Abstract
Phytophthora fragariae causes drastic damage in strawberry crops. P. fragariae infects strawberry roots and causes red stele root rot. Although P. fragariae is a quarantine organism, its spread in Finland continues as more and more fields contract the disease. The spread can be halted through developing rapid and reliable detection assays. We have developed a rapid recombinase polymerase amplification (RPA) assay for P. fragariae targeting the Phytophthora mitochondrial DNA intergenic atp9-nad9 marker. The assay is DNA-extraction free and capable of detecting as low as 10 fg of P. fragariae genomic DNA. We found the assay reliable for diagnosing field plants when samples are adequately collected. We also applied the RPA assay to the detection of the pathogen in the soil through coupling the assay with baiting with the host plant. The results suggest that if only a small number of samples are analysed, the baiting results will not be reliable.
Highlights
Phytophthora fragariae is a quarantine organism (A2 list of European and Mediterranean Plant Protection Organization (EPPO)) and causes red stele root rot of strawberry
Sensitivity and specificity of recombinase polymerase amplification (RPA) assay We evaluated sensitivity of the RPA assay through amplifying 1/10 dilution of P. fragariae (MRV1 isolate) genomic DNA ranging from 1 ng/μL to 1 fg/μL
We found all the five indicator plants from the field A were positive with the RPA assay while only one of them had typical symptom of red steles
Summary
Phytophthora fragariae is a quarantine organism (A2 list of EPPO) and causes red stele root rot of strawberry. This disease is common in regions with cool and moist climates, with damage more extensive in heavy saturated clay soils and during early or late summer. The pathogen first destroys fine roots and later progresses upwards in the stele of larger roots. Plants wilting usually first appears in low or poorly drained areas of fields and the affected area progressively widens over time. When plants with early wilting symptoms are dug out, their major roots have less lateral roots and present a ‘rat-tail appearance’. Dissecting major roots upwards displays abnormal reddish colour in internal cores known as ‘red
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