| Mapping of the complex T. sphaerococcum locus
Dalmir SINGH Genetics Division, Indian Agricultural Research Institute New Delhi - 110012, INDIA Triticum sphaerococcum Perc. (2n = 6x = 42) is characterised by short culms, dense spikes and small spherical grains. Sphaerococcum phenotype is reported to be controlled by a single gene (Ellerton 1939; Singh 1946). Sears (1947) showed that sphaerococcum (s) gene was located on chromosome 3D (XVI) which in double dose produces the sphaerococcum effect but in single dose it is relatively ineffective. It was also suggested that chromosome 3D (XVI) of T. aestivum increases apike and culm length, particularly between the dosage 0 and 1. On the basis of mutation studies, Swaminathan et al. (1963) concluded that sphaerococcum factor was not a null (c.f. Ellerton) but a functional unit that can be broken up into small mutons. Koba & Tsunewaki (1978) mapped the gene s on the long arm of chromosome 3D with a genetic distance of 5.0% between the locus and the centromere. Prabhakara Rao (1971) reported that the sphaerococcum gene s is located either very close to centromere on 3DAlpha (long arm) or it is on 3DBeta (short arm) of chromosome 3D. The long arm of chromosome 3D besides possessing the sphaerococcum gene also carries a dominant gene R1 for red seed colour in wheat var. Chinese Spring (sears 1954). Prabhakara Rao (1973) reported that the R1 gene was located distally. The present investigation was undertaken to resolve the intricacies related to the complex character of sphaerococcum and the location of red grain colour locus in T. sphaerococcum. Materials and Methods Monosomic 3D of var. Pb. C 591 (white seeded) and ditelocentric for 3D long arm (3D L) of var. Chinese Spring (red seeded) were crossed with a red seeded var. of T. sphaerococcum. All the F1 plants were raised in the field. Chromosome number and meiotic cofigurations were studied at first meiotic metaphase of all the F1 plants and their morphological characters were recorded. Seeds were harvested from all the F1 plants and sown separately in the field for raising F2 generation. All the F2 plants were pulled out from the field and data were recorded on morphological characters. Contrasting characters between T. sphaerococcum and T. aestivum were taken as follows:
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