0022-B4
Francisco M. Padua 1
Measurement of clonal parameters involving growth traits, stem form, branch characters and crown form was carried out in a 6-year-old Gmelina arborea clonal trial. The ramets were planted on 4 m by 4.5 m spacing following a randomized°Complete block design with 4 replications. Data were analyzed using the 1989 version of SAS statistical package.
Significant clonal variations were observed in all growth characters measured indicating that considerable improvement in the wood yield of forest plantation can be achieved through the selection and utilization of the identified best performing clones. The significant clonal correlations among some of the growth and stem quality parameters suggest that simultaneous genetic improvement in these characters can also be achieved through index selection. For the sole purpose of improving stem volume direct selection for diameter at breast height is quite enough. On the other hand, for concomitant enhancement in stem volume and stem quality characters, the selection index should be based on the combined diameter at breast height and height to the first branch in the form of volume.
With the growing global concern on the conservation of the remaining natural forest, tree plantations are becoming the primary if not the sole source of wood and wood products in most countries. However, with the current yield of commercial forest plantations especially in the Philippines, the soaring demand for forest products brought about by the continuous increase in human population is difficult to satisfy. FAO projection indicates that shortage in the supply of wood will be felt in Asia an in the United States by the year 2010. Some of the developing countries will also have difficulty in supplying their needs for industrial wood products due to lack of capacity to import and will have deficits of non-traded goods such as fuel wood.
In view of the foreseen problems with regards to the wood supply stability, there is a compelling need for an approach that will sustainably amplify the yield of forest tree plantations. Expanding the area of forest plantations or increasing the yield per hectare are two possible means to increase wood production. However, owing to the limitations in the land area available for commercial forest plantation and to the additional cost that may be involved in the expansion, increasing the yield per unit area seems to be more attractive.
Increasing the yield per hectare is possible through the practice of clonal forestry. Clonal propagation, testing and selection are some of the important components of clonal forestry that should be given subtle attention to optimize the gain that can be achieved in cloning. Clonal propagation is an effective tool of capturing the fullest potential of the desired tree. Through cloning an exact copy of the superior individual can be produced which is not possible through the use of open pollinated seeds. On the other hand, for the reason that the performance of clones are also limited by the environment where they will be planted, clonal testing remains an important prerequisite of mass clonal propagation. Further more, substantial added gain can be realized through the identification of clonal selection index. Through this, simultaneous improvement in two or more economically desirable traits may be achieved through selection of just one major trait.
This study aims to establish the genetic relationships among the economically important traits of white teak clones (Gmelina arborea) and through the identified association, identify the best character that can be used for index selection.
Description of the Study Area
The study site is located within the plantation of Provident Tree Farms Incorporated (PTFI) in Talacogon, Agusan del Sur, Mindanao, Philippines. This province is categorized under climatic Type II, which is characterized by having no dry season with very pronounced maximum rainfall from November to January. The annual rainfall in this area ranges from 1,805 to 3,714 millimeters with an average of about 2,760 millimeters. The temperature can go as high as 34°C and may drop to about 22°C. The mean maximum temperature of the province ranges from 28°C to 34°C while the mean minimum temperature may vary from 22°C to 24°C (DA-BSWM 1989).
The soils in the plantation area of PTFI are generally clayey in texture consisting on the average of about 62 % clay, 26 % silt and 12 % sand. The soil pH ranges from 4.0 to 6.3 with an average of about 4.99. The organic matter contents of the soils are adequate varying from 1.03 % to 3.65 % with an average of about 2.03 %. The levels of potassium in the soils are generally sufficient but the levels of phosphorus are very limiting averaging to about 0.38 meq per 100 g soil and 2.88 ppm, respectively. On the average, the percent base saturation and the cation exchange capacity of the soils is very favorable amounting to about 40.85 % and 40.51 meq per 100-g soil, respectively (Palaypayon 2000).
The Plant Material
Shoot tip cuttings were obtained from the pollarded candidate plus trees within the mature plantation stands of Gmelina arborea of PTFI. The cuttings were rooted and managed in the clonal nursery using the regular PTFI clonal propagation procedure. The rooted cuttings were then planted in the ramet multiplication garden (RMG) with a distance of 1.5 meters between rows and 1.5 meters between columns. After some time in the RMG the clones were top-pruned to induce the formation of juvenile shoots. Shoot tip cuttings from randomly selected clones were collected in the RMG and then rooted in the clonal nursery using a pure sand medium for about seven days. The rooted cuttings were then transplanted into the 2 x 2 x 5 inches polyethylene bags with a potting medium consisting of 1 /3 sand and 2 /3 subsoil.
