D-97-11

Our File
3700-2-1

I. SUBJECT

This directive contains the requirements for the production of Pre-Elite seed potatoes from material other than nuclear stock⁽¹⁾, i.e. disease free cuttings, plants, tubers, or selected clones (Seeds Regulations C.R.C. c. 1400, section 47.2). In this directive, the term nuclear stock equivalent will be used for this material.

This directive supersedes all previous drafts of this subject.

II. BACKGROUND

Although there has been a general movement toward a flush through system starting with disease tested plantlets grown in vitro (nuclear stock), there is still some interest in using other sources of seed to start new field production of seed potatoes. For comparison, Holland, the number one seed potato exporting country, is extensively using clonal selection in its own seed certification system. Therefore, the need has been identified to maintain the possibility of doing clonal selection in Canada. The present directive does specify the criteria that have to be met in order to produce Pre-Elite seed potatoes from material other than nuclear stock.

III. LEGISLATIVE AUTHORITY

Seeds Act R.S., c. S-8 and amendments 1976-77, c.28 and 1985, c.47.
Seed Regulations and their amendments, SOR/91-526, SOR/93-331, SOR/95-179, SOR/95-215 and SOR/97-118.

IV. POLICY

Any grower intending to use nuclear stock equivalent to produce Pre-Elite seed potatoes must comply with the following requirements (flowchart in Appendix 1):

1. SELECTION AND HARVEST

Mother plants must be selected from a field certified by the Canadian Food Inspection Agency (CFIA) under the Seed Potato Certification program. Selected clones are specifically chosen because they express characteristics such as freedom from visual symptoms of disease and physiological defects, uniform size and set of tubers, and varietal trueness to type.

At this point, field testing of the mother plants to eliminate material that could be infected by viruses is highly recommended but not required. Because this will permit elimination of plants affected by secondary infection, but probably only a part of those affected by primary infection, a post-harvest test is required anyway.

Growers or provincial specialists are responsible for the selection of clones. It is not the CFIA responsibility to do so.

Handling of the selected clones is the responsibility of the grower or provincial specialist, and will be monitored and audited by CFIA.

Each clone must be harvested, labelled and bagged separately.

2. TESTING

As mentioned before, post-harvest testing is mandatory to insure the elimination of plants affected by secondary infection.

Because of the uneven distribution of diseases over the tubers of a selected clone, and because low concentrations of a disease causing organism can be undetectable by laboratory testing, all tubers (or their progeny) from the selected clone(s) must be post-harvest tested, even if not all tubers are intended to be replanted to produce Pre-Elite seeds.

All required testing (bacterial ring rot, PSTVd, and viruses) must be done at growers' expense in a CFIA accredited laboratory.

2.1 Bacterial Ring Rot (BRR) testing

In the case of BRR, testing must be done directly on the tubers harvested from the selected clones. Stem testing in the greenhouse or in the field the next season, or tuber testing in the greenhouse, are not considered acceptable alternatives; indeed, an equivalent test would require every single stem or tuber to be tested.

Core samples must be taken from the stem end of each tuber harvested from the mother plant, and tested for Clavibacter michiganensis subsp. sepedonicus (Spieckermann & Kotthoff 1914) Davis, Gillaspies, Vidaver & Harris 1984, the causal agent of bacterial ring rot (see Appendix 2 for sampling details).

If any core sample tests positive for bacterial ring rot, all clones from the same farm unit will be rejected for the production of Pre-Elite seeds. All lots from that farm unit will be decertified, and standard procedures related to bacterial ring rot infection will apply.

2.2 Virus and viroid testing

Virus and viroid testing can be carried out in two ways: in the greenhouse during the winter (see section 2.2.1 for details), or in the field the spring following harvest (see section 2.2.2 for details).

If any sample tests positive for any viruses, the entire clone must be rejected for the production of Pre-Elite seeds. Positive clones may still be eligible for certification, provided all regulatory requirements are met.

If any sample test positive for the presence of PSTVd, the entire seed lot from which the clone originates will be decertified as outlined in section 52.(5)(e) of the Seeds Regulations.

When testing is done in the field (as in section 2.2.2), all positive clones must be removed from the field for certification at the Pre-Elite class. If not, the entire field will be downgraded to a lower class, provided all regulatory requirements are met.

