Twenty-five populations of Oryza rufipogon from China and 144 cultivars of Oryza sativa were selected for this study. Based on the DNA fragment of Ehd1-4 and subspecies-specific sequence-tagged site markers in different chromosomes, intraspecific differentiation in O. rufipogon from China was analyzed. The introgression from O. sativa to O. rufipogon was also analyzed based on simple sequence repeat markers. The results revealed that the DNA fragment of Ehd1-4 could distinguish the O.
Controlled and natural hybridization between cassava and wild relatives does occur. Barriers within the genus appear to be weak due to recent evolution of the group. All Manihot species examined cytogenetically have a chromosome number of 2n = 36. However, they behave meiotically as diploids. The weak interspecific barriers have led to an extremely heterozygous gene pool that may begin a sequence of hybridization followed by speciation. Introgression from cassava into a number of wild species (M. neusana, M. alutacea, M. reptans and M.