A dominant dwarf mutant in barley

N. Kurauchi1, M. Tanio2 and S. Hirose1

1College of Bioresource Sciences, Nihon University 3-34-1 Shimouma, Setagaya, Tokyo 154, Japan
2Department of Plant Breeding, National Agriculture Research Center, 3-1-1 Kannondai, Tsukuba, Ibaraki 305, Japan

Induction and selection for dominant dwarf mutants

About 6,600 air dried seeds of genic male sterility, originally developed by Falk and Kasha (1982)(GBC695, sex-msg6-Uc2-o/sex-msg6-Uc2-o), were pre-soaked for four hours in water, and treated with 8mM sodium azide (NaN3) for two hours. The sodium azide was dissolved in C6H4(COOK)(COOH)-HCl buffer at pH3. After treatment, they were washed with running water for sixteen hours. They were sown in field and were open-pollinated to reciprocal translocation homozygous lines derived from Mars, which were kindly provided from Dr. R. T. Ramage, University of Arizona.

About 5,500 M2 (F1) plump seeds obtained by above crossings were sown in field. In M2 (F1) generation, only seven plants, which have green lemmas and six rowed spikes, revealed dwarf as compared with 2,157 M2 (F1) plants.

Seed fertilities of dwarf plants showed semi-sterility (ranged from 30 to 57%; mean value was 46%). Only one plant of them was observed chromosome pairing at metaphase I of meiosis and showed one quadrivalent and five bivalents. Their rachis were not shortened and seed size were not smaller than those of plants having normal height. However, all dwarfs revealed late heading.

Shortening characteristics of dwarf plants

Mature tillers of seven dwarfs and non-dwarfs were dissected to measure internode and rachis lengths and the results are illustrated in Figure 1 (Click here to view). All internodes of dwarfs, however, were shortened in relation to the non-dwarfs and the second internode was shortened in greater degree than the other internodes(t=4.20, P<0.01). These characteristics of dwarfs were different from Dwf2 (Falk, 1994).

Inheritance of dwarf character

In M3 (F2) generation, seven dwarf lines and four non-dwarf lines were grown in field. Growing out progeny from seven selfed dwarfs has given 157 dwarf plants and 46 non-dwarf plants. This is a satisfactory fit to a 3:1 ratio expected for a single locus with two alleles, the mutant allele (D) giving the dominant dwarf phenotype (2=0.21, 0.50<P<0.75). On the other hand, all plants from four selfed non-dwarf showed non-dwarf plants.

Furthermore, reciprocal crosses were made between one dwarf M2 (F1) plant or non-dwarf (F1) plants and cultivar, Misato Golden, which have non-dwarf culm and two rowed spike. F1 progeny from one dwarf plant segregated as 12 dwarf plants and 8 non-dwarf plants, which gives a fit to a 1:1 ratio (2=0.80, 0.25<P<0.50). Another F1 progenies from non-dwarf plants did not segregate dwarf plant.

Linkage relationship of dwarf gene with smooth awn gene

One parental line, male sterility, has rough awn and another line, Mars, has smooth awn. Gene controlling rough/smooth of awn locates on chromosome 7.

M2 (F1) plants had rough awn. F2 progeny has given 140 rough awn plants and 44 smooth awn plants, which gives a good fit to a 3:1 ratio (2=0.12, 0.70<P<0.80). Segregation ratio of two genes between dwarf gene (D) and rough awn gene (R) was showed 113 DR : 26 Dr : 27 dR : 18 dr. This ratio was not fit to 9:3:3:1 (2=8.27, 0.01<P<0.05; 2L=8.13, P<0.01). The phase of hybrid F1 was coupling. Then, we calculated recombination value by using product-ratio method. Recombination value was estimated as 35.7 3.10 %. It was, therefore, concluded that dwarf gene (D) is locating on chromosome 7.

Response of dwarf gene to gibberellic acid 3

In M4 (F3) generation, 10 ppm of gibberellic acid was applied to assume dwarf homozygous line for three weeks after sowing date. After application with GA3, lengths of first leaf sheaths were measured. Mean values and standard deviations of ten plants for one line are given in Table 1. The first leaf sheath of male sterile line were elongated 107% as compared with that of non-treated plant. The percentage of elongation of dwarfs was not different from that of male sterile line or higher than that of Mars. It was, therefore, concluded that dwarf gene, D, is sensitive to gibberellic acid.

Consequently, it was clarified that a new type of dominant dwarf gene induced by sodium azide do not affect on spike length and that it was sensitive to gibberellic acid 3.

Table 1. Percentages of first leaf sheath treated with GA3 to non-treated one in parental and dwarf homozygous lines.

Generation Line Mean % Standard deviatio
P male sterility 207 15.85
P Mars 147 16.57
M4 K28-16 187 38.97
M4 K29-10 199 34.67
M4 K30-35 212 17.56
M4 K32-1 214 27.34
M4 K33.11 165 16.89

References

Falk, D. E. 1994. New dominant dwarfing gene (Dwf2) in barley. BGN.24:87-89.

Falk, D. E. and K. J. Kasha. 1982. Registration of a shrunken endosperm, male-sterile germplasm to facilitate hybridization in barley. Crop Sci.22:450.