Impact of Calonectria diseases on ornamental horticulture: Diagnosis and control strategies

Authors: AIELLO, DALIA - University Of Catania; GUARNACCIA, VLADIMIRO - University Of Torino; VITALE, ALESSANDRO - University Of Catania; Leblanc, Nicholas; Shishkoff, Nina; POLIZZI, GIANCARLO - University Of Catania

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2022
Publication Date: 2/27/2022
Citation: Aiello, D., Guarnaccia, V., Vitale, A., LeBlanc, N.R., Shishkoff, N., Polizzi, G. 2022. Impact of Calonectria diseases on ornamental horticulture: Diagnosis and control strategies. Plant Disease. 106(7):1773-1787. https://doi.org/10.1094/PDIS-11-21-2610-FE.
DOI: https://doi.org/10.1094/PDIS-11-21-2610-FE

Interpretive Summary: Plant diseases caused by a group of fungi called Calonectria are an ongoing problem for producing horticultural crops in Europe and the United States. Controlling these diseases is especially challenging for multiple reasons. Many different types of Calonectria cause diseases on horticultural crops, but a poor understanding of how they are related to each other makes it difficult to diagnose a specific disease. Ongoing DNA sequencing and discovery of new types of Calonectria is helping resolve this issue. Another challenge is that Calonectria fungi form structures called microsclerotia. These microscopic microsclerotia contaminate horticultural production systems and are difficult to remove using sanitation methods or pesticides. There is also concern that many healthy-looking plants that are sold and transported in the horticulture industry are infected with these fungi, contributing to global disease emergence. Since many horticultural crops impacted by Calonectria are perennials and have long life cycles, it takes many years to identify and breed plants that have disease resistance. Due to these many challenges, long-term sustainable management of diseases caused by Calonectria fungi requires a better understanding of pathogen biology and using multiple disease management strategies.

Technical Abstract: Diseases caused by fungi in the genus Calonectria pose a significant threat to the ornamental horticulture industries in Europe and the United States. Calonectria spp. are particularly challenging pathogens to manage in ornamental production systems and the landscape for multiple reasons. A high level of species diversity and poorly resolved taxonomy in the genus makes proper pathogen identification and disease diagnosis a challenge, though recent molecular phylogenetic studies have made significant advances in species delimitation. From a disease management perspective, Calonectria spp. produce long-lived microsclerotia survival structures that contaminate nursery production systems, are resistant to common cultural and chemical controls, and can survive multiple years in the absence of a susceptible plant host. Latent infection of plant material is poorly understood but likely contributes to long-distance dissemination of these fungal pathogens, including the clonal Calonectria spp. responsible for the global emergence of boxwood blight. Breeding for disease resistance represents a sustainable strategy for managing Calonectria diseases, but is challenging due to the perennial nature of many ornamental plants and high levels of susceptibility in commercial cultivars. Ultimately, long-term sustainable management of Calonectria diseases will require an improved understanding of pathogen biology as well as integration of multiple disease management strategies.