II. 6. Branching spike mutants from two loci in two-row barley.
H.E.B. Larsson, Department of Genetics, Swedish University of Agricultural Sciences, S-750 07 Uppsala, Sweden. "R"
1. Earbranching mutant.
Over the years many authors have reported spontaneous or induced earbranching
mutants in barley (Martini and Harland, 1942; Prasad, 1976; Chandra and
Madke, 1980).
A mutant with a "bushy', multiflorus-like appearance (Fig. la) was found in Svalöv's lax-ear assortment originating from cv Foma. Its ear is branched from the rachillae of the 1-10 bottom flowers and the normal to threadlike awns, as well as the protruding branches, are bent in all directions because of "packing" problems in the boot. The rachilla is shorthair and the normally very small, triangular meristem at its apex is differentiated into a little inflorescence (Fig. lb). The branches are progressively more developed down towards the earbase where they often give mature seeds.
Fig. la. Earbranching mutant with small branches
from rachillae at the base of the spike. Photography from about two weeks
after anthesis.
Fig. lb. A branching rachis bent down at its 7th
internode so that the rachilla of the 7th flower (and the 5th at the left)
can be seen.
The mutant gene was located to 7L using Svalöv's cytogenetic tester set (Persson, 1969). After crossing the mutant to shorthaired, s s stock the outdoor bred F1 showed shorthaired, unbranching rachillae and the F2 a 3 to 1 distribution for unbranching to branching. So the mutant gene is allelic and recessive to s. It is suggested that it is named: shorthaired inflorescent rachilla and given the symbol si.
2. Earshooting mutants.
Many workers have also reported both mutants and phenocopies with secondary
shoots from the rachis (Lawrence, T., 1955; Stephanov and Gorastev,
1976; Dormling et al., 1975).
Some lax-ear mutants originating from cvs Bonus and Foma show a strong tendency under field conditions at Uppsala, Sweden to grow secondary and also tertiary shoots from the collar and basal rachis internodes (Fig. 2a). The shoots are often clustered in a fashion very similar to those appearing from the plant base in a late, wet season. The mutants ear-shoots grow from its accordion- or meander-like rachis base (Fig. 2b) as sometimes also can be seen in the brachytic mutants. The secondary shoots often also have rootlets and cloning experiments have been successfully attempted.
Fig. 2a. Earshooting mutant b from cv Bonus with
tertiary shoot growing down at the left from secondary shoot of the oldest
culm.
Fig. 2b. Basal rachis internodes from mutant b.
The boots were up to 1/2 (left) and 2/3 of the spike before split open
for observation.
Three allelic mutants have been found and were located to 2S by using the same two-step procedure as with si. In trying to get recombinants in F2 with the marker Ee for elongated glume more than 1,600 plants were counted. As none such was found, the linkage to E-locus is very strong although there is some evidence that the mutant gene is more distal from the centromere. The proposed name for the mutants is: accordian basal rachis internodes and given the symbols abr1a abr1b and abr1c.
All mutants described are submitted to the International Committee for assigning Barley Gene Symbols.
References:
Chandra, A. and K. H. Madke. 1980. Multifloret condition in barley. BGN 10:10.
Dormling, I., A. Gustafsson and G. Ekman. 1975. Growth disorders and phenotype variability in phytotron-cultivated barley. Hereditas 79: 255-272.
Lawrence, T. 1955. The production of mutations by the irradiation of Montcalm barley. Can. J. Botany 33:515-530.
Martini, M. L. and H. V. Harlan. 1942. Barley freaks. J. Hered. 33:338-343.
Persson, G. 1969. An attempt to find suitable genetic markers for dense ear loci in barley I. Hereditas 62:25-96.
Prasad, G. 1976. Branching in barley spikes. BGN 6:50-51.
Stephanov, T. and CH. Gorastev. 1976. Using of induced mutagenesis and intravarietal hybridization in winter two-rowed barley breeding. Barley Genetics III:197-202.
