Generation mean analysis, which provides the estimates of the main gene actions
(additive and dominance) and their digenic [(i), (j) and (l)] and trigenic
[(w), (x), (y) and (z)] interactions, helps in understanding the performance
of the parents used in the crosses and potential of the crosses to be used either
for heterosis exploitation or pedigree selection. Since durum wheat is grown
under varied environmental conditions, knowledge of gene action operating under
different environments is essential, because in the absence of such information
the breeding methods used may not result in appreciable improvement. The present
investigation was therefore carried out to estimate the type of gene action
under normal and late sown conditions for selection of most efficient breeding
methodology for genetic improvement of grain weight in durum. Therefore, the
three, six and ten-parameter models have been utilized to study and analyze
the genetic control of grain weight involving six diverse cultivars of durum
wheat.
Materials and methods
The experimental material generated from six diverse parents,
comprised three crosses namely, Cocorit 71 x A-9- 30-1, HI 8062 x
JNK-4W-128 and Raj 911 x DWL 5002. In each cross combination one of
the parents (Cocorit 71, JNK-4W-128 and Raj 911) had higher grain
weight. Twelve basic generations, involved in these studies were two
parents, F1 and F2, first backcross generations
with both parents (BC1 and BC2), where
BC1 was the cross F1 x female parent and
BC2 was F1 x male parent, their selfed
progenies (BC1 F2, BC2
F2) and second backcross generations (BC11,
BC12, BC21, BC22) i.e. the
BC1 and BC2 plants again crossed with both
original parents (BC1 x female parent, BC1 x
male parent and BC2 x female parent, BC2 x male
parent). These twelve populations of each of the three crosses were
evaluated in randomized block design with three replications in two
parallel experiments, one sown on 20th November (normal sown
condition) and other sown on 20th December (late sown condition) in
the same cropping season. Each replicate was divided into three
compact blocks. The crosses, each consisting of twelve populations
were randomly allotted to the blocks. All the twelve generations were
then randomly allotted to twelve plots within a block. The plots of
various generations contained different number of rows i.e. each
parent and F1 plots consisted of 2 rows, while each
backcross generation in 4 rows and F2 and the second cycle
of backcrosses in 6 rows. Each row was 5 m long accommodating 33
plants spaced 15 cm apart, row to row distance being 30 cm. Border
rows were provided at the beginning as well as at end of experimental
rows in each block. The experiment was planted at Research Farm of
Rajasthan Agricultural University, Agricultural Research Station,
Durgapura, Jaipur, Rajasthan, India. The weight of 100 seeds (g)
counted at random from the single plant yield. The data were recorded
on 15 random plants in each parent and F1, 30 plants in
each backcross generations and 60 plants in each F2 and
second backcross generations in each replication under both the
environments.
Standard statistical procedures were used to obtain means and
variances for each generation and each environment separately, as
suggested by Snedecor and Cochran (1968). The data of each population
in both environments were analyzed separately by joint scaling test
of Cavalli (1952) to determine the nature of gene action. Components
of heterosis in the presence of digenic (Jinks and Jones 1958) and
trigenic interactions were calculated as suggested by Hill
(1966).