Virulence Patterns and Pathotype Diversity of Puccinia striiformis in Pakistan: Insights from a Himalayan Epidemiological Zone

Abstract

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), threatens global wheat production. Pakistan lies within the Himalayan epidemiological zone, a major center of Pst diversity and migration, making pathogen characterization essential for disease management and regional early-warning systems. This study characterized 277 Pst isolates collected from Pakistan’s major wheat-growing regions during 2012–2017 using 18 Yr single-gene differential lines. Overall, 127 races were identified, including 103 transient races detected in one year and 24 persistent races found across multiple years, indicating substantial virulence diversity. Virulence was widespread against Yr1, Yr6, Yr7, Yr8, Yr9, Yr17, Yr27, Yr43, Yr44, and YrExp2, reflecting adaptation to widely deployed resistance genes. In contrast, virulence against Yr10, Yr15, Yr24, Yr32, YrSP, and YrTye/Yr76 was limited or geographically restricted, while no virulence was detected against Yr5, confirming its continued effectiveness. Multivariate analyses revealed non-random phenotypic virulence patterns. Four principal components explained 57.56% of total variation and captured major infection type responses to defeated and effective resistance sources. Discriminant analysis grouped isolates into two broad virulence classes, demonstrating phenotypic structuring rather than genotypic lineage subdivision. The coexistence of common and rare profiles suggests a dynamic pathogen population shaped by local selection and regional movement. These findings highlight the need for continuous surveillance, integrated phenotypic and molecular monitoring, and strategic deployment of diverse resistance genes to support durable stripe rust management in Pakistan and the wider region through coordinated national and regional research networks.