Population Structure and Functional Diversity of Rice Landraces: A Review

Rice landraces or local varieties that have remained in cultivation on-farm are embedded within their agroecological and cultural environment. Rice landraces are genetically diverse, but with a variation that can be well structured, not random. This review examines the population structure and functional diversity revealed in the rice germplasm acquired from farmers in recent decades. Sizable areas of local varieties are found in parts of Asia with distinctive agroecological environment and cultural heritage. A tally of variety names provides a first approximation of diversity, a frequency distribution of the varieties describes a basic structure of diversity in an agroecosystem. Genetic variation is detectable by microsatellites analysis or expressed in specific functional traits, at various organizational levels of the population, even among those exhibiting uniform appearances. The population dynamics of genetically diverse landraces perpetuated by many farmers are shaped by variations in the bio-physical environment and management practices, but those relying on one or two farmers for their maintenance face a risk of extinction. Diversity in widely grown varieties may either be within the farmer’s seed cache, or among populations of the same variety maintained by different farmers. Local rice varieties or landraces continue to play a crucial role in rice farming, the economic value of some is enhanced by their unique grain quality features. Genetically diverse rice landraces that either contribute towards meeting the household’s rice requirement or those that have become commercially successful, also provide an important service in the in situ conservation of germplasm.