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Mapping the gene R1 for red seed colour on chromosome
3D of wheat M.V. PRABHAKARA RAO Biology & Agriculture Division, Bhabha Atomic Research Centre, Trombay, Bombay-85, India Chromosome 3D (formerly XVI) carries the dominant gene R1 for red seed color in the common wheat variety, Chinese Spring (SEARS 1944). It was further shown that the alpha (right) arm of 3D carries this gene (SEARS 1954). However, the crossover distance of the gene from the centromere has not been ascertained. In the present study, a ditelocentric line for the alpha arm of 3D was used to determine the location of the gene. The substitution line, sphaerococcum-3D (white seeds) was crossed to Chinese Spring ditelo-3D (alpha). The F1 plants (20II+1 hetII) were red grained. Segregation occurred for both seed color and ear type in the F2 generation. Out of 260 F2 plants, 129 were of sphaerococcum type and 131 of aestivum type indicating that there is no significant male transmission of telocentric 3D (alpha) in competition with the entire 3D. Among the sphaerococcum type plants, 86 had red seeds and 43 white seeds. Of the 131 aestivum type plants, 97 had red seeds and 34 white seeds. The segregation data give a statistically good fit to the expected ratio (3 : 1 : 3 : 1) for independent assortment of the S and R1 genes (X2=4.83; d.f.=3; P=0.25 to 0.10). PRABHAKARA RAO (1971) found that the sphaerococcum gene s is most probably located on the beta (left) arm of 3D. In the F1 plants of the present experiment, pairing and crossing-over would be limited to the alpha arm of 3D. So, the crossover distance between the genes R1 and S would correspond to the distance of the R1 gene from the centromere. Since the sphaerococcum and red seed genes segregated independently of each other, it can be concluded that the R1 gene is located 50 or more crossover units from the centromere i,e., it has a distal location on the alpha arm of 3D. Literature cited SEARS, E. R. 1944. Cytogenetic studies with polyploid species of wheat. II. Additional chromosomal aberrations in Triticum vulgare. Genetics 29 : 232-246. SEARS, E. R. 1954. The aneuploids of common wheat. Mo. Agr. Exp. Sta. Res. Bul. 572 : 59. PRABHAKARA RAO, M. V. 1971. An attempt to map the sphaerococcum gene on chromosome 3D of wheat. EWAC Newsletter 3 : 64. (Received Sept. 28, 1972) |