Molecular Assessment of Puccinia triticina and Available Wheat Genetic Resources to Combat Leaf Rust in Pakistan

This work encompasses studying behavior of pathogen (Puccinia triticina causing wheat leaf rust); factors that drive the pathogen; status of Lr-genes in wheat and devising \ud methods to monitor and manage this host-pathogen interaction effectively. For the \ud pathogen, leaf rust isolates sampled from major wheat growing areas in the country during \ud wheat season 2011-12 were assessed on 'near isogenic lines' for virulence and race analysis. \ud A race characterized as 'FHPRN' was found frequently infesting a widely cultivated Pakistani \ud variety 'Seher06'. The ITS rDNA sequences revealed its identity as P. triticina (Pt) besides depicting resemblance with the Iranian and Indian Pt isolates. The field observations focused on alternative hosts did not reveal any plant species to host Pt. Instead some aecia found and studied on Berberis lycium revealed four Puccinia species/formae speciales viz., P. graminis f. sp. tritici, P. graminis, P. striiformoides and P. brachypodii, some are found in novel association too. The phylogenetic analysis based on \ud Molecular assessment of Puccinia triticina and available wheat genetic resources to combat leaf rust in Pakistan \ud rDNA loci revealed distinction of Pt from all identified Puccinia species/formae speciales; a lack of acquaintance between Pt and B. lycium; and the likely absence of sexual recombination in Pt in Pakistan. The low genetic diversity (21.4%) among twenty eight leaf \ud rust isolates studied across genome specific SSRs further suggests the lack of recombination \ud and points to the possible wind dispersal among regional countries, likely from Iran to \ud Pakistan, India and beyond. \ud For the host, a set of thirty seven near isogenic lines (NILs), seventeen renowned \ud Pakistani varieties and thirty-two advanced wheat lines were screened against the dominant race 'FHPRN' at seedling and adult plant stages. The analyses depicted effectiveness of Lr1, Lr2a, Lr9, Lr19, Lr24, Lr10+27+31 and Lr28 while Lr12, Lr22a, Lr36 and Lr37 were found \ud moderate in response. At both locations, varieties: Chenab2000, AS02, Bhakar02 and \ud Shafaq06 showed resistance while Pasban90, Iqbal2000, Fsd08, Millat11 and Punjab11 \ud showed moderate response. Molecular markers analysis revealed frequent presence of Lr13, Lr26 and Lr34 in Pakistani varieties and advanced wheat lines, while Lr genes deemed \ud effective again FHPRN were either very rare or absent in varieties/advanced lines. Among these, an effective gene Lr28, absent in all Pakistan varieties and lines, was selected for \ud identification of a co-dominant marker. For this purpose, a doubled haploid (DH) population \ud (192 lines), developed (in Harbans Barian's laboratory, University of \ud Sydney, Australia) through a cross \ud PBW343+Lr24+Lr28/Lang was tested against Lr24 virulent Pt pathotype 104-1, 2, 3, 6, 7, 11, 13 so, segregation at leaf rust resistance loci Lr26 and Lr28 was observed. These genes produced similar seedling responses against Lr24 virulent Pt pathotype, therefore a Lr26linked marker Iag95 was used to identify a set of 123 DH lines that segregated monogenically for Lr28. Total thirty seven markers of 4AL chromosomes were used besides previously reported Lr28 linked dominant marker SCS421570 and Yr51 linked dominant marker owmF3R3. Seven markers were found linked with Lr28. Among these, mag3092 was found co-segregating with Lr28. Based on this data, a physical map was generated. The marker (mag3092) was validated on Australian, Indian and Pakistani varieties or lines. \ud Therefore, this marker can be used for marker assisted selection of most important gene Lr28 in Pakistani varieties and developing breeding material for the future