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.