Calonectria nandinae sp. nov. Causes Foliage Blight of Containerised Nandina Nursery Stock in the United States

ABSTRACT

In 2025 a survey was conducted to determine the distribution and impact of Calonectria fungi associated with leaf spot, stem canker and lower crown defoliation of containerised Nandina domestica nursery stock in Virginia, United States. In total, 47 symptomatic plants representing seven cultivars were sampled from 19 nurseries in 16 counties, resulting in 27 Calonectria isolates. Three of these isolates were identified as Calonectria kyotensis and they were recovered from the roots of three nandina plants. The remaining 24 isolates belonged to a previously unknown species in the C. kyotensis species complex. This novel species resides on a distinct branch in an eight‐locus phylogeny. It also produces 3‐septate macroconidia, a unique morphological feature distinguishing it from other species in the species complex. This new species is hereby designated as Calonectria nandinae sp. nov. This new species was isolated mostly from diseased leaves and stems, and twice from roots. To confirm its pathogenicity, one foliar (spray) and two root (dip and drench) inoculation assays were performed on N. domestica ‘Gulf Stream’ and ‘Lemon Lime’ sapling plants. C. nandinae was re‐isolated at high rates (mean 96%) from stem cankers and leaf spots of plants in the foliar inoculation assay, demonstrating C. nandinae as the causal agent of foliage blight on N. domestica . Its significance as a root pathogen is unclear due to less defined root rot symptoms, low re‐isolation rate (mean 3%) and ambiguous root‐weight‐loss results between the two root inoculation assays.