Genetic changes of populations that experience drastic size decline is a central issue in conservation genetics. The genetic changes of small populations are tightly associated with their mating pattern, because small populations generally have increased selfing and local inbreeding rates, leading to the effect of genetic drift and loss of genetic variability. Oryza rufipogon Griff. is agriculturally the most important but seriously endangered wild rice species due to rapid decline of population size. To better understand how mating system can be used for species conservation, outcrossing rate, genetic variability at maternal and seedling phases in a small population were examined at seven polymorphic microsatellite DNA loci. Thirty six reproductive individuals and 601 progenies from 20 open-pollinated seed families were measured. The family outcrossing rates varied among plants with an average of 0.318. A high correlation of matings was revealed and about 50% offspring shared the same paternal and maternal genitors, indicating a mixed mating system in the Oryza population. The level of genetic diversity in progeny population was higher than that in maternal population. The maternal population showed significant heterozygote excess, suggesting the selection advantage of heterozygotes. In contrast, significant heterozygote deficit occurred in progeny population, which might have been caused by the increasing of inbreeding in declining population. These results suggest that expanding population size is of significance for in-situ conservation of Oryza rufipogon.
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