Wheat stem rust pathogen (Pgt) Identification and Characterization in Egypt using Single Nucleotide Polymorphism (SNP) markers.

Stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is one of the most serious disease of wheat worldwide. The discovery of new Pgt races in Africa, Ug99 and its variants, brings a new threat to global wheat production. In this study, 50 single pustule stem rust samples, were collected during 2015-2016 from the International Stem rust Trap Nursery (ISRTN) and commercial wheat fields in Sakha, the most important wheat growing region in Egypt. SNP-genotyping was carried out at USDA-ARS Cereal Disease Laboratory. Infection and genotype data confirmed that none of these samples belonged to the Pgt Ug99 race group. Forty-five samples were successfully genotyped consisting of 12 multi-locus genotypes (MLGs). The majority (86.7%) of the samples belonged to three clades: 10 samples, clade III-B (MLG.04, race TTRTF) collected from Misr 3, Sakha 95 and Sids 14 wheat lines; 12 samples, clade IV-A.2 (MLG.06, race TKTTF) collected from Sr 5, Sr6, Sr7a, Sr7b, Sr8b, Sr9a, Sr9e, Sr10, Sr11, Sr15, Sr16 and Sr17 wheat lines; 17 samples, clade IV-E.2 (MLG.11, race TKKTF) from Sr13, Sr14, Sr19, SrMcN, Sr24, Misr 1, Misr 2, Sakha95 and Sids 12 wheat lines. Pgt samples belonging to clades IV-A.2 and IV-E.2 have been observed from Europe to the Middle East, and samples from clade III-B from the southern Caucasus Mountains, Middle East to northeast Africa. The remaining six samples collected from Sr12, Sr18, Sr20, Sr21, Sr22 and Sr25 wheat lines represent two new genotypes (MLG.14 and MLG.17) that have not been assigned to clades. MLG.14 was also observed in samples from Azerbaijan, Iraq and Eritrea. In contrast, this represents the first detection of MLG.17. These results suggest continued variability of the Pgt population in Egypt therefore, emphasizing the importance regularly monitoring to timely identify new races, and utilize this information in screening and identification of effective sources of resistance.