Characterization of four induced chromosome deficiencies in rice (Oryza sativa L.)

Four rice (Oryza sativa L.) deficiencies, involving chromosomes 4 (Df4), 8 (Df8), and 11 (Df11-1, Df11-2), were studied. The deficiencies were induced by means of the pseudodominance technique, i.e., strains carrying one or more recessive marker genes were fertilized with irradiated pollen of a strain carrying normal alleles at corresponding loci. No characteristic morphological features were found in the deficiencies, as compared with the normal F1 plants in the progeny. The deficiencies showed high or complete seed sterility. Genetic and cytological studies indicated deficiencies in chromosomes 4, 8, and 11. The fragment chromosomes in Df4, Df8, and Df11-2 were short, possibly being derived from the heterochromatin regions of the chromosomes, including kinetochores, and the fragment chromosome in Df11-1 was long, with about 75% of the long arm missing. At metaphase I, Df4, Df8, and Df11-2 showed only the chromosome configuration of 11 II (bivalents) + 2I (univalents), and Df11-1 only that of 12 II. It seems that the short fragments tend to stay as univalents in meiosis, probably because of their shortness. On the other hand, long fragments act as normal chromosomes and associate with their homologues. The deficiencies were not transmitted to the progenies, although only a few offspring were examined. By using the induced deficiencies Df4 and Df11-1, two morphological marker genes, lg (liguleless) and la (lazy growth habit), were located on the long arm of chromosomes 4 and 11, respectively. This is the first report in rice utilizing induced chromosome deficiencies to locate a gene on a specific arm of a chromosome. The use of induced deficiencies for studying the structure of the rice genome is discussed. Key words : rice, chromosome, deficiencies, cytology, transmission.