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Triticeae Genomics and Genetics 2013, Vol.4, No.2, 3
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characters in all crosses. In this case, higher selection
efficiency is only obtained in advanced generations,
since the increase in homozygosis, as a consequence
of selfing, leads to an increase in the strict sense
heritability (Falconer and Mackay, 1996; Bertan et al.,
2009). On the other hand, the adjustment to the
environment can proportionate higher success in the
H
2
values, since the environment factor in this case,
has a large contribution to the total variation.
σ
G
2
is generally the result of adding σ
A
2
, σ
D
2
and
epistasis, however, in the present work, σ
A
2
was the
major factor contributing to σ
G
2
for all characters, in
the majority of crosses. This is very helpful to the
breeders, since it is the only genetic effect quickly
fixable along succeeding selfing generations. The
major contribution of σ
A
2
for GY P
-1
was observed in
CR1, indicating the presence of similar alleles among
the parents, increasing the magnitude of the additive
component (Saleem et al., 2005). Thus, greater
success is obtained in the selection process, due to a
higher h
r
2
(53.08%). On the other hand, a high σ
A
2
does not mean that the character is only under
influence of additive genic action, i.e., that the genes
act additively, without any dominance or epistasis.
The σ
A
2
can originate from genes with any degree of
dominance or epistasis, and only if all σ
G
2
is additive,
it will be possible to conclude that there is neither
dominance nor episthasis.
The high σ
G
2
found in CR3 for GY P
-1
can be
explained by the genetic distance between these
parents. A study performed by our group detected,
using morphological markers, a large distance
between the genotypes used as parents in CR3,
suggesting that a higher genetic variability would be
obtained in the populations formed from this combin-
ation (Lorencetti et al., 2005). This combination will
certainly provide a high h
a
2 value, since a higher σ
G
2
will be generated from this combination. On the other
hand, the breeder would face some difficulties on
early generations, due to the higher contribution of σ
D
2
to σ
G
2
in this character. This result is corroborated by
the reduced narrow sense heritability (h
a
2
) values
found, resulting from the reduced contribution of
additive gene effects for the character. Reduced h
a
2
coefficients can be associated with a lower additive
genetic variance, higher environment variance and
higher genotype vs. environment (G x E) interactions
(Fehr, 1987).
Heritability has a predictive role, which expresses the
reliability of the phenotypic value as an estimator of
the genetic value, such as the higher the heritability,
the higher the genetic gain through selection (Hayes
and Thill, 2002). Thus, CR3 showed interesting results
for NP P
-1
, with higher h
a
2
(>70%), which can favor
larger selection gains and would be prioritized for
indirect selection aiming to increase GY P
-1
. Recent
observations have shown that the character NP P
-1
has
high positive correlation with GY P
-1
(Benin et al.,
2005). Besides, the efficiency of indirect selection is
increased when the secondary has a higher heritability
than the primary character (Fehr, 1987), as observed
here, with heritability values of 48.92% and 29.64%,
respectively for NP P
-1
and GY P
-1
, in CR3. For the
character PP, a higher contribution of σ
A
2
to σ
G
2
and a
negative value for σ
D
2
was observed in CR5. This
result can be due to estimates coming from distinct
populations, since for the estimation of σ
G
2
, both
parents and F
1
are used, while for σ
A
2
, backcross
generations are included (Silva et al., 2002). On the
other hand, Carvalho et al. (2001) pointed out the need
for the correction of this result, since the simple
subtraction of the additive variance from the genetic
variance to obtain the dominance variance can lead to
errors, expressing negative values for the dominance
action due to a superestimation of additivity. There-
fore, even with corrected values, CR5 is superior to
CR4, showing higher σ
A
2
than σ
D
2
for the character PP.
As observed in the model adjustments for the three
target characters, in some cases, the additive effect
was non-significant. This can be explained by the fact
that additivity effects represent the sum of individual
additive gene effects and, since their values can be
positive or negative, their estimates may turn out to be
non-significant, even when each of the genes involved,
individually, shows substantial additivity. This could
occur in cases where the genes act in opposing
directions, mutually cancelling their effects (Mather
and Jinks, 1982; Saleem et al., 2005).
Exploring the character GY P
-1
in early generations
can be troublesome, since episthatic effects were
observed in the five crosses tested. The episthatic
effect “a x a” always seemed inferior to one or two
interactions (“a x d” or “d x d”), which can lead to
major problems for the breeder of self-pollinating