B. Report on Chromosome Numbering System

As reported in RGN2, the chromosome numbering system proposed by Shastry et al. (1960) was accepted by Rice Genetics Cooperative. In this system, the chromosomes are numbered according to the decreasing order of their length at pachytene stage of meiosis. This nomenclature was confirmed by Kurata et al. (1981). Two primary trisomic series have been established and utilized for associating linkage groups with respective chromosomes. The extra chromosomes of the Indica trisomic series established at IRRI (Khush et al. 1984) were identified following the nomenclature of Shastry et al. (1961). The extra chromosomes of the Japonica trisomic series established at Kyushu University (Iwata and Omura 1984) were identified following the nomenclature of Kurata and Omura (1978) where chromosomes are numbered according to their somatic length. Because different nomenclatures have been used to identify the trisomics of the two series, differences in the identifications naturally exist. In order to reconcile these differences, Dr. G.S. Khush invited Dr. N. Kurata and Dr. R.J. Singh to IRRI to jointly examine the Indica trisomic series at pachytene stage of meiosis. Drs. Kurata and Singh visited IRRI from June 5 to 27, 1986 and examined the trisomics. On the basis of their observations the identification of 6 trisomics (Nos. 1,2,5,7,9 and 10) were confirmed. However, there was not enough time to confirm the remaining trisomics. Dr. H.K. Wu of the Institute of Botany, Taipei, is now examining the remaining trisomics. His observations will be reported in RGN4. -(G.S. Khush)


References

Iwata, N. and T. Omura, 1984. Studies on trisomics in rice plan (Oryza sativa L.) 6. An accompolishment of a trisomic series in japonica rice plants. Jpn. J. Genet. 59: 199-204.

Khush, G.S., R.J. Singh, S.C. Sur and A.L. Librojo, 1984. Primary trisomics of rice: origin, morphology, cytology and use in linkage mapping. Genetics 107: 141-163.

Kurata, N. and T. Omura, 1978. Karyotype analysis in rice. I. A new method for identifying all chromosome pairs. Jpn. J. Genet. 53: 251-255.

Kurata, N. and T. Omura and N. Iwata, 1981. Studies on centromere, chromomere and nucleolus in pachytene nuclei of rice, Oryza sativa microsporocytes. Cytologia 46: 791-800.

Shastry, S.V.S., D.R.R. Rao and R.N. Misra, 1960. Pachytene analysis in Oryza. I. Chromosome morphology in Oryza sativa. Ind. J. Genet. Plant Breed. 20: 15- 21.