Experimental Design
The clonal test was established following a randomized complete block design. The stecklings were planted in the field and spaced at 4 meters by 4.5 meters with the longer distance aligning on the east-west direction. Each unit plot composed of five stecklings from a single clone and the experimental set up was replicated 4 times.
Measurement of Clonal Parameters
Tree heights were measured with the use of an abney level. For all trees, data on the total height (Ht), merchantable height (Hm) and height up to the first major branch (Hb) were collected. Ht was reckoned from the ground level up to the main terminal or apical bud. The Hm on the other hand, was measured starting from the ground level up to the 10-centimeter top diameter outside bark or up to the commercially acceptable stem quality. Hb was measured from the ground level up to the largest branch within the lower 1/3 of the crown.
To compute for the diameter at breast height (D1.3), circumference reading was taken and was divided by the value of.
The crown of each individual tree was measured by projecting the tree crown on the ground. The horizontal distance from the center of the stem to the edge of the crown was measured with the use of standard forester's meter tape. Four crown radius readings were taken, one in each of the four cardinal directions, the North, South, East and West (Sorlin and Bell 2000). The crown area (Ac) was calculated using the formula A = _r 2 . Other crown expressions such as crown diameter (Dc), crown height (Hc), crown profile (Pc), and crown volume (Vc) were also computed. Crown height was estimated by deducting the height to the first major branch to the total height (Ht - Hb). Crown profile was computed by multiplying the crown height to the crown diameter (Hc x Dc) and crown volume was estimated by multiplying the crown area with the crown height (Ac x Hc).
The angle formed by the largest branch (Anb) within the lower 1 /3 of the live crown length in each tree was estimated with the use of a modified protractor. Two arms made up of 6 inches rulers, one movable and the other fixed, were attached to a standard protractor. The fixed arm was aligned at the zero scale of the protractor. The movable arm on the other hand was attached such that it can be adjusted according to the angle formed by the branch. To measure the branch angle, the fixed arm of the modified protractor was aligned on the main stem and the movable arm was adjusted to coincide with the branch orientation. The diameter (Db) and length (Lb) of the largest branch within the lower 1 /3 of the live crown of all trees were measured with the use of a meter tape. The branch circumference was measured with the use of standard meter tape and was later converted to diameter. Db reading was taken at about 10 cm from the main stem due to the observed swelling near the base of the branch. Lb on the other hand was reckoned from the base to the main tip of the branch.
Taper (Ts) was determined by measuring the diameter of each individual tree in every 2 meters change in height. The first diameter reading was taken at the 1.3-m (D1.3) mark from the ground. Stem cylindricity (Cs) at breast height was determined by taking two diameter readings on each tree with the use of a tree caliper. One caliper reading was taken at the NS direction the other at the EW direction. The cylindricity grade was estimated by deducting the difference of the two caliper readings with 10 (i.e. 10 - (NS-EW)). Stem straightness was subjectively graded based on the procedure adopted by Keiding, Lauridsen and Welledorf (1984) for Tectona grandis. The number of bends along the merchantable length of each individual tree was actually counted and classified as either minor or major depending on the severity of the bend. A bend was considered as major if the side of the stem curves outside a straight imaginary line drawn through the length of a bend or if bends can be recognized at breast height.
Statistical Analysis
Analysis of variance was performed for each measured parameter using the Statistical Analysis System or SAS. In the analysis of variance clones and blocks were assumed as fixed effects. The data were analyzed using RCB design with unequal number of sub-plots. This was achieved by using the SAS command known as Proc GLM in the analysis of variance (Silva et al. 1997). The linear mathematical model employed in this study was as follows:
Yijk |
= |
|
|||||
Where: |
|||||||
Yijk |
= |
observed value of the kth ramet of the jth clone at the ith block | |||||
|
= |
overall mean | |||||
BI |
= |
effect of the ith block | |||||
Cj |
= |
effect of the jth clone | |||||
BCij |
interaction between the ith block and the jth clone | ||||||
e(ij)k |
= |
effect of the kth ramet within the ith block and the jth clone | |||||
Heritability Estimates
The estimated components of variance were matched to their genetic counterpart to compute for the heritabilities. Clone x block and trees within plots components of variance was equated to the δ 2 GE and δ 2 E, respectively.
In the computation of heritability, the negative variances were considered as zero (Membrahtu and Hanover 1989). The broad sense heritability of the clonal mean was calculated as follows (Lambeth et al. 1994; Nielsen and Roulund 1996).
