BGN 2: Problems in barley genetics: Report from overall coordinator for genetic and linkage studies of barley BARLEY GENETICS NEWSLETTER, VOL. 2, IV. REPORTS FROM COORDINATORS
Tsuchiya, pp. 153-156

IV.10. Problems in barley genetics: Report from overall coordinator for genetic and linkage studies of barley.

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

In reviewing the literature on barley genetics and/or conducting genetic experiments with barley we encounter difficulties in many ways. It seems to be important to understand the present status in barley genetics research, particularly the problems we have now. This report includes a part of these problems, others are presented in "Current Linkage Maps of Barley" on page 162 of this issue. We should try to find out a way to solve these problems or to avoid the repeat of mistakes we made in the past. We need volunteers to attack these problems.

A. General

1. Limited usefulness of some genetic markers such as Lclc and other similar kinds of genes for lax and compact spikes including erectoides, h for plant height and many other genes for quantitative characters. The expression of these genes is different in different genetic backgrounds and different environmental (growing) conditions. Many erectoides genes will not show the characteristic trait in other than the original variety genetic background, particularly when ert mutants are crossed with more compact varieties than ert mutant. Therefore, before these genes for quantitative characters are used for critical genetic analysis as markers, allelism testing should be made with previously designated similar type varieties. Otherwise the number of genes will increase rapidly and the handling of genetic stocks becomes much more difficult.

2. Lethal genes are also limited in their usefulness.
    a. Problems in crossing heterozygous plants, though this will be overcome by introducing a new technique (Eslick, unpublished; Tsuchiya, 1972, BGN 2:119.

    b. Lack of one class in F2 generation in which the recessive homozygote for the lethal cannot be classified for adult characters combined in a cross with the lethal gene: always get 9:3:4 data and the last 4 are lethal. Using viable chlorophyll mutants and the other seedling character(s) such as glossy seedling (leaves) and brachytic or uzu (both show diagnotic coleoptile character) multiple marker stocks will become much more useful.

3. There is no official description of the characteristics of some genetic stocks; these have been assigned mostly by personal correspondence in the "Summary" published by Robertson and coauthors: rb for ribbongrass, sp for spotted, zb for zebra, and many other cases. Some stocks may need special treatment to express their diagnostic traits, such as zb which needs about 10 days of cold treatment at early seedling stage. Workers who found and studied such mutants are asked to prepare a description for their genetic stocks following the format published in Barley Genetics Newsletter (BGN, Vol. 1:103-193; BGN 2:172).

4. Insufficient understanding of diagnostic traits of the mutants.
    a. This is partly ascribed to the situation just mentioned above (no official description).

    b. uz has a good qualitative and fairly consistent quantitative characters in coleoptile, glume, rachilla and other organs. Plant height has been, however, used often as the characteristic trait of uzu (uz). Gene symbols uz2 and uz3 were designated based on the insufficient understanding and improper experiments (Tsuchiya, 1972 BGN 2:86).

    c. The expression of the gene K for hood in lk and lk2 background (and possibly other short awned background). The K gene cannot express its trait in these short awned backgrounds. The gene (symbol) K2 was thus given, because of insufficient understanding of the genetic behavior of a gene (Ramage, unpublished data).

5. Lack of enough information for some genetic traits.

    a. Genetic nature of purple color (Prpr, Pcpc, Re2 re2, etc.) has not been critically analyzed. Most purple color genes have been associated with chromosome 2. The interrelationships among those genes have not been analyzed thoroughly. The two gene or three gene system for purple color expression is not completely understood.

    b. Ii series for the development of lateral florets in relation to Vv series have been studied. Some questions remain, however, to be solved. The gene lr for awnless lateral florets in six-rowed variety is not fully understood. A critical experiment is necessary (Leonard, 1942; Haus, 1972, BGN 2:203).

