SSR Variability of Stem Rust Pathogen on Spring Bread Wheat in Russia

Area of Science:

• Plant Pathology
• Agricultural Science
• Genetics

Background:

• Wheat stem rust, caused by *Puccinia graminis* f. sp. *tritici*, has become a significant threat to spring bread wheat production in Russia's temperate regions since 2009.
• Previous understanding identified it primarily as a winter wheat disease in southern Russia, but its impact has shifted.
• The pathogen's genetic diversity and population structure are crucial for understanding its epidemiology and developing effective control strategies.

Purpose of the Study:

• To investigate the genetic diversity and population structure of *Puccinia graminis* f. sp. *tritici* isolates collected from spring bread wheat in Russia.
• To identify distinct genetic clusters and understand the reproductive modes shaping the pathogen population.
• To pinpoint specific genotypes that may indicate rapid evolutionary changes and potential disease outbreaks.

Main Methods:

• Collected 222 *Puccinia graminis* f. sp. *tritici* isolates from susceptible spring bread wheat cultivars across Central, Volga, Omsk, and Novosibirsk regions in 2019.
• Genotyped isolates using 16 simple-sequence repeat (SSR) loci to assess genetic variability.
• Analyzed data for number of alleles, heterozygosity, and deviation from Hardy-Weinberg equilibrium to determine population structure and reproductive strategies.

Main Results:

• The *Puccinia graminis* f. sp. *tritici* population in Russia's temperate zone is divided into two main genetic clusters: 'European' (Central region) and 'Asian' (Volga, Omsk, Novosibirsk).
• Both populations exhibit a mixed reproductive mode (sexual and clonal), with differing inoculum sources potentially influencing genotype structure.
• A unique group of genotypes from Omsk showed high variability, near-zero inbreeding, and low observed heterozygosity. Two specific SSR genotypes from Asian samples warrant close monitoring.

Conclusions:

• The genetic structure of *Puccinia graminis* f. sp. *tritici* in Russia is characterized by distinct regional populations with mixed reproduction.
• The identified Omsk genotypes and singular Asian SSR genotypes require special attention for early detection of pathogen evolution.
• Targeted monitoring of these specific genotypes is essential for preventing unexpected disease outbreaks and managing wheat stem rust effectively.