Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2003
Publication Date: 10/7/2003
Citation: McVey, D.V., Nazim, M., Leonard, K.J., Long, D.L. 2003. Patterns of virulence diversity in Puccinia triticina on wheat in Egypt and the United States in 1998-2000. Plant Disease. 88:271-279. Interpretive Summary: Wheat, an important food crop in Egypt, is damaged by frequent leaf rust epidemics. Lack of knowledge of where rust spores come from each year to infect wheat in Egypt and limited information on races of leaf rust in Egypt made breeding resistant wheat varieties difficult. We collected samples of leaf rust in 1998-2000 from Egypt and from suspected source countries for leaf rust epidemics, Israel, Sudan, Turkey, and Romania. We tested them for virulence on wheat lines with 20 different genes for resistance to identify leaf rust races. We characterized patterns of diversity of leaf rust races in Egypt and other countries and compared them with patterns found in seven regions of the United States. Similarity of virulence patterns showed that leaf rust spores commonly move between Egypt and Israel but rarely spread into Egypt from Sudan, Turkey, or Eastern Europe. Common races recurred in Egypt in successive years, which means that the rust fungus must survive through the summer in Egypt to reinfect newly planted wheat each winter. This year to year survival accounts for natural selection of more virulent races in Egypt to overcome race-specific resistance used in Egyptian wheat varieties. If the oversummering sites for wheat leaf rust in Egypt can be identified, the cycle of selection of more virulent races can be broken and yield losses to leaf rust can be controlled.
Technical Abstract: 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 were also 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 were also 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 1998-2000 was similar to that of collections from the Southern and Central Plains of the United States in 1998-2000. 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 U.S. is consistent with oversummer survival of P. triticina within Egypt or in a neighboring country.