BGN 2: Cytogenetics of telotrisomics in barley BARLEY GENETICS NEWSLETTER, VOL. 2, II. RESEARCH NOTES
Tsuchiya, pp. 93-98

II.36. Cytogenetics of telotrisomics in barley.

T. Tsuchiya. Department of Agronomy, Colorado State University, Fort Collins, Colorado 80521, U.S.A.

*Reports II.33. (p.80) through II.42. (p.108) by T. Tsuchiya and co-workers are based on the results of researches supported by NSF Research Grants GB4482X and GB30493 and Colorado State University Experiment Station Project (Hatch 8).

Supported in part by Biomedical Science Support Grant (NIH) at Colorado State University No. 31-1801-4518 (1970-1971) and 31-1170-7213 (1971-1972).

1. Cytological identification of two telocentric and one small metacentric chromosome.

Translocation tester stocks have been used for the identification of two telocentric chromosomes and one small metacentric chromosome. Telo 2B was obtained in the selfed progeny of a primary trisomic plant for chromosome 2 in Shin Ebisu 16. Telo 3A was found in an F1 hybrid between a primary trisomic plant for chromosome 3 and KM 200, an incompletely dominant short awned mutant in variety Hakata No. 2. The small metacentric chromsome was obtained in the selfed progeny of primary trisomic 3 in Shin Ebisu 16. All these fragment chromosomes occurred as the extra chromosome. The three aneuploids were tentatively named as follows:

Telotri 2B - Telotrisomic for chromosome 2 (Telo 2B).

Telotri 3A - Telotrisomic for chromosome 3 (Telo 3A)

Smallmetatri 3A - Trisomic for small meta chromosome 3 (Smallmeta 3A) (A and B denotes that arm or segment designation has not been determined)

Telotri 2B plants have less conspicuous morphological traits compared to Telotri 2L (telotrisomic for the long arm of chromosome 2) which appears exactly like plants of the primary trisomic for complete chromosome 2. Telotri 2B has slightly narrower and darker green leaves from early seedling stage to near maturity. Plants are tall with long stem internodes; spikes are long with long rachis internodes. Kernels are large with long lemma awn. The fertility is low with 59% of seed set in selfing and 78% in the cross Telotri 2B x diploid.

Telotri 3A plants and Smallmetatri 3A plants are both similar to the primary trisomic for complete chromosome 3 in many respects. Both are pale green having pale green leaves with abundant hairs on the young leaves (2nd, 3rd and 4th). They have relatively compact spikes with short awns in Telotri 3A and long, normal awns in Smallmetatri 3A. Rachilla is short in both trisomics. With these diagnostic characteristics, these trisomics are easily distinguishable from diploid siblings and other telotrisomics and aneuploids.

These aneuploids should be useful in cytogenetic studies of barley, particularly for linkage analysis and the study of the genetic architecture of barley chromosomes. In order to identify these chromosomes cytologically these three aneuploid lines were crossed with appropriate translocation tester stocks (RT testers) as shown in Table 1. Meiotic configurations of the F1 hybrids were studied with the results given in Table 1.

Table 1. Chromosome configurations at meiotic metaphase of Fl hybrids between three aneuploids and four RT testers.

The results given in Table 1 indicate that Telo 2B is one arm of chromosome 2, most likely the short arm, since the plant morphology is different for telotri 2L. Two fragments (Telo 3A and Smallmeta 3A) obtained in the progenies of primary trisomic for chromosome 3 would appear to be one arm and a segment of chromosome 3, respectively.

At metaphase I of Smallmetatri 3A, ring trivalents were observed frequently (Fig. 1). From these results it is assumed that the small metacentric chromosome 3A is a kind of pseudo-isochromosome missing large segments of the chromosome 3 with the centromere and both telomere unchanged.

Figure 1. Chromosome configuration at metaphase I of Smallmetatri 3A, showing a ring trivalent (arrow) plus five bivalents (a) and V-type trivalent plus six bivalents (b).

2. Telotrisomic analysis of 23 marker genes on five chromosomes (1-5).

Preliminary results of telotrisomic analysis of 22 marker genes belonging to five chromosomes (1-5) are shown in Table 2. For the gene symbols and the detailed descriptions of the genetic stocks used in this study the leaders refer to Barley Genetics Newsletter Vol. 1 and 2.

Table 2. Summary of the preliminary results from telotrisomic analysis of 21 genetic markers.

From the results so far obtained the seven telocentric chromosomes are designated as shown in Table 3.

Table 3. Designation of seven telocentric chromosomes based on the preliminary results from telotrisomic analysis.

