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Triticeae Genomics and Genetics 2014, Vol.5, No.2, 1-11
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6
obtain desirable results. Different researchers have
different opinions in explaining the phenomena of
heterosis. According to Cox & Murphy (1990) and
Picard et al., (1992) opportunity of obtaining superior
genotype is dependant if both parents have at par
performance instead of one parent being lesser or
better in terms of one or more traits. However, in the
studies of Fonseca & Patterson, 1968; Baric et al.,
2004 genetic variability between parents is a criterion
to develop superior hybrids. In this experiment, the
spotlight was on the development of hybrids by using
parental sources having tolerance ability against heat
shocks so that they can be effectively utilized in future
breeding programmes.
Plant height is an important trait and largely
contributes in biological yield of wheat. Negative
percentages of heterosis and heterobeltiosis for plant
height are preferred over their mid and better parents
in wheat breeding because short stature is a desirable
character as it confer resistance against lodging thus
produce higher yield. Desirable recombinants from
such genetic material through selection can be
obtained. Present results showed many desirable
negative estimates which are in accordance with the
results of Abdullah et al. (2002) and Rasul et al.
(2002).
For tillers per plant under both conditions many
crosses showed increase both in mid and better
parental values which may be exploited in later
generations. Increase in vigor for tillers per plants was
reported by Chowdhry et al. (2001) and Shah et al
.
(2004), but negative heterosis for tiller number per
plant was observed in the studies of Knobel et al.
(1997) and Farooq and Khaliq (2004). For peduncle
length under both environments positive and negative
estimates were observed, however peduncle length in
hybrid wheat was found to increase grain yield in
many crosses (Chowdhry et al., 2001).
In the current studies many crosses offer and
opportunity to increase 1000 grain weight which is
another important yield component. By exploiting
heterosis for this trait, researchers found this trait as
direct contributor for increasing grain yield in hybrid
wheat (Shah et al., 2004; Akbar et al., 2007).
Yield and yield related characters having significant
positive heterosis and heterobeltiosis are important for
selection of these characters in crosses for future
breeding programme. Grain yield is related with
various traits such as morphological, physiological
and yield components. As a result of the research
conducted by many researchers on hybrid wheat found
the ranges of heterosis for grain yield from 6%
(Borghi et al., 1986) to 41% (Zehr et al., 1997). In the
current studies the values of maximum heterosis for
yield was 28.07% under normal and 27.02% under
stressed conditions while better parental values were
from 15.58% under normal and 13.62% under stress
conditions. The value of mid parent heterosis for grain
yield was observed as high as 72 % under normal
irrigation conditions and it increased to 127 % under
water stress conditions (Solomon et al. 2006).
Similarly some researchers reported negative heterosis
for grain yield (Farooq and Khaliq, 2004).
The results of heterosis indicated that hybrid vigour is
accessible for the commercial production of wheat and
selection of desirable crosses having heterotic and
heterobeltiotic effects. The cross combinations like
Inqilab-91 × Shalimar-88, Shalimar-88 × Maya/Pavon,
Chenab-2000×Punjab-85, Maya/Pavon×Chenab-2000,
Shalimar-88×Uqab-2000 and Uqab-2000×Maya/Pavon
are the best hybrids which maybe further exploited
because of their ability to perform well under normal
and even heat stress conditions.
3 Material and Methods
The experimental material developed after screening
against heat was comprised of seven wheat cultivars
including five locals Shalimar-88 (Tolerant),
Chenab-2000 (Tolerant), Inqilab-91 (Moderately
tolerant), Uqab-2000 (Susceptible but yielder) and
Punjab-85(Susceptible but yielder) and two exotic
CIMMYT originated cultivars Weebli-1 (Susceptible
but yielder) and Maya/Pavon (Tolerant) were sown in
the field on 5
th
of November, 2006 in the Department
of Plant Breeding and Genetics and later hybridized in
all possible combinations including reciprocals
following diallel mating system. During next crop
season, seven wheat varieties/lines (parents) and their
hybrids (F
1
) were planted in field in two sowing dates
on 10th of November, 2007 and 25
th
of December
following a triplicated randomized complete block
design. Thirty plants of each genotype were grown in
a 5 m long row in each replication. The plants were
spaced 15 and 30 cm apart within and between the
rows, respectively. To keep uniformity in the distance