Colletotrichum acericola sp. nov. from seeds of invasive alien Acer negundo in Poland: delayed pathogen introduction after its host appearance?

Abstract

The boxelder maple (Acer negundo, Sapindaceae) is one of the most common tree species of the genus Acer natively growing in North America. In the 17th century A. negundo was introduced to Europe as an ornamental plant, and from this point forward it started uncontrolled expansion on new territories, as an alien invasive species (IAS), threatening local ecosystems and human’s safeness. Etiological symptoms of fungal development on boxelders’ seeds and petioles, were observed in 2017 and 2021 in the municipality of Wrocław (SW Poland, Europe), outside of host native occurrence. Morphological analyses combined with multilocus phylogenetic analyses (using rDNA ITS, gapdh, act, tub2, chs-1, and his3 sequences), indicated that isolated strains belong to a new species of Colletotrichum, from the rare Colletotrichum agaves species complex. Name Colletotrichum acericola is proposed for this fungus, after its host on which it was found. It is the second species of the Colletotrichum agaves species complex described from the dicotyledonous host and outside host plants of the family Asparagaceae. Based on phylogenetic analyses and deposited in NCBI-GenBank environmental sequences (ex endophytes of Dalea purpurea and Panicum virgatum in prairies of USA) assigned here to this species, it is likely that Colletotrichum acericola is native to North America and introduced to Europe after its host plant appearance, maybe on nursery material. The possible future invasion of C. acericola on Acer negundo and its spillover to other (native) Acer species in Europe are discussed.