Plant Disease March 2004
Volume 88, Number 3
The American Pathological Society (APS)
Interpretive summary

Patterns of Virulence Diversity in Puccinia triticina on Wheat in Egypt and the United States in 1998-2000
D. V. McVey, United States Department of Agriculture-Agricultural Research Service (USDA-ARS), Cereal Disease Laboratory, St. Paul, MN 55108; M. Nazim, Faculty of Agriculture, Minufiya University, Shibin el-Kom, Egypt; K. J. Leonard and D. L. Long, USDA-ARS, Cereal Disease Laboratory, St. Paul, MN. Plant Dis. D-2003-1222-01R, 2004 (online). Accepted for publication 7 October 2003.

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 cultivars difficult. We collected samples of leaf rust in 1998 to 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 re-infect 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 cultivars. 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.

http://www.apsnet.org/pd/summaries/dma04sum.asp