1Faculty of Agriculture, Minufiya University, Shibin el-Kom, Egypt; 2 Plant Pathology Institute, ARC, Giza, Egypt

Background and objectives
Wheat leaf rust caused by Puccinia recondita f. ;sp. tritici is widespread on most varieties of wheat grown in Egypt. It caused severe losses in grain yield, reaching 23% on some varieties [1]. Moreover, it was the cause of eliminating many varieties because of their susceptibility to the prevailing virulences. The failure of such varieties was mainly due to the appearance of new virulences which were able to attack them. Therefore, study the distribution frequency of the virulence genes in leaf population in Egypt, is of utmost importance. Such information is very useful in planning successful breeding programmes for leaf rust resistance.

Materials and methods
Infected leaves with the rust fungus P. recondita f. ;sp. tritici were collected during 1993-96 from the wheat commercial fields and a trap nursery prepared for this purpose. Isolation, inoculation and rust assessment were carried out according to Stakman et al. [2]. The distribution frequency and virulence shifts were estimated as the percentages of virulent isolates to a set of local varieties, i.e. cvs Giza 155, Giza 157, Giza 160, Giza 162, Giza 163, Giza 164, Giza 165, Giza 166, Giza 167, Sakha 8, Sakha 61, Sakha 69, Sakha 92, Gemmeiza 1, Gemmeiza 3, Beni Suief, Sohag 1, Sohag 2, Sohag 3, Sids 1, Sids 2 and Sids 3. Also the isolate obtained were tested against a set of selected monogenic lines carrying Lr 1, Lr 2a, Lr 3, Lr 3a, Lr 3a, Ir 3ka, Lr 9, Lr 10, Lr 11, Lr 16, Lr 17, Lr 18, Lr 21, Lr 22a, Lr,23 Lr 24, Lr 26 and Lr 30.

Results and conclusion
The virulence survey was started with 154, 165, 130 and 142 single pustule cultures obtained from infected leaf materials collected in 1993, 1994, 1995, 1996 from the commercial fields and the susceptible entries that were included in the Egypt trap nursery. The results obtained revealed that virulences to all tested Lr genes and the local varieties were detected. The frequency of virulence of isolates on lines possessing the resistance genes Lr 9, Lr 18 and Lr 21 was lower than those found on the rest of lines. Shifts in virulences in the different seasons was found on most of the Lr genes . No dramatic shifts were found on lines carrying the genes Lr 2c, Lr 3, Lr 3a, Lr 16, Lr 22b and Lr 26 in the different seasons This indicates that varieties having Lr 2c, Lr 3, Lr 3a, Lr16, Lr 22b and Lr 26 are liable to be infected and epidemics may be expected, whereas, varieties having Lr 9, Lr 18 and Lr 21 will be less infected. In general, rapid shifts in virulence on the most of the tested Lr genes and the local varieties. However, increasing in virulence frequencies was pronounced on all varieties except cvs Sakha 69, Sahel 1 and Sids 1. This also indicates that resistance of the varieties should be supported by effective genes for leaf rust resistance.

1. Nazim M, El-Shehidi AA; Abdou YA, Daoudi YH, 1983. 4th Conference on Microbiology, Cairo, p. 17-27.
2. Stakman EC; Stewart DM, Leogering WMO, 1962. ARS, USDA Agricultural Service Bulletin E 617.