Testing of farm-retained and carryover seed
Author: Ken Cunliffe | Date: 26 Feb 2019
Take home messages
- Seed is the most valuable operational input even if it is low cost.
- A seed test and comprehensive seed analysis certificate can help avoid financial losses associated with a failed crop establishment.
- When seed testing, you have a right to a seed analysis certificate and ask for an interpretation if necessary.
- Seed is a living organism and needs an occasional health check. Multiple seed tests may be needed.
- Take samples that properly represent the entire seed lot and not just a single bag or the first take from the header.
Seed quality standards
Seed is just one of many operational inputs. On a per hectare basis seed is a low-cost item, but, poor seed quality can lead to massive opportunity costs on top of the losses from every other operational input.
Seed quality is essential as poor germination, or a lost season cannot be brought back! In some cases, farmers have also been left with significant weed problems that they never had previously from planting “cheap” seed.
It is also possible to face a law suit for infringing Plant Breeders Rights legislation where protected varieties are traded illegally for use as planting seed.
Plan your seed requirements early!
The Australian Seeds Federation (ASF) is the peak industry body for the Australian Seed Industry. Under the ASF Code of Practice, all seed for sale must be supported by a seed testing analysis certificate which must be made available on request. All Australian laboratories that are accredited by the International Seed Testing Association (ISTA) or National Association of Testing Authorities (NATA) to test seed follow the ISTA Rules for seed testing. As such, a seed analysis certificate is based on internationally prescribed test methods. That is the seed quality benchmark that all growers should subscribe to, when purchasing new, farm-retained or on farm carryover seed.
If seed is purchased from a reputable seed company or reseller, that seed will likely have a current seed analysis certificate that reports purity, germination, 1000 seed weight, tetrazolium, and possibly vigour results. A current seed analysis certificate should be no more than 12 months old from the date of sale. A grower should require no less and should be even more rigorous with retained or carryover seed.
Reputable seed suppliers endeavour to ensure that seed sold complies with acceptable quality standards. A seed analysis certificate should provide information about the supplier, the kind of seed, variety, lot identification, lot weight and test results. This is the purchaser’s assurance that the product in the bag is what it says it is and that it meets the standards stated.
Seed is a fragile living organism. There are some important implications. A test report is very specific to a sample and is only representative of a moment in the history of a seed lot.
- Adverse growing conditions through to harvest can markedly affect seed quality. For example, dry conditions at seed fill can lead to small seed that is not fully formed. Predation by sucking insects can leave almost invisible penetration points on the surface of the seed that will become infection sites for bacteria or fungi. Such seed may appear perfectly normal but will not perform.
- Sometimes seed is harvested at a moisture content that is too high for safe storage and must be dried down. Excessive heating during the drying process kills or deteriorates seed rapidly.
- Seed needs to be stored cool, dry and pest (rodents and insects) free. Conditions in on farm storage of seed can be quite variable – some being notoriously bad. If seed is to be stored on farm (even purchased seed), ensure that conditions are suitable – cool, dry and pest free.
Figure 1. Influence of temperature on wheat germination stored at 12 percent moisture content (Source: CSIRO)
- The impact of mechanical damage that comes from harvesting and handling seed should not be underestimated. It may appear sound on the surface but underneath there could be damage that renders that seed useless. Seed requires gentle harvesting and subsequent handling.
- Chemical treatment, including fumigants, fungicides and insecticides, particularly with unapproved chemicals can damage seed and reduce viability. Only use products that are registered for use on seeds and refer to the label for any crop safety comments prior to use.
- Unclean planting seed is a primary source of disease infection and the spread of unwanted weed seed or genetic mixing for subsequent crops.
- Does farm-retained seed contain the required genetics? You cannot grow second generation hybrid seed and expect the same performance as the first generation. That is because first generation hybrid seed maximises heterogeneity. Subsequent generations become progressively inbred increasing the frequency of homozygous genes, which may be recessive, which leads to reduced performance and increased variability.
Seed testing is a valuable decision tool for farmers!
Whenever a laboratory receives a sample of seed for testing the results provided are only applicable to the sample that they receive. So, it is imperative that the sample provided is representative so that the results are applicable to the entire seed lot. The best way to achieve this is to combine subsamples from multiple access points to the entire seed lot. Seed samples should be securely contained (in a moisture proof container if a moisture test is required) and delivered to your laboratory as soon as possible. Never leave samples in a hot car.
Immediately after harvest a moisture test will indicate if further drying is necessary. This is important for both seed and grain. Germination and vigour tests can be used to determine the suitability of that harvest for seed. If the viability is questionable at harvest it will certainly be no better after a lengthy storage period in the lead up to planting time and it would be better to dispose of the crop to grain markets. While germination may be satisfactory, a poor vigour test may mean the same thing.
