The brachytic class of semidwarf mutants in barley
J.D. Franckowiak
Department of Plant Sciences, North Dakota State University,
Fargo, ND 58105, U.S.A.

The collection of plant height or semidwarf mutants in barley contains several phenotypic groups or classes of mutants (Franckowiak and Pecio, 1992). The mutants in one of the more distinctive classes are those which have a brachytic phenotype. The coleoptile and the first foliage leaf are shorter than normal and the seedlings fail to respond to the application of gibberellin (Boulger et al., 1982). The leaf blades, culms, spikes, awns, and kernels of brachytic mutants may be shorter than in normal sister lines. Alleles at two loci, the br1 (ari-i) locus in chromosome 1S (Powers, 1936) and the br2 locus in chromosome 4S (Tsuchiya, 1980), have been reported to control expression of the brachytic phenotype in barley. But, other mutants have a similar phenotype (Tsuchiya, 1974; 1976) and some lines without these genes are insensitive to gibberellic acid treatment (Boulger et al., 1982; Franckowiak and Pecio, 1992).

Bowman backcross derived lines from entries in the barley semidwarf collection, which exhibited several brachytic traits (Franckowiak and Pecio, 1992), were plant in the 1994 spring greenhouse nursery (Table 1). These lines were used because the original stocks included both spring and winter barley cultivars and showed variable responses to photoperiod. Nearly all of the selected lines had a short blade on the first true leaf. Reduced plant height, coiled neck, long basal rachis internode, short awn, and short kernel were observed in some, but not all lines.

Lines having similar phenotypes were noted and few crosses were made to determine allelism. The F1 progenies in which the plants exhibited brachytic characteristics and provided evidence for allelism are listed in Table 2. The results show that DWS1038, DWS1224, and FN53 each have a mutant gene at the br1 locus. The ari-l.3 gene is the mutant in the breviaristatum series of loci which is allelic at the br2 locus. The DWS1002 and DWS1230 stocks contain brachytic mutants which are alleles. The mutants in the DWS1036 and DWS1037 stocks are alleles. Allelism between these two groups was not tested. However, neither is allelic at the br1 locus (Table 2). The crosses, which are needed to demonstrate that these mutants represent new loci, have not been made.

References

Boulger, M.C., R.G. Sears, and W.E. Kronstad. 1982. An investigation of the association between dwarfing sources and gibberellic acid response in barley. Barley Genet. IV:550-553.

Franckowiak, J.D., and A. Pecio. 1992. Coordinator's report: Semidwarf genes: A listing of genetic stocks. BGN 21:116-127.

Table 1. A list of mutants from the barley semidwarf collection placed in the brachytic phenotypic class.




ıAllele symbols recommended for mutants in the brachytic class of semidwarf genes. A period is use to separate the locus and allele portions of the gene symdol. If the br symbol is followed by a number, the mutant gene is assigned to a specific locus. If it is not, adequate allelism testing has not been completed to assign the mutant gene to a specific locus.

Powers, L. 1936. The nature of the interactions of genes affecting four quantitative characters in a cross between Hordeum deficiens and vulgare. Genetics 21:398-420.

Stoy, V., and A. Hagberg. 1967. Effects of growth regulators on ear density mutants in barley. Hereditas 58:359-384.

Tsuchiya, T. 1980. BGS157. Brachytic 2, br2 (revised). BGN 10:115.

Tsuchiya, T. 1974. Allelic relationships of genes for short-awned mutants in barley. BGN 4:80-81

Tsuchiya, T. 1976. Allelism testing of genes between brachytic and erectoides mutants. BGN 6:79-81.

Table 2. Crosses among selected lines to determine allelism among mutant genes which control the brachytic growth habit.

_________________________________________________________
 Female    Male     Allele symbolsı  No. of  Phenotype
 parent    parent  ________________  plants  of F1 plants
                   Male      Female             
_________________________________________________________
DWS1078   FN53     br1.a     br1.ae     15    Brachytic
DWS1132   DWS1038  ari-i.38² br1.t      11    Brachytic
DWS1132   DWS1224  ari-i.38  br1.x      15    Brachytic
DWS1136   DWS1152  ari-m.28  br1.e       9    Normal

DWS1079   DWS1136  br2.b     ari-m.28    9    Normal
DWS1135   DWS1079  ari-l.3   br2.b      18    Brachytic

DWS1002   DWS1132  br.g      ari-i.38    9    Normal
DWS1002   DWS1230  br.g      br.y       15    Brachytic

DWS1036   DWS1037  br.r      br.s        8    Brachytic
DWS1036   DWS1152  br.r      br1.e       9    Normal
__________________________________________________________
ıThe recommended allele symbols are listed in Table 1 and are modified to indicate the results of the crosses considered in this report.

²Positive allelism tests for the ari-i.38 and br1.e mutants at the br1 locus were eported by Tsuchiya (1974) and Szarejko and Maluszynski (1984), respectively.