Phylogenetic relationships in the genus Oryza based on mitochondrial RFLPs

Restriction fragment length polymorphism (RFLP) of mitochondrial DNA in the genus Oryza was surveyed using 20 accessions including 11 species and a single endonuclease, EcoRI. RFLPs were visualized by Southern hybridization with eight rice mitochondrial DNA probes labeled non-radioactively with digoxigenin-dUTP. A total of 66 bands were obtained from all of the accessions. The total number of fragments per plant was higher in diploid A-genome species (an average of 35.3) than that in diploid B- and C-genome species and allotetraploid BC- and CD-genome species (an average of 28.2). The extent of the polymorphism in the RFLP patterns was various depending on the probes used. A diverse polymorphism was observed with most of the probes used, i.e. the cob, cox I, atp6, rrn18, rrn26 and atp9 regions, whereas, no polymorphic band was observed with a probe for the coxII region. The genus Oryza was separated into two large clusters. One cluster was comprised of A-genome species and the other cluster was comprised of B-, BC-, C-, and CD- genome species. Within A-genome species, the genetic variation was relatively high. Even in O. sativa species, the RFLP patterns of japonica and indica subspecies were clearly different from each other when three probes were used. However, there was no polymorphism between O. glaberrima and O. barthii. Within the genomes of B, BC, C, and CD, RFLP patterns were similar to each other and they showed a closer affinity except for O. minuta (BBCC). Within the BC genome species, the patterns of O. punctata and O. minuta were largely different from each other and separated into two different subclusters. Thus, the mitochondrial genomes of the two BC species (O. punctata and O. minuta) apparently evolved independently. Among CD genome species (O. latifolia and O. alta), the patterns of one accession, O. alta W0017 were largely different from those of the other accessions of CD genome species.