1 Faculty of Agriculture, Minufiya University, Shibin el-Kom,Egypt. 2 Plant Pathology Institute, A.R.C. Giza, Egypt

Background and objectives
Leaf rust of wheat, Puccinia recondita Rob. Ex Desm f.sp. tritici Eriks. & Henn. is a widespread disease in Egypt and all countries of Middle East (1). It occurs at high level of severity in Lower Egypt than the rest of the country. When virulent isolates exist, the loss in grain yield may reach high levels. Unfortunately most of the Egyptian wheat varieties are susceptible, in terms of infection types. However, some varieties exhibited low level of rust incidence and consequently low level of loss in grain yield (2). Therefore, study the partial resistance in such varieties is necessary since resistance of the currently used cultivars is of this type.

Materials and methods
Components of partial resistance of four varieties i.e. Giza 155, Giza 164, Sakha 69 and Sakha 92 which showed field resistance were studied in comparison with the highly susceptible variety Giza 139.All varieties were grown in a randomized complete block design in four replicates for two seasons (1994 and 1995). The experiment was surrounded by a susceptible spreader (a mixture of cvs Thatcher, Baart and Giza 139). which was inoculated several times with a mixture of the prevailing virulences. Rust was assessed as severity of infection, AUDPC, rate of rust increase (r-value ). The histology of partial resistance was also studied using different virulent isolates of the causal organism. Colony area, uredinium size, number of erupted pustules and latent period were determined.

Results and conclusion
The slow rusting varieties exhibited significantly lower mean of finial and maximum levels of rust severity as well as rate of disease increase (r-value) than those on the check variety, in both 1994 and 1995 growing seasons. Moreover, area under disease progress curve (AUDPC) was significantly lower with the tested varieties than the check variety during the two growing seasons (1994 and 1995). This indicates that cvs. Giza 155, Giza 164, Sakha 69 and Sakha 92 showed the ability to delay and slow-down the incidence and development of leaf rust. The histological studies that were carried out also on the adult plant stage against the same virulences revealed that the number of pustules/cm2 and the number of erupted ones were lower on the four varieties than those on the susceptible check (cv. Giza 139). Also the latent periods were longer on the slow rusting varieties than that found on the check. Generally, the results obtained here indicate that. cvs. Giza 155, Sakha 69 and Sakha 92 are convenient sources of partial resistance.

1. El-Daoudi, Y. H.; Mamlouk 0. F.; Bekele E; Ahmed M. S.; Solh, M. B.; Ghanem, E; Bahamish, H., 1997. Arab Plant Protection Conference, Beruit, Lebanon, 1997. 2. Nazim,M. ; El-Shanawani, M.Z.; El-Shennawy, Z. ; Boulot, 1990. Congress of the Egyptian Phytopathological Society. Cairo, 1990, Part 1, pp. 77-97.