station, Tifton, 31793-0748; and second author: ICRISAT, B.P. 320, Bamako, Mali. Cooperative research project among the U.S. Department of Agriculture, Agricultural Research Service, the University of Georgia College of Agricultural Experiment Stations, and the International Crops Research Institute for the Semi-Arid Tropics

Resistance to Striga hermonthica in 274 wild Pennisetum glaucum subsp. monodii and stenostachyum accessions was evaluated at Samanko, Mali in 1997 and 1998, and at Cinzana, Mali and Sadoré, Niger in 1998. Data recorded included 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). Across 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 across trials, and was negatively correlated (P < 0.01) with maximum striga within trials. Days to Pennisetum flowering ranged from 54 to 74 days across trials. Host flowering was correlated (P ≤ 0.05) positively with maximum striga at Samanko in 1997 and 1998, but negatively at Cinzana. Downy mildew incidence ranged from 10 to 32% across trials, and was negatively correlated with maximum striga in three trials. Days to striga emergence and Pennisetum flowering were significant covariates affecting maximum striga values, but downy mildew incidence was not. Least squares means of maximum striga across trials averaged 5.7, and ranged from -0.2 to 19.1 striga per host plant. Broad-sense heritability of observed maximum striga was estimated to be 0.55. Agar-gel assays conducted in the laboratory were ineffective in identifying differences in stimulating striga seed germination among selected accessions. Variables not directly related to genetic resistance can affect maximum striga emergence in the field, and their identification may allow more effective resistance screening.