Where: |
||||||
b |
= |
Number of blocks |
||||
w |
= |
Harmonic mean number of trees within plot | ||||
Genetic Correlation
The formula below was used to estimate the genetic correlation (Membrahtu and Hanover 1989).
Where:
|
= |
the clonal component of covariance between traits x and y. |
|
= |
the clonal component of covariance for trait x with itself |
|
= |
the clonal component of covariance for trait y with itself |
The procedure applied in the computation of covariances was the same as that applied in the estimation of clonal variances. The observed mean cross products were equated to their Type III expectations of mean cross products. The MANOVA statements of the SAS PROC GLM provided the sum of the cross products. The option HTYPE III = 3 and ETYPE = 3 were used to give the matrices of the sum of cross products (Silva et al. 1997)
Efficiency of Clonal Selection
The efficiency of clonal selection was calculated using the formula below (Lambeth et al. 1994).
E |
= |
rg hCy |
hCx |
Where:
hCy and hCx are the square roots of the clonal mean heritabilities of traits y and x, respectively
rg = genetic correlation between trait x and y
Growth Performance
The growth data of the tested clones are presented in Table 1. The growth of white teak clones was generally exceptional despite of the fact that no special silvicultural treatment such as fertilization, thinning or pruning was applied in the test site. The mean D1.3 varied significantly from 21.585 cm to 29.285 cm. Comparing to the mean of all clones, the top ranking clone (clone 26) was approximately larger by 15.86%.
The mean Hb was notably high ranging from 12.11 m to 16.84 m. Clone 25 was observed to be the best in this respect and was taller by 16.22 % than the mean of all tested clones. The average Hm ranged from 13.82 m to 20.12 m. Compared to the overall clonal mean, the top ranking clone was relatively higher by 20.33 %. Ht varied from 20.34 meters to 24.26 meters. Similar with other height parameters, clone 25 was the best performer and taller by 9.91 % than the overall clonal mean.
Mean Vb ranged from 0.3067 m 3 to 0.6347 m 3 . Volume was significantly higher in clone 25 (0.6347 m 3 ) followed by clone 26 (0.6099 m 3 ). When compared to the overall clonal mean, clone 25 was higher by 38.87 % in terms of volume. The average Vm also varied from 0.314 m 3 to 0.725 m 3 . The highest volume recorded was in clone 26 and followed by clone 25. Clone 26 was considerably higher by 45.40 % to the mean of all clones.
To a certain extent, uniformity within clone in terms of height and diameter was apparent in the field especially when the high performing clones happen to be adjacent to the low performing one. Among the three height parameters used, Hm and Hb seams to have greater genetic control than Ht as shown by their higher clonal component of variance. This could mean that the chance for improvement would be greater in Hm and Hb than in Ht. The highly significant clonal variations in D1.3, Hb, Hm, Ht, Vb and Vm suggest that significant improvement in yield can be achieved thought the selection and utilization of the identified best performing clones.
| Table 1. Mean values of clonal growth parameters |
Clone |
D1.3 |
Hb |
Hm |
Ht |
Vb |
Vm |
26 |
29.28 a |
13.58 ab |
18.02 ab |
23.44 ab |
0.610 ab |
0.725 a |
25 |
28.91 ab |
16.84 a |
20.12 a |
24.26 a |
0.635 a |
0.675 ab |
23 |
26.26 abc |
12.11 b |
14.91 bc |
20.34 b |
0.436 abc |
0.489 bc |
31 |
25.42 abc |
12.15 b |
14.64 bc |
20.88 ab |
0.419 bc |
0.464 bc |
33 |
24.51 abc |
14.53 ab |
16.91 abc |
22.38 ab |
0.462 abc |
0.499 bc |
10 |
24.46 abc |
15.22 ab |
16.22 bc |
20.78 ab |
0.383 c |
0.394 c |
7 |
23.70 abc |
15.50 ab |
17.96 ab |
21.95 ab |
0.441 abc |
0.484 bc |
2 |
23.43 bc |
15.28 ab |
16.84 abc |
22.13 ab |
0.392 bc |
0.412 c |
6 |
23.37 bc |
14.01 ab |
15.25 bc |
21.70 ab |
0.402 bc |
0.423 c |
4 |
22.93 c |
14.81 ab |
17.07 abc |
21.48 ab |
0.379 c |
0.416 c |
1 |
21.58 c |
13.72 ab |
13.82 c |
21.18 ab |
0.307 c |
0.314 c |
Genetic Correlation
The genetic correlations among clonal parameters are presented in Table 2. Significant positive genetic correlations were observed among the measured clonal growth parameters except between Hb and D1.3 and Hb and Vm. This indicates that simultaneous genetic improvement can be achieved in most of these characters. However, selection base on Hb alone will not result to a consequent improvement in D1.3 and Vm while improvement in Hb will not be possible through the direct selection of either D1.3 or Vm due to the very weak clonal correlation between these characters.
