Section 10 - Disease Tolerance for Certification

1. Montana certified seed potatoes that test within the maximum PVY tolerance limits in Table 2 are designated as “PVY Generation” seed potatoes. Testing for PVY will be done during the summer using lab methods.
   1. “PVY tolerance limits” means the maximum percentage of detection of potato virus Y at the time and place of a virus test. These limits do not affect the qualification of a lot of seed for certification. EXCEPTION: The PVY maximum tolerance limit for planting in Montana will be based on summer testing.
   2. Disease tolerance limits means the maximum allowable observation of any overt symptoms for certain diseases at the time and place of the inspection.
   3. The maximum PVY tolerance limits set by MSU for each class of Montana certified seed potatoes are specified in Table 2.
   4. All seed classes must be summer tested for PVY, except Generation 3 and 4 seed that will not be planted back in Montana for recertification, and Generation 5 seed. If summer testing was not performed on Generation 3 or 4 seed to be planted back for recertification, PHT results may be substituted for summer test results at the discretion of the managing director. Seed exceeding the maximum PVY tolerance limits cannot be planted for certification purposes in Montana. Note: If Generation 3 seed is being sold out of state for recertification as seed, growers are advised to test for PVY during the summer growing season.
2. Montana certified seed potatoes that exceed the maximum PVY tolerance limits in Table 2 by lab test will have no prefix before the given generation.
3. In the case of a positive lab test for Clavibacter michiganensis subsp. sepedonicus
   1. Traceback will be initiated on all sister lots and contact lots (storage or equipment).
   2. 100% laboratory testing of all see lots on farm at 4600 tubers per lot.
   3. Seed from CMS positive farm can only be sold for commercial planting after testing clean.
   4. Mandatory testing of 100% of G2-G5 for 5 years after last detection.
4. In the case of a visual bacterial ring rot diagnosis:
   1. No seed from that farm can be certified for that crop year.
   2. Traceback will be initiated on all sister lots and contact lots (storage or equipment).
   3. Mandatory testing of 100% of G2-G5 for 5 years after detection. See Section 8 D.2
5. An indication of zero tolerance means that a particular disease must not be observed during various field inspections, cellar visits or lab tests. Note: a “0” (zero) recorded for a disease does not mean that a lot of seed potatoes is free from a certain disease or cause of disease. It means only that a disease was not observed during regular certification procedures.
6. Certified Seed Production Field disease tolerances are list in Table 1 and 2.

   1.  Required steps for production of seed stocks. Each subsequent generation is the progeny the previous generation.                                                                                                                                                                                                                                                                             

   2. Pre-Nuclear must be tissue culture plantlets cut from disease-free materials or greenhouse produced minitubers produced from disease-free plants.

   3. Nuclear

      1. Seed source must be pre-nuclear and/or growers selected lines grown in Montana.
      2. One hundred percent (100%) of the mother materials must be tested for all diseases of concern.
      3. Seed must be planted as tuber units and hill units if a selected line is used; or as family units if meristem plantlets were used.
      4. There must be two (2) feet between plants and three (3) feet between units.
      5. One hundred percent (100%) of LS-nuclear shall be tested for PVY by ELISA during summer disease testing. Testing of M-nuclear for PVY is optional. PVA and PVX testing optional unless post-harvest test indicate increase in inoculum. Exception: if source of nuclear is tissue culture plantlets grown in an insect-proof greenhouse, one and one-half percent (1.5%) of the plants must be tested for PVA and PVY.
      6. Nuclear plants must be free from all diseases of concern (Table 1 and Table 2).
      7. Post-harvest testing is optional for seed no to be sold. Post-harvest testing at the Montana winter test plot is required for all seed to be sold. Note: Nuclear seed is not to be sold out-of-state.
   4. Generation 1
      1. Source of Generation 1 must be nuclear seed.
      2. Seed must be planted as hill units. Exception: Seed generated from insect-proof greenhouses may be exempt from this rule.
      3. One hundred percent (100%) of plants or hill units will be tested for PVY by ELISA in the summer testing. PVA and PVX testing will be conducted when post-harvest testing detections in the previous crop indicate significant inoculum is present in the growing area.
      4. There is zero (0%) tolerance for all diseases of concern (Table 1 and Table 2).
      5. Post-harvest testing is required.
   5. Generation 2
      1. Seed source must be Generation 1.
      2. Two hundred (200) plants per acre shall be tested for PVY by ELISA in the summer testing. PVA and PVX testing will be conducted when post-harvest detections in the previous crop indicate significant inoculum is present in the growing area.
      3. 10 tubers per acre or a minimum of 400 tubers per seed lot will be tested for CMS (Clavibacter michiganensis subsp.sepedonicus) by PCR on tuber cores collected after harvest.
      4. Post-harvest testing is required.
   6. Generation 3
      1. Seed source must be Generation 2.
      2. Testing plants (100 plants per acre) for PVA, PVX and PVY during the regular growing season is optional for seed that will not be planted back in Montana for recertification.
      3. 10 tubers per acre or a minimum of 400 tubers per seed lot will be tested for CMS (Clavibacter michiganensis subsp.sepedonicus) by PCR on tubers collected after harvest.
      4. Post-harvest testing is required.
   7. Generation 4
      1. Seed source must be Generation 3
      2. Testing plants (50 plants per acre) for PVA, PVX and PVY during the regular growing season is optional.
      3. 10 tubers per acre or a minimum of 400 tubers per seed lot will be tested for CMS (Clavibacter michiganensis subsp.sepedonicus) by PCR on tuber cores collected after harvest.
      4. Post-harvest testing is required.
   8. Generation 5
      1. Seed source must be Generation
      2. Testing plants (50 plants per acre) for PVA, PVX and PVY during the regular growing season is optional.
      3. 10 tubers per acre or a minimum of 400 tubers per seed lot will be tested for CMS (Clavibacter michiganensis subsp.sepedonicus) by PCR on tuber cores collected after harvest.
      4. Post-harvest testing is required
7. Identities
   1. Line-selection (LS): Seed potatoes produced through the process of line selection will be given LS as identity. To qualify for line selection, selected units must be planted in the field for comparison of plant performance and yields for at least two years. The best line can be used as a source of nuclear plants. LS identity can only be carried to Nuclear and Generation 1.
   2. Meristem (M) : Seed potatoes generated through meristem methods and propagated in vitro will be given M as identity. Meristem and propagation work must be done in a laboratory approved or recognized by Montana State University (Appendix B). M identity can only be carried to Nuclear and Generation 1.

VISUAL INSPECTION TOLERANCES FOR CERTIFICATION

* Diseases caused by Phytoplasmas including Haywire, Witches Broom, Purple Top and Zebra Chip (Candidatus liberobacter solanacearum). 

IMPORTANT NOTE: The 0.0% tolerance is not intended, nor may it be construed, to mean that the lot inspected is free from the disease. In cases of bacterial ring rot and Columbia root knot nematode, it means only that said disease was not identified during the inspection process. In cases of other disease, it means only that the disease infection should be rogued to zero.

SUMMER RANDOM LEAF TESTING

PVY SEED CLASS AND REQUIREMENTS **

** NOTE:  Percentage of infection is based on ELISA test

NOTES:

1. Enzyme-linked Immunosorbent Assay (ELISA) for all virus disease(s) of concern shall be required each year for Nuclear and
2. Generation 5 seed shall not be used for the purpose of recertification in
3. The 0.0 tolerance means that all infected plants must be rogued o u  t  .