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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Disease and Pest Management Research Unit » Research » Publications at this Location » Publication #390073

Research Project: Integrated Disease Management of Exotic and Emerging Plant Diseases of Horticultural Crops

Location: Horticultural Crops Disease and Pest Management Research Unit

Title: Taxonomic reclassification of the fungal pathogen causing dry berry disease of caneberries into the division Ascomycota as Monilinia rubi

item Weldon, William
item McGhee, Gayle
item JONES, LISA - Non ARS Employee
item Stockwell, Virginia

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2022
Publication Date: 4/20/2022
Citation: Weldon, W., McGhee, G., Jones, L.A., Stockwell, V.O. 2022. Taxonomic reclassification of the fungal pathogen causing dry berry disease of caneberries into the division Ascomycota as Monilinia rubi. Plant Disease.

Interpretive Summary: Dry berry of Rubus spp. was described as a destructive disease in the Pacific Northwest causing periodic crop losses of 30-50% in the 1950’s. The fungal pathogen, that infects flowers and kills up to 50% of berries on fruit laterals, was identified as a basidiomycete and given the name Rhizoctonia rubi based on hyphal morphology. We isolated the pathogen from dead raspberries and blackberries collected in northern Washington. Morphological characteristics and DNA analysis of our isolates and the original R. rubi revealed that the pathogen is a member of the Ascomycetes and specifically a novel Monilina species. In this manuscript, we propose renaming R. rubi as Monilinia rubi. The reclassification of the pathogen as a Monilinia spp. will impact our understanding of the disease cycle, how the pathogen overwinters and spreads in fields, and influences the selection of fungicides used for disease control.

Technical Abstract: As molecular genetic techniques improve and sequence data becomes available for more species, taxonomic classifications historically based upon growth morphology alone are being revisited and occasionally reclassified. Herein, we present such an instance for the fungal pathogen that causes dry berry disease of cane berries. The organism was previously classified as the basidiomycete fungus Rhizoctonia rubi based upon the pathogen’s production of rhizoctonia-like angular branching hyphae. Utilizing molecular genetic techniques unavailable when the pathogen was first characterized in 1959, four housekeeping gene loci (ITS1/ITS4, ITS5/NL4, beta tubulin, and G3PDH) were sequenced across 13 modern dry berry isolates, as well as the original 1959 type strain, CBS382.59. The resulting neighbor joining, maximum likelihood, and Bayesian phylogenies for single and multi-gene sequences provide strong evidence that the dry berry pathogen was misclassified. This data, in addition to a revisiting of in vivo macroscopic and microscopic growth morphology, again comparing modern dry berry isolates to the CBS382.59 type strain, suggests that the causal organism is a new species within the genus Monilinia that we propose be classified as Monilinia rubi. A transition from being classified as a basidiomycete fungus to an ascomycete fungus could have implications on chemical management decisions, as well as the assumptions made about cell structure and the pathogens putative life cycle.