In the assumption that trees with smaller crown are superior to those with larger crown, consequent improvement in crown size is not possible through the direct selection either of D1.3, Vb or Vm. This is for the reason that direct selection for any of these traits will yield to a consequent increase in Dc, Ac, Hc, Pc and Vc. On the other hand, the significant negative correlation of Hb to Hc, Pc and Vc suggest the possibility of improving these traits through the selection of Hb. Direct selection for Hb however will result to a consequent increase in Dc. The significant negative correlation of Hm to Hc and its strong positive correlation to Dc, Ac and Vc indicate that selection for clone with better Hm will consequently improve Hc but will result also lead to an increase in Dc, Ac and Vc.
The significant positive clonal correlation of Hm, D1.3, Vb, and Vm to Anb indicate that clone with larger Hm, D1.3, Vb, and Vm will tend to have wider branch angle. This suggests that simultaneous improvement in Anb is possible through the direct selection of any of these traits. The insignificant correlation of Hb to Anb however indicates that these characters are independent to each other and therefore should be considered separately in selection. Clone with larger D1.3, Vb and Vm however will tend to have bigger Db and longer Lb while clone with longer Hb will tend to have smaller Db and longer Lb indicating that simultaneous genetic improvement is only possible for Db through the selection of Hb.
Cs and Ss were not significantly correlated to any of the measured growth parameters. This indicates that selection for any of the identified growth traits will have no consequent effect on Cs and Ss. Because of this, growth characters, Cs and Ss should be considered separately in selection. However, the strong positive correlations of D1.3, Vb and Vm to Ts indicate that clone with larger D1.3, Vb, and Vm will tend to have greater taper. On the other hand, selection for better Hb or Hm will have no consequent effect on Ts due to the weak correlation between these traits.
| Table 2. Genetic correlation among the measured clonal parameters |
Hb |
Hm |
D1.3 |
Vb |
Vm | |
Hb |
- |
0.76 |
0.00 ns |
0.26 |
0.14 ns |
Hm |
0.76 |
- |
0.55 |
0.76 |
0.70 |
Ht |
0.60 |
0.99 |
0.61 |
0.83 |
0.78 |
D1.3 |
0.00 ns |
0.55 |
- |
0.94 |
0.94 |
Vb |
0.26 |
0.76 |
0.94 |
- |
0.99 |
Vm |
0.14 ns |
0.70 |
0.94 |
0.99 |
- |
Dc |
0.72 |
0.58 |
0.82 |
0.85 |
0.84 |
Ac |
0.14 ns |
0.54 |
0.80 |
0.83 |
0.82 |
Hc |
-0.65 |
-0.28 |
0.37 |
0.28 |
0.33 |
Pc |
-0.40 |
0.07 ns |
0.65 |
0.61 |
0.65 |
Vc |
-0.23 |
0.23 |
0.73 |
0.73 |
0.75 |
Anb |
-0.02 ns |
0.38 |
0.25 |
0.31 |
0.37 |
Db |
-0.59 |
-0.16 ns |
0.37 |
0.22 |
0.31 |
Lb |
-0.42 |
0.11 ns |
0.55 |
0.44 |
0.52 |
Cs |
-0.02 ns |
-0.08 ns |
-0.02 ns |
0.02 ns |
0.01 ns |
Ss |
-0.05 ns |
-0.06 ns |
0.02 ns |
-0.01 ns |
0.00 ns |
Ts |
-0.18 ns |
-0.05 ns |
0.59 |
0.36 |
0.31 |
Efficiency of Clonal Selection
The efficiencies of clonal selection are presented in Table 3. Among the measured growth parameters, the efficiency of consequently improving Vb and Vm were highest in the direct selection of D1.3. This suggests that for the lone purpose of improving stem volume, direct selection for D1.3 is enough. This finding partly support the assertion of Van Wyk (1990) that measuring dbh only at about mid-rotation age could assess volume production of families. However, direct selection for D1.3 alone will not result to a subsequent improvement in Hb due to the weak correlation between these traits. In addition, selection for D1.3 will result to a lower efficiency on indirectly improving Hm and Ht. Because of this, for products that need not only stem volume but also the length of Hb and Hm, such as plywood and lumber, direct selection for Vb should be employed.
