Origins of Cultivated Rices

Recent studies on wild rices related to the two cultivated species of rice, can be availed of to understand their origins. For this purpose, it is essential investigate jointly the antiquity, the center of origin, the taxa occurring in that center along with the genetic processes involved in their evolution. Since Oryza glaberrima and O. sativa had probably independent parallel origins they must have a common ancestor which could only be the long anthered perennial species represented by O. perennis Moench emend Sampath, in Asia. Since the oldest trace of rice is from Central Thailand, O. sativa must have originated in that zone and wild rice taxa not found in that zone can be excluded from its ancestry. The African perennial species is allogamous and heterozygous and inbreeding releases variability giving scope for selection. In Asia, it is conjectured that natural crossing between different populations of O. perennis followed by inbreeding gave scope for selection for increased productivity through annual forms having compact panicles and heavier grains.