RESULT AND DISCUSSION 1 Growth and genetic parameters
Bogor, 21-22 October 2015
765 ………λλλλλλλλλλλλλλ. 5
where, b
j
is the coefficient of weight for the j-th trait, and x
ij
is the adjusted least square estimate of the i-th family on the j-th trait.
The coefficient of weight b was calculated as a form vector by the following matrix formula:
λλλλλλλλλλλλλλλ..λλ..λλλλλλλλλ6 where, P, G and a are phenotypic variance covariance matrix, that of family and vector of
relative economic weight for the traits, respectively. The adjusted least square estimate was calculated by the following formula:
[ ⁄
] ⁄
........................................................................................7 where, a
ij
, σ
2 fj
, σ
2 ej
and n
i.
are the lest square estimate of the i-th family on the j-th trait, the family variance component of the j-th trait, that of error variance and number of plots of the
i-th family, respectively. For the convenience of analysis, expected genetic gain brought by family selection based on
the index value is calculated by assuming one unit of selection intensity with the formula as follows:
[ ]
λλλλλλλλλλ.λλλ..λλλλλλ..λλλ8 Comparisons for variances, genetic parameters and genetic gain between the two groups of
family: type-1+2 and type-1+2+3 were made to observe the impact of “recycled genetic resources”
in the third-generation progeny trial of A. mangium.
3. RESULT AND DISCUSSION 3.1 Growth and genetic parameters
Along the first three year ages, growth and form traits varied among the three Types of family Table 1. Plus trees families from Type-1 which were improved through two cycles of
breeding generally performed better than the families from Type-2 and Type-3 in all traits with superiority ranged from 0.8 - 9. Subsequently the Type-2 were generally better than Type-
3, except for stem straightness. This result indicated that the series of selection practiced in the first and second-generation breeding cycles were done properly to achieve higher positive
genetic gain accumulatively from generation to generation. The superiorities resulted in this study were in agreement with the report of realized genetic
gain observed in second-generation seedling seed orchard Nirsatmanto et al., 2004; Nirsatmanto et. al., 2013. It should be noted here that the superiority is a response to family
and plus trees selection in the orchard and the gain seemed to become greater in operational if compared to the unimproved seed. This is because the sub-line B used in this study consisted
of family originated from Oriomo region which was recognized as the most productive of PNG provenances Harwood Williams, 1991, Kari et al., 1996.
Bogor, 21-22 October 2015
766 Combining 57 families from all Types Type-1+Type-2+Type-3 resulted similar family
variation as those combining from only 44 families Type-1+Type-2, except for height at two years of age. This similar family variation seemed due to an identical by descent in family
between Type-1 and Type-3. This is because selected family in Type-3 added into third- generation is same as those in Type-1. As a result, the magnitude of family variation was
maintained similarly between both groups of type family 57 families and 44 families. On the other hand, however, the magnitude of variation from the 44 families was accompanied by
increasing of their error variance. This is indicated that the reduction number of families is subject to greater experimental error, even though the increasing of error variance was not
reflected in the estimates of heritability. The value of heritability was more reflected by the magnitude of family variance.
Table 1: Mean of height, dbh, stem straightness and genetic parameters from three years of age measurements
Family and genetic
parameters height m
dbh cm stem straightness
age-1 age-2
age-3 age-2
age-3 age-2
age-3
Type-1 2.50±0.03
7.19±0.06 11.88±0.05
6.7±0.09 11.4±0.12
3.6±0.03 3.6±0.04
Type-2 2.48±0.04
7.07±0.08 11.66±0.06
6.3±0.12 10.8±0.15
3.3±0.05 3.4±0.05
Type-3 2.45±0.04
6.95±0.09 11.57±0.07
6.0±0.12 10.6±0.18
3.5±0.05 3.6±0.05
Grand mean 2.48±0.02
7.11±0.04 11.75±0.03
6.4±0.06 11.1±0.08
3.5±0.02 3.5±0.02
Family variance component
2 f
0.0126 0.0155
0.0791 0.0633
0.0900 0.0904
0.3126 0.3173
0.5203 0.5213
0.0134 0.0186
0.0345 0.0411
Error variance
2 e
0.2396 0.2618
0.9999 1.0274
1.1351 1.1456
2.8162 3.0069
6.5981 6.6526
0.7018 0.6937
0.7755 0.8086
Individual heritability h
2 i
0.13 0.15
0.18 0.14
0.27 0.27
0.32 0.30
0.27 0.27
0.07 0.09
0.15 0.17
Family heritability h
2 f
0.26 0.29
0.31 0.27
0.54 0.54
0.52 0.51
0.54 0.54
0.21 0.25
0.37 0.41
Note: number in parentheses is the parameter that was calculated based on combination of 44 families from type- 1 and type-2 only type-3 excluded
Table 2: Observed significance associated with the analysis of variance for three years measurements of height, dbh and stem straightness
Source of variance
p-value height year
dbh year Straightness year
age-1 age-2
age-3 age-2
age-3 age-2
age-3
Replications .0001
.0001 .0001
.0001 .0001
.0001 .0001
.0001 .0001
.0001 .0001
.0001 .0001
.0001 Type of family
0.4317 0.4641
0.0043 0.0361
0.0001 0.0029
.0001 0.0005
0.0001 0.0029
.0001 .0001
0.0012 0.0035
Family within Type .0.0001
.0001 .0001
.0001 .0001
.0001 .0001
.0001 .0001
.0001 0.0939
0.0366 .0001
.0001 Family x replication
.0001 .0001
.0001 .0001
0.0093 0.0233
.0001 .0001
0.0093 0.0233
0.0006 0.0001
0.0004 0.0060
Note: number in parentheses is the observed p-value based on combination of 44 families from type-1 and type-2 only type-3 excluded
Bogor, 21-22 October 2015
767 Adding the Type-3 into third-generation breeding population tended to increase the family
variation, but the magnitude of variation seemed to be reduced as tree getting older Table 2. Except for stem straightness at two years of age, variation of the family within the types
showed a similar significance among the 57 families and 44 families. It confirmed a consistently significance of the family variations among the two groups along the three year
measurements, except for stem straightness at two years of age. This result indicated that the amount of genetic improvement could be continuous attained through third-generation of tree
improvement. In addition, the increased of error variance in 44 families group was not reflected into the weakness of significances.