Direct selection for either of the identified growth parameters was similarly ineffective in concomitant improvement of Ss and Cs due to insignificant genetic correlations of growth traits to cylindricity and straightness. For stem taper, the efficiency of clonal selection was highest in the direct selection of D1.3 followed by Vb and Vm. These imply that selection based on D1.3, Vb or Vm will consequently increase stem taper and the increase will be highest in the direct selection of D1.3. Therefore, direct selections for D1.3 will improve stem volume but will also lead to a greater reduction in stem quality through the increase in taper.
It is a known fact that trees with smaller branches and narrow crowns are more superior to those trees with wider crowns due to their effects on stem quality and wood volume production per hectare (Noor et al. 1989; Isik and Isik 1999). Because of this, indirect improvements in Db, Lb and crown traits are not possible through the direct selection of D1.3, Vb or Vm. This is for the reason that selection for any of these traits will result to a consequent increase in branch and crown size. On the other hand the negative efficiency values of Db, Ab, Lb, Hc, Pc and Vc to Hb indicate that consequent improvement in these traits are possible. Unfortunately, selection based on Hb alone will not bring improvement in D1.3 and Vm due to the very weak correlations of Hb to these traits. Direct selection of Hm was the most efficient in consequently increasing branch angle followed by Vm and Vb. Unfortunately, selection based on Hm will lead to a lower efficiency in improving stem volume while selection for Vm will result to a lower gain in Hb. Because of these, there is a need for an index that will result to a better gain in volume but will also minimize the increase in branch and crown size. In this respect, Vb is a good candidate. The lower positive efficiency of Vb in improving branch and crown characters compared to other growth parameters indicate that minimum undesirable increase in branch and crown size can be achieved through the direct selection of Vb.
| Table 3. Efficiency of clonal selection |
Correlated |
Selection Index | ||||
Traits |
Hb |
Hm |
D1.3 |
Vb |
Vm |
Hb |
100 |
63 |
0 |
22 |
- |
Hm |
92 |
100 |
61 |
77 |
67 |
Ht |
13 |
18 |
12 |
15 |
14 |
D1.3 |
- |
50 |
100 |
86 |
82 |
Vb |
31 |
75 |
103 |
100 |
94 |
Vm |
- |
73 |
108 |
104 |
100 |
Ts |
- |
- |
59 |
33 |
27 |
Ss |
- |
- |
- |
- |
- |
Cs |
- |
- |
- |
- |
- |
Db |
-60 |
- |
34 |
19 |
25 |
Lb |
-54 |
- |
65 |
47 |
53 |
Anb |
- |
11 |
8 |
9 |
10 |
Dc |
75 |
50 |
79 |
74 |
70 |
Hc |
-76 |
-27 |
40 |
28 |
31 |
Ac |
- |
44 |
72 |
69 |
65 |
Pc |
-47 |
- |
71 |
60 |
61 |
Vc |
-26 |
21 |
74 |
68 |
67 |
Significant clonal variations were observed in all growth characters indicating that considerable improvement in the yield of forest plantation can be achieved through the selection and utilization of the identified top ranking clones. Among the 11 tested white teak clones, clone 25 and clone 26 were the best performers in terms of growth performance. The significant clonal correlations among some of the growth and stem quality parameters suggest that a certain degree of simultaneous genetic improvement can be achieved in some of these characters through index selection. The degree of consequent improvement for specific characters varied depending in the genetic correlation between the trait directly selected and the indirect traits and the heritablity of both characters.
For pulpwood production where stem volume in general is much more important than stem form, direct selection for the diameter at breast height is quite enough due to the very high efficiency of diameter in consequently improving stem volume. However for products that require not only stem volume but also stem quality, such as plywood and lumber, direct selection for the combined diameter at breast height and clear bole length in the form of volume is more desirable. Further more, for an added gain, direct selection for clear bole volume should be coupled with a separate selection procedure for stem straightness and stem cylindricity due to the weak clonal correlation of the stem form characters to clear bole volume.
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1 Research and Development Department, Provident Tree Farms Incorporated, Phimco Compound, Felix Y. Manalo St., Punta Sta Ana, Manila, Philippines.
E-mail: [email protected] or [email protected]
+ Bi + Cj + BCij + e(ij)k
2 xy