VIRIDI ELISA KITS™
The product is a locally produced, cost-effective plant health diagnostic tool. A collection of plant virus antisera is maintained at the Virology unit of ARC-Plant Health and Protection (ARC-PHP). The antisera were manufactured from plant viruses obtained from various crops in South Africa, thus ELISA sero-reagents, such as Immunoglobulin G (IgG) and conjugate, generated from the antisera will be unique to agriculturally important viral strains from South Africa. The production pipeline will focus initially on ELISA kits specifically targeting the detection of Tomato Spotted Wilt Virus (TSWV) and Cucumber Mosaic Virus (CMV) as both of these viruses have a broad host range. Both of these viruses are listed amongst the top five most economically important plant viruses worldwide. However, more viruses will be added annually to the offering based on economic importance to the agricultural sector.
Two plant viruses, Cucumber Mosaic Virus (CMV) and Tomato Spotted Wilt Virus (TSWV) have been identified for the development of commercial diagnostic tool kits. Both these viruses have extensive host ranges, affecting amongst others, different types of vegetables. CMV can affect cucurbits, such as melons and peppers, but also other crops such as beans, tomato, carrots, celery, lettuce, spinach and beets. TSWV affect many vegetables, (groundnut) peanut and tobacco crops and can be transmitted by thrips (small sucking insect vectors), but it is not transmitted by seed. CMV is transmitted by seed and aphids.
The value chain of vegetable seed production includes the plant breeding programs that produce high yielding, disease-resistant hybrid varieties, the production of hybrid seed for local and international use, the certification of seed, the production of seedlings by nurseries to supply the growers and the production process of the crops. During the breeding process of developing hybrid vegetable varieties for registration, inbred parental lines are developed through the process of successive self-pollinations after initial crosses have been made. Plant breeders screen segregating self-pollinating populations for the presence or absence of disease resistance genes under field and/or laboratory conditions. Observed symptoms in the field or greenhouse often need to be confirmed to verify the presence and/or absence of the suspected disease in breeding populations. Various research projects at academic or private institutions are focused on the triad of pathogen, host and environment. Vector and disease relationships and interactions need to be studied in controlled environments to elucidate the existence and development of new viral strains and their response to the existing resistance genes being utilized in commercial breeding programs. Therefore, these projects often require in-house diagnostic capabilities relating to a specific project, for which the investment of capacity development for a specific test is not warranted.
Once a hybrid variety has been developed, certified, registered seed are produced for sale locally and internationally. These seed productions may occur at localities in South Africa or at international sites aimed to speed up the process of producing varieties by utilizing different climatic zones. Verification of symptoms or the absence of symptoms is routinely done as part of the inspection process during the various crop cycles. Seedlings are usually grown by nurseries based on orders placed by growers for specific varieties targeted at specific planting windows based on the maturity profile of the variety and the targeted market access during a specific time. The nurseries are responsible for producing healthy, disease free and vigorous seedlings to the growers. Once the seedlings have been transplanted and the crop production cycle commences, the growers are continuously scouting for the presence of diseases that may impact negatively on yield and ultimately the profitability of the planting. Due to the high production inputs, the correct identification of disease symptoms are of vital importance and growers will readily submit take and transport or courier samples over vast distances to diagnostic laboratories with expertise to identify the diseases symptoms for accurate identification or to rule out the presence of a disease.
All participants in the value chain of vegetable production require the ability to identify diseases accurately, reliably and cost-effectively. Currently, the methods available to consumers include the delivery of samples to a diagnostic laboratory or the purchase of “do-it-yourself” kits. Laboratories can utilize a number of different tests to identify viruses in diseased plants. Most of these tests are based on molecular methods for detection due to the small size of virus particles (not visible with standard microscopy, but require specialized electron microscopy) and also due to the fact that viruses cannot be cultured on a medium, as is the case with fungi and bacteria. The preferred method for large scale, reliable and cost-effective virus screening is the use of ELISA kits or the method itself performed in a laboratory.
The potential consumers, which have been identified, include seed companies, plant breeders, government agencies, private laboratories, seedling nurseries, growers and academic institutions. The consumers are distributed across the entire geographic area of South Africa, as vegetable production is not confined to open fields anymore, but includes intensive undercover (greenhouse) farming enterprises as well. Expansion into the SADC region and ultimately Europe is anticipated due to the wide applicability and need for the technology. Currently, the customers either send plant samples to our or other diagnostic laboratory for identification or deliver them themselves. Some customers import ELISA kits directly from the suppliers or via a local distribution agency. Benefits
The locally produced Elisa kits compete extremely favourably with imported kits on cost/unit/test. The cost effectiveness results due to an absence of an unfavourable exchange rate and import taxation. The kits are available during the season on a pre-order basis and include the selection of positive and negative controls. The process of sending samples to a laboratory as well as the administrative processing is eliminated as the end-user now has the required kits to perform the test themselves within a basic laboratory set-up. In addition, the ELISA kits produced from strains detected in locally grown crops are more effective for the detection of South African specific strains and therefore negate the need for repeat testing. Repeat testing is sometimes required when the visual symptoms clearly indicate a specific viral infection, however, the imported Elisa kits test negatively for the infection.
ELISA kits imported from the USA and Europe are most often directed against viral strains which are found in their specific countries of origin. This can lead to the false-negative detection of plant viral strains unique to South Africa. This process eventually becomes laborious, time-consuming and expensive. This may inadvertently lead to the spread of the disease, making crops more vulnerable to further losses.
There are currently no locally produced commercial ELISA kits available that can accurately and reliably detect South African specific plant viral strains associated with some of the most economically important plant viruses, such as TSWV and CMV
The antisera within the ARC collection was derived from locally grown crops infected with viral strains specific to South Africa. The efficacy of the antisera to detect viral strains in South Africa has been proven through the use of in-house ELISA diagnostic tests performed in the laboratory for many years an extensive client base. No other ELISA kit manufacturer or plant diagnostic laboratory has access to South African-produced antisera and therefore the ELISA kits which will are produced locally are unique in this regard. Increased accuracy with the identification of local virus strains will contribute positively to an efficient and productive agricultural value chain in South Africa.
Idea behind technology
The science underpinning the ELISA method has been extensively studied and is well understood. Thousands of peer-reviewed publications are available in which the efficiency and application of ELISA has been proven in plant virus research and diagnostics. Therefore the idea of a locally produced ELISA kit for the detection of plant viruses is not novel, however, the use of antiserum derived from local viral strains is new in South Africa and can greatly contribute to plant health in the agricultural sector.