Perennial ryegrass (Lolium perenne L.) is an important turf and forage species that often becomes infected with Puccinia coronata f. sp. lolii, the causal pathogen of crown rust. Disease control through clavicipitaceous endophytes has been proposed as a potential biocontrol. Two field experiments were designed to determine the influence of native Epichloë endophyte infection on natural rust development across a diverse panel of perennial ryegrass germplasm. Experiment 1 used an isogenic population design in which infected (E+) or endophyte-free (E−) clonal plants were nested within 14 perennial ryegrass entries. Experiment 2 consisted of isofrequent E+ and E− progeny from isogenic parents. Results showed the endophyte had no consistent main effect on crown rust severity among or within entries; however, several isogenic host pairs did show either favorable or antagonistic effects. Despite these sporadic effects, no differences were found between isofrequent family pairs, indicating the presence of a host × endophyte interaction. Genotypic and phenotypic data revealed that endophyte isolates were similar within entry, indicating that host genotype could be responsible for the highly specific endophyte effect on crown rust. The preponderance of host resistance in mediating rust severity was supported by large broad (>.75) and narrow-sense (.76) heritability estimates. These findings support the conclusion that endophyte infection does not play a substantial role in mediating crown rust severity on a population scale in perennial ryegrass.
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We would like to thank Dr. Ya Yang (Department of Plant and Microbial Biology, University of Minnesota) for her guidance with phylogenetic analysis. For his succor in debugging R code and effectual statistical counsel, we thank Dr. Jeffrey Neyhart (Agronomy and Plant Genetics, University of Minnesota). We also thank Dr. Brian Steffenson (Plant Pathology, University of Minnesota) and Dr. R. Ford Denison (Ecology, Evolution, and Behavior, University of Minnesota) for their thoughtful reviews of this manuscript. For research assistance in the field and laboratory, the authors thank Michael Miller and Brooke Ashbrenner. Funding for this work was provided by the Minnesota Turf Seed Council and the Minnesota Agricultural Experiment Station Project, no. 21–051.
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