Correlations within growth traits height and dbh using the data from 57 families were higher than the correlation between growth traits and form trait Table 3. The correlations between
the growth traits and form trait were generally weak, and for some cases were negative. On the other hand, genotypic correlation was consistently higher than phenotypic correlation for
almost all traits, indicating that stronger relationships existed in genetic than that in phenotype. The high genetic correlation accompanied with high estimates of heritability would
become essential factor for observing the family performances using selection index. This is because the index would be constructed by combining information from several traits. The
value of genetic correlation and heritability obtained in this study seemed to be sufficient for constructing the selection index for A. mangium, especially for the traits at two years of age. On
the other hand, the weak and negative correlation based on the data in three years of age brought the data from this age would not sufficiently available for selection index analysis.
Table 3: Phenotypic correlation bellow diagonal and genotypic correlation above diagonal among the measured traits from 55 families
Traits height-1 height-2 height-3 dbh-2
dbh-3 straightness-2 straightness-3
height-1 -
1.0285 0.7668
0.6526 0.7612
0.5710 0.6798
height-2 0.7940
- 0.9089
0.9926 0.9013
0.4658 0.3184
height-3 0.6769
0.7748 -
0.9452 1.0000
0.3310 -0.1316
dbh-2 0.7049
0.8630 0.9023
- 0.9450
0.3347 -0.0912
dbh-3 0.6746
0.7717 0.9999
0.9020 -
0.3187 -01365
straightness-2 0.2007
0.2492 0.2066
0.1853 0.2032
- 0.6874
straightness-3 0.1144
0.0971 -0.1077 -0.1407
-0.1099 0.410
-
3.2 Selection index In current study, selection index was constructed based upon the data from two years of age
instead of the data from three years of age, involving tree height, dbh and stem straightness. This is because the weak of correlation among the traits at three years of age, especially for
stem straightness. Due to the difficulty and limitation of the available data, for convenience the relative economic weight value was calculated as an inverse of the phenotypic standard
deviation of family mean in each trait. Among the traits used for index calculation, growth traits height and dbh received higher
coefficient weight than form trait stem straightness in the both groups of family type Table 4. The lower weight for stem straightness might reflect the low of family variance as
indicated by the weak and non-significant differences among the tested families Table 2. By assuming the same number of selected family 22 families, that is intensity of selection at 1.00
for Group 1 and at 0.789 for Group 2, the selection index provided a positive value of selection differential for all traits. The highest selection differential was found at dbh, which
was then followed by tree height and stem straightness. Except for stem straightness, selection
Bogor, 21-22 October 2015
768 differential for family in Group 1 was higher than that in Group 2. Although the mean value
of each trait was lower, absolute gain in Group 1 was higher than that in Group 2 and it provided increases of relative genetic gain at around 15 - 25 for tree height and dbh. It
indicated that adding some amount of number family from the original founder families in first generation grandparents increased genetic gain in third-generation breeding cycles,
especially for the traits which having high heritability.
Table 4: Summary of coefficient weight and expected genetic gain based on selection index at the two years of age from matrix analysis
Group Family
Trait b
Selection Differential
1
Absolut e gain
1
Mean
1
Relative gain
Type Number
1 Type-1 + 2 + 3
57 Height-2
0.863 0.533
0.209 7.031
3.0 Dbh-2
0.849 0.789
0.351 6.364
5.5 Straightness-2 0.409
0.064 0.030
3.473 0.9
2 Type-1 + 2
44 Height-2
0.696 0.423
0.171 7.068
2.4 Dbh-2
0.717 0.642
0.309 6.465
4.8 Straightness-2 0.567
0.086 0.031
3.461 0.9
Note:
1
In meter unit for height-2 and centimeter unit for dbh-2. Intensity selection was set up at the same number of selected family 22 families: I=1.00 for Group 1
and I= 0.798 for Group 2.
