What is Nucleus Seed
It is the initial amount of pure seed of improved variety or parental lines of a hybrid produced under supervision of the plant breeder who has evolved that variety of hybrid. The nucleus seed is genetically cent percent pure and does not contain other physical impurities. The nucleus seed is produced strictly under isolation so as to avoid both genetically and physical contamination. Nucleus seed should retain original vigour of the variety or parental line.
About 500 to 1000 individual plants (IPS) which are vigorously growing and healthy are selected from the nucleus bulk-plot before flowering starts. Observations are recorded on each IPS for all the important morphological characters viz plant height , stem colour, hairiness, pigmentation, growth habit, colour and shape of different plant parts, days to flowering and maturity. The IPS which are a) Off types or b) affected by seed borne disease are removed and discarded. The individual IPS selected are harvested and threshed separately and their seed produce is dried, cleaned and stored in separate cloth bags or paper bags with proper labeling. The seed of each IPS is examined for seed characters and for oil content if it is an oil seed crop. The seed produce of each IPS is weighed. The seed yield per IPS , 1000 (or 100) seed weight and data on other quantitative characters more than mean+ S.E are retained as source for raising next year’s nucleus seed and of rejected IPS is bulked with general produce.
Seed produce of IPS selected during preveious year is grown as plant to row progeny during subsequent year. Observations are recorded in all the plants form each IPS for important characters. The IPS which shows off types are discarded and harvested before flowering so as to avoid contamination. 500 to 1000 vigorous growing healthy and true to type IPS are selected from remaining progeny rows and their produce is subjected to harvesting, processing and statistical analysis as described earlier. The produce of selected individual (IPS) is utilized for raising plant to row progenies in the next year.
The selected plant to row progenies are harvested and processed in individual bulks. Their seed is examined, weighted and subjected to statistical analysis for mean and S.E. The progenies which show seed yield more than mean+ S.E are bulked together which becomes source for breeder seed.
In case of cross pollinated crops it is essential to self IPS as well as each plant from every bulk before flowering for preveious cross pollination.