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

Background and objectives
Leaf rust of wheat, Puccinia recondita tritici, is a widespread disease in Egypt and all countries of the Middle East [1]. It occurs at higher levels of severity in lower Egypt than in the rest of the country. When virulent isolates are present, 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 a low level of rust incidence and a consequently low level of loss in grain yield [2]. A study of 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, 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 and 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 final 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, AUDPC was significantly lower in 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 carried out 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 YH, Mamlouk OF, Bekele E et al., 1997. Arab Plant Protection Conference, Beruit, Lebanon, 1997.
2. Nazim M, El-Shanawani MZ, El-Shennawy Z, Boulot O, 1990. 6th Congress of the Egyptian Phtopathological Society, Cairo, Part 1, pp. 77-97.