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Spike length in mutant strains derived from different
cultivars significantly enhanced as compared to their
respective controls, except mutant strain No. 10 of Nayab in
which spike length is signfiicantly (P>=0.05) reduced
whereas, in mutant No. 13 of Indus-66 spike length was
non-significantly decreased. Mean spike length of mutant
strains derived from C-591 cultivar were reasonably
homogenoeous. Similar significant shifts in mean values for
spike length was also observed by LARIK (1975a, b,. SIDDIQUI
and GHAFOOR (1974).
For spike length, the mutant strains derived from mutagenic
treatments of Indus-66 cultivar exhibited an increase of
genetic variance as compared to all other mutant strains,
this could be due to low yielding mutant strains (Table
2). Similar conclusions have also been drawn by GAUL
et al. (1966) and SIDDIQUI and GHAFOOR ARAIN (1974).
The heritability and genetic gain expected from selection
also showed same tendency as the genetic variance. These
estimates were of higher magnitude for the mutant strains of
Indus-66 cultivar compared with C-591 and Nayab control.
Thus indicated greater gains from selection for spike length
are anticipated among the strains of Indus-66 (GHAFOOR
ARAIN, 1973).
Spikelets per spike, seeds per spike and seed index
(1000-seed wt.) are important yield components and are
considered a reliable measure of yielding ability BOROJEVIC
and BOROJEVIC (1972) as the frequency of induced changes in
next generation depends on the number of seeds which
transmit them (LARIK, 1978). The best criteria for the
evaluation of superior genotypes is a comparison of its
1000-seed weight with the mother variety (GUSTAFFSON et
al, 1971). Mean values for these quantitative characters
were significantly (P>=0.01 and 0.05) reduced, except
mutant strain No. 44 and 37 of Nayab and Indus-66 for
spikelets per spike, mutant No. 44 and 13 of Nayab and
Indus-66 for seeds per spike and mutants No. 27 and 44 of
Nayab for seed index. These mutant strains displayed
significant (P>=0.01, 0.05) increase for these
quantitative characters over their respective controls. In
the present study, the shift of mean values for these
quantitative characters is mostly in negative direction, it
provides support for the hypothesis of GAUL and AASTVEIT
(1966) which states that the change in the mean values for
the quantitative characters occurs both in positive and
negative direction and is associated with reduced vitality
independent of the genotype used.
Spike length of mutant-13 of Indus-66 and seeds per spike of
mutant-7 and 28 and mutant-27 of C-591 and Nayab
respectively were not significantly alterd from that of
their respective controls. The non-significant shift in mean
values of these characters is in agreement with findings of
GHAFOOR ARAIN and SHEPHERD (1977) in wheat and OKA et
al. (1958) in rice.
Highest genotypic co-efficient of variation was given by
mutant strains No. 37 of Indus-66 for spikelets per spike,
seeds per spike and seed index, indicates the potential for
the improvement of these characters in the mutant
populations. Heritability and genetic advance were of higher
magnitude for the mutant strain No. 37 of Indus-66 for
spikelets per spike and seed index and mutant No. 44 of
Nayab for seeds per spike. This indicates that greater gains
from selection for these characters are anticipated among
the strains of Indus- 66 and Nayab.
The present studies conclude that selection for superior
genotypes for yield and yield components having low
heritability values and low genetic advance is very
difficult. It is therefore imperative from the breeders
point of view to select those attributes displaying high
heritability values among the mutant strains. The present
studies have provided an evidence on the induction of
genetic variability connected with yield and yield
components of wheat crop. Thus, induced genetic variability
can effectively be exploited for evolving mutant strains
possessing desirable attributes.
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