Detection of blueberry stunt phytoplasma in Eastern Canada using cpn60-based molecular diagnostic assays

Abstract

Blueberry stunt phytoplasma (BBSP; ‘Candidatus Phytoplasma asteris’) is an insect-vectored plant pathogen that causes severe yield losses in blueberry (Vaccinium corymbosum), which is the most valuable fruit crop in Canada. Rapid, field-based diagnostic assays are desirable tools for the control of BBSP, as part of an integrated, proactive approach to production management termed biovigilance. We designed and validated a chaperonin-60 (cpn60)-targeted LAMP assay for detection of BBSP, providing a rapid, low cost, field-deployable diagnostic option. Our validation demonstrates that the assay is reproducible, with high analytical specificity and improved sensitivity when compared with 16S rRNA nested PCR. We applied the validated LAMP assay to nearly 2000 blueberry samples from Québec and Nova Scotia over three growing seasons (2016–2018). Our surveys revealed that BBSP is present in most sites across both provinces, though detection of the pathogen in individual plants varied in different tissues across sampling dates and across years, and evidence of spread between plants was limited. To quantify pathogen load in select plants, we designed additional qPCR and ddPCR assays, also based on cpn60. We found that pathogen load fluctuates in individual plants, both within and between growing seasons. Finally, we designed an interactive map to visualize the results of our surveys. These results provide a validated diagnostic assay that can be used as part of a biovigilance strategy for detecting and controlling infections caused by BBSP.

A decade of hidden phytoplasmas unveiled through citizen science

“…This could explain why we see how the number of samples for certain hosts is high in some years and then decreases in the following years. That could be the case for BbSP, a disease we know has been present during all the past decade in Quebec (Pérez-López et al 2019;Rosete et al 2019;Hammond et al 2021), but we only see a high number of samples up to 2015, and an increase later in 2020 (Table 1, Fig. 1B).…”

“…P. phoenicium’-related strain infecting blueberry plants, which previous studies showed to be typically infected by ‘ Ca . P. asteris’ causing blueberry bushy stunt disease (BbSP) (Pérez-López et al 2019; Arocha-Rosete et al 2019; Hammond et al 2021). However, blueberry plants have been reported infected by ‘ Ca .…”

Leafhoppers as vectors of phytoplasma diseases in Canadian berry crops: a review in the face of climate change

“…Few studies have reported leafhoppers in strawberries and raspberries (Linck and Reineke 2019). However, a new study from our group identified a high diversity of leafhoppers in strawberry fields (Plante et al 2023), evidence that the low number of reports might not be linked to host preference but probably to the economic importance of other crops and/or relevant phytoplasma diseases detected affecting those crops, and therefore, demanding primary studies (e.g., blueberry and lingonberry stunt phytoplasma diseases, grapevines yellows disease, and strawberry green petal disease) (Olivier et al 2014, Arocha-Rosete et al 2015, 2019, Pérez-López et al 2019, Hammond et al 2021, Brochu et al 2022, Plante et al 2023). Although many leafhopper species are associated with commercial crops, the number of known vectors is relatively low (Fig.…”

“…Because of their economic importance in Canada and the United States, blueberries have been one of the main crops studied to survey potential vectors (Pagé 2013), improve phytoplasma detection (Hammond et al 2021), and disentangle associations between viruses and phytoplasmas in the blueberry stunt disease complex (Arocha et al 2019). However, those studies were primarily done in Canada.…”

“…However, the number of hosts affected by phytoplasmas in this geographic region has tripled in the last decade, indicating either an increase in the abundance of leafhopper vectors or the presence of yet-to-be-identified vectors (Brochu et al 2023). Additionally, access to new technologies and improved molecular diagnostic methods has been crucial in the increasing discovery of diseases associated with phytoplasmas (Pérez-López et al 2018, Hammond et al 2021). In this short review, we summarize the current knowledge on phytoplasmas, berries, and leafhoppers and discuss future paths to comprehend the effects of climate change in this complex pathosystem.…”