Morphological and Molecular Characterization of Uromyces appendiculatus Races Causing Common Bean Rust

Abstract

Common bean rust caused by Uromyces appendiculatus is a destructive foliar disease that significantly reduces yield and seed quality in bean-growing regions. The present study aimed to characterize pathogen races associated with rust outbreaks through integrated morphological and molecular approaches. Rust-infected leaf samples exhibiting characteristic reddish-brown pustules were collected from major common bean production areas. Urediniospores were examined for morphological traits including size, shape, wall ornamentation, and germ pore characteristics using light microscopy. Inoculation of differential host lines under controlled conditions enabled race identification based on virulence patterns. Molecular characterization was performed using ITS rDNA sequencing, confirming the identity of isolates as U. appendiculatus with high similarity to reference sequences. Phylogenetic analysis revealed genetic variation among isolates, indicating the presence of multiple rust races circulating within bean production systems. Pathogenicity tests demonstrated differential host responses, confirming variability in virulence among isolates and supporting race differentiation results. Disease development was strongly influenced by high humidity and moderate temperatures, which enhanced spore germination and infection efficiency. The integration of morphological observations, molecular diagnostics, and host differential reactions provided a robust framework for accurate race characterization. These findings highlight the dynamic nature of U. appendiculatus populations and their ability to overcome host resistance, emphasizing the need for continuous monitoring. The study underscores the importance of deploying resistant cultivars with diverse genetic backgrounds and implementing timely disease management practices. Overall, the results contribute to a better understanding of the epidemiology and genetic diversity of bean rust pathogen populations and provide essential insights for developing durable resistance strategies in common bean improvement programs.