Table 5: Family ranking of the three types of family determined using selection index basedn on the traits at two years of age
Type-1 Type-2
Type-3 Family no.
Index Rank
Family no. Index
Rank Family no.
Index Rank
1 14.276
9 28
13.278 23
45 12.952
27 2
13.929 12
29 11.640
50 46
11.871 46
3 14.405
6 30
14.436 5
47 12.017
45 4
13.324 21
31 11.497
52 48
12.817 29
5 13.589
16 32
12.215 42
49 12.496
35 6
12.486 36
33 12.399
37 50
11.426 53
7 12.917
28 34
12.665 30
51 11.746
49 8
12.269 40
35 13.310
22 52
11.575 51
9 14.527
4 36
13.165 25
53 13.450
19 10
14.951 2
37 10.126
57 54
11.819 48
11 13.511
18 38
10.965 55
55 14.367
7 12
14.111 11
39 12.530
33 56
12.347 38
13 13.178
24 40
14.559 3
57 13.886
14 14
11.336 54
41 11.840
47 15
12.324 39
42 13.334
20 16
12.507 34
43 13.596
15 17
12.581 32
44 12.060
44 18
14.151 10
19 12.267
41 20
10.690 56
21 12.198
43 22
12.972 26
23 14.351
8 24
12.600 31
25 13.920
13 26
13.555 17
27 15.500
1
Bogor, 21-22 October 2015
769 The increased of genetic gain in Group 1 compared to Group 2 was mainly due to the
increasing number of high quality plus trees family, which is some of them coming from the Type-3 Family. According to the family ranking generated using selection index value, out of
13 families from Type -3 that was added into the third-generation progeny trial around 23 families of them classified into the top twenty family ranking, followed by 30 into the
middle twenty and 53 into the lowest ranking Table 5. These numbers of families are equivalent to the 15 of the total top twenty family ranking, 25 of the total middle twenty
and 35 of the total lowest family ranking Figure 1.
Figure 1: Proportion number from three types of families classified based on the family ranking
Among the top twenty family rankings, the ranks value of family from Type 3 were 5 - 65 superior to the ranks value of family from Type-1 and Type-2. It means that among the top
ranking, selected families from Type-3 is not always poorer compared to those from Type-1 and Type-2, even they showed more productive in some cases. This result revealed that the
uses of within-family variation is potential for A. mangium breeding. This is one of the essential factors to apply the
“recycled genetic resources” for advanced-generation breeding of A. mangium.
3.3 Pedigree control for advanced generation breeding Maintenance of pedigree control is critical in a breeding population. The pedigree control
would become more complex as the advanced generation breeding cycles progressed. Moreover the increase of relatedness in advanced generation population coupled with the
near-universal importance inbreeding depression in forest trees lead the management of inbreeding would become a key issue in the development and implementation of all
advanced-generation breeding program White, 1996. Therefore generating genetic structure through controlling the pedigree should be taken into account in order to maintain the genetic
diversity and to achieve the long term genetic gain. One of the rules for achieving a great genetic gain while maintaining genetic diversity in
advanced-generation breeding population is the limitation maximum number of plus trees
within each selected family. In this study, maximum two plus trees per family is a τrule of thumb” applied for controlling the pedigree in establishing advanced-generation breeding of
A. mangium. Therefore identical by descent of family should be handled carefully in advanced
10 20
30 40
50 60
70
Type-1 Type-2
Type-3
N u
m b
e r
o f
Fa m
il ie
s
Types of Family
Total Top-20
Middle-20 Lowest-17
Bogor, 21-22 October 2015
770 generation breeding program. Concerning the need of pedigree control as described above,
the “recycled genetic resources” as proposed in this study that is a re-uses of the original founder
families of first generation grandparents into third-generation breeding population, could be adopted with some necessarily requirements as follows:
a. Families from grandparent population founder families should be selected based on the
result of family selection in second-generation breeding population, for this, pedigree of the selected families should be always confirmed back to the original parents or ancestors
Figure 2. b. Selected family from grandparent population founder families could be inserted into third-
generation breeding population only if the number of plus trees for respective family and their identical by descent family selected in the second-generation is less than two plus
trees. As a result the total maximum number of plus tree per family is finally only two, including the plus trees family from grandparent population.
Figure 2: Flow chart of pedigree control from certain family ex. No. family 100 into their successive generations up to third-generation
Based on the requirements as described in preceding paragraph, the “recycled genetic resources”
would be an alternative method to optimize the genetic resources for A. mangium advanced generation breeding program. This is because the genetic diversity of A. mangium was reported
as low, especially diversity within population Butcher et al., 1998. Concerning the important of large genetic diversity for achieving long term genetic gain, infusion from new selection
families in natural forest would be one of the solutions. However, recently the availability of such infusion families was much reduced and not always available either in quantity or in
quality.
The results of this study revealed that the τrecycled genetic re source” through re-uses of the original
founder families of first generation grandparents into third-generation breeding population is applicable for maintaining genetic diversity and increasing genetic gain of A. mangium.
However, pedigree control of the families should be taken into account to reduce inbreeding incidence in the population.
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771