Molecular discovery of new allele associated with loose smut resistance gene Ut-X in spring wheat
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Genes of resistance to loose smut incited by the fungus Ustilago tritici (Pers.) Rostr. are still unknown in the Egyptian spring wheat. Loose smut incidence (LSI) was assessed in ten wheat cultivars through a two-year field trial during 2018–2020. All of the tested cultivars exhibited various percentages of susceptibility (> 10–70% LSI) to the disease except cultivar Misr-3 which exhibited resistance. The most susceptible cultivars were Sakha-93 (60%), Giza-168 (42.1%), and Misr-2 (34.28%). However, the resistant cultivar Misr-3 recorded the least LSI amounting to 5%. The wheat cultivars were screened by the SCAR marker (Xcrc4.2) to identify the presence/absence of loose smut resistance gene Ut-X. Molecular data revealed that the SCAR marker (Xcrc4.2) generated two alleles in cultivars with PCR fragments size of 800-bp and ≃200-bp. The favorable allele 800-bp was generated only in the resistant Egyptian cultivar ‘Misr-3’ and the resistant check cultivar ‘Biggar’, indicating the presence of the gene. Meanwhile, another allele ≃ 200-bp was generated in seven Egyptian cultivars, Giza-168, Giza-171, Misr2, Sakha-93, Gemmeiza-12, N-95, and Shandweel-1, indicating the absence of the resistant gene. This is the first study to report resistance genes to loose smut in Egyptian spring wheat, by detecting Ut-X in cultivar Misr-3. In addition, the study documented the first report of another allele ≃200-bp associated with SCAR marker (Xcrc4.2). Findings also revealed that the race-specific resistance gene Ut-X confers effective resistance to local U. tritici races, including race T10 which could be widely incorporated in breeding programs to control the disease.