| | Seed selection and purchase | Whole versus cut seed | Sanitation, handling and storage of seed lots
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.Seed Selection and Purchase
No amount of cultural management will make up for a seed lot with poor vigor. It is important to select seed that is:
- Certified
- Free from seed-borne diseases
- From a grower with a good reputation
- Free from decay
- Firm (stored properly)
- Physiologically young (produced without major stresses)
- Small in size - 8 oz (225 g) or less
- Uniform in size
These factors contribute to the production of a complete stand of uniform plants with the potential for high yields of top quality tubers.
Selecting seed that is classified by the Canadian Food Inspection Agency (CFIA) as Certified or better will ensure that the seed meets minimum standards for disease, trueness to variety, physical soundness and tuber size. See Seed Potato Production Pyramid in Seed Potato Act and Regulations for more details regarding seed classes. In Alberta, provincial legislation specifies that only certified seed potatoes are permitted for planting, unless formal permission is granted by the Potato Growers of Alberta. In Saskatchewan, the Bacterial Ring Rot Control Regulations, included under the Pest Control Act, indicates that a potato grower must plant seed that is certified as foundation or higher class. This also applies to market gardeners. In Manitoba, non-certified seed may be planted, however, much of the potato production is grown under contract for processing and the contract stipulates that the seed must be certified as Elite 4 or higher class.
Insist on receiving a copy of the post harvest test results before agreeing to purchase seed. Viral diseases do not produce visible symptoms on the outer surface of the tubers, so visual appearance is not necessarily a complete indication of quality seed. The incidence of viruses in a certified seed lot can be determined from the post harvest test results issued by CFIA accredited laboratories or CFIA reports of winter nursery tests. See Post Harvest Testing for more information.
When purchasing seed, ensure that the seed grower has a good reputation. Also, check that the growing area has a history of producing quality seed. A visit to prospective seed suppliers both during the growing season and once the crop is in storage will help to assess the grower and the crop.
Determine the conditions under which the seed was produced and stored. The potato seed should not be stressed in the field. Seed should be stored at temperatures between 37 and 39°F (3 and 4°C) to ensure viability. Although potato seed may appear healthy, it may have poor germination and poor vigor if it was grown under stress, or if it was chilled or frozen in the field or in storage.
Assess the uniformity and size of the seed tubers. Performance of cut-seed pieces is affected by size of the uncut mother tubers. Smaller, uniformly sized mother tubers result in:
- Uniform, blocky cut-seed pieces
- A higher proportion of the most productive seed piece sizes (1.5-3 oz (43-85 g))
- Better planter performance, which contributes to high plant stands and correct spacing.
Seed-piece types cut from different sized mother tubers.
Oversize seed tubers result in many cut-seed pieces that are too large or too small. Small seed pieces (less than 1.5 oz or 45 g) produce weak,unproductive plants. Large seed pieces (greater than 3 oz or 90 g) are no more productive than ideal (1.5-3 oz (43-85 g)) seed pieces but cost more to plant. Variably sized and shaped seed pieces do not flow well and may not be picked up by planter picks or cups causing a reduction in plant stand.
On average, seed pieces cut from large mother tubers (>8 oz (225 g) are not as productive as pieces of the same weight cut from smaller tubers. Seed pieces cut from larger tubers have fewer eyes and may result in blind seed pieces (no eyes), causing a reduced stand.
Negotiate terms of the seed purchase. When negotiating purchase of a seed lot, determine the method of delivery, date of delivery, desired tuber size distribution, tuber temperature and degree of sprout development.
Seed should be inspected upon delivery, and if the commercial grower has concerns about the grade, quality or physical condition, both the seed supplier and CFIA should be contacted within two days to request a re-inspection. If an inspection is requested, a CFIA inspector will carry it out within five working days of receipt of the request. The commercial grower should have unopened seed potato bags on hand or a bulk-movement certificate (in the case of bulk lots) so that the proper information can be obtained regarding the seed lot purchased. Seed tags or bulk-movement certificates are a grower's assurance that inspected seed potatoes have been purchased.