A purity test after harvest can help determine the presence of unwanted weed seeds and the grading losses necessary to bring the seed to a satisfactory standard. This test may also help to identify appropriate grading methods, such as screening, gravity separation or a combination. A post-grading purity test and 1000 seed weight test are useful in conjunction with germination or vigour tests to calculate optimum planting rates.
It is important to restate that if initial post-harvest testing indicates that seed is suitable for storage, then the seed should be stored under cool, dry and pest free conditions. Time is a tyranny for quality seed and if conditions are less than optimal, viability can decline very rapidly. I have tested seed that had a 90% germination prior to being loaded into a farm silo. With mid-summer temperatures well above 40oC and a silo in the full sun for just four weeks, the germination of seed on the western side of the silo was reduced to just over 40%. Deterioration can occur under any conditions simply because seed is a fragile living organism.
The reason that you need good quality, vigorous seed is so that you can achieve the optimal plant population of strong healthy plants in the paddock that give the best chance of maximising crop yield and at the same time providing for a uniform and easily managed crop. Seed quality is measurable via purity, germination and vigour tests. Under time pressure, a tetrazolium test can be used for viability in place of a germination and vigour test with caution and understanding the limitations of the test. Ideally these tests need to be carried out as close to planting as practicable.
A purity test delivers percentages of pure seed, inert matter and other seeds. Pure seed is as per a specific definition given by ISTA for the species. For example, wheat seed must be more than half of the original size. Thus, a broken seed is considered a pure seed if it is more than half the size of an entire seed. Inert matter consists of damaged seed that does not fit the definition for pure seed, straw, soil and other matter that will not grow. Other seeds include seeds of any other crop or weed species. These are listed on the certificate of analysis and should be carefully considered to avoid introducing unwanted weeds to your farm.
A germination test will report the percentages of normal, abnormal, fresh, hard and dead seeds.
- Normal seedlings show the potential to develop into satisfactory plants when sown into good quality soil under favourable conditions of moisture, temperature and light.
- Abnormal seedlings develop but are damaged, deformed or decayed to the point that they will not develop into normal healthy plants. Frequently these plants have the same negative effect on production as weeds.
- Fresh seeds take up water but otherwise remain unchanged throughout the duration of the test. This may be because of dormancy, which could break at a later stage or they may never develop.
- Hard seeds do not take up water for the entire duration of the test. They are considered dormant and may develop at a later stage.
- Dead seeds decay and do not develop at all.
For the purposes of determining planting rates, only the normal seedlings should be considered. A germination test report will usually report a first and final normal seedling count. This may be used as a guide to vigour.
There are many different types of vigour test. In general, they report the ability of seeds to germinate and emerge from a specified depth of soil within a set time period and subject to specified conditions. Different vigour test types may impose a stress factor on the germinating seed, such as cold or high humidity. In general, the vigour result for high quality seed should be approximately the same as the normal percentage from a germination test. As with all laboratory tests, the laboratory that issued the certificate should be able to assist with interpretation. Vigour drops off more rapidly than germination. So, seeds which germinate well may not emerge well under adverse conditions.
A tetrazolium test is a rapid biochemical test for viability. Live seed tissue is stained red during the process. In order to be considered viable, all essential parts of the seed embryo must stain red. Viable seeds are expressed as a percentage. It is important to note that no distinction is made between normal, abnormal, viable hard and viable fresh seeds. The test does not account for dormancy. Your testing laboratory can assist with the interpretation of results.
Relationship between seed size and seed vigour test in canola
In the laboratory, there is no definite relationship between seed size and germination/vigour tests.
Figure 2. Canola: seed size vs germination %. Does larger seed size in canola mean better germination?
Although in the laboratory, there is no link between seed size and germination/vigour tests, research in the field by Rohan Brill from NSW DPI shows that there is a relationship between seed size and seed establishment in canola, especially under challenging conditions (e.g. deep sowing). For further information, please read Rohan’s papers on page 59 of this link (Canola establishment - does seed size matter?) Provided that you are able to obtain the variety that you want, purchasing or grading farmer-retained seed for larger seed size may perform better in the field than smaller seed where the germination and vigour are the same.
Irrespective of the origin of the seed that you plant it is worth securing a recent seed test certificate from a reputable laboratory to ensure that your seed is what you think it is and that it is fit for purpose.
Consider the cost of a crop failure that could arise after preparing your land, applying fertilizer and chemicals, irrigation water and the impact of sowing sub-standard or dead seed! While seed is a relatively low-cost input on a per hectare basis, it is an essential start that will set your paddock up for profit or loss.
Staff of AgEtal Pty Ltd Agricultural Testing laboratory
Australian Seed Federation
National Association of Testing Authorities (NATA)
International Seed Testing Association (ISTA)
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