The rapid assay Sss AgriStrip for Spongospora subterranea f. sp. subterranea detection is produced by BIOREBA and has been validated in cooperation with the Swiss Federal Institute of Technology (SFIT/ETH), and the Swiss College of Agriculture (SHL). This project was supported by the Innovation Promotion Agency (CTI) of the Swiss government. The rapid assay enables confirmation of the presence of the powdery scab pathogen in suspicious samples; in particular to distinguish powdery scab from very similar symptoms of common scab caused by Streptomyces sp. (Fig. 2).
Hence, it is a valuable tool for the disease assessment in seed certification as part of a sustainable disease management of powdery scab. In this context, the Sss AgriStrip plays an important part in the implementation of the postulated preventive control concept: „Clean seed in clean soil“ described in Merz U. and R.E. Falloon, 2009. Review: Powdery scab of potato - Increased knowledge of pathogen biology and disease epidemiology for effective disease management. Potato Research 52 (1), 17-37
A. The traditional broad-spectrum PVY reagent («PVY monoclonal»), made against isolate PVYN605 and on the market since 1982, recognizes isolates belonging to the tobacco veinal necrosis (PVYN), common (PVYO) and stipple streak (PVYC) strain groups of PVY (7). The reagent is based on a monoclonal antibody (Mab) to a common antigenic determinant. All of today’s known PVY isolates are recognized by this Mab with the exception of a few atypical isolates (e.g. PVYO768) belonging to subgroup PVYOb (8). This reagent also recognizes PVYNTN(involved in the potato tuber necrotic ringspot disease) (9) and the Wilga type PVYNW (2). The reagent has proven its validity over the past quarter of a century in variable testing set-ups all over the world. As the first monoclonal-based reagent that became commercially available for phytodiagnostics, it really has become a true PVY standard reagent.
B. The full-spectrum PVY reagent («PVY monoclonal cocktail«) contains complementary monoclonal antibodies to isolates from different strain groups (7, 8). It recognizes the whole range of PVY isolates from the tobacco veinal necrosis (PVYN), common (PVYO) and stipple streak (PVYC) strain groups of PVY (Table 1). All recently described isolates such as PVYO768 (belonging to subgroup PVYOb) (8) or PVYNTN (involved in the potato tuber necrotic ringspot disease) (9) and the Wilga type PVYNW (2) are also recognized. This reagent generally gives a more uniform reaction with the virus and a lower background than polyclonal antibodies from rabbit or sheep serum. The current reagent that became available in 2002 is an improved version of the reagent introduced in 1994. It consists of a «cocktail» of different complementary monoclonal antibodies. No cross-reaction with any other known potato virus has been observed.
C. The polyclonal PVY reagent («PVY polyclonal«) was made against isolate PVYN605. It recognizes, similar to «PVY monoclonal cocktail», the whole range of isolates from the tobacco veinal necrosis (PVYN), common (PVYO) and stipple streak (PVYC) strain groups of PVY, including the more recently described isolates such as PVYO768 (belonging to subgroup PVYOb) (8) or PVYNTN (involved in the potato tuber necrotic ringspot disease) (9) and the Wilga type PVYNW (2). But contrary to the monoclonal-based reagent, some variability from batch to batch in recognizing isolates of different strain groups is inevitable with the polyclonal-based reagent.
D. The necrotic strain group-specific PVY reagent («PVY necrotic») specifically recognizes isolates belonging to the tobacco veinal necrosis (PVYN) strain group of PVY («old» N-type group), including subgroup of PVYNTN (involved in the potato tuber necrotic ringspot disease) (9). In an independent study, carried out in 1991 (COST 88 PVY ring-test, unpublished), where nearly 50 PVY isolates from Europe and other continents were compared in biological and serological tests, all isolates of PVYN (old N-type group) were recognized with our PVYN reagent. On the other hand, Wilga type PVYNW isolates (2) are not recognized (PVYNW isolates are recognized with our other PVY reagents, i.e. «PVY monoclonal», «PVY monoclonal cocktail», and «PVY polyclonal» described in sections A, B and C). Our PVY reagents thus provide a suitable tool for differentiating PVYN subgroups (M. Chrzanowska, personal communication, and 2). The PVYN reagent is based on monoclonal antibodies, developed against PVYN605 (7, 8). The coating reagent consists of broad-spectrum, the conjugate of N-specific Mab (7). The PVYN reagent has been developed for double antibody sandwich ELISA (DAS-ELISA) (3, 6). This format is essential to ensure the described N-specificity.
