IMPLICATIONS OF THE VARIANCE EFFECTIVE POPULATION-SIZE ON THE GENETIC CONSERVATION OF MONOECIOUS SPECIES

The concept of variance effective population size [Ne-(v)] and other expressions are reviewed and described for specific sampling steps in germplasm collection and regeneration of monoecious species. Special attention is given to procedures for computing the variance of the number of contributed gametes [V(k)] to the next generation. Drift, as it occurs between generations, was considered to contain a component due to the sampling of parents and a subsequent component due to the sampling of gametes. This demonstrates that drift, caused by reduction of seed viability, damages the genetic integrity of accessions stored in germplasm banks. The study shows how mating designs, such as plant-to-plant or chain crossings with additional female gametic control, can partially alleviate this problem. Optimal procedures for increasing Ne-(v) when collecting germplasm in the field are also discussed. The effect of different female and male gametic control strategies on Ne-(v) is considered under several situations. Practical examples illustrating the use of V(k) and Ne-(v) expressions are given.