Based on the results shown above and those obtained by Fedak (1969) and Tsuchiya (1971), the centromere position of five chromosomes is tentatively given as follows:

Since the arm designation of most of the telocentric chromosomes has been completed by cytological and genetic studies of telotrisomic plants, the new designation of telotrisomic types are adopted (Table 4) following the system used in tomato (Khush and Rick, 1968).

Table 4. Designation of telotrisomic types in barley

3. Further information on the morphology of telotrisomics and other trisomics.

Seedling characters of the telotrisomics and other trisomic plants have been reported previously (Tsuchiya, 1971, BGN 1:58-60). Further results on the morphological characteristics and fertility are briefly reported in this article.

Telotrisomic for 1L (Triplo 1 L): Tsuchiya, T. 1971. Barley Genetics II (Proc. IInd Intern. Barley Genet. Symp.):72-81.

Telotrisomic for 1 S (Triplo 1 S): This telocentric chromosome (1 S) was introduced in Shin Ebisu 16 background by two back crosses. The plants are vigorous with large spike, long awn, and high fertility. It is impossible to distinguish telotrisomic plant for 1 S from diploid siblings. For detail see Barley Genetics II:72-81 (1971) by T. Tsuchiya and Fedak et al. (1971).

Telotrisomic for 2 L (Triplo 2 L): Tsuchiya, T. 1971. Barley Genetics II:72-81, and Fedak et al. (1971).

Telotrisomic for 2 B (Triplo 2 S): Arm designation of this telocentric chromosome has not been positively made yet. The plants are rather tall with slightly thinner stems than diploid siblings; leaves are narrow, short, dark green and do not droop; spikes are very lax and narrow; awns long; kernels larger than diploid sibs. It is rather easy to distinguish this telotrisomic plant from diploid siblings and Triplo 2 L at later stages of growth. Fertility is rather low with about 59% seed set in selfing and 77.8% in 2x + 1 telo 2 B x 2x.

Telotrisomic for 3 S (Triplo 3 S): Plant color is slightly pale green with drooping leaves; spikes and plant height are similar to normal diploid; the second and third leaves have abundant hairs and leaves revoluted. The seed set was considerably high in many F1 hybrids between Triplo 3 S and some genetic marker stocks.

Trisomic with 14 + 1 acrocentric chromosome 3 (Acro 3 A): Morphologically very similar to the primary trisomic for chromosome 3 (Pale). In the Shin Ebisu 16 background the seed fertility is very high in spite of very compact spikes.

Trisomic with 14 +1 small metacentric chromosome 3 (Small meta 3 A): Morphologically very similar to the primary trisomic, pale, with short stem, pale green plant color, very compact and almost completely sterile spike. The second and third leaves have abundant hairs.

Telotrisomic for 4 S (Triplo 4 S): Telotrisomic analysis of several genetic marker genes on chromosome 4 showed that the telocentric chromosome of this telotrisomic type is the short arm of chromosome 4 (Tsuchiya, 1972) based on the present linkage map (Robertson, 1971). Many characteristics are very similar to the primary trisomics, Robust, with thick stem, wide, short and dark green leaves. The spikes are, however, more compact and plant height is taller in telotrisomics than in the primary trisomics.

Trisomic with 14 + 1 acrocentric chromosome 4 (Acro 4 A): See Tsuchiya, 1971, BGN, Vol. 1 58-60.

Telotrisomic for 5 L (Triplo 5 L): Cytogenetic studies showed that the telocentric chromosome of this type is the long arm of chromosome 5 (Tsuchiya, BGN, 2:90-92) rather than 5 S mentioned by Fedak (1969). The telocentric chromosome is in the process of being introduced to the Shin Ebisu 16 background. In the two back cross generation the telotrisomic is rather similar to its primary trisomic, Pseudonormal, in many morphological traits: Plants are slightly shorter than diploid sibs with revoluted and yellowish and/or yellow-striped leaves. Fertility is very high.

References:

Fedak, G. 1969. Ph.D. Thesis, University Manitoba, Winnipeg, Canada, 110 pp .

Fedak, G., T. Tsuchiya and S. B. Helgason. 1971. Can. J. Genet. Cytol. 13:760-770.

Haus, T. E. 1972.  BGN 2:132.

Khush, G. S. and C. M. Rick. 1968. Cytologia 33:137-148.

Tsuchiya, T. 1971. Barley Genetics II 72-81.

Tsuchiya, T. 1971. BGN 1:58-60.

Tsuchiya, T. 1971. BGN 1:61-62.

Tsuchiya, T. 1971. BGN 2:95.

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