Cytogenetical studies of two amphidiploids in the genus Oryza

Results of cytogenetic studies of 2 amphidiploids, O. glaberrima-sativa and O. sativa-breviligulata, are reported for the first time in the genus Oryza. All the 3 species have 2n=24 chromosomes. They were produced by treating buds of F₁ stubbles with 0.1% colchicine solution.The gigas effect of polyploidy was observed in both the amphidiploids. While the F₁ hybrids were completely sterile polyploidy resulted in 75.0% pollen fertility in both, with 47.0% spikelet fertility in O. glaberrima-sativa and 12.7% in O. sativa-breviligulata. Meiosis in the 2 amphidiploids was generally similar. Quadrivalents ranging from 0 to 12 were observed with 2 modes at 6IV and 8IV. The average number of IVs in the C₂ and C₃ generations ranged from 6.2 to 7.8. Segregation of characters was observed in the C₂ and C₃ generations in O. glaberrima-sativa. The C₂ plants segregated for spikelet size and hairiness. Of the 4 C₃ progenies studied, one segregated in the ratio 3:1 for the presence of anthocyanin pigmentation and hairiness of spikelets.The occurrence of IVs in high frequency and the segregation for differences in characters of the original parents noted in O. glaberrima-sativa are similar to the results reported from autotetraploids of O. sativa. It is suggested that these results point out to the rather close structural similarity in the chromosome complements of the 3 species and provide experimental evidence to the theory that the 2 cultivated species O. sativa and O. glaberrima have evolved independently from a common species O. perennis.