Long-Term Studies of Wheat Leaf Rust in the North-Western Region of Russia

Abstract

Leaf rust, caused by Puccinia triticina (Pt), is a widely occurring disease of wheat in the North-Western Region of Russia. Annual Pt surveys of wheat in this region have been conducted between 2001 and 2021. In total, 740 single urediniospore isolates were analyzed over 20 years. Virulence to Lr9, Lr19 and Lr24 were rare in 2001–2010 and was not detected after 2010. Temporal variation in virulence was determined on Thatcher lines with Lr1, Lr2a, Lr2b and Lr2c genes and was found to be relatively high. Virulence to Lr1 increased to 100% from 2001 to 2014. Until 2010, most northwestern Pt isolates were avirulent to Lr2a and virulent to Lr2b and Lr2c. In the middle of 2010, avirulence to Lr2a, Lr2b, Lr2c and Lr15 began to increase. Strong variability between years was revealed for virulence to Lr20 and Lr26. Based on a set of 20 differential lines, 122 virulence pathotypes were detected. More than half of those were observed only once across all years. Pathotypes were divided into groups of B-, C-, D- and F-, virulent to Lr1 and Lr2a, dominating until 2009. From 2010 pathotype groups M- and P-, virulent to Lr1 and avirulent to Lr2a, began to dominate. Temporal differentiation of northwestern Pt population for virulence was determined. High similarity was observed for Pt accessions in 2001–2009 and 2010–2015 and these two groups differed moderately from each other. Pt accessions from 2016–2019 and 2020–2021 differed from each other and from accessions from the previous collection period. Field response of Lr differential lines was studied in the North-Western Region during 1998–2022. Wheat genotypes with genes Lr9, Lr19, Lr23, Lr24, Lr25, Lr28, Lr29, Lr35, Lr39, Lr42, Lr43, Lr45, Lr47, Lr48, Lr49, Lr50, Lr51, Lr53 and Lr57 remained resistant throughout the period of the study. Leaf rust severity in lines TcLr12, TcLr21, TcLr22a, Gatcher (Lr27+31), TcLr44 and Pavon (Lr46) varied from 1% to 30% before 2014 and significantly decreased after 2014. A general trend of decreasing virulence of the Pt pathogen has been observed in the North-Western Region over the recent years.