Seed testing plays an integral role in the production and marketing of high quality seed by minimising the risk of sowing seed which does not have the ability to produce a worthwhile crop.
Historically seed testing dates back to 1869 when Professor Friedrich Nobbe founded the first seed testing laboratory in Saxony. This was rapidly followed by laboratories in Austria, Hungary, Belgium, Denmark, Russia and the USA. In 1876, Nobbe published his famous “Handbook on Seed Testing”, the forerunner of the “International Rules for Seed Testing” which now form the basis of seed testing throughout most of world. “The Rules”, as they are popularly known, are published by the International Seed Testing Association (ISTA) which was founded in 1924.
The first Australian seed testing laboratory was established by the NSW Department of Agriculture around 1909-1910 and was followed by laboratories in all other states. At the present time, there are five ISTA-accredited seed testing laboratories in Australia.
Why test seed?
An adequate plant population is essential for efficient agricultural production and sowing poor quality seed will usually result in poor crop establishment and reduced yields. As the cost of seed usually represents a relatively small proportion of the overall cost of crop production, the use of high quality seed is a wise investment.
Seed testing plays an important role at many stages from harvest through to sowing and information provided on a statement of seed analysis can assist with decisions such as:
- Is the seed lot worth processing or would it be better to sell it for stock feed?
- Does the seed lot comply with legislative or contractual requirements or will it require further processing?
- Is the seed lot likely to store well? All seed deteriorates in storage but high quality seed is more likely to carry across to the next season.
- Is the seed lot worth buying? Does it meet the buyer’s requirements?
- What sowing rate will I need to use to achieve an adequate plant population?
The ISTA Rules form the basis for testing conducted in most Australian seed testing laboratories. The tests performed most frequently are those which measure the germination capacity, physical purity and moisture content of the seed lot. It must be noted however, that the results of the tests will be indicative of the quality of the entire seed lot only if they are carried out on a sample drawn in such a way as to be representative of the entire seed lot. See article on accurate sampling.
Germination
A laboratory germination test measures the proportion of seed which is capable of producing normal seedlings – i.e those seedlings which show the ability to establish and produce useful plants under favourable conditions. The test will also report the proportion of abnormal seedlings, fresh and/or hard seeds and dead seeds.
Germination tests are carried out under controlled, standardised conditions to enable the comparison of different seed lots or the performance of the same lot over a period of time.
Purity analysis
A purity analysis determines the proportion of pure seed, other seed and inert matter in the seed lot.
Pure Seed is defined as the species nominated on the sample. It includes intact seeds even if they are undersized, immature, shrivelled, diseased or have sprouted. Broken and damaged seeds are included as Pure Seed provided that they are larger than half their original size. The purity analysis does not consider the potential germinability of the seed.
The Other Seeds fraction will include the seeds of all other species present in the sample being analysed. The seeds will be identified as fully as possible – usually to species level but sometimes it is not possible to identify the seed beyond its genus.
Inert Matter comprises all of the extraneous matter in the sample and includes plant matter, soil, sand, stones, fungal bodies and all matter and structures not specifically classified as pure seed or other seed.
Examination of the analysis results will reveal whether or not the seed lot in question meets the requirements of a certification scheme, contractual agreement or individual buyer; contains seeds of any species which may have been declared noxious or prohibited in a particular region or market; or requires further processing to improve the overall quality of the seed lot.
Moisture Content
The two most important external factors affecting seed longevity are the temperature and relative humidity of the environment in which the seed is stored and these two factors are interdependent. Seed is hygroscopic and its moisture content will come to equilibrium with the storage environment, so seed stored under conditions of high relative humidity will take up moisture from that environment.
Seed held at high moisture content will deteriorate far more rapidly than seed held at low moisture content. A basic “rule of thumb” is that “except in extreme conditions, for each 1 percent drop in moisture or 5 degree C reduction in temperature, the storage life of seed is doubled.” (Harrington J F 1960 – Thumb Rules of Drying Seed)
The two most important external factors affecting seed longevity are the temperature and relative humidity of the environment in which the seed is stored and these two factors are interdependent. Seed is hygroscopic and its moisture content will come to equilibrium with the storage environment, so seed stored under condition of high relative humidity will take up moisture from that environment.
A moisture test conducted by the seed testing laboratory will indicate whether it is necessary to dry the seed lot further before placing it into storage, or may be used to indicate if appropriate seed moisture content is being maintained in a particular storage environment.
Other tests
Seed testing laboratories also conduct a number of other tests on seed. These include the tetrazolium test (a rapid indicator of seed viability), various seed health tests and species and variety tests, such as the fluorescence test to determine the level of annual ryegrass in samples of perennial ryegrass.