Saskatchewan sometimes experiences cool growing conditions resulting in delayed seeding and slow crop development. When early fall frosts impact immature crops, seed quality can be drastically impaired.
Seed quality can be adversely affected and result in short supply good quality seed for the following year. Development of a crop can be hindered by insufficient growing degree days (GDD) or by an early frost impacting crops during a vulnerable growth stage. These events can lead to the harvest of frost-damaged grain and thus uncertainty questions regarding seed quality for planting in the upcoming year. Questions may arise such as, "How will the frost affect seed germination and seedling vigour?"
Different crop types will suffer different degrees of damage due to the way crops develop during the growing season. If food reserves within the seed are adversely affected, the quality for future propagation will be reduced. If good quality seed is in short supply, it may be advisable to secure your seed supply as soon as possible and test for seed quality.
Frost damaged seed can be categorized in four different categories depending on the degree of frost damage:
- Type A - Sound seeds with no apparent damage from frost.
- Type B - Some amount of bran frost.
- Type C - Moderate frost damage.
- Kernels may show slight shrivelling, but retain reasonable weight.
- Type D - Kernels severely damaged by frost.
- Kernels are substantially shrunken or shrivelled.
- Low bushel weight.
The effect of the damage (Type B, C and D) described above can impact crop germination and emergence.
Research has indicated that bran frosted wheat could be used for seed, provided the 1,000 kernel weight was close to normal, and germination levels are high (Type B). Damaged seed showing significant shrunken or shrivelled kernels should not be used for seed (Type C and D).
Frosted seed was more apt to suffer loss due to seed rots and seedling blights. Therefore, seed treatment is highly recommended if planting frost damaged seed. However, this becomes an additional cost to the farmer. Furthermore, a poor plant stand is less competitive with weeds, which requires diligent weed control during the growing season. Deep seeding of frost damaged seed led to reduced emergence and seedling vigour.
Research undertaken by Dr. Gusta and Agriculture and Agri-Food Canada (AAFC) though the 1990s showed the negative results of frost damage on quality of seeds.
Germination of the frozen seed was over 90 per cent; however, only 20 per cent of the seedlings emerged when planted at the 7.6 cm (three in.) depth. Frozen seed planted 3.8 cm (1.5 in.) deep had emergence of 70 per cent but emergence was delayed by two days. In unfrozen seed, seedlings emerged one day earlier planted at a 3.8 cm (1.5 in.) depth compared to 7.6 cm (three in.).
Dr. Gusta's findings show that germination may be acceptable but vigour is especially important. Vigour can be described as the ability of a seed to germinate and grow rapidly under a wide range of field conditions. Deep seeding causes additional stress on frozen seed so it is vitally important to have a vigour test conducted and take action to mitigate stresses by using seed treatment, shallow seeding or any other agronomic practice to hasten emergence.
The chart below compares frozen and unfrozen Flanders flax sown at depths of 1.9 cm (0.75 in.) and 3.2 cm (1.25 in.). Complete emergence occurred in unfrozen seeds that were seeded at 1.9 cm (0.75 in.) and emerged about a day earlier than those seeded at 3.8 cm (1.5 in.).
Frozen seeds planted at 1.9 cm (0.75 in.) emerged approximately two and one-half days later than unfrozen seeds sown at the shallow depth. Additionally, the frozen seeds had only about 50 per cent emergence. Frozen flax sown at 3.2 cm (1.25 in.) took three and one-half days longer for 50 per cent emergence compared to unfrozen seed sown at the shallow depth.
After 10 days, the frozen flax seed produced only 65 per cent of the number of seedlings compared to unfrozen seed. Seedling emergence also occurred over a longer period which would contribute to non-uniform plants in the field, as well as uneven maturity.
The U of S results also showed that canola seedlings had the most significant frost injury compared to flax and wheat, as shown in Figure 3. Whether sown at 1.9 cm (0.75 in.) or 3.8 cm (1.5 in.), very few seedlings emerged from the frozen seed lot and emergence occurred over eight days. The plants were also small and spindly. This was likely due to the fact that canola was the smallest of the seeds tested and, consequently, most subject to reductions in energy reserves.
Testing for germination and vigour
Farmers are encouraged to use the best seed possible, preferably non-frosted seed. A germination test is a must when there is possible frost injury. Before you begin, consider that "seed of most wheat varieties has a natural dormancy that causes low germination for several weeks after harvest." The grain should be given a cold treatment before testing, or germination tests should be delayed for about four weeks after harvest." (Shroyer, Mikesell, Paulsen, Spring Freeze Injury To Kansas Wheat, Kansas State University, March Frost Damage to Wheat).
