One clonal lineage of calonectria pseudonaviculata is primarily responsible for the boxwood blight epidemic in the United States

Vanina L. Castroagudín, Jerry E. Weiland, Fulya Baysal-Gurel, Marc A. Cubeta, Margery L. Daughtrey, Nicole Ward Gauthier, James LaMondia, Douglas G. Luster, Francesca Peduto Hand, Nina Shishkoff, Jean Williams-Woodward, Xiao Yang, Nicholas LeBlanc, Jo Anne Crouch

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Boxwood blight caused by Calonectria pseudonaviculata and C. henricotiae is destroying cultivated and native boxwood worldwide, with profound negative economic impacts on the horticulture industry. First documented in the United States in 2011, the disease has now occurred in 30 states. Previous research showed that global C. pseudonaviculata populations prior to 2014 had a clonal structure, and only the MAT1-2 idiomorph was observed. In this study, we examined C. pseudonaviculata genetic diversity and population structure in the United States after 2014, following the expansion of the disease across the country over the past 5 years. Two hundred eighteen isolates from 21 states were genotyped by sequencing 11 simple sequence repeat (SSR) loci and by MAT1 idiomorph typing. All isolates presented C. pseudonaviculata-specific alleles, indicating that C. henricotiae is still absent in the U.S. states sampled. The presence of only the MAT1-2 idiomorph and gametic linkage disequilibrium suggests the prevalence of asexual reproduction. The contemporary C. pseudonaviculata population is characterized by a clonal structure and composed of 13 multilocus genotypes (SSR-MLGs) unevenly distributed across the United States. These SSR-MLGs grouped into two clonal lineages (CLs). The predominant lineage CL2 (93% of isolates) is the primary contributor to U.S. disease expansion. The contemporary U.S. C. pseudonaviculata population is not geographically subdivided and not genetically differentiated from the U.S. population prior to 2014, but is significantly differentiated from the main European population, which is largely composed of CL1. Our findings provide insights into the boxwood blight epidemic that are critical for disease management and breeding of resistant boxwood cultivars.

Original languageEnglish
Pages (from-to)1845-1853
Number of pages9
Issue number11
StatePublished - Nov 2020

Bibliographical note

Publisher Copyright:
© 2020 The American Phytopathological Society.


  • Buxus
  • Emerging disease
  • Population biology
  • Population structure
  • Woody ornamentals

ASJC Scopus subject areas

  • Agronomy and Crop Science
  • Plant Science


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