Mating System and Genetic Structure of Natural Populations in Wild Rice Oryza rufipogon*

Abstract

Abstract Variation in mating system in the common wild rice Oryza rufipogon was studied in relation to life‐history traits to examine its effect on the genetic structure of natural populations. Results of general survey in Asian populations and of a detailed population study carried out in Thailand are presented. Estimated outcrossing rates of Asian wild rices ranged from 5 to 60%, though cultivated rices are predominantly selfing. Interpopulational comparison showed mating system is associated with life‐history traits, resulting in the differentiation into two ecotypes; predominantly selfing annuals having high reproductive effort and mixed‐mating perennials having low reproductive effort. Resource allocation to pollen production vs. seed production (pollination effort) proved to be correlated with outcrossing rate. Isozyme study showed that both mating system and reproductive system jointly influence genetic structure of populations such as the level of intrapopulational variability and the extent of interpopulational differentiation. Evolution of selfing in this plant group might have been promoted by selection for seed propagation which was brought by environmental change and/or habitat disturbance.