Virulence Spectrum and Race Determination of Puccinia recondita f. sp. tritici Causing Brown Rust on Wheat

Abstract

Brown rust of wheat caused by Puccinia recondita f. sp. tritici remains a major constraint to wheat production due to its rapid evolution and ability to overcome host resistance. The present study aimed to assess the virulence spectrum and determine physiological races of the pathogen collected from wheat-growing regions. Rust-infected leaf samples showing characteristic uredinial pustules were collected and urediniospores were used for inoculation of a set of standard wheat differential lines carrying known leaf rust resistance genes. Disease reactions were recorded based on infection type, and race classification was carried out using established virulence/avirulence coding systems. Results revealed a diverse virulence spectrum among isolates, indicating the presence of multiple physiological races in the pathogen population. Certain isolates exhibited broad virulence, overcoming resistance genes in several differential lines, while others showed limited virulence, indicating differential host specificity. Race analysis confirmed the predominance of highly virulent pathotypes capable of infecting widely deployed resistant cultivars, explaining recent field breakdown of resistance. Molecular variability among isolates, supported by ITS-based sequencing, suggested genetic diversity correlating with observed virulence patterns. Disease development was favored by moderate temperatures and high humidity, which enhanced urediniospore germination and infection efficiency. The study highlights the dynamic nature of P. recondita populations and their continuous evolution under selection pressure from resistant wheat varieties. These findings emphasize the importance of regular race monitoring and deployment of diverse resistance genes in wheat breeding programs. Overall, the results provide critical insights into pathogen variability and virulence structure, contributing to improved strategies for durable resistance and effective management of wheat leaf rust in diverse agroecological conditions.