GENETICS OF GENETIC CONSERVATION .2. SAMPLE-SIZE WHEN COLLECTING SEEDOF CROSS-POLLINATING SPECIES AND THE INFORMATION THAT CAN BE OBTAINEDFROM THE EVALUATION OF MATERIAL HELD IN GENE BANKS

Provided that the seed collected from each plant in natural population s of a species is kept separate from that of every other, a rough esti mate of the heritability of a quantitative character can be obtained f rom the natural progenies raised from this seed in a randomised evalua tion trial; a knowledge of the reproductive biology of the species can help to make this estimate of the heritability of the character more precise. The theory employed in this evaluation procedure can be used to investigate the possibility of reducing the number of plants visite d in a population, when species set all of their seed by cross-fertili sation, by taking several seeds from each. We show that it is not wort h taking more than eight seeds from each plant and that, in the absenc e of precise information about the paternity of this seed, it might be better to follow the general recommendation of Lawrence et al. (1995) , by taking only one seed from each of the 172 plants. Having investig ated the minimum sample size for genetic conservation in the narrow se nse, we broaden discussion to consider sample size for evaluation and regeneration. It is pointed out that it is not necessary to take more than about ten seeds from each of 20-30 randomly chosen plants in each population visited and;that it is possible to reduce this number of p lants if material from a number of populations is evaluated in a singl e trial. Finally, we draw attention to the possibility of regenerating seed from a composite population founded by raising one plant from th e seed taken from each plant of the original collection, as an alterna tive to regenerating the seed of each accession independently from tha t of every other.