The seed potato certification review identified a number of initiatives to improve seed potato quality. One of these was to require growers to have in place a Quality Assurance system for monitoring the quality of seed tubers during grading. Another was to provide further information on best practices in seed potato handling and storage.

Seed tuber inspection by growers

Advantages of using the inspection procedure are:

• Real time check of effectiveness of grading
• Provides early opportunity to correct errors
  • Focus staff on the problem
  • Slow the grading line
  • Re-grade part of a line
• Provides a record of the condition of the seedline at time of grading
• Reduces failures at official inspection
• Provides customers and seed tuber inspectors with better information on quality of seedline.

A copy of the draft guideline and inspection record form is provided here. Seed grower feedback on the usability of the procedure are invited – please contact Ron Gall, Secretary.

• Grower guide to seed potato tuber inspection

Best practice guide

The Authority has developed the best practice guide to establish what might be considered best practice in the handling and storage of seed potatoes in New Zealand. This guide is intended to inform both seed growers and ware growers of factors that can affect seed potato quality and how to best manage these. This is part of the Authority's and the potato product group's commitment to ongoing improvement of seed potato quality.

It is important to recognise that the New Zealand Seed Potato Certification Authority provides certification that seed lines do not exceed acceptable pest and disease tolerances during growth and certifies trueness to variety. The certification applies to the seed at the time of final tuber inspection. The Authority does not provide any assurances of how the seed is handled after the point of certification – the diagram illustrates the boundaries of responsibilities.

The best practice guide focuses on factors that can affect seed tuber quality after harvest:

Temperature

1. don't harvest too hot or too cold
2. allow wound healing to occur at 13-15.5oC
3. ensure cooling (0.3oC per day) or warming is gradual
4. don't handle cold tubers
5. don't allow temperatures to fluctuate widely
6. ensure forced ventilation air is slightly cooler (as little as ½ a degree) than the tubers to prevent condensation
7. check temperatures in storage – infrared thermometers can detect hotspots, which may indicate a disease or ventilation problem
8. ensure cut seed is cured before transport

Humidity

1. use humidifiers to increase humidity to 95% in storage
2. always humidify air that is forced through stacks of seed tubers

Ventilation

1. ventilate storage facilities
2. ventilate consignments being transported
3. in transport leave a small part of the load uncovered (rear of tarp) to improve airflow
4. remove covers when parked for any length of time (e.g., on ferry crossing)
5. don't remove covers when parked if raining – park under cover and in the shade

Bruise prevention

1. don't handle potatoes below 8oC
2. don't allow tubers to drop more than 15cm
3. use cushioning material, such as foam, in drop areas (bins, trucks)
4. ensure drivers don't walk on the tubers while covering the load

Light

• cure in diffuse light to induce dormancy

A full copy of the best practice guide is provided here:

• Best practice guide (PDF) for storage and handling of certified seed potatoes

References and links on seed potato quality

General seed quality reference:

Physiological aging:

Potato Seed Management: Seed Size and Age. Bohl, W.H.; Nolte, P.; Kleinkopf, G.E.; and Thornton M.K. 2000. PDF

Physiological Aging of Seed Tubers. Pavlista, A.D. 2004. Nebraska Potato Eyes Vol. 16 (1):1-4. PDF

Potato seed: Physiological age, diseases and variety testing in the Nordic countries. Proceedings of NJF Seminar 386. Crop Science, Sigtuna, Sweden February 1-2 2006. PDF NOTE – 2MB file.

Evaluation of Seed Aging to Enhance Performance of New Russet Potato Varieties. Rykbost, K.A.; Carlson, H.L.; Charlton, B.A.; and Kirby, D. 2001. Annual Report, Klamath Experimental Station, Oregon. pp27-35. PDF

Storage:

Potatoes – Storage and quality maintenance in the Pacific Northwest. Ititani, W.M. and Sparks, W.C. 1985. Pacific Northwest Cooperative Extension Bulletin PNW 257, 12pp. PDF

Potato Storage Management. PDF

Cutting:

Potato facts – Selecting, cutting and handling potato seed. Johnson, S.B. University of Maine Cooperative Extension. Bulletin #2412. PDF

Also available by "interloan" through your local library (ask your librarian for further information):

Struik, P.C. and Wiersema, S.G. 1999. Seed Potato Technology. Wageningen Pers, Wageningen, The Netherlands. 382pp.

Thornton, M. and Bohl, W. 1998 (Eds.). Preventing potato bruise damage. University of Idaho Cooperative Extension System. Bulletin 725 (Revised) 12pp.