Cucurbit Genetics Cooperative Report 18:55-55 (article 26) 1995
Powdery Mildew Attacks Commercial Watermelon Cultivars in Sudan
Sadig K. Omara and M. Taha
National Institute for Promotion of Horticultural Exports, University of Gezira, P.O. Box 20, Wad Medani, Sudan
Powdery mildews have always been serious diseases on cultivated cucurbits in Sudan. Squashes, pumpkins, melons, cucumbers and snake cucumbers are susceptible to severe attack when grown during the mild dry winters. Susceptible cultivars survive only after the application of strong chemical control measures. However, commercial watermelon cultivars such as 'Congo' and 'Charleston Grey' have not been observed to develop powdery mildew symptoms and generally do not require chemical measures to protect the crop. On the other hand, viruses, like WMCSV, WMMV 1 and 2, ZYMV and CABYV, may cause serious damage to watermelon, and breeding programs are directed toward screening for resistance to these viruses.
The only reported incidence of powdery mildew attacking watermelon sin Sudan was from a germplasm collection mission from the University of Gezira (1). While collecting seeds of land races grown in Western Sudan, one plant was observed with clear symptoms of the disease. Then, during December 1994, while evaluating a population of parents, F2 s and backcrosses for resistance to WMCSV, powdery mildew was noticed to develop in all of the material grown. Mildew colonies developed in stems, petioles and leaves. Towards mid-January, profuse sporulation was noticed in some land races and in a commercial hybrid from France, 'Confire', leading to dryness of foliage and death of plants. Commercial cultivars like 'Congo' and 'Charleston Grey', and some land races, developed clear symptoms but seemed less susceptible.
Not a single land race or commercial cultivar proved resistant. Parental lines of other powdery mildew resistant cucurbits, like melons and snake cucumber grown in the same field were not attacked. 'PMR 5', 'Ananas PMR', 'Augen', 'Gallia' F1, 'PMR Honey Dew', and a number of PMR snake cucumber breeding lines remained free of the disease. It is not known at the moment whether this indicates the evolution of a new race, or whether a more conducive environment enhanced the aggressiveness of an existing race belonging to any of the powdery mildew fungi known to attack cucurbits in Sudan. the first assumption seems more likely, but the final word will require more investigation on the subject.
- Fadlalla, Y. 1992. Personal communication.
Coordinators note: Dr. Omara has written that he would like to receive germplasm from anyone who believes they have material that could be of value to their breeding program, Of course, he is happy to share their material with interested individuals.