Coffee leaf rust (Hemileia vastatrix) from the recent invasion into Hawaii shares a genotypic relationship with Latin American populations

Authors: RAMIREZ-CAMEJO, LUIZ - Purdue University; Keith, Lisa; Matsumoto Brower, Tracie; Sugiyama, Lionel; FUKADA, MACH - Hawaii Department Of Agriculture; BRANN, MIA - Purdue University; MOFFITT, A - Purdue University; LIU, JINGYU - Purdue University; AIME, M - Purdue University

Submitted to: The Journal of Fungi
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2022
Publication Date: 2/15/2022
Citation: Ramirez-Camejo, L.A., Keith, L.M., Matsumoto Brower, T.K., Sugiyama, L.S., Fukada, M., Brann, M., Moffitt, A., Liu, J., Aime, M.C. 2022. Coffee leaf rust (Hemileia vastatrix) from the recent invasion into Hawaii shares a genotypic relationship with Latin American populations. The Journal of Fungi. 8(2). Article 189. https://doi.org/10.3390/jof8020189.
DOI: https://doi.org/10.3390/jof8020189

Interpretive Summary: Hawaii has long been one of the last coffee-producing regions of the world free of coffee leaf rust (CLR) disease, caused by the biotrophic fungus Hemileia vastatrix. However, CLR was discovered in coffee farms and feral coffee on the island of Maui in late October 2020 and subsequently on other islands of the Hawaiian archipelago. To gain insight into the probable source of inoculum of H. vastatrix for Hawaii, simple sequence repeats (SSRs) that are specific to CLR were used to genotype H. vastatrix isolates from Hawaii and around the world. Results suggest that the most probable source of inoculum for the outbreak in Hawaii comes from Central America or Jamaica. Examination of global weather patterns during the months preceding introduction of CLR make it unlikely that the pathogen was windborne to the islands.

Technical Abstract: Hawaii has long been one of the last coffee-producing regions of the world free of coffee leaf rust (CLR) disease, caused by the biotrophic fungus Hemileia vastatrix. However, CLR was discovered in coffee farms and feral coffee on the island of Maui in late October 2020 and subsequently on other islands of the Hawaiian archipelago. The source of the outbreak in Hawaii is not known, and CLR could have entered Hawaii from more than 50 coffee-producing nations that harbor the pathogen. To determine the source(s) of the Hawaiian inoculum, we analyzed a set of eleven simple sequence repeat markers (SSRs) generated from Hawaiian isolates within a dataset of 434 CLR isolates collected from 17 countries spanning both old and new world populations and then conducted a Minimum Spanning Network (MSN) analysis to trace the most likely pathway that H. vastatrix could have taken to Hawaii. Forty-two multilocus genotypes (MLGs) of H. vastatrix were found in the global dataset, with all isolates from Hawaii assignable to MLG 10 or derived from it. MLG10 is widespread in Central America and Jamaica, making this region the most probable source of inoculum for the outbreak in Hawaii. Examination of global weather patterns during the months preceding introduction of CLR make it unlikely that the pathogen was windborne to the islands. Likely scenarios for the introduction of CLR to Hawaii are accidental introduction of infected seedling or plant material by travelers or seasonal workers or improperly fumigated coffee shipments originating from Central America or the Caribbean islands.