Relationships between linkage groups and cytologically identifiable chromosomes of rice

Abstract

Twelve linkage groups of rice have been established. The 12 chromosomes have been identified and numbered according to decreasing order of length either at the pachytene stage of meiosis or in somatic cells. Primary trisomic series have been established by several workers. Extra chromosomes of the trisomic series of IRRI, Los Baños, and CRRI, Cuttack, have been identified according to the numbering system of pachytene chromosomes, and those of the University of Kyushu series according to the numbering system of somatic chromosomes. The IRRI trisomic series and the Kyushu trisomic series have been utilized for associating linkage groups with respective chromosomes and for testing the independence of different linkage groups. Linkage groups corresponding to each of the 12 chromosomes were identified both at IRRI and at Kyushu. There is a need to adopt one of the two chromosome numbering systems universally. Future investigations should aim at determining the arm locations of markers and the positions of centromeres on the linkage maps. Series of tertiary, secondary, and telo-trisomics are needed for this purpose. The exact location of the marker genes on the cytological map can be determined by radiation induced deficiencies.