The origin, identification, and plant morphology of five rice monosomics

Five different monosomics of rice (Oryza sativa L.) were obtained by treatment of pollen with gamma irradiation, as a by-product of attempts to determine the cytological loci of certain marker genes, i.e., mature pollen carrying normal alleles at all loci was given gamma rays and used for pollinating strains that were homozygous for recessive marker genes. The monosomics showed distinguishable morphological features and had complete seed sterility. Cytological studies revealed that one monosomic was tertiary, the others primary. The tertiary monosomic was related to chromosome 10. Two primary monosomics for chromosomes 10 and 11 were identified. At metaphase I, the tertiary monosomic showed the chromosome configurations 1 III + 10 II, 11 II + 1 I, and 10 II + 3 I, and all primary ones showed the configuration 11 II + 1 I. All five monosomics showed very poor crossing ability and were not transmitted to the few progenies observed. A few trisomic plants were found in the progenies of a cross between monosomic and normal pollen in one monosomic. This is the first time that many monosomics in rice have been characterized. This information will be useful in studies of rice aneuploidy and cytogenetics. Key words : rice, monosomics, morphology, cytology, transmission, trisomics.