Summary of doctoral thesis: Study on growth characteristics, wood properties and sterility of triploid acacias providing scientific bases for breeding and afforestation

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Objectives of the study: Determining the growth characteristics and adaptability of some triploid acacia clones in 3 ecological regions (Northeast, North Central and Southeast); đetermine the basic wood properties for some promising triploid acacia clones; identify some reproductive characteristics of some triploid acacia clones

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Nội dung Text: Summary of doctoral thesis: Study on growth characteristics, wood properties and sterility of triploid acacias providing scientific bases for breeding and afforestation

MINISTRY OF EDUCATION MINISTRY OF AGRICULTURE AND TRAINING AND RURAL DEVELOPMENT VIETNAMESE ACADEMY OF FOREST SCIENCES ---------    --------- PHAM VAN BON STUDY ON GROWTH CHARACTERISTICS, WOOD PROPERTIES AND STERILITY OF TRIPLOID ACACIAS PROVIDING SCIENTIFIC BASES FOR BREEDING AND AFFORESTATION Speciality: Forest tree genetics and breeding Code: 9 62 02 07 SUMMARY OF DOCTORAL THESIS Ha Noi, 2021 Hanoi - 2020
This work has been completed at the Vietnamese Academy of Forest Sciences Supervisors: 1. Dr. Ha Huy Thinh 2. Dr. Nghiem Quynh Chi TS. Phí Hồng Hải Chairman: Assoc. Prof. Dr. Phi Hong Hai Reviewer 1: Assoc. Prof. Dr. Pham Duc Tuan Reviewer 2: Assoc. Prof. Dr. Nguyen Van Viet Reviewer 3: Dr. Doan Ngoc Dao The thesis was defended in front of the institute’s thesis-judging council meeting at the Vietnamese Academy of Forest Sciences at the hour minute day month year 2021 The thesis can be referred at the National Library of Vietnam and the Vietnamese Academy of Forest Sciences
PUBLISHED SCIENTIFIC PAPERS RELATED TO THE THESIS 1. P. V. Bon, C. E. Harwood, Q. C. Nghiem, H. H. Thinh, D. H. Son and N. V. Chinh (2020), “Growth of triploid and diploid Acacia clones in three contrasting environments in Viet Nam”, Australian Forestry 83(4): 265-274. https://doi.org/10.1080/00049158.2020.1819009. 2. Bon PV, Harwood CE, Chi NQ, Thinh HH and Kien ND (2020), “Comparing wood density, heartwood proportion and bark thickness of diploid and triploid acacia hybrid clones in vietnam”, Journal of Tropical Forest Science 32(2), pp. 206-216. https://doi.org/10.26525/jtfs32.2.206.
INTRODUCTION 1. Rationale Developing mono species plantation with large scale, acacia plantation in Vietnam have been meeting high risk of disease, especially wilt disease caused by Ceratocytis sp and pink disease caused by Corticium samonicolor, leading to seriously reducing wood productivity of plantation. Another thing has been receiving attention from experts, some acacia species may become invading grasses competing with indigenous species, requiring further work on breeding Acacia varieties is being carried out in order to create varieties of acacia that are able to limit the risks for acacia plantations in the future. In addition to continuing to research and select acacia varieties according to traditional methods, the triploid acacia breeding method is considered a new and highly practical direction. The triploid acacia variety is expected to have fast growth, good adaptability, improved wood quality and especially poor fertility, so the above risks can be minimized for acacia plantations. In Vietnam, research on triploid breeding for some commercially valuable acacia species such as Acacia mangium, A. acacia and A. hybrid has been carried out since 2002, so far, some important results have been obtained such as: developed method of selection, breeding and propagation of triploid acacias; some created triploid acacia clones and initially selected a number of promising triploid hybrid acacia clones to put into production. Inheriting a part of the results of the project: "Research on selection and breeding of fast-growing triploid acacia for large timber plantations" and additional research on wood properties and infertility of triploid acacia in the trials has been established, the thesis "Study on growth characteristics, wood properties and infertility of triploid acacia as a basis for breeding and afforestation" was carried out in order to supplement the scientific basis for further research and development of triploid acacia cultivars in Vietnam. 2. Study objectives  General objectives 1
