This is a guide to the techniques required to produce pure and vigorous seed from varieties of this cross - pollinated crop. Multiplication rates , through sequential breeder,foundation, and certified seed stages, are high : 3 kg of seed are adequate for sowing 1 ha, subsequently producing 1 tonne of clean seed. Nucleus seed plots (stage 0 ), sown for regeneration once every 4 years, should be effectively isolated . They should be between 0,1 and 0.2 ha in size , and contain at least 3000 plants . Plots of breeder seed (stage 1) should similarly be well isolated , and rigorously inspected and rogued, and not more than 1% of off - types should be permitted at final inspection. Plot sizes are normally between 0.1 and 0.5 ha, according to how much certified seed is required , using a conservative multiplication factor of X200. At the end of the foundation seed stage (stage 2) , through protective perimeter planting , inspection, and rogueing, off - types should be less than 2%. At the final certified seed stage(3) , the permitted level of off - types is 5%. Six points of guidance are given for extension staff to pass on to farmers who (as may be expected) attempt to multiply their own improved seed.