While plant height of the timopheevi-like mutant was found to be
greater than that of T. turgidum dicoccoides and similar to that
of T. timopheevi lines, tillering was slightly higher than T.
turgidum dicoccoides and higher than that of T. timopheevi (Table
2). A significant deviation of the somatic mutant was in spikelet number
per head (Table 1) which increased from a mean
value of 13.50 in the dicoccoides mother plant to a mean of 22.12
in the mutant with a significant increase in head density from 15.50 to
26.38 spikelets (per 10 cm length of rachis) respectively. In both characters
the timopheevi-like mutant exhibited close similarity to the lines
of T. timopheevi. Despite decreased grain number per spikelet and
percentage fertility in the timopheevi-like mutant head compared
with the dicoccoides mother plant it exhibited increased grain number
per head which could probably enhance its survival and spread in natural
environments. The reasonably high fertility, high grain number per head
and genetic stability,i.e. homozygous nature (KUSHNIR & HALLORAN 1983a,
1983b) of the mutant appears to have provided it with a high potential for
immediate fitness in natural environments. The close similarity in growth
habit between the timopheevi-like mutant and the lines of T. timopheevi
indicates that the potential for ecological adaptation is provided by the
macromutation in addition to the chromosome and plant morphology modifications
that occurred in the timopheevi-like somatic mutant. A similar type
of macromutation (the erectoides mutation) with a wide range of drastic
modifications was described in Golden barley and, similar to the timopheevi-like
mutant, caused changes in plant morphology, karyo-morphology and cross-sterility
and ecological adaptation were reported (GUSTAFFSON 1954; VON WETTSTEIN
1954).
The origin of T. timopheevi from T. turgidum dicoccoides from
chromosome interchange was suggested by WAGENAAR (1966) and his view is
supported by the physiological evidence in this study. The similarities
in morphology and growth habit between the timopheevi-like mutant
and the lines of T. timopheevi investigated in the present study,
and the uniformity of these characters found in all the introductions of
T. timopheevi from USSR studied by WAGENAAR (1966) indicate the possibility
for some "pre-tendency" for the occurrence of a particular pattern of rearrangement
of the dicoccoides chromosome complement giving rise to a phenotype
similar to T. timopheevi. Such a "pre-disposition" might account
for the lack of intermediate forms between T. timopheevi and T.
turgidum dicoccoides and the possibility of repetitive evolution of
the timopheevi form of wheat from a turgdium prototype. It
is also possible that alternative chromosome rearrangements, if they were
to occur, might not be viable and thus eliminated. |