Whole Versus Cut Seed
There are several advantages to using whole over cut seed.Uniform lots of small, whole tubers ranging in size from 2 to 4 oz (60 to 110 g) can produce plants with:
- High vigor
- Increased stem counts
- Increased tuber set
- Uniform tubers that tend to be smaller because of the heavier set
- Less disease
Eliminating cutting reduces the risk of spreading tuber-borne diseases. Since there are no cut surfaces, seed decay is less likely; therefore, seed piece fungicides are not normally applied to whole seed. However, some growers apply fungicides for control of Rhizoctonia when black scurf is present on whole seed. If late blight is suspected on the seed tubers, use a seed treatment with an active ingredient effective in controlling seed-borne late blight.
Unfortunately only a small amount of whole seed is available in Western Canada. Many North American varieties do not produce large tuber sets, so it is not economical to produce whole seed tubers. Often whole seed tubers are obtained by grading out the 2 to 4 oz (60 to 110 g) tubers from the seed lot. These small whole tubers sell at a premium. The capital and operating costs of cutting must be weighed against the benefits of reduced handling, and higher cost of purchasing whole seed.
Sanitation, Handling and Storage of Seed Lots
Seed lots should be stored, cut and handled under sanitary conditions to prevent the spread of disease and reduce losses from disease organisms that cause rot. Sanitation consists of cleaning and disinfecting all equipment, storage, tools and pallet boxes that contact the seed potatoes. Since most disinfectants are inactivated by soil and plant debris, it is essential that this material be removed by thoroughly-cleaning equipment and storage with a pressure washer or steam cleaner before the disinfectant is applied. The seed storage and all equipment coming in contact with the seed lot should be disinfected with a quaternary ammonium compound such as Ag-Services Incorporated General Storage Disinfectant, Bardak 2210 Disinfectant Sanitizer, or DMR-23 Disinfectant. Surfaces must remain wet for at least 10 minutes for the disinfectant to destroy disease organisms.
A commercial grower may be required to provide several different storage environments depending upon the time of seed delivery and the method of seed cutting used. Whole seed is typically delivered between February and April and should be stored at 37 to 39°F (3 to 4°C) and 90% R.H. until just before cutting. Growers can choose between two seed cutting methods: 1) standard seed cutting where seed is cut, treated and planted the same or next day or 2) pre-cutting, where the seed is cut, treated, stored for up to 3 weeks before planting.
The standard seed cutting method is the most common. Before cutting, seed should be warmed to 50-55°F (10-13°C) for 10 days, unless sprouts have already appeared. Warming helps break the dormancy maintained during cold storage and will accelerate emergence. If the tubers are beginning to sprout then dormancy is already broken. In this case, warm tubers to 45° F (7°C) to avoid shatter bruises caused by handling and cutting. Shatter bruises affect seed vigor and the bruises can become infected with Fusarium dry rot, causing poor emergence.
The pre-cutting method helps spread out the work load at planting time, however, this practice should only be attempted if recommended temperature, airflow, and humidity can be maintained. Before cutting, seed should be warmed to 45-50°F (7-10°C) to avoid shatter bruises caused by handling and cutting. The depth of the cut-seed pile is limited by the ability of the ventilation system to maintain a proper temperature throughout the pile. Typically cut seed is piled no deeper than 3 to 8 feet (1 to 2.5 metres). After cutting, maintain the seed pile at 45-50°F (7-10°C), 90% R.H. for 5 days to allow the cut surfaces to suberize (heal). After suberization is complete, cool the cut seed pile to 41-46°F (5-8°C).
Precautions should be taken during cutting, storage and at planting time to ensure that the cut seed pieces are not exposed to drying conditions and direct sun. Trucks, which are transporting cut seed to the field for planting, should be tarped to reduce exposure to dry air and sunlight.
Written by L. Delanoy, C. Schaupmeyer, D. Ziprick, D. Kirkham |
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