Seed certification and the requirement for plot testing

Seed certification schemes, controlled pedigree systems and rules and regulations for seed growing and distribution are all aimed at maintaining cultivar authenticity and purity of the seed (Hampton, 1 99 1 ). The detennination of cultivar purity was developed to assess the quality of the cultivar before the seed is sown (Baekgaard,

1 964; ISTA, 1 993).

The word "quality" when linked with seed has several meanings. According to

Kelly (1973), these can best be made clear by posing three questions:

1 . Is the seed of the right cultivar?

2. Is the seed healthy and capable of vigorous germination?

3. Is the seed unadulterated by weed seed, other crop seeds and inert matter?

Seed quality was defined by Esbo ( 1980) as "a collection of seed properties which are considered to be important for the value of seed for sowing purposes". One of these is cultivar purity. A high standard of cultivar purity can be assured by controlling the production of seed. Although absolute control over all of the operations involved is not possible, control is exercised as far as is practical in two ways (Thompson, 1979):

1. By ensuring that seed is multiplied in such a way as to minimize the risk of mechanical and genetic contamination.

that the cultivar can be identified. This can be done by checking plants from ·

which the seed is to be harvested.

Seed certification is primarily for the purpose of assuring trueness to cultivar and purity. The first certification schemes were started to improve the assurance of trueness to cultivar, and were based on field inspection only. For the check of trueness to cultivar and cultivar purity, field inspection was complemented by

check plot tests (Esbo, 1 980).

Seed certification under the OEeD scheme is based on trueness to cultivar (i.e. lots are certified true to the cultivar's characters, including any variation as described by the breeder), and require post control plot tests (Thompson 1979). The main object of the post control plot test is to ascertain that the scheme is operating satisfactorily, and to detennine that the cultivar's characters have remained unchanged (OEeD, 1968). According to the OEeD scheme the plot tests are conducted for the following main purposes (DEeD, 1968):

1. To check that a breeder' s or basic seed lot is true to name, and that as a result of maintenance over a period of years, the cultivar is not showing any "shift" in expression of its distinguishing characters. This type of test requires objective measurement of individual plants in a spaced plant test in comparison with the standard sample (which may be from certified seed or blend of such seed, basic seed or even breeders' seed as appropriate).

2. To check that a particular certified seed lot is true to the cultivar name and has not been mixed with other cultivars or otherwise altered during multiplication. Such tests can normally be performed in row or sward plots in comparison with basic seed lots of known satisfactory cultivar authenticity.

Verification of stability of plant morphological chal'acters in the field and the glasshouse

or more generations to authenticated basic: seed of the cultivar. Satisfactory conditions for the production and processing of basic seed and certified seed must be ensured and verified by field inspection and post control plot test testing.

Post control testing is nonnally conducted within an independent organisation such as a research station or agricultural college, where there is suitable land and adequate equipment. Therefore, characteristics of growing plants can be observed by skilled workers at the optimum time. This provides unbiased opinion of the quality of the seed under test, and also access to skilled personnel and equipment in such organizations (Hampton, 1 9 9 1). Plants in check plots are planted in such a way that the cultivar characters are emphasised (eg. by spacing the plants).

The characters recommended by OEeD (1968; 1988) for assessment of trueness of cultivars varies from species to species. The following characters are recommended to be recorded from individual plants in the plot test for cultivar certification of lucerne seed lots moving in international trade:

1. Height of plant in the spring, when the first sign of growth appears on the earliest cultivar in the trial.

2. Height of plants one month later. 3. Growth during the month ( 1 -2).

4. Length and width of leaflet in mm (at early flower bud stage on 4th leaf below bud, both measurements on the terminal leaflet). The combination of leaflet length and leaflet width will sometimes serve to distinguish between cultivars having the same or similar leaflet length.

5. Angle of growth at early flower bud stage.

6. Date of flowering, when three florets are open.

7. Height of longest stem at flowering to top of inflorescence.

8. Flower colour; each plant can be classified according to the colour: blue, violet, variegated, white or yellow.

Note: Each cultivar is cut after all plants of the latest cultivar in the trial have flowered.

9. Recovery height, three weeks after cutting.

10. Recovery height, six weeks after cutting.

Note: All cultivars are cut again six weeks after the cutting at 10.

11. Recovery height , three weeks after second cutting

12. Disease observations (eg. resistance to Pseudopeziza medicaginis).

13. Percentage of plants killed in winter.

In addition, other characters such as plant colour and the growth habit (erect, semi erect, medium), are also recommended by UPOV ( 1 988) for testing uniformity, distinctness and stability (DUS test) of lucerne cultivars.

As discussed in the following sections, some of the morphological characters and physiological behaviour of lucerne plants may be influenced by environmental factors and also by management systems. This suggests that two populations of plants which are, for example, different for a morphological character at one site, may not be necessarily different if the plants are grown under different sets of environmental conditions. This appears to be a potential problem associated with DUS testing on the basis of morphological data from plot testing .

In addition, as the OEeD recommended characters for lucerne plants are based on experiments in England, it has been suggested by OEeD that where climatic conditions are different, it is necessary to determine which characters should be used for plot testing (OEeD, 1 968). This implies that the usefulness of a particular morphological character for identification of cultivars might vary from country to country, or even within a country. This suggests that finding the most stable and highly discriminating morphological and physiological characters is the key for performing successful plot tests for certification of the seeds being produced.

Verification of stability of plant morphological characters in the field and the glasshouse