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Mean performances of the
eighteen crosses are presented in Table
2, which revealed
presence of hybrid vigour for most of the characters studied. The
hybrids manifested varied performances to their better parents for
most of the traits evaluated. In case of specific flag leaf area,
majority of hybrids, particularly those of involving HABA 20 and LABA
9 indicated increased vigour over their parents. Maximum flag leaf
area was observed in LABA 9 x LU26S while minimum value was found in
LABA 7 x Pak. 81. The average of the hybrids presented 7.8% increase
over the average of parents. Most of the hybrids showed decrease in
epidermal cell size. Maximum value was observed in LABA 9 x Pak. 81
and minimum in HABA 20 x K-1595. On the average 6.8% decrease was
observed in hybrids compared to the parents. Stomatal size was less
variable in hybrids. However, increase in vigour was observed in some
cases. Maximum value was observed in LABA 20 x LU26S which also
exceeded its better parent LABA 20 by 18.2%. Minimum stomatal size
was observed in HABA 7 x Pak. 81.
Tillers per plant were more variable in hybrids than in parents and
most of the hybrids showed reduced tillers compared to their parents,
particularly the hybrids involving HABA 9, LABA 7 and LABA 20.
Maximum tiller number was observed in LABA 9
x Pak. 81 while minimum number was obtained in HABA 7 x
LU26S which was also less
than its lowest parent HABA 7. Maximum number of grains per spike was
observed in HABA 7 x Pak.
81 hybrid while
minimum was exhibited by LABA 7
x LU26S. In case of
grain yield per plant most of the hybrids showed increase over their
parents. Some hybrids like LABA 9 x Pak. 81, HABA 7 x K-1595,
HABA 20 x K-1595,
LABA 7 x
LU26S and LABA 9 x K-1595 exceeded their better parents. On average
basis 8.7%
increase was observed in
hybrids over the parents.
Combining ability studies
(a) General combining ability (GCA)
General combining ability is the mean performance of a parent in a
series of crosses. GCA estimates for all the characters are given in
Table
3 to
identify potential parents for subsequent breeding. Flag leaf is the
most important among all leaves. In case of specific flag leaf area,
negative GCA effects are desirable. Therefore, selection of wheat
genotypes having greater leaf weight and smaller leaf area are
preferred since they may enable the limited photosynthetic activities
to be continued under moisture stress. LABA 20 and Pak. 81 showed the
highest negative GCA effects for this character as female and male
parent, respectively. Mccree and Davis (1974) concluded that cell
enlargement was adversely affected by moisture stress. Negative GCA
effects are desirable for epidermal cell size. LABA 20 among the
female parents and K-1595
among males were the best general combiners which seemed to be
promising to decrease the epidermal cell size.
Plants with smaller size of stomata can better tolerate the moisture
deficiency as they efficiently and economically regulate the supply
of water. Spence et al. (1986) concluded
that the geometry of resulting mechanical properties of small stomata
gave the capability of opening or maintaining open pores with lower
guard cell pressure, relative to the turgor of the surrounding
epidermal cells. Through this mechanism, evaporation rate through
stomata is much reduced as there will be greater resistance in the
path-way of water during evapotranspiration through stomata. As a
result photosynthetic efficiency of a plant may be increased or
maintained, thus ultimately increasing the final grain product. So
negative GCA effects are given importance for stomatal size. For this
point of view K-1595
among males and HABA
7 among females
showing highest negative GCA effects were found to be useful.
Productive tillers per plant is a major yield component. Therefore
parents such as LABA 9, HABA 20 and Pak. 81
seemed to be good combiners for increasing tillering ability.
Similarly grains per spike is also an important yield contributing
factor. The useful parents depicting positive GCA effects for this
trait included Pak. 81, LABA 7, LABA 9
and HABA 7. The
suitable parent showing high GCA effects for grain yield were HABA 7,
LABA 7 and LABA 9.
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