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Host-Pathogen Relationships of Wheat and Septoria tritici. M. Van Ginkel, Former graduate student, Agricultural Research Service, U. S. Department of Agriculture, Montana State University, Bozeman 59717, Present address: CIMMYT, c/o International Livestock Center for Africa (ILCA), P.O. Box 5689, Addis Ababa, Ethiopia; A. L. Scharen, Research plant pathologist, Agricultural Research Service, U. S. Department of Agriculture, Department of Plant Pathology, Montana State University, Bozeman 59717. Phytopathology 78:762-766. Accepted for publication 18 December 1987. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1988. DOI: 10.1094/Phyto-78-762.

A total of 65 crosses were made among 13 durum wheats obtained from crop improvement programs in North Africa and the Middle East. The parental generations, the F1s, and the F2s were evaluated for their reaction to a highly pathogenic isolate of S. tritici from Tunisia. Means and variances of these generations were used to establish the number of effective factors governing reaction to S. tritici in the parents when crossed. The values varied between 1 and 68, with the majority less than 20. Transgressive segregation was also observed. In separate trials, the parents were tested for reaction to 34 isolates of S. tritici from seven countries in the Mediterranean area. Differences due to cultivars and isolates were highly significant. The cultivar isolate interaction component was relatively very small and not significant. The major role of fungal host-species specialization as opposed to cultivar specialization is proposed. Isolates would thus vary in aggressiveness and cultivars in horizontal resistance.