Evaluation of the Sss AgriStrip rapid diagnostic test for the detection of Spongospora subterranea on potato tubers

Abstract

Spongospora subterranea, f.sp. subterranea (Sss), which causes powdery scab, is mainly spread through infected seed tubers and survives in contaminated soil for many years. The visual assessment of tuber lots by inspectors carries the risk of misidentification due to the difficulty of distinguishing lesions caused by either Sss or Streptomyces spp.. To avoid this, the "Sss AgriStrip", a rapid and lab-independent test tool based on a lateral flow immunoassay has been developed, and we assessed its accuracy and sensitivity for detecting Sss. The Sss AgriStrip performed as well as other lab-based identification methods. The Sss AgriStrip, microscopy, ELISA, PCR, and real-time PCR techniques identified infection with S. subterranea in all tubers with typical powdery scab lesions. When lots with tubers showing a mixture of typical and atypical (suspicious) symptoms were tested, the presence of S. subterranea was confirmed in all lesions by all methods. The DNA content was generally lower in atypical than in typical lesions. Diverse and suspicious symptoms, which were difficult to assign to either powdery or common scab, tested negative with Sss AgriStrip and the other methods. This was despite microscopic observation of sporosori-like structures in some samples. Isolation and molecular identification confirmed that these lesions were mostly caused by Streptomyces spp. The Sss AgriStrip is as sensitive as DAS-ELISA with a detection limit between 1 and 10 sporosori per ml buffer. It is ideal for rapid and selective detection of Sss on farms and border inspection points to prevent spread of the pathogen.

Modeling Pathogen DNA Content and Visual Disease Assessment in Seed Tubers to Inform Disease in Potato Progeny Root, Stolon, and Tubers

“…Root galling and sto lon pruning (Figs. [4][5][6] were measured in the 2011 and 2012 trials with Innovator only.…”

“…Further, qPCR was able to detect the higher DNA levels (from symptomless seed tubers) that were more likely to promote galling than symptomless seed tubers with low DNA readings. Others have reported detection of pathogens present on seed tubers as contami nants without obvious symptoms (4,36) and there are reports of powdery scab following planting of visually "clean" seed into soil with low inoculum pressures (28,36), suggesting accurate pathogen inoculum detection on seed is essential for quantifying potential disease. In these cases, more rigorous pathogen detection tools such as qPCR may provide a superior means of determining seed tuber health to traditional visual assessment.…”

“…Recent innovations in PCR based technologies have enabled de tection, differentiation, and quantitation of specific pathogens (4,24,33) from both soil and seed tuber peel. Commercial soil tests are now available that quantify specific pathogens and provide a threshold risk analysis for planting potato tubers into these soils; such tests are available for black dot (20), root knot nematode (24), and powdery scab (5,24).…”

Grower perceptions of biotic and abiotic risks of potato production in South Africa

“…Firstly, powdery scab symptoms can easily be confused with those of common scab, especially in the early stages of the disease (Bouchek-Mechiche et al, 2011;Qu et al, 2011). Growers not trained to distinguish between the two diseases might easily make an incorrect diagnosis.…”