Identify the elite characteristics of triploid acacia varieties as the basis for breeding and afforestation.  Specific objectives + Determining the growth characteristics and adaptability of some triploid acacia clones in 3 ecological regions (Northeast, North Central and Southeast). + Determine the basic wood properties for some promising triploid acacia clones. + Identify some reproductive characteristics of some triploid acacia clones 3. Study materials and range  Study materials Used materials in this study included 10 triploid Acacia hybrid clones, 4 triploid A. auriculiformis and 7 diploid A. hybrid and A. auriculiformis clones which were approved as national or advanced cultivars. More detail information as below table. Genetic informations Order Clone Ploidy Code Mother Father 1 X101 3x AM A. auriculiformis 2x (Aa6) A. mangium 4x (Am44) 2 X102 3x AM A. auriculiformis 2x (Aa6) A. mangium 4x (Am44) 3 X201 3x AM A. auriculiformis 2x (Aa6) A. mangium 4x (Am36) 4 X204 3x AM A. auriculiformis 2x (Aa6) A. mangium 4x (Am36) 5 X205 3x AM A. auriculiformis 2x (Aa6) A. mangium 4x (Am36) 6 X01 3x MA A. mangium 4x Unknown 7 X11 3x MA A. mangium 4x Unknown * 8 X1100 3x MA A. hybrid 2x (BV33) A. hybrid 4x (10L590) * 9 X1200 3x MA A. hybrid 2x (BV16) A. hybrid 4x (10L590) * 10 X1201 3x MA A. hybrid 2x (BV16) A. hybrid 4x (10L590) 11 X21 3x Aa A. auriculiformis 2x (Aa84) Selfing (no father) 12 X31 3x Aa A. auriculiformis 2x (Aa83) Selfing (no father) 13 X41 3x Aa A. auriculiformis 58.5 Selfing (no father) 14 X42 3x Aa A. auriculiformis m 7.6 Selfing (no father) 15 BV10 2x ĐC - - 16 BV16 2x ĐC - - 17 BV73 2x ĐC - - 18 AH7 2x ĐC - - 19 TB12 2x ĐC - - 20 Ctl18 2x ĐC - - 21 Ctl26 2x ĐC - - 2x = diploid; 3x = triploid; 4x = tetraploid; AM = A. auriculiformis 2x × A. mangium 4x; MA = A. mangium 4x × free pollination ; MA* = A. hybrid 2x × A. hybrid 4x; ĐC = control (commecial A. hybrid, A. auriculiformis). 2
 Scope of the study Growth characteristics were studied in 3 ecological regions (Northeast, North Central and Southeast); Wood properties were carried out in 2 ecological regions (North Central and South East) and only for some promising acacia strains; Infertility was carried out in only one ecological region (Southeast region) where the most favorable conditions for reproduction of some acacia species were performed and was performed for all triploid acacia clones included in the trials. The parameters of sterility were performed by monitoring and measuring methods on open pollinating populations without conducting artificial crosses with each specific parent. 4. Meaning of the thesis  Scientific meaning Contributing to some additional scientific bases on growth characteristics, wood properties and infertility of triploid acacia as a basis for breeding and afforestation.  Practical meaning + Identified four triploid acacia hybrid clones with fast growth, good adaptability and poor reproductive ability to put into afforestation. + Identifying some basic wood properties of triploid acacia helps to suggest the direction of using triploid acacia wood. 5. New contributions of the thesis + Identify some growth characteristics, wood properties and infertility of triploid acacia. + Identify a number of fast growing triploid acacia hybrid clones that are promising for research and production forest planting. 6. Structure of the thesis The thesis includes 130 pages with 36 tables and 37 photos Introduction (5 pages) Chapter 1. Overview in relative materials (29 pages). Chapter 2. Contents and study methods (23 pages) Chapter 3. Results and discussion (69 pages) Conclusion and recommendation (4 pages) The thesis used 138 references, in which 33 ones in Vietnamese and 105 others in foreign language. 3
Chapter 1 OVERVIEW IN RELATIVE MATERIALS 1.1. In the word  Research on improving varieties according to growth traits for some acacia species Research on improving varieties for growth traits of some commercially valuable acacia species has been carried out relatively methodically and systematically in countries in the region. Many fast growing acacia varieties with high yield (over 30 m3/ha/year) have been selected in different countries. Theoretical genetic gain of A. mangium reached over 5% for growth traits and real genetic gain compared to commercial plantations can reach 24-44% for growth and 53 – 90% for stem volume trait. The family-level heritability of Acacia mangium in Costa Rica may reach 0.68. The heritability at the individual level of A. auriculiformis in Indonesia reached 0.33 – 0.40 for growth traits D1.3 and Hvn and at the family level it gained 0.76 – 0.84. Selection of Acacia hybrid, acacia hybrid with strong differentiation, heritability coefficient was very high (0.96 according to clone and 0.59 according to individual). Some acacia hybrid clones have superior growth compared to their parents (A. mangium and A. auriculiformis). In Malaysia, D1.3 growth of artificial acacia hybrid was 16-17 cm after 3-4 years of age. In addition, some studies showed that acacia hybrid has better resistance to wilt disease than A. mangium.  