A microsatellite-based identification tool used to confirm vector association in a fungal tree pathogen

Abstract

Many fungi live in close association with insects, and some are specifically vectored by them. One of the best examples is found in the so-called Ophiostomatoid fungi, including species of Ceratocystis and other genera in the Ceratocystidaceae. Our understanding of vectorship in these fungi is based predominantly on either their frequency of isolation from insects or the success with which these fungi are isolated from their insect vectors. The fact that Ceratocystis species mostly have casual as opposed to highly specific relationships with their insect vectors makes it difficult to prove insect vector relations. In order to provide unambiguous support for Ceratocystis species being vectored by insects, we interrogated whether genotypes of the tree pathogen, Ceratocystis albifundus, would be shared between isolates retrieved from either infected trees or nitidulid beetles. Ceratocystis albifundus isolates were collected from nitidulid beetles and from naturally occurring wounds on trees in the Kruger National Park (KNP) in South Africa. The genotypes of these isolates were then determined using eight microsatellite markers, and they were compared using a haploid network analyses. A high frequency of Multi-Locus Haplotypes (MLHs) derived from nitidulid beetles was found to be shared with those from wounded trees across the KNP. This provides robust support showing that nitidulid beetles play an important role in the dispersal of C. albifundus in the KNP.