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Triticeae Genomics and Genetics 2013, Vol.4, No.2, 3
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plants, where one expects “a x a” interaction values to
be higher than “a x d” and “d x d” values.
Theoretically, in a linear direction, the episthatic effect
“a x a” can be a fixable component of the genetic
variation, easily explored for some characters through
single hybridizations and selection procedures.
Episthatic interactions such as “a x d” and “d x d”, are
not directional and can not be fixed through selfing in
self-pollinating plants and, therefore, would not be
favorable to the development of inbred lines for GY
P
-1
. They could be, however, interesting for hybrid
development (Saleem et al., 2005).
The detection of at least one type of epistasis in the
five crosses evaluated for GY P
-1
, gives support to the
idea of using the complete model for the analysis of
complex inheritance characters. On the other hand, in
the breeding of self-pollinating crops, the techniques
that beneficiate from a higher σ
A
2
and from the
interaction “a x a” are the most important in obtaining
genetic gains. As observed in this work, for the
character GY P
-1
, the effects “a” and “a x a” were
significant in all crosses, with exception of CR5. In
the crosses CR1 and CR4, only the interaction “a x a”
was detected as a significant episthatic effect, reaching
higher selection gains. The detection of a reduced
contribution of episthatic effects for the control of GY
P
-1
in CR1 and CR4 can not be disregarded, even if
the episthatic effect in this crosses is of “a x a” type,
showing the importance of an analysis considering the
complete additive-dominant-episthatic model, for
quantitative characters. Genic interactions between
non-allelic or episthatic genes can not be disregarded
in the elucidation of basic genetic mechanisms (Gravi-
na et al., 2004) and genetic models that disregard
epistasis can have some kind of bias (Cockerham,
1954; Valério, 2008). On the other hand, estimates
obtained from genetic parameter analyses are only
valid for the population from which the samples are
taken and also only for the environmental conditions
in which the study was conducted (Gravina et al.,
2004). Contrasting results found for the significance
of episthatic effects for the characters NP P
-1
and PP in
the different crosses, reveal some direct environmental
influence. This is more important when only one
environment is studied, where the g x e interaction can
have some influence on the episthatic effect. The
presence or absence of epistasis can be environmen-
tally dependent and, therefore, not related to the
genotype’s inheritance (Saleem et al., 2005).
As observed for the characters NP P
-1
, in CR3 and
CR5, where there was no significant episthatic interac-
tion detected, interpretations have to be made
cautiously since they present differences in sign and
significance of dominance effects, because the
negative and significant “d” effect (CR3) reduces the
character, therefore, not being a priority for breeding
programs, even if the three parameter model is
sufficient to explain variations for the genetic control
of this character. Thus, CR5 appears to be quite
interesting, since the “d” effect was non-significant,
even if the cross shows higher contribution of σ
D
2
to
σ
G
2
for this character. This is due to the fact that
variance and genic effect tests make use of different
information bits, which should be interpreted as
complementary data and should not be mixed. CR1
displays the highest difficulty for the selection of PP
in initial generations, due to the higher complexity of
genic effects that influence this character in this cross.
For the other crosses, substantial genetic gains can be
observed at early generations, since no significant
episthatic effects are detected. The best performance
was observed for CR4, which had the highest
additive/dominance ratio in the genetic control of the
character. As observed in this study, for the character
GY P
-1
, CR3 and CR5 crosses showed higher comple-
xity, having significant non-allelic interactions (“a x
a”, “a x d” and “d x d”). Many authors point out the
prevalence of epistasis in the genic effect of quantita-
tive characters in a range of populations (Falconer and
Mackay, 1996; Allard, 1960). Recent results reveal
large contributions of epistatic effects of “a x d” and
“d x d” type for the genetic control of PG P
-1
(Saleem
et al., 2005). Therefore, episthatic interactions were
substantially significant and should be taken into
account for the better understanding of the genic
effects acting in each cross, requiring attention from
the breeder when selection is performed.
There is presence of significant episthatic interactions
for the character grain yield per plant. The results
suggest that specific crosses in oats can lead to high
genetic gains in the selection at early generations. The
characters number of panicle per plant and panicle
weight presented the lowest complexity for the
estimated genic effects to more effective in selection.