BGN 10: Further studies on the telotrisomic plant for the short arm of chromosome 6, Triplo 6S, in barley BARLEY GENETICS NEWSLETTER, VOL. 10, II. RESEARCH NOTES
Seip and Tsuchiya, pp. 64-65

II. 27. Further studies on the 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 Research Grant No. 12-14-5001-265 from USDA/SEA to the junior author.

Morphological and limited meiotic information for the telotrisomic plant, Triplo 6S, were reported in BGN 9 (Seip and Tsuchiya, 1979).

Further data concerning meiotic behavior and transmission rates of the telocentric chromosome 6S have been obtained and are reported here. At the diakinesis stage of meiosis, the satellite chromosomes 6 and 7 associate with the nucleoli. One mean of definite identification of telocentric 6S is its association with the nucleolus. Telo 6S was seen to associate with the nucleolus as a univalent (7II + 1I) in 52.36% of the sporocytes and as a trivalent (1III + 6II) in 47.64% of the sporocytes. The high value of univalent formation may be partially due to artifacts of preparation, causing broken trivalents. At metaphase I, Telo 6S was found as a univalent in 24.18% of the sporocytes and as a trivalent in 75.82%. The most common types of trivalents were ring-and-rod and tandem chain.

The telocentric chromosome remained at the equatorial plate as a laggard in 13.24% of the anaphase I sporocytes. This value is quite comparable with that found by Singh (1974) in the other seven telotrisomic types (16.27%).

Transmission rates of the telocentric chromosome were determined for three conditions: self-pollinated and reciprocal crosses between the Triplo 6S plant and S.E. 16 diploid. In selfed F2 populations, the transmission was 40.87%. Using the Triplo 6S plant as a female, the female transmission rate was 48.0%. Using the Triplo 6S plant as male, the transmission rate was 10.53%. These three values exceed those determined by Singh and Tsuchiya (1977) for the average of seven telotrisomics and by Tsuchiya (1972) for Triplo 1L. Especially high is the male transmission of 10.53%, compared with 1.2% for the average of seven telotrisomics (Singh and Tsuchiya, 1977). This high male transmission may be due to time of pollination, condition of the plants, and the behavior of the Triplo 6S pollen. Although no ditelotetrasomic plants were found in this study, it should not be difficult to obtain such a plant with these high male transmission rates.

The next step in this work is to cross the Triplo 6S plants with several mutant marker lines such as uc2, o and gs4 to more accurately map these genes and eventually to locate the centromere on the genetic linkage map of chromosome 6.

References:

Seip, L. and T. Tsuchiya. 1979. Telotrisomic plant for the short arm of chromosome 6 (Triplo 6S) in barley. Barley Gen. Newsl. 9:91-92.

Singh, R.J. 1974. Cytogenetics of telotrisomics in barley. Ph.D. Thesis, Colorado State Univ., Fort Collins, Colorado.

Singh, R.J. and T. Tsuchiya. 1977. Morphology, fertility and transmission in seven monotelotrisomics of barley. Z. Pflanzenzüchtg. 78:327-340.

Tsuchiya, T. 1972. Cytogenetics of telocentric chromosome of the long arm of chromosome 1 in barley. Seiken Ziho. 23:47-62.

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