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Results and Discussion
Simple correlation coefficients (phenotypic) between all
possible combinations of four quantitative traits were
estimated (Table 2). Results
reveal that grain yield per plant exhibited a strong
positive correlation (P>=.01) with tiller number per
plant and seeds per spike. The correlations reported by
BHATT (1973), VIRK and VERMA (1972) and LARIK (1978) also
revealed similar associations. Seeds per spike were
positively correlated (P>=.05) with spike length but
negatively correlated with tiller number per plant. However,
negative correlation of seeds per spike with tiller number
per plant did not reach the significance level.
The high positive correlation coefficient indicates that
selection based on tiller number per plant and seeds per
spike could be more rewarding and will equally improve the
grain yield. Non-significant positive correlation between
spike length and grain yield indicate that the selection on
the basis of longer spikes do not guarantee the high yield.
Out of 6 possible combinations, only one combination
produced negative relationship. A negative correlation occur
when two developing structures of a plant compete for a
common nutrient supply and a negative correlation may arise
if one structure is favoured over the other in amount of
nutrient supply (ADAMS, 1967).
The pathways through which the three yield components
operate to produce their phenotypic associations with grain
yield reveal their direct and indirect contributions
(Table 3) and are demonstrated
diagramatically in Fig. 1. The path
coefficient analysis showed that the direct effect of tiller
number on grain yield was high and positive (0.6013). The
indirect effect via spike length (0.0083) and seeds per
spike (0.0893) was negligible. The total correlation
coefficient (0.6074) between grain yield and tiller number
was mainly due to direct effect. Other workers (BHATT, 1973
; LARIK, 1978 and VIRK and SINGH, 1972) have also concluded
that tiller number per plant is an important yield component
in wheat mutants. Indeed under most agricultural
environments tillering is a valuable mechanism to enable the
crop to exploit fully the environment (KIRBY and FARIS,
1972). Production of effective tiller has also evolutionary
significance (LARIK, 1978) and spikes per plant are known to
exert a preponderant effect upon yield in wheat (JAIMINI
et al., 1974).
The direct effect of spike length on grain yield was
positive but not so pronounced (Table
3). The indirect effect via tiller number and seeds per
spike was also positive but very low in magnitude. Hence the
total effect of spike length on grain yield remained rather
low. Therefore spike length cannot be used as a reliable
criterion in the selection of high yielding mutant
genotypes.
In contemporary model of yield (WORLEY et al., 1976)
seed is recognised as the basic unit of yield. Semi-dwarf
cultivars of wheat have achieved their yield advantage over
tall cultivars primarily because of seeds per spike (DIEHL
and WELSH, 1972). All the genotypes included in the present
study are classified as semi-dwarf (LARIK, unpub.) and
therefore, the highly significant (P>=.01) positive
association of seeds per spike with grain yield is quite
understandable (Table 2). This
behaviour was also confirmed by path coefiicient analysis in
which seeds per spike have shown highest direct effect
(0.7234) on grain yield (Table 3).
However, indirect effect via tiller number (-0.0806) and
spike length (-0.0512) have somewhat diluted the direct
effect. A number of complex and interlocking systems
(WALTON, 1972), contribute to the expression of a
quantitative character like yield. The high residual effect
observed in present studies (Fig. 1)
suggest that the path coefficient obtained within the
constraint of the construct do not reflect the influences of
the second order components.
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