Patterns of virulence diversity in Puccinia triticina on wheat in Egypt and the United States in 1998-2000

Frequent epidemics of leaf rust in Egypt have been attributed to the appearance of new races virulent on commonly grown wheat cultivars. In 1998, 1999, and 2000, 726 isolates of Puccinia triticina collected in Egypt were tested on a set of 20 single Lr gene differential wheat lines, and 160 races were identified. Three races, MBDLQ, MCDLQ, and TCDMQ, were found in Egypt in all 3 years. Race MCDLQ occurred at >20% frequency each year. Virulences to wheat lines with Lr1, 3, 10, 14b, 15, 17, 23, and 26 occurred at >45% each year. Seven races found in Egypt also were found in either Israel, Sudan, Turkey, or Romania in 1998 or 1999, although the one race common to Sudan and Egypt was rare in Egypt (only 1 year, <1%). Four races found in Israel also were found in Egypt, and the similarity of virulence frequencies in Israel and Egypt indicate at least some exchange of inoculum. Romania and Turkey did not appear to be major sources of inoculum for leaf rust epidemics in Egypt. The level of genetic diversity in leaf rust collections in Egypt in 1998 to 2000 was similar to that of collections from the Southern and Central Plains of the United States in 1998 to 2000. The high diversity of races and the recurrence of common races in each year in Egypt as in the Southern and Central Plains of the United States is consistent with oversummer survival of P. triticina within Egypt or in a neighboring country. The buildup of races virulent on cultivars with the most commonly used Lr genes for resistance in Egypt also is consistent with year-round survival within Egypt or cyclical exchange of inoculum between Egypt and a neighboring country.