Exobasidium maculosum, a new species causing leaf and fruit spots on blueberry in the southeastern USA and its relationship with other Exobasidium spp. parasitic to blueberry and cranberry

Abstract

Exobasidium leaf and fruit spot of blueberry (Vaccinium section Cyanococcus) is an emerging disease that has rapidly increased in prevalence throughout the southeastern USA. To determine whether this disease is caused by a new species of Exobasidium, we studied the morphology and phylogenetic relationship of the causal fungus compared with other members of the genus, including the type species E. vaccinii and other species that parasitize blueberry and cranberry (V. macrocarpon). Both scanning electron microscopy and light microscopy were used for morphological characterization. For phylogenetic analyses, we sequenced the large subunit of the rDNA (LSU) from 10 isolates collected from leaf or fruit spots of rabbiteye blueberry (V. virgatum), highbush blueberry (V. corymbosum) and southern highbush blueberry (Vaccinium interspecific hybrid) from Georgia and North Carolina and six isolates from leaf spots of lowbush blueberry (V. angustifolium) from Maine and Nova Scotia, Canada. LSU was sequenced from isolates causing red leaf disease of lowbush blueberry and red leaf spot (E. rostrupii) and red shoot (E. perenne) of cranberry. In addition, LSU sequences from GenBank, including sequences with high similarity to the emerging parasite and from Exobasidium spp. parasitizing other Vaccinium spp. and related hosts, were obtained. All sequences were aligned and subjected to phylogenetic analyses. Results indicated that the emerging parasite in the southeastern USA differs morphologically and phylogenetically from other described species and is described herein as Exobasidium maculosum. Within the southeastern USA, clustering based on host species, host tissue type (leaf or fruit) or geographic region was not detected; however, leaf spot isolates from lowbush blueberry were genetically different and likely represent a unique species.

The Opportunistic Pathogen Sphaeropsis Sapinea is Found to be one of the Most Abundant Fungi in Symptomless and Diseased Scots Pine in Central-Europe

“…26 OTUS were assigned to the Exobasidiaceae, which usually form colonies with single-celled conidia but without hyphae. Members of this basidiomycetous Family are commonly none-pine host-speci c plant pathogens[79]. In total 312 (25%) of all detected OTUs with HTS may represent species with yeast or yeast-like stages.…”

Elevated Genetic Diversity in the Emerging Blueberry Pathogen Exobasidium maculosum

“…Exobasidium leaf and fruit spot of blueberry is an emerging disease that has rapidly increased in prevalence since 2011 throughout the southeastern USA in the commercial blueberry production regions of Georgia, North Carolina, and Mississippi [ 14 , 15 ]. The disease occurs on rabbiteye blueberry ( Vaccinium virgatum ), highbush blueberry ( V .…”

“…The fruit stage of the disease can result in losses of 60–70% in some plantings [ 16 ]. The causal pathogen was recently described as a new species, Exobasidium maculosum [ 14 ]. Although Exobasidium leaf and fruit spot was first documented in the southeastern USA on highbush blueberry in North Carolina in 1997 [ 16 ], it was sporadic and occurred in isolated fields.…”

“…However, E . maculosum populations from the southeastern USA are genetically distinct from populations from lowbush blueberry in northeastern North America based on the large subunit of the rDNA (LSU) [ 14 ]; but, reciprocal monophyly between populations, which would provide support for distinct species based on a phylogenetic species recognition concept [ 19 ], was not observed. Sequences from additional loci are necessary to use genealogical concordance to identify if these are distinct species or genetically different populations of the same species.…”

“…Sequences from additional loci are necessary to use genealogical concordance to identify if these are distinct species or genetically different populations of the same species. Cross-inoculation studies with the genetically distinct populations onto different Vaccinium hosts have not been successful due to difficulty in reproducing disease symptoms [ 14 ], so it is difficult to determine if these populations are host specialized or geographically isolated.…”