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b) Specific combining
ability (SCA)
Specific combing ability effects for the eighteen crosses are
presented in Table
4. For specific
flag leaf area five crosses showed negative SCA effects of which HABA
20 x LU26S exhibited the maximum value. For epidermal cell size ten
crosses showed negative SCA effects. If smaller cell size is required
then the crosses HABA 20 x LU26S, LABA 7 x Pak. 81, LABA 9 x K-1595,
LABA 9 x LU26S and HABA 9 x K-1595 may be useful. In case of stomatal
size, seven out of eighteen crosses showed negative SCA effects. For
this trait crosses HABA 9 x LU26S, LABA 20 x Pak. 81 with negative
SCA effects are suitable. SCA effects for tillers per plant were
lower. However, 50% crosses showed positive SCA effects. Useful
crosses were LABA 7 x LU26S, LABA 9 x Pak. 81 and HABA 20 x K-1595.
In case of grains per spike, nine crosses showed positive SCA
effects. The potential crosses with high SCA effects were LABA 7 x
K-1595, LABA 9 x Pak. 81 and HABA 7 x Pak. 81. As regards the grain
yield per plant, 50% crosses showed positive SCA effects. The
prominent crosses were LABA 9 x Pak. 81, LABA 20 x LU26S, HABA 7 x
Pak. 81 and HABA 9 x LU26S.
The main goal of plant breeder is to search out better yielding lines
through hybridization programme. But when he breeds for drought
resistance, his main emphases would be on the selection of those
segregants which possesses maximum drought resistance combined with
high yield potential. Stress related characters are needed to be
incorporated in the existing high yielding cultivars thus enabling to
combat drought effectively. So keeping these points in mind and
observing the results of the experiment, it is suggested that Pak. 81
was the best tester and HABA 7 was the best line. This was suggested
because maximum values for the yield related traits and minimum for
epidermal cell size were observed in Pak. 81 (Table
2). Furthermore
all the crosses indicating maximum values for yield characters and
minimum for specific flag leaf area and stomatal size, involved Pak.
81 as tester. Pak. 81 was also best general combiner for yield traits
and specific flag leaf area. Similarly HABA 7 showed desirable
negative G- CA effects for specific flag leaf area, epidermal cell
size, stomatal size and desirable positive GCA effects for yield
characters. Cross HABA 7 x Pak. 81 showed the suitable SCA effects
for all the characters except for epidermal cell size. Although the
SCA effects of the cross HABA 20 x LU26S for the stress related
traits were more suitable but negative SCA effect of this cross for
grain yield made it less attractive. Similarly among the lines, HABA
7 performed well. It was good general combiner for all the traits
except for tiller number. Although LABA 20 showed highest desirable
negative GCA effects for specific flag leaf area and epidermal cell
size but its GCA effect for grain yield was negative while HABA 7
showed positive GCA effect for grain yield and acceptable negative
GCA effects for specific flag leaf area, epidermal cell size and
stomatal size (Table
3).
Maximum positive SCA effects for grain yield was observed in the
cross LABA 9 x Pak. 81 but again SCA effects for stress related
characters were also positive which are not desirable. The most
suitable cross with acceptable positive SCA effects for yield related
characters and acceptable negative SCA effects for specific flag leaf
area and stomatal size was HABA 7 x Pak. 81 (Table
4). Further
selection in the subsequent generations may produce plants combined
with drought tolerance and yield characters.
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