Evidence for Vector Transmission of the Blueberry Pathogen Exobasidium maculosum, Cause of Exobasidium Leaf and Fruit Spot

Abstract

Exobasidium leaf and fruit spot of blueberry, caused by Exobasidium maculosum, results in significant yield losses if not properly managed. To determine if an arthropod is involved in transmission, we conducted arthropod exclusion and trapping studies at two field sites in Georgia from 2018 to 2020. In each field, 10 pairs of potted trap plants were placed under blueberry bushes for 2 weeks during the known infection window in early spring. In each pair, one potted plant was covered with exclusion nets before being taken to the field, and the other was left uncovered. The covered plants developed significantly fewer leaf spots (mean = 2) than the uncovered plants (mean = 128), indicating that an agent necessary for infection was excluded. To identify possible vectors, a variety of traps were used to collect arthropods in both fields during the known infection window. A total of 181 insects were selected from traps, then crushed and plated on potato dextrose agar to assess for growth of E. maculosum. A species-specific PCR assay was developed and conducted to test for E. maculosum. We recovered E. maculosum from one gall midge (Diptera: Cecidomyiidae) and detected it in three additional insects by PCR. One could not be identified, and two were two long-legged flies (Diptera: Dolichopodidae). Bioassays with spotted-wing drosophila (Drosophila suzukii) and brown marmorated stink bugs (Halyomorpha halys) did not show transmission of the disease. Although we did not conclusively identify specific vectors, we provide evidence of vector involvement in transmission of E. maculosum. [Figure: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Keywords

• arthropod
• Cecidomyiidae
• fungal vectors
• gall midge
• Vaccinium