Improvement of varieties according to wood properties for some acacia species Studies have shown that the provenance, family and individual trees have an influence on the woody properties of A. mangium, A. auriculiformis and A. hybrid. Most wood properties were improved associated with increasing age. The mechanical properties of wood are strongly correlated with the density of the wood  Research on reproductive traits Reproductive characteristics of A. mangium and A. auriculiformis have been studied in a number of countries to serve the selection and breeding of A. hybrid. Study results indicated that the flowering and fruiting seasons of the two species are different between the study sites. A. 4
mangium flowered earlier than A. auriculiformis. However, there are times when two species flowered at the same time.  Research on selection and breeding of triploid varieties in forestry Triploid varieties in forestry have been discovered since 1935 in Popuplus tremula and there have been some basic studies since then. However, the study and development of triploid cultivars in forestry has been really interested in recent times. In which, the most remarkable success was for some species of poplar (Populus sp) in China, many triploid poplar varieties have been used for industrial afforestation with rapid growth, good resistance to pests and diseases and significantly improved wood fiber length compared to the commercial variety. Currently, China is continuing to study and select triploid varieties for eucalyptus by applying new methods to crossbreeding triploid varieties in order to shorten the time compared to previous methods and have obtained a number of results. results (the time to create triploid trees was only a few months, the percentage of triploid plants reached 6.3%, the growth and physiological indicators were superior to that of the parent plants). For acacias, a number of natural triploid screening studies have been carried out and triploidy has been detected in some populations of some acacia species with a wide distribution but very rare in populations of commercially valuable acacia species, such as A. mangium, A. auriculiformis. Research on creating artificial triploids has also been carried out with A. mearnssi and A. nilotica but have not been successful so far. 1.2. In Vietnam  Research on improving varieties according to growth traits for some acacia species Since the early 1990s, seedlot trials of some acacia species have been developed relatively uniformly throughout the country. Many provenances, families, individuals of A. mangium, A. auriculiformis with fast growth and good adaptability were selected. The provenances, families, and plus trees have been selected as the source of seeds for further breeding studies (selecting families according to generations, individuals, clones) later. Acacia hybrid varieties in our country has been started since 1993. Many acacia hybrid clones with fast growth, high yield and good disease resistance have been selected. Besides, research on artificial hybrid acacia 5
(controlled hybridization) has also been carried out since 1997 and has obtained many important achievements. Many artificial hybrid clones with fast growth and high yield have also been bred.  Improvement of varieties according to wood properties for some acacia species Many improvement studies for wood characteristics have been carried out for A. mangium, A. auriculiformis and A. hybrid. Thereby, many varieties of acacia that have both fast growth and good wood properties have been selected to put into production.  Research on reproductive characteristics Research on reproductive biology of two species of A. mangium and A. auriculiformis has been carried out relatively methodically in Vietnam to serve the breeding work. A. mangium flowered earlier than A. auriculiformis. There was only a short time that the two species bloom at the same time. Differences in reproductive biology between tetraploid and diploid A. mangium and diploid A. auriculiformis have also been shown to provide the basis for the hybridization of triploid varieties.  