2.2.1 Virus and viroid testing in the greenhouse during the winter (alternative 1)

One eye from each tuber in the clone can be sprouted and/or grown out. When removing the eye appropriate care has to be taken to avoid any possibilities of cross contamination between clones. To reduce the risk of contamination it is recommended to disinfect knives and equipment between each tuber. Leaf or sprout tissues produced from each excised eye must be tested for PLRV, PSTVd, PVA, PVM, PVS, PVX, PVY^o, PVYⁿ and RLSV (see Appendix 3 for details). Clones of the same variety that test negative for all diseases can be planted in bulk, and do not need to be kept separate, as no further testing is required.

2.2.2 Virus and viroid testing in the field, the spring following harvest of selected clones (alternative 2)

After planting of the selected clones the spring following harvest, terminal three leaflets from fully expanded young compound leaves are taken from at least one plant from each tuber unit and tested for PLRV, PSTVd, PVA, PVM, PVS, PVX, PVY^o, PVYⁿ, and RLSV (see appendix 3 for sampling details). Each clone must be properly identified and planted separately in the field. Clones must be planted so that no contact is possible between them before positive ones can be removed. Cut seed must be planted as tuber units, and spacing between each unit is required.

3. FURTHER MULTIPLICATION

When tubers are tested (as in section 2.2.1) and are confirmed to be disease free, further multiplication is allowed before planting in the field. Cuttings must be produced in a protected environment. No further testing is required for these cuttings. If the process of multiplication started before all required testing is completed, care must be taken to avoid any possible cross contamination between clones and every clone must be kept separate and clearly identified.

Plants that are field tested (as in section 2.2.2) may only be planted as whole seed or be multiplied by cutting the tubers. Extra care must be taken, if tubers are being cut, to avoid cross contamination between clones. To reduce the risk of contamination it is recommended to disinfect knives and equipment between each tuber.

4. APPLICATION FOR CERTIFICATION

Application for seed potato crop inspection and field inspections will be the same as for the production of Pre-Elite from nuclear stock. At the time of first inspection or earlier the applicant for crop inspection must show to the satisfaction of the inspector that all the testing has been completed. Documentation on clonal selection, clone identification, testing results etc... must be made available to the inspector anytime.

V. DEFINITIONS

Clone: all tubers and progeny of one mother plant.

Clonal selection: process by which field grown tubers are used to initiate a new line of seed potatoes.

Disease free: seed potatoes tested following official protocol and found negative on all the tests.

Mother plant: any individual plant, or plant part that will be used to start a multiplication process; the progeny of such entity forms a clone.

Nuclear stock: Refer to section 47.11 (3) of the regulations.
(a) produced from potato tissue culture material which has been tested and found free of bacterial ring rot, PSTVd and viruses;
(b) laboratory tested within 12 months prior to the completion of the multiplication process and found free of bacterial ring rot, PSTVd and viruses;
(c) produced in an aseptic or protected environment;
(d) visibly free from varietal mixtures;
(e) free from pathogenic bacteria or viruses, saprophytic contamination or other symptoms of diseases that could affect the quality of the material; and
(f) if produced in a protected environment,
(i) inspected by an inspector at least once during the growing period; and
(ii) grown in a medium that has not been previously used.

Nuclear stock equivalent: "cuttings or plants that were produced in a protected environment or from tubers or selected clones, and that were determined by laboratory tests to be free from any disease that could affect the quality of the seed."(refer to section 47.2 (a). of the regulations)

Official protocol: protocols that must be followed by laboratories that are accredited by the CFIA to perform diagnostic tests outlined in this memo.

Primary infection: The first infection of a plant by the overwintering or oversummering pathogens.

Protected environment: means a facility for which there are appropriate procedures and physical barriers to prevent the entry of plant pathogens and insects.

Secondary infection: Any infection caused by inoculum produced as a result of a primary infection or a subsequent infection.

Selected clones: mother plants selected in a certified field following quality and freedom from disease criteria: this selection process is usually known as clonal selection.

Tuber unit: means the separate pieces of one tuber that are planted consecutively in two or more hills in a row.

VI. LIST OF APPENDICES

Appendix 1: A flowchart for the production of Pre-Elite seed potatoes from other sources than Nuclear Stock (nuclear stock equivalent).
Appendix 2: Sampling procedure for the detection of Clavibacter michiganensis subsp. sepedonicus (Spieckermann & Kotthoff 1914) Davis, Gillaspies, Vidaver & Harris 1984, the causal agent of bacterial ring rot, in nuclear stock equivalent seed potatoes.
Appendix 3: Sampling procedure for viruses and viroid (PSTVd) testing of nuclear stock equivalent seed potatoes.

Dr. J.E. Hollebone
Director
Plant Protection Division

Attachment