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Triticeae Genomics and Genetics 2013, Vol.4, No.2, 3
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7
Considering the significant episthatic interactions
present in these crosses, contributing values of
15.65%, 47.96% and 15.04% on the means of studied
generations were detected in CR1, CR3 and CR4,
respectively. For GY P
-1
, the larger contributions of
episthatic interactions were observed in CR2 and CR5,
with 56.53% and 35.01%, respectively (Table 3).
Besides, CR5 indicated effects of higher complexity,
since it did not present a significant additive (a) effect,
and considerable magnitudes in all episthatic interac-
tions. For the character NP P
-1
, significant interactions
can be observed for CR1, CR2 and CR4, with
different contributions of these effects on the genera-
tion means: 14.31%, 45.87% and 7.61%, respectively.
Also, additive significant effects influencing the
generation means were found in CR1 (64.07%) and
CR4 (88.89%). Regarding the character PP, CR4 was
distinguished by a higher contribution of the additive
when compared to the dominant component in the
genetic control of the character (Table 3).
2 Discussion
Besides the use of mean and variances, genetic param-
eter estimates such as heritability and phenotypic
variance components have been considered as of great
importance in validating populations with high genetic
potential in breeding programs, serving to guide
towards more efficient selection (Vencovsky, 1969;
Lorencetti et al., 2005). In this sense, through the
parameters analyzed, it can be observed the presence
of genetic variability for the majority of the crosses
studied, suggesting that there is a great potential for
hybrid combinations in the rescue of superior individu-
als in segregant oat populations.
The occurrence of a higher genetic variability in
segregating generations, especially in F
2
, is supported
by the hypothesis of a larger number of segregating
loci when compared to the backcross generation. On
the other hand, the observation of reduced variance
values in the F
1
generation, according to Carvalho et
al. (2001), is due to the fact that this generation
presents a more stable behavior (higher homeostasis),
which can lead to the observation of plants in the
population with lower environment variation when
compared to the other fixed genotypes. The analysis
of mean and heterosis values at the F
1
generation for
the characters GY P
-1
and PP, reveals the presence of
positive heterosis for all crosses evaluated. According
to Fehr (1987), heterosis or hybrid vigor can be
defined as the superiority of individuals from F
1
gene-
ration, which can be significant in oat (self-pollinated),
since it can lead to higher genetic class amplitudes for
selection in the next generation. Regarding to F
2
, it
can be highlighted in all crosses, for the characters GY
P
-1
and PP, the presence of transgressive segregation,
except in CR4, for GY P
-1
. The transgressive segrega-
tion occurs when the phenotype of a segregating
population is much higher than the parental mean
value (Ibrahim and Quick, 2001), and in many cases
surpassing the best performing parent. This phenome-
non is suggested to come from contributions of
complementary genes from both parents, which is
routinely exploited in plant breeding when superior
individuals are selected (Ibrahim and Quick, 2001).
However, it was possible to obtain genetic variability
from crosses involving parents with similar means, as
observed in CR2 and CR3, for the character PP. This
is probably due to the fact that genes controlling this
character are complementary distributed between the
parents, i.e., present in distinct loci between both
parents, which, at the time of the cross are reunited
and accumulate as favorable alleles in the progenies.
The positive heterotic effect found in CR1 is an
indication of the presence of a large number of
dominant alleles at heterozygous loci in the F
1
generation, resulting in higher vigor loss for GY P
-1
,
NP P
-1
and PP in the F
2
generation. Crosses that reveal
heterosis in F
1
, followed by loss of vigor loss (LV) in
F
2
, can produce a higher number of genotypic classes
for selection, and these information can be extremely
useful for the breeder, especially regarding selection
intensity and the most adequate moment for its
application (Allard, 1960; Crestani et al., 2012).
The small contribution of σ
E
2
was due to the reduced
variances obtained for the fixed generations (P
1
, P
2
and F
1
) observed in this study. This parameter is
extremely important, because the variance caused by
the environment cannot be removed, since it represen-
ts, by definition, all the non-genetic variation, and a
large proportion of it is outside experimental control
(Falconer and Mackay, 1996). Therefore, for all
crosses evaluated a larger contribution of genetic
variance for the total (phenotypic) variance. However,
a small value for σ
G
2
(GY P
-1
) was observed, resulting
in the lowest H
2
(58.63%) estimate among all