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Mutation in the length of internodes of wheat
Kiril DJELEPOV
The Institute for Wheat and Sunflower, nearby General Toshevo, Bulgaria
Shortening of the last internode as a result of an influence with X-rays
was being observed with some hard wheat experiments (DJELEPOV and CHAVDAROV
1969). In all cases up to now, this kind of mutation has a modificational
character.
QUALSET et al. (1970) have, for the first time, selected through
an influence with gamma-rays, a mutant in M2, distinguished
for the shortening of the first internode beneath the ear by 33 per cent
as also of the second internode by 15 per cent which resulted in the total
height of the mutant being shortened by 18 per cent compared to that of
the starting variety.
The present article reports on an induced mutant in wheat, distinguished
for its first internode beneath the ear being shortened by 30 per cent
and for the curtailment of its second internode by 50 per cent.
Seeds of Mironovskaya 808 were subjected to X-ray treatments at doses
of 10, 15 and 20 kR. A portion of the seeds in M2 were treated
with EMS at concentrations of 0.2 and 0.4 per cent. An immediate field
sowing of the seeds followed the treatment and the rinsing with water.
In the progeny of a plant of the 10 kR. plus 0.4 per cent variant, two
of a total of eight plants with a greatly-shortened last but one internode
and a shortened last internode were selected. The mutant plants produced,
in their subsequent generations, plants with a mutant phenotype alone.
Normal plants broke down into normal and mutant plants, at a ratio similar
to that noted above. These data suggest of a recessive mutation, which,
after a self-pollination in M2, exhibits itself in a part of the plants
which happen to be in a state of recessive homozygosis
Table 1 gives the morphological characteristics of the mutant and
of the starting variety. The analysis done was based on good levelled
and consolidated plants of M6.
As seen, the mutant form is comparatively lower in size than the starting
variety, it possesses a greater tillering ability and a shorter ear with
less spikelets and grains in it. Rachis of the ear appears in a zigzag
shape and shorter and more rounded are its spikelet glumes. Grain is small,
rounded and less in number as a result of a partial sterility. The most
essential difference between the mutant and the starting variety proves
to be the length of the internodes. There is lengthening in the first
to the third internodes, while the forth and fifth internodes shorten.
Leaves of the third and fourth node envelope the ear. The straw between
the last node and the ear appears very thin and brittle. Compared to the
starting variety, ear let out the leaves considerably later ; then the
last internode lengthen, yet, to the end of the vegetation process it
remains shorter than that of the starting variety. The height of the mutant
plants lessens in its average by 30-35 per cent than that of the starting
va riety (Fig. 1).
The similar mutant, described by QUALSET et al. (1970) is characteristic
for the strong shortening of its last internode controlled by a dominant
gene. To our case, more strongly is the shortening of the last but one
internode and the data from the mutation manifestation show the mutation
to be a recessive one.
The reduced values of the components which characterize the yielding and
the partial sterility display the induced mutant to be with a lowered
viatality. Cytological analysis indicates a normal chromosome number (2n=42).
It is probably that the reasons for these abnormalitise should lie in
the semilethal effect of the recessive homozygotic condition.
The induced mutant M 189/255 represents a new sourse of dwarfness, which
can be put to use in the selection of low-sized wheat varieties.
Literature cited
DJELEPOV, K. P., G. A. CHAVDAROV 1969. Problems of Soft Wheat Selection
and Agronomical Practices, Sofia.
QUALSET, C. O,. G. N. FICK, M. J. CONSTANTIN and T. S. OSBORNE 1970. Science
169, No. 3950.
(Received August 17, 1972)
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