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

Provided that the seed collected from each plant in natural populations of a species is kept separate from that of every other, a rough estimate of the heritability of a quantitative character can be obtained from the natural progenies raised from this seed in a randomised evaluation 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 visited in a population, when species set all of their seed by cross-fertilisation, by taking several seeds from each. We show that it is not worth taking more than eight seeds from each plant and that, in the absence 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 investigated the minimum sample size for genetic conservation in the narrow sense, 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 plants if material from a number of populations is evaluated in a single trial. Finally, we draw attention to the possibility of regenerating seed from a composite population founded by raising one plant from the seed taken from each plant of the original collection, as an alternative to regenerating the seed of each accession independently from that of every other.