Hawaii has long been one of the last coffee-producing regions of the world free of coffee leaf rust (CLR) disease, which is caused by the biotrophic fungus Hemileia vastatrix. However, CLR was detected in coffee farms and feral coffee on the island of Maui in February 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 Hawaii inoculum, we analyzed a set of eleven simple sequence repeat markers (SSRs) generated from Hawaii 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. MLG 10 is widespread in Central America and Jamaica, making this region the most probable source of inoculum for the outbreak in Hawaii. An examination of global weather patterns during the months preceding the introduction of CLR makes it unlikely that the pathogen was windborne to the islands. Likely scenarios for the introduction of CLR to Hawaii are the accidental introduction of spores or infected plant material by travelers or seasonal workers, or improperly fumigated coffee shipments originating from Central America or the Caribbean islands.

Drosophila melanogasterhas become a model system to study interactions between innate immunity and microbial pathogens, yet many aspects regarding its microbial community and interactions with pathogens remain unclear. In this study wildD. melanogasterwere collected from tropical fruits in Puerto Rico to test how the microbiota is distributed and to compare the culturable diversity of fungi and bacteria. Additionally, we investigated whether flies are potential vectors of human and plant pathogens. Eighteen species of fungi and twelve species of bacteria were isolated from wild flies. The most abundant microorganisms identified were the yeastCandida inconspicuaand the bacteriumKlebsiellasp. The yeastIssatchenkia hanoiensiswas significantly more common internally than externally in flies. Species richness was higher in fungi than in bacteria, but diversity was lower in fungi than in bacteria. The microbial composition of flies was similar internally and externally. We identified a variety of opportunistic human and plant pathogens in flies such asAlcaligenes faecalis,Aspergillus flavus,A. fumigatus,A. niger,Fusarium equiseti/oxysporum, Geotrichum candidum,Klebsiella oxytoca,Microbacterium oxydans, andStenotrophomonas maltophilia. Despite its utility as a model system,D. melanogastercan be a vector of microorganisms that represent a potential risk to plant and public health.

Aspergilloses are fungal diseases in humans and animals that is caused by members of the genus Aspergillus. Aspergillus flavus is an important opportunistic pathogen, second only to A. fumigatus as a cause of human aspergillosis. Differences in virulence among A. flavus isolates from clinical and other substrates and mating types are not well known. The fruit fly Drosophila melanogaster has become a model organism for investigating virulence of human pathogens due to similarities between its immune system and that of mammals. In this study we used D. melanogaster as a model host to compare virulence among A. flavus strains obtained from clinical sources as compared with other substrates, between isolates of different mating types, and between isolates of A. flavus and A. fumigatus. Anesthetized flies were infected with A. flavus; mortality ranged from 15% to >90%. All strains were virulent, but some were significantly more so than others, which in turn led to the wide mortality range. Clinical strains were significantly less virulent than environmental strains, probably because the clinical strains were from culture collections and the environmental strains were recent isolates. Mean virulence did not differ between MAT1–1 and MAT1–2 mating types and the phylogeny of A. flavus isolates did not predict virulence. A. flavus was on average significantly more virulent than A. fumigatus on two lines of wild-type flies, Canton-S and Oregon-R. D. melanogaster is an attractive model to test pathogenicity and could be useful for identifying genes involved in virulence.