II. 43. Telotrisomic plant for the short arm of chromosome 6 (Triplo 6S) in barley*.
Lindy Seip and T. Tsuchiya. Department of Agronomy, Colorado State University, Fort Collins, Colorado 80523, U.S.A.
* Supported in part by the USDA Research Grant 12-14-5001-265 to T. Tsuchiya.
The use of telocentric chromosomes has enhanced trisomic analysis in barley by allowing more precise location of genes. Centromere position can be determined using this method, as well as the arm of the chromosome on which a gene is located.
Current linkage maps do not show the position of the centromere on chromosomes 6 and 7 due to the lack of telocentric stock for these two chromosomes. Metcalfe (unpublished) found a telo for chromosome 6 but no information was published as to its morphological and cytological effects. Recently, however, the telocentric chromosome for the short arm of chromosome 6 (Telo 6S) has been found and studied.
Telotrisomics originated most frequently in the progeny of autotriploids and primary trisomics (Tsuchiya, 1971, 1972; Singh and Tsuchiya, 1977). In the present case, the cross of the Purple trisomic (Triplo 6) x Angustifolia heterozygous mutant produced several irregular plants, including one plant of 2n=23, one with a possible 2n=15 + 1 telo 6L (?) which did not survive to produce seed, and the 2n=14 + telo 6S.
Addition of a telocentric chromosome to a diploid complement varies in its effects: plants with telos for 1L, 2L, 3S, 4S and 5L have characteristics similar to the corresponding primary trisomics, while telo 1S more closely resembles the diploid (Tsuchiya, 1971; Singh and Tsuchiya, 1977).
The effect of telocentric 6S on plant morphology appears similar to the primary trisomic in some features and intermediate between the trisomic and the diploid in others. Measurements are given in Table 1.
Selfed progeny of the telo 6S plant included 20% monotelo, 70% diploid and one ditelo plant, indicating that there is transmission of the telo through both female and male gametes.
Limited meiotic study of the Triplo 6S plant showed 30% 7II + II and 70% 6II + 1III at metaphase I.
Further studies of the offspring of this Triplo 6S plant will be done to determine transmission rates, fertility, and additional meiotic information. Multiple marker stocks are being developed to facilitate the further mapping of chromosome 6.
References:
Singh, R.T. and T. Tsuchiya. 1977. Morphology, fertility and transmission in seven monotelotrisomics of barley. Z. Pflanzenzüchtg. 78:327-340.
Tsuchiya, T. 1971. Telocentric chromosomes in barley. Barley Genetics II: 72-81.
Tsuchiya, T. 1972. Cytogenetics of the telocentric chromosome of the long arm of chromosome 1 in barley. Seiken Ziko 23:47-62.
