IMPLICATIONS OF THE VARIANCE EFFECTIVE POPULATION-SIZE ON THE GENETICCONSERVATION OF MONOECIOUS SPECIES

The concept of variance effective population size [Ne-(v)] and other e xpressions are reviewed and described for specific sampling steps in g ermplasm collection and regeneration of monoecious species. Special at tention is given to procedures for computing the variance of the numbe r of contributed gametes [V(k)] to the next generation. Drift, as it o ccurs between generations, was considered to contain a component due t o the sampling of parents and a subsequent component due to the sampli ng of gametes. This demonstrates that drift, caused by reduction of se ed viability, damages the genetic integrity of accessions stored in ge rmplasm banks. The study shows how mating designs, such as plant-to-pl ant or chain crossings with additional female gametic control, can par tially alleviate this problem. Optimal procedures for increasing Ne-(v ) when collecting germplasm in the field are also discussed. The effec t 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.