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					   Title                         :    Genetic architecture of yield and its
                                      components in a spring x winter diallel cross
                                      of wheat (Triticum aestivum L.)
   Name of the student           :    Peer Arif Sultan
   Guide                         :    Shafiq A. Wani
   Degree                        :    PhD
   Year                          :    2004
   Key words                     :    Combining ability, genetic components of
                                      variance, graphical analysis, variability,
                                      correlation, path analysis, Spring and Winter
                                      wheats (Triticum aestivum)

                                        ABSTRACT

Genetic architecture of yield and its attributing traits were studied in a full spring x winter
diallel cross of wheat (Triticum aestivum L.) using five winter and five summer ecotypes.
The experimental materials, evaluated over two random environments in a completely
randomized block design revealed considerable variability for days to 50% heading, plant
height, productive tillers plant-1, leaf area index, spike length, spikelets spike-1, grains
spike-1, 100-seed weight, days to maturity, harvest index and grain yield plant-1.
Significant G x E interaction was also observed for most of the traits including grain
yield plant-1 revealing that the behaviour of the parents and crosses was not similar in the
set of random environments. Different sets of gene complexes were observed to affect the
yield component and maturity traits. Phenotypic and genotypic coefficient of variation
was high for productive tillers plant-1; moderate for plant height, spikelets spike-1, grains
spike-1, 100-seed weight and grain yield plant-1; and low for days to 50% heading, days to
maturity, leaf area index, spike length and harvest index.
Broad sense heritability was high for days to 50% heading, plant height, spikelets spike-1
and 100-seed weight ; moderate for productive tillers plant-1, spike length and harvest
index, whereas, narrow sense heritability was high only for plant height and moderate for
productive tillers plant-1, leaf area index and 100 seed weight. The low additive genetic
heritability (breeding value) is expected in the F1 hybrids because of high level of
heterzygosity at loci arising from the coming together of the different gene complexes.
On the basis of data pooled over environments, genetic gain was low for almost all the
characters indicating the role of environment in the expression of characters and higher
magnitude of heterotic behaviour in the crosses. This genetic gain is expected to increase
in the subsequent generations after following selective mating system (bi-parental
mating).
         Grain yield exhibited significant positive genotypic and phenotypic correlation
with all the component traits studied. However, it was negative and significant with
maturity traits at both the levels. This significant negative correlation of grain yield plant-
1
     with maturity traits might have arisen since under Kashmir valley conditions the
temperatures abruptly increase during May/June, which enhances the maturity
(flowering & physiological maturity). This needs to be further investigated into before,
scientific conclusions could be drawn for selection of early maturing high yielding
genotypes. For yield components, significant positive association was revealed between
the traits and similar inter-relationship was observed with leaf area and harvest indices.
Based on the study of cause and effect relationship, the direct contribution to grain yield
was observed from grains spike-1, productive tillers plant-1, plant height, and leaf area
index. High positive indirect effects were, however, observed via grains spike-1 and
productive tillers plant-1 in almost all the traits. The improvement in grain yield through
selection for yield component traits via., grains spike-1 and productive tillers plant-1 would
result in the isolation of putative high yielding genotypes in the present set of materials.
         None of the parents exhibited significant and desirable gca effect for all the traits.
The parents with desirable gca effect for grain yield plant-1 were SKW-192, SKW-209,
SKW-210 and SKW-211. For maturity traits the spring wheat parents demonstrated
earliness. Similarly, among the cross combinations none revealed the desirable sca
performance for all the traits. However, several cross combinations were identified to be
superior for various yield and maturity traits based on sca and per se performance. Five
top ranking and desirable crosses on the basis of sca performance for grain yield were
observed to be HS-240 x SKW-210, HS-240 x SKW-209, SKW-210 x HS-295, SKW-
209 x HS-365 and SKW-211 x HS-240. These crosses were mostly the result of high x
average or average x average general combiners. On the basis of per se performance five
top ranking cross combinations for grain yield included HS-240 x SKW-193, HS-295 x
SKW-192, SKW-211 x HS-295, VL-845 x SKW-210 and HWP-220 x SKW-211. By and
large, there was no correspondence between sca and mean per se performance for almost
all the traits. Manifestation of desirable sca effects due to contribution of more favorable
alleles and their interactions, could be used to generate desirable segregants. The two best
crosses possessing desirable sca effect for grain yield plant-1 and productive tiller plant-1
were HS-240 x SKW-193, HS-295 x SKW-192 and HS-240 x SKW-193 and SKW-209 x
HS-240.
         Graphical and component analysis of genetic variance revealed the significance
of additive gene action for plant height, productive tillers plant-1, leaf area index, days
to maturity and grain yield, whereas, components of variance due to dominance deviation
were significant for all the traits indicating the preponderance of non-additive gene
action in the inheritance of various traits. Average degree of dominance was in the over
dominance range for all the characters but in the graphical analysis their dominance for
most of the traits was in partial to complete dominance range. This upward bias in the
dominance variation in the component analysis was observed to have arisen due to
epitasis and/or linkage effects. Dominance was unidirectional for grain yield, spikelets
spike-1, grains spike-1 and maturity traits, whereas the gene distribution was observed to
be asymmetrical for all the traits except grain yield and harvest index. However, epistasis
appeared to govern the inheritance of days to heading, spike length, spikelets spike -1 and
grains spike-1.
Crossing of the spring x winter wheat genotypes would broaden the genetic base of the
population for selection of potent homozygous lines possessing high yield potential.
Further, introduction of elite winter wheat genotypes and their exploitation through
winter x spring wheat crosses is suggested to generate larger spectrum of variability for
use in developing suitable genotypes for high altitude Valley conditions by following a
selective diallel mating system to slow the process of the fixation of alleles.

				
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