BGN 13: Additional information on the Triplo 7S in barley BARLEY GENETICS NEWSLETTER, VOL. 13, II. RESEARCH NOTES
Shahla and T. Tsuchiya, pp. 22-23

II. 9. Additional information on the Triplo 7S in barley. (1)

A. Shahla and T. Tsuchiya, Department of Agronomy, Colorado State University, Fort Collins, C0 80523 U.S.A.

(1) Supported in part by U.S.D.A. Competitive Research Grant No. 5901-0410-9-0334-0 and No. 82-CRCR-1-1020 to T. Tsuchiya.

In BGN 12 (Shahla and Tsuchiya, 1982) the possible establishment of telotrisomic 7S in the progeny of a plant with 2n=15+1 telo 7S was reported. Later a few plants were recovered with 2n=14+1 telo 7S (Triplo 7S). Morphological traits of telotrisomic 7S plants resemble very closely those of normal diploid plants. It is clear that like other telotrisomics for the short arms of barley chromosomes the extra telocentric 7S has no effect on morphological characteristics.

A detailed study has been done on the meiotic behavior, pollen fertility, seed set and transmission of the extra telocentric chromosome 7S.

At diakinesis the satellite chromosomes 6 and 7 associate with the nucleoli. At this stage of meiosis in some sporocytes, the extra telocentric chromosome 7S showed association with nucleolus as a univalent or as a component of the trivalent. The frequencies of 1III + 6II was 43.4% and 7II + 1II configuration was 56.6% at diakinesis. At MI, the extra chromosome 7S remained as univalent in 52.8% of the cells and the trivalent configuration increased to 47.2%. The most common types of trivalents were tandem V-shape with an average frequency of 74.75% followed by ring-and-rod with 14.86% and rod-shape with 10.39%.

At AI, 45% of the sporocytes showed the normal 8-7 separation. In 32% of the cells the extra telocentric chromosome 7S remained at the equatorial plate as a laggard and showed 7-1-7 separation. At late anaphase I cells the lagging chromosome started to divide giving 7+1-7+1 formation (23%).

Pollen fertility was very high in this trisomic type. From 800 pollens studied, 98% showed two well-developed sperm nuclei and one vegetative nucleus.

The fertility of telotrisomic 7S was studied for three conditions as shown in Table 1. Fertility was highest in the self-pollinated spikes. Also this value is higher than the average of seven telotrisomics (69.1%) studied by Singh and Tsuchiya (1977).

Table 1. Seed fertility of telotrisomic 7S.

Transmission rates of the telocentric chromosome were also studied for the three conditions (Table 2).

Table 2. Transmission of telotrisomic 7S.

The male transmission rate of the extra telocentric chromosome 7S (5.3%) is less than the 10.53% male transmission reported for telotrisomic 6S (Seip and Tsuchiya, 1980), but higher than the average value of 1.2% reported for seven telotrisomics (Singh and Tsuchiya, 1977). Ditelotrisomic plants with 2n=14+2 telo 7S have been obtained in this study.

Current linkage waps do not show the position of the centromere on chromosome 7 due to the lack of a telosomic trisomic for this chromosome. Multiple marker stocks are being developed and they will be used in telotrisomic analysis with Triplo 7S and the centromere position in chromosome 7 will be determined.

References:

Seip, L. and T. Tsuchiya. 1980. Further studies on the telotrisomic plants for the short arm of chromosome 6, Triplo 6S, in barley. BGN 10:64-65.

Shahla, A. and T. Tsuchiya. 1982. Telocentric chromosome for the short arm of chromosome 7 (telo 7S) in barley. BGN 12:33.

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

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