A home test is not an acceptable test for seed for sale. Seed for sale must have a germination test done as part of the grading and purity analysis from an accredited seed laboratory. When purchasing seed, the farmer should ask for a Certificate of Analysis from an accredited lab.
Any crop treated with glyphosate for pre-harvest weed control should not be used for planting seed as poor seedling vigour and emergence can occur.
Germination can decrease in the bin over the winter, especially if the seed was green, frost or mechanically damaged, or had high moisture content at harvest. For seed lots of questionable quality in the fall, it is a good investment to conduct another germination test in the spring to make sure the quality did not decrease further in the bin.
Increasing the seeding rate will compensate for low germination to a certain extent; however, if the reduced germination was a result of disease, an increased seeding rate may result in more disease inoculum in the field.
Testing for seed-borne diseases
Testing for germination serves as an indicator for overall seed quality but will not determine if the seed is carrying specific seed-borne diseases. Therefore, it is also recommended to have seed tested at an accredited laboratory to assess the levels of seed-borne pathogens. Preferably, buy only certified seed that has known good quality but keep in mind that "certified seed" (according to The Seeds Act) has to meet standards for germination and purity but not for all diseases.
It is recommended to ask to see a copy of the seed lab report before purchasing seed to find out whether testing for seed-borne diseases was also conducted.
It is important to talk to the lab before submitting the seed sample to confirm which pathogens will be identified, the price for the test, the procedure used and how to submit the sample.
- Cereals: Fusarium species, loose smut in barley
- Pulses: Ascochyta, anthracnose, botrytis, and sclerotinia
- Oilseed: Blackleg
- Various: some labs will provide additional tests if requested
There are a number of accredited seed testing laboratories in Saskatchewan. Commercial labs are members of the Commercial Seed Analysts Association of Canada, Inc. (CSAAC), and follow a standard protocol for testing seed for germination, purity and seed-borne diseases. For more information, visit the Commercial Seed Analysts Association of Canada Inc. website.
Seed-borne disease testing is not yet considered an accredited test (i.e. as recognized by the Canadian Food Inspection Agency) but labs are required to follow a standard protocol to provide consistent and accurate information to their clients.
Accredited seed laboratories use the following protocol to test seed for diseases
- The seed sample is screened to remove the majority of debris or very shrivelled seed.
- This cleaning process is not as thorough as a commercial seed cleaner.
- Producers can ask the lab to further screen and size the seed.
- Producers planning to clean their seed should do so prior to testing to remove shrivelled, infected or immature green seed.
- A representative sample is selected from the sample submitted and is surface sterilized with 10 per cent bleach to remove any external contaminants.
- The seed sample is then drained.
- Under sterile conditions, the seed is plated onto petri dishes containing growth medium.
- Seed that is severely broken or chipped will not be used in the test.
- The sample size plated (200 to 1,000 seeds) depends on the type of crop and purpose of the test.
- The plates are incubated for up to 10 days, after which the pathogen colonies are identified and counted.
- Features such as colony appearance and presence of fruiting bodies are used for identification.
Guidelines for "safe" levels of seed-borne diseases
There is an on-going attempt by people in the industry to provide suggestions for "safe" levels of seed-borne diseases in various seed cultivars.
Ultimately, seed choice is the farmer's decision and will depend on his or her situation, which may be influenced by a variety of factors affecting risk, including:
- The cost and availability of disease-free seed with good germination,
- The cost and availability of registered seed treatments,
- The weather conditions and disease pressure typical of that region/soil climatic zone,
- The type of crop,
- The type of disease; and
- Plans for in-field scouting; availability and application of foliar fungicides.
Frost-damaged or diseased seed is often shrunken or discoloured. Cleaners and colour sorters can be used to remove some diseased or damaged seed. It is recommended that producers have their seed cleaned and sized to allow for consistent flow in seeding equipment.
The next step
Selecting good quality seed is integral to a healthy crop-but managing for crop health must continue throughout the growing season.
Things to consider:
- Crop rotation
- Seed bed preparation
- Residue management
- Seeding depth and rate
- Fertilizer application
- Pest control
The farmer must make plans to scout the crop early and often during the season to identify problems and implement management practices if necessary.