B. Genetic and Linkage Studies

1. Many genetic studies have been side products of breeding programs. Lacking enough information of allelic relation of the genes used in the breeding program with the previously designated genes, authors have assumed that new genes exist. Referring to the literature, most of the smooth awned varieties are derived from crosses with Lion as a parent. No one has checked the allelic relation with Lion of the new gene symbols for smooth awn that have been given (Nilan, 1964). For other examples, refer to this issue (Tsuchiya, T. BGN 2:156;163)..

2. Confusion in nomenclature and gene symbolization.
    a. The gene designation for glume characters have been very confusing; e, Log and log, w, are often used erroneously.

    b. Different gene symbols have been given to one kind of trait; rb, va, va3, w, alb (as), and wst for white streak mutants. The symbols lc, l, ert, and many other l series for short rachis internode length. The symbols cer, gs, NGB, Ge (glaucus ear) for glossy sheath (and spike) mutants.

3. Problems in linkage studies.
    a. Lack of three point tests. In many cases, just two point tests have been made. In many other cases only one marker was used. For details refer to this issue (Tsuchiya, T. BGN 2:163).

    b. No definite centromere position has been located on the linkage map. Therefore, it has been impossible to establish multiple marker stocks which carry 3 to 4 good markers in each arm.

    c. Inadequate methods have been used for mapping. Because of uncertainty of breakage points and difficulty of arm designation, some marker genes travel all over the chromosomes (see Tsuchiya, T., BGN 2:163) when in cases when the translocation method was used for mapping.

C. Stock Center

1. No genetic stocks are available in the Stock Center in Fort Collins for many mutants which have been given gene symbols (officially or privately).

2. Difficulty of collecting genetic stocks.

    a. Very few workers have sent genetic stocks without request. Requests have been ignored in some cases.

    b. There is no way, if at all, of collecting some old stocks used long ago by now deceased workers.

D. Nomenclature and Symbolization

Gene symbols have been requested without giving enough information; no description, no picture, no genetic data, no evidence for allelism tests against previously designated similar type mutants. Yet I have been criticized rather severely by some workers for not giving gene symbols. In most cases no seeds have been supplied to the Stock Center in Fort Collins so that there is no way of knowing the characteristics of the mutants or of comparing it with other similar type mutants.

The purpose of this report is not to blame individuals but to let everyone know the present status, particularly the problems, in genetics and linkage studies of barley. Certainly we have received great heritage from our elders. What we should do with this heritage is not just keep it in the condition in which we received it but to improve or at least try to improve it. With the restless efforts of our elders we are now in a condition that these treasures could be used far more efficiently than ever before.

My proposal of improving these treasures is as follows:

1. Use of cytogenetic techniques for association of new genes to the chromosomes. With the use of aneuploids and RT stocks it has become very easy to accurately associate a mutant gene to the specific chromosome. With a little effort of cytological work we can get positive results of chromosome-gene relations in aneuploid analysis. With RT stocks no cytology is necessary. These techniques are highly efficient and effective compared to conventional methods with which multiple marker stocks with one or two genes from all or most of seven chromosomes are used.

After chromosomal assignment of a gene, telotrisomic analysis is conducted to assign the gene to specific arm of that chromosome. Now we are ready to step ahead toward linkage analysis.

2. Use of multiple marker stocks for each arm with three to four genes. Referring to the literatures, our linkage data are rather fragmental for many genes with which the new mutants have to be tested against one or two markers. In many cases the linkage analysis was conducted in different genetic background and varied environmental conditions. If we use the multiple marker stocks for each arm with 3 - 4 marker genes, it is possible to conduct 3 or 4 point test, with which more reliable data are obtained. Highly reliable information of gene order in each arm is obtained by telotrisomic analysis with multiple marker stocks as already demonstrated in tomato.

Cooperative work is essential to conduct this type of research work efficiently and effectively, Cooperation of all coordinators and many volunteers who are willing to join this project is greatly appreciated.
 

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