BGN 13: The occurrence of polyploid plants in the progenies of primary trisomic plants in barley BARLEY GENETICS NEWSLETTER, VOL. 13, II. RESEARCH NOTES
Chapman & Tsuchiya, pp. 71-72

II. 38. The occurrence of polyploid plants in the progenies of primary trisomic plants in barley.(1)

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

(1)Supported by USDA-SEA Competitive Research Grant No. 82-CRCR-1-1020 and CSU Hatch project.

I. A tetraploid plant.
A barley plant with 2n=4x=28 chromosomes was found in the F1 progeny of the cross Triplo 5 (Shin Ebisu 16) X Leafless or deficient lamina (Kmut 255) heterozygote. The F1 hybrid of the crosses yielded five diploid plants, two trisomics and one 2n=28 tetraploid plant. Plant growth is vigorous with leaf shape and color resembling that of the trisomic sibs.

The mutant gene used in the cross is incompletely dominant (Tsuchiya, 1969). At the four leaf stage, heterozygous plants show vigorous growth with auricle-like appendages developing along the leaf margins. Homozygous plants remain approximately 10-12 cm tall with extremely reduced leaf blades and auricle-like appendages until later growth stages when one culm may elongate and develop a spike. At the time that the diagnostic trait was being expressed in the trisomic sibs, this tetraploid plant showed no auricle-like appendages on the leaves.

Many possible explanations exist for the development of a tetraploid barley plant. A haploid (n=7) egg may have spontaneously doubled and redoubled to produce the tetraploid plant. More likely would be the fusion of a haploid egg and a haploid pollen grain which did not carry the mutant trait. This fusion followed by a doubling of the chromosome number would also produce a tetraploid plant.

The single root tip available for chromosome counts showed numerous cells with 2n=28 chromosomes in various stages of division and only a small number of 2n=14 cells. Approximately 25 days after germination, six more root tips were collected. Chromosome counts of each root tip showed the normal diploid chromosome number. To verify chimeras, meiosis will be studied.

II. A hypertriploid plant.
In the F1 progeny of the cross Triplo 6 (Shin Ebisu 16) X Leafless or deficient lamina (Kmut 255) a barley plant with 2n=3x+2=23 chromosomes was found. The only other offspring of this cross was a diploid plant. The single root tip available for chromosome counts showed all cells with 2n=3x+2=23 chromosomes. A count made about three weeks later again verified the 2n=3x+2=23 condition. The hypertriploid plant has similar characteristics to the primary trisomic for chromosome 6. The plant showed the diagnostic trait which is characteristic of the incompletely dominant mutant at a later time than other F1 plants.

The most plausible explanation for the origin of a hypertriploid plant with 2n=3x+2=23 chromosomes would be the fusion of two nuclei (one egg nucleus and another nucleus with 8 chromosomes)in female side followed by fertilization with n=7 pollen. This process would give a hypertriploid plant with 2n=8+8+7=23.

Study of meiosis should reveal six trivalent and one quinquevalent. Crossing with a diploid plant should provide plants with variety of somatic chromosome numbers.

Reference:

Tsuchiya, T. 1969. Characteristics and inheritance of radiation-induced mutations in barley. I. Several extreme mutations. Induced mutations in plants. Proc. Intern. Symp. on Nature, Induction and Utilization of Mutations in Plants:573-590.

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