Nucleus and Breeders seed production

 The initial handful of seeds obtained from selected individual plants of a particular variety, for the purposes purifying and maintaining that variety, for the purposes and purifying and maintaining that variety, by the originating plant breeder and its further multiplication under his own supervision, or the supervision of a qualified plant breeder, to provide Breeder’s Seed constitutes the basis for all further seed production. The varietal purity of subsequently multiplied foundation, registered and certified seed largely depend upon the quality of the nucleus/breeder’s seed. Unless the nucleus/ breeder’s seed is of highest purity and quality the seed multiplied from it cannot be regarded as of satisfactory genetic purity. Unsatisfactory genetic purity, especially in cross pollinated crops, could ultimately severely affect the performance of a variety. It is therefore, of utmost importance that the nucleus/breeder’s seed is produced in such a manner that satisfactory genetic purity, identity and the other good qualities of seed are maintained.

Methods of maintence of nucleus and breeder’s seed in self fertilised crops

Methods of maintaining nucleus seed/breeder’s can be conveniently divided into the following two groups:

  1. Maintenance of newly released varieties
  2. Maintenance of established varieties

Maintenance of Nucleus Seed of Pre-released or Newly Released Varieties

The procedure outlined by Harrington (1952) for the maintenance of nucleus seed of pre-released or newly released varieties is described below:

  1. Sampling of the variety to obtain nucleus seed. New numbers, lines or selection which are highly promising, on the basis of performance in breeding nurseries and yield trials, should be sampled for seed purification. These samples provide a beginning for purifying new varieties and for possible increase and distribution to farmers. Not more than fifteen new varieties in any one crop at a station should be sampled in one year.

  2. Table examination of samples: The two hundred plants of each sample should be threshed separately and the seed should be examined in piles on the table. Discard any pile appearing obviously off type, diseased or otherwise unacceptable. The seeds of each two hundred plant samples or less is now ready to be sown in a variety purification nursery called as nucleus.

  3. Locating and seeding of nucleus: Each nucleus seed should be grown on clean fertile land at an experiment station in the region or in area in which this new variety could be grown, in the event of its release. The land must not have had a crop of the same kind in the previous year.

  4. Inspection of nucleus two-row plots and removal of off types: Throughout the season of growth, from the seedling stage until maturity, the nucleus plot should be examined critically. Differences in the habit of early plant growth, leaf colour, rate of growth, time of heading, height head characteristics and diseases reactions should be looked for. If a plot differs distinctly from the average in the preheading stages of growth, it should be removed before heading.

  5. Harvesting and threshing of nucleus; Each remaining plot, of which there should be at least 180 out of the original 200. should be harvested individually with a sickle and tied in a bundle. The total bundles of each nucleus should be labelled and stored until the current years yield rests for trials are obtained. The nucleus bundles of any new variety should be discarded, if it is found unworthy of being continued.

Later the seed should be cleaned in a fanning mill or by hand methods, the grain from each nucleus plot being placed in a pile on the seed table. The 180 or more piles of seed of one nucleus must be examined for approximate uniformity of seed appearance, and any pile, which appears to be off type discarded. All the remaining piles of the of seed should be masked together in one lot. This should treated with fungicide and insecticide, bagged, labelled and stored as "Breeder’s Stock Seed" for use in the next year. Breeder’s stock seed is the original purified seed stock of a new variety in the hands of the plant breeders.

Maintenance of Breeder’s Seed of Pre-released or Newly Released Varieties

The following steps are involved in the maintenance of breeder’s seed.

  1. Breeder’s stock seed from the nucleus should be sown on the clean, fertile land, which did not grow a crop of the same kind in the previous year. The space required for the seeding the breeder’s stock is about 1.2 ha in the case of wheat and as much as 3 ha in the case of transplanted rice.

  2. The field should properly isolated.

  3. The best farm procedures should be used in the sowing, raising and harvesting of breeder’s stock.

  4. It should be produced at the experiment station in the area in which the new variety has been bred.

  5. The seeding should be done in such a way as to make the best use of the limited amount of seed available and to facilitate roguing. The row spacing should be sufficient to permit examination of plants in rows for possible mixture or off types.

  6. Roguing: All plants not typical of the variety should be pulled and removed. There should be very few plants to rogue out if the previous years nucleus breeder’s stock seed was well protected from natural crossing and careful roguing was done and there were no impurities during cleaning etc. The rouging should be done before flowering, as was done for the nucleus/breeder’s stock seed.

  7. Harvesting the breeder’s stock: In the breeder’s stock is harvested and threshed, the equipment used must be scrupulously clean and free from seeds of any other varieties. This cleanliness should be extended to cards and bags as well as threshing machine it self. The seed should now be about 99.9 per cent pure as to variety. These breeder’s seed is ready now for increase of foundation seed. A portion of this breeder’s seed should be retained by the breeders to sown a continuation breeders seed of the variety.

Maintenance of breeder’s seed of established varieties: The breeder’s seed of established varieties could be maintained satisfactorily by any one of the following methods)

a) By raising the crop in isolation. The breeder’s seed of local varieties could be maintained by growing them in isolated plots and by very rigorous roguing during various stages of crop growth, where the various plant characters are observable. The method of handling the breeder seed crop is the same as described earlier for breeder’s seed of newly released varieties.

B) By bulk selection. The genetic purity of established varieties could be satisfactorily improved by bulk selection. In this method 2,000 to 2,500 plants typical of the variety are selected, harvested ,and threshed separately. The seeds from each plant are examined and any pile which shows any obvious off-types, or otherwise appears dissimilar, are discarded. The remaining piles of seed are bulked to constitute the breeder’s seed. The other practices of handling remains the same.

Carry-over Seed

The breeder must carry-over at least enough seed to safeguard against, the loss of variety if there is a complete failure during the foundation seed multiplication phase. In addition,the breeder should further safeguard variety by arranging to have a portion of the seed originally released stored under the ideal conditions.  


Ag.
Technologies
(Seeds)