Virulence Variation and Race Identification of Puccinia triticina (Wheat Leaf Rust) Isolates in North East Nigeria

Wheat leaf rust caused by Puccinia triticina remains the most economically damaging foliar disease of wheat in Nigeria's irrigated production zones of the North East, yet virulence variation and race composition of local pathogen populations have not been characterised at the molecular level. Understanding virulence structure is critical for determining the effectiveness of deployed resistance genes in current varieties. This study characterised virulence variation among 45 P. triticina isolates collected from irrigated wheat farms across Gombe, Borno, and Yobe States during the 2023 and 2024 dry seasons. Virulence characterisation was performed using a set of 20 near-isogenic lines carrying individual Lr resistance genes, according to international rust differential protocols. Molecular phylogenetic placement of selected isolates was carried out using the urediniospore ITS and beta-tubulin gene sequences. Race analysis identified nine physiological races, with race PHNT and THTT (using standard four-letter USDA code notation) collectively accounting for 64 percent of tested isolates. Virulence to Lr1, Lr3a, Lr17a, and Lr26 resistance genes was detected in more than 70 percent of isolates, indicating that varieties relying on these genes alone are at high risk of field failure. Conversely, Lr19 and Lr34 resistance remained effective against all characterised isolates, representing durable resistance options. Molecular phylogenetic results placed Nigerian isolates in a clade distinct from East African populations, suggesting separate evolutionary lineages. Findings directly inform variety deployment decisions and resistance gene deployment strategies in Nigeria's irrigated wheat zones. Keywords: Puccinia triticina, wheat leaf rust, virulence, resistance genes, North East Nigeria.