A Database for Triticeae and Avena
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.
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this will be overcome by introducing a new technique (Eslick, unpublished;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.
BGN 2 toc
BGN Main Index