The collection of barley (Hordeum vulgare L.) semidwarfs is a diverse grouping of cultivars, breeding lines, and induced mutants in which plant height, spike density, seed shape, or awn length are modified compared to parental lines or closely related cultivars. Entries are best adapted to an array of different environments. Thus, phenotypic effects of the mutated gene(s) present in some entries were not observed in test environments. The expressivity of height genes was modified by environmental factors, especially heat and moisture stress.

Some induced mutants in barley cause plant height reduction as a pleiotropic effect; thus, no precise criteria for inclusion or exclusion of specific lines from the semidwarf collection were established. The collection contains lines having well-characterized genes, groups of induced mutants (which may or may not have been described in the literature), lines from collections of kernel or spike morphology mutants, semidwarf cultivars, and selected entries from other germplasm collections.

Entries in the barley semidwarf collection were assigned a dwarf stock number (DWS). Numbering was initiated with 1001 to avoid confusion with other sets of numbers assigned to breeding program lines. The donor or source of each entry, the cultivar name or line number, and the parental line or recurrent parent are listed in Table 1 for each entry. The gene symbol previously assigned to selected entries is listed in the gene symbol column. Further information on some entries has been published previously (Konishi, 1977; Kucera, et al., 1975; Larsson, 1985; Persson and Hagberg, 1969; Scholz and Lehmann, 1958; Tsuchiya, 1986).

Identification of semidwarf genes

Entries in the collection were crossed to one cultivar, Bowman, in order to identify and isolate the mutated gene in a common genetic background. Bowman is a two-rowed spring barley, which was developed for production in western North Dakota. This cultivar was selected as a recurrent parent because it has tolerance to heat stress and produces relatively short plants in greenhouse plantings. Bowman does not have a strong gene for photoperiod response or reduced height except for h. Visual traits present in Bowman include: teeth on lemma, G; small sterile laterals, i; short glume awns, Iga; narrow leaves, semi-smooth awns, r; long rachilla hairs, S; and two-rowed spike, V.

If F₂ plants with a mutant phenotype could be identified, seed was harvested and F₃ plants were grown in the fall greenhouse for backcrossing to Bowman. The number of times each entry was crossed to Bowman is listed in Table 1. The phenotype(s) recovered from each entry is indicated by gene symbols in Table 1. A simply inherited mutant gene was recovered from many entries, but some contained genes having pleiotropic effects on several plant parts. For example, entries with a recessive allele at the ari-e locus had a more erect growth habit, reduced plant height, and relatively short awns. Spikes were shorter, kernels were smaller, and tiller number was increased. Therefore, the recovered phenotype was characterized using more than one gene symbol.

More than one plant height gene was recovered from a few entries. But for other entries, a specific mutant phenotype could not be identified in-the Langdon, North Dakota environment. A few F₂ progenies were grown at Yuma, Arizona in order to improve the probability of identifying mutant phenotypes. The phenotypic effects of the sdw gene, for example, were difficult to observe most years at Langdon, but at Yuma sdw plants were distinctly shorter and later than normal sibs. Entries from which a mutant-phenotype could not be identified have no information in the phenotype recovered column.

Screening for gibberellic acid response

Some height mutants in barley have been reported to be insensitive to gibberellic acid (GA) treatment (Stoy and Hagberg, 1958). Thus, most entries in the semidwarf collection were tested during early backcross generations for response to GA. Tests were conducted to identify potential alleles and those entries having a normal response to this hormone.

Data were collected on elongation of the coleoptile and subcrown internode of seedlings with or without GA₃ application, using procedures modified from Boulger et al. (1982). Seeds were placed 4 cm deep in a potting medium and watered with a modified Hoagland's solution. One ml of a 100 ppm solution of GA₃ were added to each 10-cm clay pot every other day prior to watering. Five applications of GA₃ were made and measurements were taken 14 days after planting.

Seedlings of lines having the uz gene, which showed no subcrown internode elongation with or without GA application, served as a control in individual experiments. Seedlings of the second control, Bowman, had variable elongation when not treated with GA. Marked elongation occurred when Bowman seedlings were treated. Variable elongation of Bowman seedlings was unexpected and made the results difficult to interpret. However, the data subcrown internode length seemed to provide a better estimate of GA response than the coleoptile length data. The entries were classified as GA sensitive, GA insensitive, or GA constitutive, even though a continuous array of responses were observed (see column 2 in Table 1).

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.

Konishi, T. 1977. Effects of induced dwarf genes on agronomic characters in barley. In Gamma-Field Symposia No. 16: Use of dwarf mutation. pp. 21-38.

Kucera, J., U. Lundqvist, and A. Gustafsson. 1975. Induction of breviaristatum mutants in barley. Hereditas 80:263-278.

Larsson, H. E. B. 1985. Morphological analysis of laxatum barley mutants. Hereditas 103:239-253.

Persson, G., and A. Hagberg. 1969. Induced variation in a quantitative character in barley. Morphology and cytogenetics of erectoides mutants. Hereditas 61:115-178.

Scholz, F., and C. O. Lehmann. 1958. Die Gaterslebener Mutanten der Saatgerste in Beziehung zur Formenmannigfaltig Keit der Art Hordeum vulgare L. s. 1. I. Kulturpflanze 6: 123-166.

Søgaard, B., and P. von Wettstein-Knowles. 1987. Barley: genes and chromosomes. Carlsberg Res. Commun. 52:123-196.

Story, V., and A. Hagberg. 1958. Effects of gibberellic acid on erectoides mutations in barley. Hereditas 44:516-522.

Tsuchiya, T. 1986. List of genetic stocks with BGS numbers. BGN 16:81-121.