Research on breeding triploid varieties in forestry Research on selecting triploid varieties for forest trees has only been interested in the last 2 decades for Melia azedarach and acacia species. + M. azedarach: Researched to create triploid successfully from endosperm culture (100% of the plants produced were triploid). The method helped to shorten the breeding time compared to the method of hybridization between diploid and tetraploid plants (reduced from 12 years to 5 months). However, there has had no published documents on the growth and development of triploid varieties of M. azedarach that have been created. + Group of acacia species: Research on breeding triploid for some commercial acacia species in our country has been carried out since 2002, through 02 projects funded by the Australian Government and 01 national project, so far has obtained some important results such as: (i) A system of hybrid orchard between tetraploid and diploid acacia has been established to select and create triploid acacia varieties; (ii) The technological process of artificial triploid acacia hybridization has been completed; (iii) The vegetative propagation process for promising triploid acacia lines has been completed; (iv) A number of triploid acacia clones have been created and clonal tests have been carried out in a number of ecological regions 6
throughout the country. Initially, a number of triploid acacia hybrids have been selected with good prospects. 1.3. Summury for overview From the overview of published research works, some main points are as follows: Research on improving varieties according to growth traits, wood properties for A. mangium, A. auriculiformis and A. hybrid has been carried out methodically and systematically in a number of countries in Southeast Asia, including Vietnam. Studies have shown the important role of breeding in improving growth, yield and quality of wood for some acacia species. Research on reproductive biology of two species of A. mangium and A. auriculifolia has been intensively studied in a number of countries in the region, providing a scientific basis for the selection and breeding of A. hybrid in countries. Triploid varieties in forestry have been discovered since 1935, some of their preeminent characteristics have also been recorded such as: fast growth, good adaptability and poor fertility. However, research on developing triploid cultivars in forestry in the world so far is still limited. Most of the studies have just stopped at detecting and describing morphological characteristics. Except for the Populus sps, the research and development of triploid varieties has been carried out relatively methodically and systematically and has been widely applied in practice in some countries, especially in China but the growing area of this species is relatively narrow. Meanwhile, the key economic forest tree species in many tropical countries such as eucalyptus and acacia species have not been given due attention to select triploid varieties for afforestation. In Vietnam, research into triploid breeding for forest trees has also been interested in the last 2 decades for the acacia species, Melia azedarach, and has obtained some important results such as: (i) The method of selecting and creating triploid varieties suitable for each species of plant has been identified and a considerable number of triploid varieties have been selected for field testing; (ii) Initially, some promising triploid acacia hybrids were selected for planting. However, this is a new object that still has many issues that need to be further studied in both breadth and depth. 7
Chapter 2 CONTENTS AND RESEARCH METHODS 2.1. Study contents To gain above objectives, some contents were carried out following: (1) Research on growth traits and some stem quality figures of triploid acacia clones. (2) Research on some physical and mechanical wood properties of triploid acacia clones. (3) Research on sterility of triploid acacia clones. 2.2. Study methods 2.2.1. Methodology The study is inherited, using existing data and additional empirical research on research sites that have been developed from previous research programs. Apply research methods that are commonly applied to research on breeding, silviculture, ecology, wood science to carry out experimental studies and combine with mathematical statistical analysis methods to obtain comprehensive results and ensure reliability to meet the set objectives. 