Services > Potatoes

Plantovita specializes in the determination of the presence of pathogens and diseases of potatoes, that is to say, the detection of viruses and bacteria in planting material. In the Diagnostic Section these services are extended to the identification of fungi on tubers and physiological deviations. Plantovita undertakes the following:

  • All samples of any client are handled with confidentiality, maintaining integrity and keeping the test results secure.
  • Results generated in respect of any sample are sent on a confidential basis to the client and records are stored securely for 5 years.
  • Records pertaining to the receipt, processing and testing of samples, as well as test results are generated, maintained and subsequently stored securely and confidentially.
  • All samples are tested in accordance with protocols and procedures approved for Potato Laboratory Service.

The following viruses and bacteria are involved:

Viruses:
PVY, PLRV, PVX, PVM, PVA, PVS and TSWV
Bacteria:
Bacterial wilt (Ralstonia solanacearum) and bacteria causing soft rot/black leg including Pectobacterium carotovorum ssp carotovorum, Pectobacterium atrosepticum, Pectobacterium carotovorum subsp brasiliensis, Dickeya spp.

Virus Tests

The monitoring of potatoes for the presence of the potato viruses mentioned above takes place using the enzyme-linked Immunosorbent Assay (ELISA test). This serological technique resorts under the most sensitive techniques suitable/appropriate for large-scale routine testing. A standard procedure or protocol is followed to ensure the successful completion of this simple, but accurate test. For the determination of the presence of viruses in potato samples, either in tubers or leaves, a distinction is made between official and unofficial samples.

Tuber samples

Official tuber samples are defined as samples statistically sampled, sealed and submitted by certification officers. Official tuber samples originate from registered plantings or plantings designated for certification or from plantings registered in terms of the Table Scheme and can only be tested at a laboratory approved by the Independent Certification Council for Seed Potatoes. Results in respect of statistical field and store samples are used to facilitate certification. The results are reported directly to the regional office of Messrs Potato Certification Service in the region from which the samples originated (unless indicated otherwise) via e-mail or fax and not by telephone.

Leaf samples

Official leaf samples are defined as any number of leaves, statistically sampled, sealed and submitted for testing by a certification officer. Official leaf samples only originate from greenhouse plantings. The testing of official leaf samples can only take place at laboratories approved by the Independent Certification Council for Seed Potatoes. Results in respect of official leaf samples determine the certification status of a planting. Results are reported directly to the regional office of Messrs Potato Certification Service in the region from which the sample originated (unless indicated otherwise) via e-mail or fax and not per telephone.

Unofficial leaf samples can be described as leaf samples containing any number of leaves and may be sampled by a person other than the certification officer. Test results in respect of unofficial leave samples can under no circumstances affect the certification of a planting and shall only serve as a management tool. Results are reported directly to the client (either person who submitted the sample or the person responsible for payment as indicated on the documentation) or as indicated on the Sample Reception Form.

Diagnostic samples

Single plants or tubers sent by any client on an ad hoc basis, including Messrs Potato Certification Service or Potatoes South Africa or samples not sampled or sealed or sent by certification officers, or submitted to the laboratories by growers or representatives of growers or by any other company will be considered as diagnostic samples. The results are reported directly to the client (either the person who submitted the sample or the person responsible for payment) or as indicated on the Sample Reception Form.

Bacterial tests

Bacterial wilt tests

Ralstonia solanacearum is the organism causing bacterial wilt and a zero-tolerance is applicable in respect of the presence of the organism in the case of all propagation material destined for certification. The ELISA test is used for the detection of bacterial wilt in seed potatoes. The specific test kit was developed locally by the Department of Biochemistry of the University of Stellenbosch. A standard procedure or protocol is followed to ensure the successful completion of this simple, but accurate test. Because of the danger of the disease, all subsamples which generate a positive reading during the ELISA test are confirmed by Plantovita by way of a conventional method entailing a molecular (PCR) and a series of biochemical tests.

Soft rot and black leg

Pectobacterium spp. and Dickeya spp. are the pathogens causing soft rot and black leg in potatoes. The testing of all in vitro plants (test-tube plants) and G0 seed potatoes for the presence of these organisms is mandatory. It is necessary in order to determine whether the source material for the production of seed potatoes in terms of the South African Seed Potato Certification Scheme is free from these pathogens. Conventional methods are followed and these entail the isolation and identification of the pathogens by means of a series of biochemical tests.

The tolerance in respect of the presence of the following pathogens in in vitro planting material and G0 seed potatoes is zero:

  • Pectobacterium carotovorum subsp carotovorum,
  • Pectobacterium carotovorum subsp brasiliensis,
  • Pectobacterium atrosepticum,
  • Dickeya spp,
  • Internal contamination (saprophytic and endophytic organisms).

In the role of controlling laboratory of the potato industry Plantovita also renders the following services:

Defused lighting

Seed potatoes which have been registered for certification are subjected to a certain light intensity in order to encourage sprouting. The sprouts of every cultivar are unique and it is possible, in cooperation with Messrs Potato Certification Service, to determine whether the samples which have been submitted are true to type, that is to say, that no mixing of cultivars has taken place in the seed-lot or that the cultivar of the seed lot is as indicated.

Confirmation of all positive bacterial wilt results

In view of the fact that the ELISA test is under exceptional circumstances (inter alia the presence of saprophytes in the soil or on the plant) also able to non-specifically detect other organisms, the test can generate positive readings as a result. It is therefore necessary to make absolutely sure whether readings generated higher than the cut-off value have been caused by the target organism. This is essential because the presence of Ralstonia solanacearum has tremendous implications for the growers of seed potatoes. Conventional isolation together with PCR is at present used as the method for the confirmation of the presence of this pathogen. Conventional confirmation entails the isolation and identification of the pathogen by means of PCR and a series of biochemical tests.

Testing of imported planting material

Messrs Potato Certification Service has the responsibility to draw samples of imported planting material at the port of entry. Sampling takes place under the supervision and with the approval of the APIS officials of the Department of Agriculture. For certification purposes the samples have to be tested for the presence of Potato leaf roll virus (PLRV), Potato virus Y (PVY), Potato virus X (PVX), Potato virus M (PVM), Potato virus A (PVA), Potato virus S (PVS), Tomato spotted wilt virus (TSWV) and the following bacteria: Ralstonia solanacearum, Pectobacterium carotovorum, Pectobacterium atroseptica and Dickeya spp. The testing of sprouted tubers for the presence of the above-mentioned viruses only takes place once the material has tested negative for the presence of the afore-mentioned bacteria. For the detection of the bacterial diseases conventional methods are followed. For the detecting of viruses the ELISA method is applied.

Testing in the case of disputes in respect of the results of virus tests

A grower of seed potatoes has the right to appeal against the result of a virus test. The appeal is considered by the Technical Manager of Potato Certification Service and either approved or rejected. Plantovita handles all virus disputes except when the field sample was tested by Plantovita. With due consideration of the type of virus, the Technical Manager of Potato Certification Service shall indicate whether the original sample shall be used to resolve the dispute or the drawing of a new sample or a store sample shall take place to facilitate dispute resolution. The monitoring of dispute samples for the presence of potato viruses takes place using the Enzyme-linked Immunosorbent Assay (the ELISA test). The test result generated is final and results are used in the certification or not of a seed-lot.