Three novel Ambrosia Fusarium Clade species producing multiseptate ‘dolphin-shaped’ conidia, and an augmented description of Fusarium kuroshium

Authors: AOKI, TAKAYUKI - National Agriculture And Food Research Organization (NARO), Agricultrual Research Center; LIYANAGE, PRADEEPA - University Of Colombo; KONKOL, JOSHUA - University Of Florida; PLOETZ, RANDY - University Of Florida; SMITH, JASON - University Of Florida; KASSON, MATT - West Virginia University; FREEMAN, STANLEY - Volcani Center (ARO); GEISER, DAVID - Pennsylvania State University; O Donnell, Kerry

Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2021
Publication Date: 8/3/2021
Citation: Aoki, T., Liyanage, P.N.H., Konkol, J.L., Ploetz, R.C., Smith, J.A., Kasson, M.T., Freeman, S., Geiser, D.M., O'Donnell, K. 2021. Three novel Ambrosia Fusarium Clade species producing multiseptate ‘dolphin-shaped’ conidia, and an augmented description of Fusarium kuroshium. Mycologia. 113(5):1089-1109. https://doi.org/10.1080/00275514.2021.1923300.
DOI: https://doi.org/10.1080/00275514.2021.1923300

Interpretive Summary: Foreign wood boring, fungus farming Euwallacea ambrosia beetles from Asia have recently spread around the world where they are now threatening production of cacao, avocado, rubber, and tea. These invasive insect pests and the plant pathogens they farm are also threating forest ecosystems, urban landscapes, and avocado production in the U.S. and several other countries. Female Euwallacea beetles farm 1-2 different species of Fusarium as a source of nutrition in diverse woody hosts. Because the fungi can block transport of water and nutrients from the roots, blockage of the woody hosts vascular system can cause wilting of leaves and branches, and even tree death. To foster accurate communication about the beetles and the fungi they farm within the scientific community, we identified molecular genetic and morphological data that can be used to accurately identify the plant pathogenic Fusarium species farmed by three different Euwallacea ambrosia beetles. The detailed information on the host range, genetic diversity, and geographic distribution of these economically important insect pests and the pathogens will aid diverse agricultural scientists and quarantine officials in preventing them from being introduced into the U.S. and those of our trading partners.

Technical Abstract: The Ambrosia Fusarium Clade (AFC) is a monophyletic lineage within clade 3 of the Fusarium solani species complex (FSSC) that currently comprises 19 genealogically exclusive species. These fungi are known or predicted to be farmed by adult female Euwallacea ambrosia beetles as a nutritional mutualism (Coleoptera: Scolytinae; Xyleborini). To date, only eight of the 19 AFC species have been described formally with Latin binomials. We describe three AFC species, previously known as AF-8, AF-10, and AF-11, based on molecular phylogenetic analysis of multilocus DNA sequence data and comparative morphological/phenotypic studies. Fusarium duplospermum (AF-8) farmed by E. perbrevis on avocado in Florida, USA, is distinguished by forming two morphologically different types of multiseptate conidia and brownish orange colonies on potato dextrose agar (PDA). Fusarium drepaniforme (AF-10), isolated from an unknown woody host in Singapore and deposited as Herb IMI 351954 in the Royal Botanic Gardens, Kew, UK, under the name F. bugnicourtii, is diagnosed by frequent production of multiseptate sickle-shaped conidia. Fusarium papillatum (AF-11), isolated from mycangia of E. perbrevis infesting tea in Kandy, Sri Lanka, forms multiseptate clavate conidia that possess a papillate apical cell protruding toward the ventral side. Lastly, we prepared an augmented description of F. kuroshium (AF-12), previously isolated from the heads or galleries of E. kuroshio in a California sycamore tree, El Cajon, California, USA, and recently validated nomenclaturally as Fusarium. Conidia formed by F. kuroshium vary widely in size and shape, suggesting a close morphological relationship with F. floridanum, compared with all other AFC species. Maximum likelihood and maximum parsimony analyses of a multilocus data set resolve these three novel AFC species, and F. kuroshium, as phylogenetically distinct based on genealogical concordance. Given the promiscuous nature of several Euwallacea species, and the overlapping geographic range of several AFC species and Euwallacea ambrosia beetles, the potential for symbiont switching among sympatric species is discussed.