II. 50. Acrocentric chromosome 1L1S in barley.*
T. Tsuchiya, Department of Agronomy, Colorado State University, Fort Collins, Colorado 80523, U.S.A.
* This work is supported by the Research Grant from National Science Foundation (GB 30493) and from USDA (12-14-5001-265).
An acrocentric chromosome was found in a population (SE75-4) derived from telotrisomic for 1S (Triplo 1S) which originally was obtained from Herta X Wong triploid hybrid barley by Kerber (1954, 1958) (Tsuchiya, 1969). Ten out of 28 plants in the line SE75-4 had 2n=14+1 acrocentric chromosomes (35.7%). This indicates that the parental plant, SE73-7-3, was the new trisomic which is tentatively called "acrocentric trisomic." Further back in the pedigree, the sibling (SE73-7-4) of the SE73-7-3 in the line SE73-7 was also an acrocentric trisomic. Based on this finding, it is assumed that the parental plant of the line SE73-7, SE71-1-23 must have been the same acrocentric trisomic as its progenies. The record of chromosome studies showed that SE71-1-23 and its parent SE70-30-1 had 2n=15. In these cases the chromosome counts were made by another person but not the present author. Therefore, it is possible that the technician considered it as 2n=15 instead of 14+1 acrocentric chromosomes. In order to determine the chromosome constitution of SE71-1-23, the seeds of selfed spikes are germinated. The results will be obtained soon.
The line SE70-39 was a bulk F2 population from 7 F1 plants (I tr 69-13) of the cross between Triplo IS(KT 69-1-23) X SE16, 2x. A large number of F2 seeds from 7 F1 plants with 2n=14+1S were germinated, and only off-type plants were selected for chromosome study. Chromosome numbers of 14 off-type plants were counted with the following results:
2n=15
3 plants
2n=14+1 telo 5 plants
2n=14
6 plants
14 plants
The three 15-chromsome plants were designated as:
SE70-39-1
SE70-39-2
SE70-39-8
In the progenies of the last two plants, SE70-39-2 and SE70-39-8, only primary trisomic plants with 2n=15 chromosomes have been found. This finding suggests that the two parental trisomic plants must have had normal chromosome complement for primary trisomic, Bush, or Triplo 1.
Detailed analysis of chromosome constitution in the progenies and the sibling of SE71-1-23 will provide the origin of the new acrocentric chromosome. The line SE71-1 produced 26 plants of which 9 plants were observed to have 2n=15. The progenies of seven out of nine 15-chromosome plants were raised for chromosome studies. The results will be obtained in the near future.
The morphology of the acrocentric trisomics for 1L1S is exactly the same as that of primary (Triplo 1) and telotrisomic for 1L (Triplo 1L). It has been assumed, based on the morphology, that the acrocentric chromosome consists of the complete long arm and a segment of the short arm of chromosome 1. Thus the symbol 1L1S was tentatively given to the acrocentric chromosome.
The transmission of the acrocentric chromosome was calculated as 39.17% from 6 populations. This transmission rate is similar to that of telocentric 1S but higher than Telo 1L (Singh and Tsuchiya, 1977).
Detailed cytological and genetic analyses are now under way to study the cytogenetic nature of this acrocentric chromosome.
References:
Kerber, E.R. 1954. Trisomics in barley. Science 120:808-809.
Kerber, E.R. 1958. A study of autotriploids and trisomics of common barley, Hordeum vulgare L. Ph.D. Thesis, University of Alberta, Edmonton, Canada.
Singh, R.J. and T. Tsuchiya. 1977. Morphology, fertility and transmission in seven monotelotrisomics in barley. Zeits. Pflanzenzucht. 78:327-340.
Tsuchiya, T. 1969. Status of studies of primary trisomics and other aneuploids in barley. Genetics 40:216-232.