Stem rust has been one of the most serious diseases on wheat in Egypt, particularly on the late sowings. The locally produced wheat cultivars have been developed as field resistant to stem rust regardless their reaction in terms of infection types. Many of them served in agriculture for long time since their release showing low levels of disease severity. Out of these cultivars, ten were tested in a randomized complete block design experiment, in four replicates for three seasons at two locations, i.e. Nubariya and Sids Agricultural Research Stations in Egypt. The experiment was surrounded by a spreader area of highly susceptible cultivars, inoculated with a mixture of rust races as source of inoculum. Rust data were recorded as rust severity (%). The area under disease progress curve (AUDPC) was estimated as a reliable and good measure of adult plant resistance (APR), partial resistance. According to the levels of rust severity and AUDPC values, the
tested cultivars could be classified into two main groups; a) slow rusting cultivars; including cvs. Sids 1, Sids 13, Gemmeiza 7, Giza 168, Sakha 93 and Sakha 94. b), and Fast rusting cultivars; including cvs. Giza 160, Giza 164, Sakha 8 and Sohag 3 showing high level of rust severity and high estimates of AUDPC. Under greenhouse conditions, the numbers of probable genes for stem rust resistance were postulated by testing the ten local wheat cultivars and twenty monogenic lines for stem rust against fifteen cultures of Puccinia graminis f.sp. tritici [the cv. Giza 160, characterized by high level of rust severity and high estimates of AUDPC was used as check cultivar]. Gene postulation showed that the cvs. Giza 160 and Sakha 8 do not have any of the tested genes. In addition, the fast rusting cultivars, i.e. cvs. Giza 160, Giza 164, Sakha 8 and Sohag 3, have low number of genes (2 genes of the tested genes or not have any genes). While, the slow rusting cultivars, i.e. Sids 1, Sids 13, Gemmeiza 7, Giza 168, Sakha 93 and Sakha 94 have higher number of genes (from 4 to 13 of the tested genes). As many as the resistance genes are accumulated in any wheat cultivar, both the rust severity and AUDPC value become lower and its resistance becomes more durable.