Molecular identification of Botryosphaeria dothidea as a fungal associate of the gall midge Asphondylia prosopidis on mesquite in the United States

Abstract

The gall midge, Asphondylia prosopidis Cockerell, is considered a potential biological control agent for invasive mesquite (Prosopis species) populations in South Africa. Asphondylia species induce galls on mesquite plants by inserting an egg into a bud, and also carry conidia of specific fungal associates in their mycangia that are transferred into the galls. However, fungal associates have not been characterized in flower bud galls formed by A. prosopidis on mesquite. It is essential to identify the fungal associates in the galls formed on natural populations of mesquite prior to host specificity testing. In this study, we showed that Botryosphaeria dothidea (Moug. ex Fr.) Ces. & De Not. is the fungal associate in the flower bud galls on mesquite induced by A. prosopidis in New Mexico by characterization of the internal transcribed spacer (ITS) region. Further, isolates of B. dothidea in A. prosopidis galls formed on mesquite were genetically identical to isolates of B. dothidea carried by other Asphondylia species, particularly on the confamilial Acacia species in South Africa. Our result suggests that A. prosopidis is safe to utilize as a biological control agent for mesquite, if A. prosopidis shows a narrow host range in the pre-release risk assessment, since B. dothidea appears to be ubiquitous. To our knowledge, this is the first report of the association between Asphondylia species and B. dothidea in the United States. We anticipate that A. prosopidis will associate with indigenous B. dothidea in South Africa.