Location: Forage Seed and Cereal Research UnitTitle: Stem rust resistance in USDA perennial ryegrass germplasm
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 10/3/2019
Publication Date: N/A
Technical Abstract: Stem rust on perennial ryegrass (Lolium perenne L.) is a damaging disease currently controlled with fungicides; host resistance could reduce fungicide use. Resistant germplasm developed by the USDA, Corvallis is more useful if the resistance is consistently expressed in diverse environments, but nothing is known about the stability of resistance in this germplasm. The objective of this research was to determine the stability of resistance in 52 clones from 18 accessions or crosses used for stem rust resistance breeding by the USDA. Germplasm was chosen based on previous selection for resistance, genebank data indicating resistance, or from known susceptible cvs. Clones were transplanted in replicated field experiments in Aurora, Corvallis, and Crabtree, OR in 2016 and 2017 and rated bi-weekly for disease severity (percent diseased foliage) from April to June the following year. The second-year plants from the 2016 plantings were also reevaluated in 2018, resulting in nine separate environments. Disease occurred from naturally occurring inoculum. The standardized area under the disease progress curve (sAUDPC) was calculated using disease severity data. Disease levels varied across environments, with four environments having a median sAUDPC of 0.0 and two environments having extensive disease (sAUDPC > 1.4). The other environments had median sAUDPC between 0.3 and 1.0. Clones previously selected for resistance generally had lower disease (clone median sAUDPC range: 0.0 to 0.14) than known susceptibles (clone median sAUDPC range: 0.0 to 1.28). Rank correlations among all environments that tested first-year plants and second plants in Crabtree and Corvallis were significant (P<0.05) and ranged from 0.30 to 0.82. Correlations involving second year plants in Aurora were less than 0.27 and not significant. Significant agreement between clone rankings across environments was found using Kendall’s coefficient of concordance (W = 0.42; P = 0.006), indicating consistent performance in this germplasm across the nine tested environments.