Genetical studies of two barley mutants differing in their GA response
A. Börner and V. Korzun
Institut für Pflanzengenetik und Kulturpflanzenforschung, Corrensstraße 3
06466 Gatersleben, Germany

The exploitation of dwarfing genes is one of the main strategies for breeding lodging resistant barley varieties. One example, the denso dwarfing gene has been widely used in European barley breeding programs and is present in many current varieties (Laurie et al. 1993). To enable the breeders to use several alternative dwarfing genes the identification and genetical characterization of further mutants is always necessary. The aim of the present paper was to study of the genetics of the two dwarfing mutants 'Hv287' (GA insensitive) and 'Hv288' (GA sensitive), derived from the variety 'Monte Cristo'. From Favret et al. (1975) it was already known, that the dwarfing gene of 'Hv287' is located on chromosome 2H and associated (linkage data was not described) with the V locus (2-row/6-row). For 'Hv288', however, no information about the genetics was available.

Materials and Methods

Both 2-rowed dwarfs 'Hv287' (GA insensitive) and 'Hv288' (GA sensitive), selected at INTA Castelar, Argentina and kindly provided by J. E. Flintham, JIC Norwich, UK were crossed with the varieties 'Betzes' (2-rowed, normal type) and 'Monte Cristo (6-rowed, normal type). 108 individuals of each F2 population from the crosses of 'Hv287' with both 'Betzes' and 'Monte Cristo' were classified for their response to exogenously applied GA\3 (Börner, 1991) and afterwards cultivated in the greenhouse. The F2 progenies (n=132) of the crosses including 'Hv288' (GA sensitive) were also grown in the greenhouse, without any GA test. Because 'Hv288' determines an extreme dwarfism the final plant height could be used for scoring the F2 populations.

To gain a more precise location of the GA insensitive dwarfing gene leaf material was cut from the F2 of the combination 'Hv287' x 'Betzes' for an RFLP analysis. DNA extraction and digestion, gel electrophoresis, Southern transfer, probe labeling and filter hybridization were performed as described by Devos et al. (1992). Two DNA probes (MWG557, cMWG669) known to be located on chromosome 2HL, linked to the V locus (Graner et al., 1991) and kindly supplied by A. Graner, Institute for Resistance Genetics, Grünbach, Germany were used for hybridization.

At harvest time the F2 populations of 'Hv287' x 'Monte Cristo' and 'Hv288' x 'Monte Cristo' were scored for the 2-row/6-row character.

Results and Discussion

The F2 histograms for GA response of the crosses 'Hv287' x 'Betzes' and 'Hv287' x 'Monte Cristo' (Fig. 1) give clear evidence for monogenic segregation. The (X²-tests gave a good fit to the 1 : 3 (insensitive : sensitive) ratio. Thus in contrast to hexaploid wheat where all known alleles for GA insensitivity are (partial) dominant, 'Hv287' carries a recessive allele, possibly comparable to the recessive alleles for GA insensitivity in rye (Börner, 1991).

In figure 2 the graphs of the crosses of the GA sensitive mutant 'Hv288' with both 'Betzes' and 'Monte Cristo' are shown. Again monogenic 1 : 3 segregation, this time for final plant height, was evident.

Of special interest was the analysis of the genetic relationships between the 2-row/6-row character and the two dwarfing genes, linked with insensitivity ('Hv287' x 'Monte Cristo') or sensitivity ('Hv288' x 'Monte Cristo') to GA. In both crosses a 3 (2-rowed) : 1 (6-rowed) segregation was significant ((X² = 0.04 and (X² = 2.24, respectively). It was found that in the F2 populations all GA insensitive plants (28 from 108) and GA sensitive dwarfs (35 from 132) of the combinations 'Hv287' x 'Monte Cristo' and 'Hv288' x 'Monte Cristo' were 2-rowed. Therefore it could be concluded that the dwarfing genes of both mutants are linked to the V locus.

The RFLP analysis confirms the linkage between the loci determining the 2-row/6-row character and GA insensitivity in 'Hv287' described by Favret et al. (1975). Whereas for the clone cMWG669 no polymorphism was detected, a recombination frequency of 9.0 ± 2.1 % could be calculated between Xmwg557 and the locus for GA insensitivity. The former was shown to be linked to the V locus by Graner et al. (1991). It could be concluded that within the Triticeae loci for GA insensitivity are not only located on the homoeologous groups 4 (wheat) or 5 and 7 (rye) (Börner et al., 1996), but also on group 2 in barley.

References:

Börner, A. 1991. Genetical studies of gibberellic acid insensitivity in rye (Secale cereale L.). Plant Breeding 106:53-57.

Börner, A., J. Plaschke, V. Korzun and A.J. Worland. 1996. The relationships between dwarfing genes of wheat and rye. Euphytica, in press.

Devos, K.M., M.D. Atkinson, C.N. Chinoy, C.J. Liu and M.D. Gale. 1992. RFLP-based genetic map of the homoelogous group 3 chromosomes of wheat and rye. Theor. Appl. Genet. 83:931-939.

Favret, E.A, G.C. Favret and E.M. Malvarez. 1975. Genetic regulatory mechanisms for seedling growth in barley. Barley Genet. III:37-42.

Graner, A., A. Jahoor, J. Schondelmaier, H. Siedler, K. Pillen, G. Fischbeck, G. Wenzel and R.G. Herrmann. 1991. Construction of an RFLP map of barley. Theor. Appl. Genet. 83:250-256.

Laurie, D.A., N. Pratchett, C. Romero, E. Simpson and J.W. Snape. 1993. Assignment of the denso dwarfing gene to the long arm of chromosome 3(3H) of barley by use of RFLP markers. Plant Breeding 111:198-203.

Fig. 1. F2 segregation patterns for shoot lenght after GA\3 treatment of thecombinations 'Hv287' x 'Betzes' (left) and 'Hv287' x Monte Cristo¹ (right).The means of the paretnt are marked by the arrows.

Fig. 2. F2 segregation patterns for final plant hight of the combinations'Hv288' x 'Betzes' (left) and 'Hv288' x Monte Cristo¹ (right). The means ofthe paretnt are marked by the arrows.