Evidence of pathogenic variation in Sclerospora graminicola populations from pearl millet growing regions in Senegal

Downy mildew of pearl millet induced by Sclerospora graminicola is a major disease that causes significant yield losses in most pearl millet production areas worldwide. The pathogenic variability of S. graminicola populations from four agro-ecological zones in Senegal was assessed under field conditions. A set of 19 pearl millet lines, including 12 downy mildew-resistant differential lines with five improved cultivars and two local checks was evaluated during two consecutive rainy seasons (2015 and 2016) at Bambey, Nioro, Kolda and Sinthiou, representing the main pearl millet-growing zones of Senegal. Significant differences were observed among the tested lines, pathogen origin, year and their interactions for resistance to S. graminicola. Except for ICMR 356 and 7042 S, the downy mildew-resistant differential lines differed in their resistance to the pathogen from the four agro-ecological zones over the years, providing evidence that the S. graminicola isolates represented different races of the pathogen. Among the locations where the experiments were established, the highest average of downy mildew incidence over the two years was recorded at Nioro (18.7 ± 2.6%), Kolda (17.6 ± 1.8%) and Bambey (12.1 ± 2.3%), while the mean downy mildew incidence was lowest at Sinthiou (6.9 ± 2.9%). This finding indicated that populations of pathogen from Kolda, Nioro and Bambey are more virulent compared to the one from Sinthiou.