Phylogenetic study of the Colletotrichum species on imported citrus fruits uncovers a low diversity and a new species in the Colletotrichum gigasporum complex

- A diversity of four Colletotrichum species is recovered on nine citrus fruit types from 17 geographically diverse countries.
- Prevalence of Colletotrichum highly varies among citrus fruit types, and is greatest on fruits of Citrus sinensis.
- Colletotrichum citri-maximae sp. nov. is described from Citrus maxima.
- Shortness of GAPDH sequence characterizes C. citri-maximae and further three taxa in the C. gigasporum complex.

Colletotrichum species associated with citrus fruits are fragmentarily known and it lacks accordingly accurate information on the diversity carried alongside the trade of these commodities from producer countries to Europe. In this study, we investigated the molecular phylogenetic diversity, colonisation, and prevalence of Colletotrichum isolated from asymptomatic and diseased tissues of nine citrus fruit species from 17 geographically diverse countries. Totally 454 isolates were morphoculturally characterised, and multilocus analyses (ACT, ApMat, CHS-1, GAPDH, ITS, TUB2) was performed on a subset of representative morphotype isolates. Results led to the identification of three previously known species (Colletotrichum gloeosporioides, Colletotrichum karstii, Colletotrichum siamense) and one novel lineage comprising endophytic isolates from Citrus maxima. Based on this lineage, Colletotrichum citri-maximae is described as a new species in the Colletotrichum gigasporum complex, and is characterised by a long deletion in the GAPDH sequence, a character shared with three of its phylogenetic sister taxa. Prevalence of Colletotrichum varied among citrus species and was greatest on Citrus sinensis fruits. C. gloeosporioides was the most common species followed by C. siamense. Except for the new species, all other isolated Colletotrichum spp. also colonise citrus leaves, but the overall diversity on fruits may be lower than that of leaves.