Powdery scab of potatoes in Alberta: molecular diagnostics and fungicide efficacy

Powdery scab, caused by the soil-borne pathogen Spongospora subterranea f. sp. subterranea, forms root gall and tuber lesions in potatoes and vectors the Potato mop-top virus (PMTV) that causes spraing in tubers. Seven field sites with a history of powdery scab were selected, and the pathogen’s presence in soil was confirmed by using the molecular diagnostics targeting the ITS region (ITS1-5.8S-ITS2). BLAST analysis showed 99-100% similarity with S. subterranea f. sp. subterranea in the NCBI database. Field trials over three years (2022, 2023, and 2024) evaluated the efficacy of five Syngenta-designed fungicide treatments: A21008A, Allegro (low, medium, and high doses), and A24367B. Three cultivars, Shepody, Russet Burbank, and Lady Claire, were planted in naturally infested fields. Root galls were assessed during the growing season, and tubers were evaluated for disease severity and yield in August-September. In 2023, Allegro was most effective in reducing root galls, followed by A24367B, whereas A21008A performed poorly at root gall reduction but was most effective in reducing tuber lesions. All treatments significantly suppressed the disease in Lady Claire. In the 2024 trials, none of the treatments suppressed galls in Russet Burbank, whereas all but Allegro-low significantly reduced galls in Lady Claire. No significant differences in total tuber yield were observed across treatments or cultivars. These findings highlight that treatment efficacy varies depending on the potato cultivar and the type of disease symptoms (root galls vs. tuber lesions). In bioassay, conducted by growing plants in the presence of controlled quantities of S. subterranea, visible symptoms of powdery scab were observed when the soil contained more than 15 cystosori per gram of soil. This underscores the need for targeted management strategies to control powdery scab in potato crops effectively.

Authors

• Shafique, Muhammad Subhan
• University of Lethbridge. Faculty of Arts and Science

• Spongospora subterranea
• potatoes
• potato cultivars
• powdery scab
• fungicide treatment efficacy

Identifier

hdl:10133/7153

OAI identifier oai:identifier

oai:opus.uleth.ca:10133/7153