Characterization and molecular differentiation of 16SrI-E and 16SrIX-E phytoplasmas associated with blueberry stunt disease in New Jersey

A Decade of Hidden Phytoplasmas Unveiled Through Citizen Science

Climate change is impacting agriculture in many ways, and a contribution from all is required to reduce the imminent losses related to it. Recently, it has been shown that citizen science could be a way to trace the impact of climate change. However, how can citizen science be applied in plant pathology? Here, using as an example a decade of phytoplasma-related diseases reported by growers, agronomists, and citizens in general, and confirmed by a government laboratory, we explored how to better value plant pathogen monitoring data. Through this collaboration, we found that in the last decade, 34 hosts have been affected by phytoplasmas; 9, 13, and 5 of these plants were, for the first time, reported phytoplasma hosts in eastern Canada, all of Canada, and worldwide, respectively. Another finding of great impact is the first report of a 'Candidatus Phytoplasma phoenicium'-related strain in Canada, while 'Ca. P. pruni' and 'Ca. P. pyri' were reported for the first time in eastern Canada. These findings will have a great impact on the management of phytoplasmas and their insect vectors. Using these insect-vectored bacterial pathogens, we show the need for new strategies that can allow fast and accurate communication between concerned citizens and those institutions confirming their observations.[Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

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

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 novel 'Candidatus Phytoplasma asteris' subgroup 16SrI-(E/AI)AI associated with blueberry stunt disease in eastern Canada

Phytoplasmas ('Candidatus Phytoplasma' species) are phytopathogenic bacteria vectored by insects and are associated with crop diseases that cause severe yield losses by affecting reproductive tissue development. Infection of northern highbush blueberry plants (Vaccinium corymbosum; Ericaceae) with phytoplasma leads to yield losses by altering plant development resulting in stunting and subsequent plant death. Samples collected from symptomatic blueberry plants in two important blueberry-producing areas in Canada, in the provinces of Québec and Nova Scotia, were analysed for the presence of DNA sequences associated with phytoplasma. Analysis of the 16S rRNA gene sequences demonstrated that the plants were infected with a strain of 'Candidatus Phytoplasma asteris', which was previously identified as blueberry stunt phytoplasma (BBS; 16SrI-E). Examination of further bacterial sequences revealed that two distinct 16S rRNA-encoding gene sequences were present in each sample in combination with a single chaperonin-60 (cpn60) sequence and a single rpoperon sequence, suggesting that this strain displays 16S rRNA-encoding gene sequence heterogeneity. Two distinct rrnoperons, rrnE and the newly described rrnAI, were identified in samples analysed from all geographic locations. We propose, based on the sequences obtained, delineating the new subgroup 16SrI-(E/AI)AI, following the nomenclature proposed for heterogeneous subgroups. To our knowledge, this is the first report of a heterogeneous phytoplasma strain affecting blueberry plants and associated with blueberry stunt disease.