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CROP BREEDING, GENETICS & CYTOLOGY

Variance Effective Population Size under Mixed Self and Random Mating with Applications to Genetic Conservation of Species

^a Dep. Genetica, ESALQ-Univ. Sao Paulo, Cx.P. 83, 13.400-970, Piracicaba, SP, Brazil
^b Biometrics and Statistics Unit, International Maize and Wheat Improvement Center (CIMMYT), Lisboa 27, Apdo. Postal 6-641, 06600 Mexico, D.F., Mexico

jcrossa{at}cimmyt.mx

When collecting and regenerating genetic resources, genetic drift affects the representation of a population and occurs at two stages: when sampling the parents and when gametes are sampled from these parents. The variance effective population size [N_e(v)] quantifies genetic drift. In this study, a model for calculating N_e(v), that considers the two-stage sampling of mixed self and random mating species, is developed. For germplasm collection, as the rate of natural or artificial self-fertilization (s) increases, N_e(v) is reduced and becomes increasingly dependent on the number of seed parents (P) and is less influenced by the number of seeds sampled per parent (n/P). Female gametic control (GC) leads to higher N_e(v) than with random sampling of seeds (RS), but its effect is tangible only when n/P is small. For accession regeneration, maintaining accession integrity (the proportion of functional parents, u) at an adequately high level and adopting GC are required for assuring N_e(v) equal to or greater than the actual size of the accession (N_e(v) n). The importance of these two factors is enhanced as s increases. For arbitrary rates of selfing (0 s 1), under inbreeding equilibrium (IE) and with constant population size (n = N), N_e(v) can be adequately maintained through GC with a loss of 20% within accessions. For large sample size (n ), an accession loss of 33% can be recovered. For maintaining adequate N_e(v), artificial selfing followed by GC is more efficient than accession regeneration by natural reproduction. For achieving appropriate N_e(v)s, increasing the rate of self-fertilization in polymorphic materials makes collection more difficult but regeneration easier for minimal loss (20%) within accessions.

Abbreviations: GC, female gametic control • RS, random sampling • IE, inbreeding equilibrium • UI, unrestricted inbreeding

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