Introduction
In the last two decades there has been an unprecedented and worldwide emergence of fungal pathogens threatening animal and plant biodiversity (Fisher et al. 2012). Recently, there has been increasing concern over the emerging fungal pathogen Fusarium in endangered sea turtles, which causes hatching failure in eggs of sea turtles worldwide (Smyth et al., 2019). So far, reports of the pathogenesis and distribution of this pathogen has been limited to sea turtles, and it is unknown whether this pathogen also poses a threat to freshwater and terrestrial turtle species, of which there are 356 known species (Rhodin et al., 2017).
First reports of sea turtle eggs colonized by fungi were done by Wynecken et al. (1988), who described hatching failure of diseased eggs within natural and artificial nests. Since then, several studies have reported the presence of fungi (Phillott & Parmenter, 2001) and bacteria (Craven et al., 2007) in unhatched eggs and female cloaca, indicating that turtle eggs are not laid sterile and have a commensal surface microbiome. Fungi from the genus Fusarium were identified as pathogenic to sea turtle eggs (Sarmiento-Ramírez et al., 2010), and in 2012 Fusarium solani was recognized as a new fungal emerging infectious disease (EID) that may be contributing to population declines in sea turtles (Fisher et al., 2012). Infections caused by ~60 species belonging to the Fusarium solani species complex (FSSC) have been reported in sea turtles around the globe (Brofft Bailey et al., 2018; Candan, 2018; Sarmiento-Ramírez et al., 2014).Fusarium has been isolated from both diseased and asymptomatic sea turtle eggs, and infection may be vertically transmitted from the mother cloaca or horizontally transmitted from the environment (Sarmiento-Ramírez et al., 2014). Given the large number of Fusarium species and their global range, it is possible that this fungal disease is not limited to sea environments and may also be spreading to freshwater environments. Indeed, Fusarium is thought to thrive in water and damp environments (Smyth et al., 2019), and therefore fresh-water turtle species may also be at risk, yet there has been to date little surveillance of non-oceanic turtle species.
In this study, we screened 680 eggs from artificial nests of an endangered freshwater turtle species (P. unifilis ) that inhabits the Amazon and Orinoco basin in South America for visual symptoms of fusariosis and assessed hatchability. We tested 68 eggs by PCR forFusarium infection and sequenced eight of those amplicons on an Illumina platform to screen for members of FSSC.