2.2.2. Specific research methods 2.2.2.1. Methods of research on growth and quality of stems a) Experimental design for clonal trials Clonal testing trials were established by the national project: “Study on selection, breeding of fast-growing triploid acacias for saw-log plantation” at three contrast environments (Northeast, North Central and Southeast regions). Each site included two clonal trials (10 trees or 49 trees in plot). The experiment designed as completed random block with 4 replicates for 10 trees plot trial and 3 replicates for 49 trees plot trial. b) Measuring tree growth Survival rate, annual diameter at breast height (DBH), height top (Ht) were measured all trees in each plot, using popularly methods for tree investigating. c) Measuring monthly DBH increment Choosing 6 trees in 49-tree-plot, with 2 trees from each of three size categories spanning the range of tree diameter (small, medium and large). DBH changes were measured from markings on nylon cable ties which 8
fitted snugly and expanded automatically as stem diameter increased. d) Measuring LAI (leaf area index) LAI in plots was estimated by digital photography, using Fiji win 64 image analysis software with specific macro, ImageAnalysisDSMblueFilter.ijm. In each plot, photographs were taken at ten positions in two parallel lines, diagonally the middle of the plot. e) Measuring stem quality Stem straight (Dtt), branch size (Dnc), top development (Ptn) and health (Sk) were measured by scoring with 5 categories (1 – 5). Using the methods are popularly applying in Vietnam. 2.2.2.2. Methods for studying the physical and mechanical properties of wood a) Collecting wood sample Wood samples were collected at three sites: Cam Lo (Quang Tri), Vinh Cuu (Dong Nai) with 3,8-year-trees (46 months) and Xuan Loc (Dong Nai) with 3,0-year-trees (36 months). Sample trees: For each site, choosing 5 trees which have mean diamter of each clone, no disease and scattering whole trials. Sample cut: Wood diskes with 5 cm thick for measuring bulk density, heartwood and wood fibre were cut at 0,3 m; 1,3 m; 3 m; 4,5 m; 6 m and 7,5 m height. Wood samples for measuring shrinkage, modulus of rupture and modulus of elasticity were wood logs from 0,3 – 1,3 m. b) Analysing wood sample - Basic density: Volume of wood disks were estimated based on Archimedes principle. Wood samples were weighed in water bath. Then they were dried at 105oC to constant mass and then re-weighed. Basic density was calculated as oven-dry mass/volume of water displaced, assuming weight of 1 lite equal 1 kg. - Heartwood ratio: Heartwood percentage was determined on the water-soaked discs after the estimation of green volume described above and prior to oven-drying. The boundary between sapwood and heartwood on each disc was identified by the colour change, which was obvious. Disc diameters and the positions of heartwoodsapwood boundaries were measured in N–S and E–W directions, and the total cross-sectional under- bark wood area and the area of heartwood calculated as the respective ellipses. 9
- Wood fibre: Wood fibre length was measured according to standard ASTM D5103-07 (2012). - Wood shrinkage: Radial and tangential shrinkage of wood were measured according to Vietnam Nation Standard TCVN 8048-13:2009 and volume shrinkage was measured according to Vietnam National Standard 8048-14:2009. - Modulus of rupture (MOR): MOR was measured according to Vietnam National Standard TCVN 8048-3:2009. - Modulus of elasticity (MOE): MOE was measured according to Vietnam National Standard: TCVN 8048-4:2009. 2.2.2.3. Mothods for studying sterility a) Floral characteristics Choosing 3 of 10 above trees to collect inflorescence samples; each tree picked up 20 spikes in the middle height of canopy and in four directions; measuring parameters including flower colour, length of spike, number of flowers or male lowers per spike. b) Inflorescence and pods production Estimated by scoring with 4 categories: (0) nil; (1) flower or pod was found less than 1/3 canopy; (2) flower or pod was from 1/3 – 2/3 of canopy; and (3) flower or pod was more than 2/3 canopy. Observed trees: 10 trees. c) Seed quality Pods after collection were kept in room for 2 – 3 days for even ripening, then peeled to count the number of seed/ pod and classify the seeds (fill and no fill). Each seed was coded for further study. See size was measured by electronic caliper with 0,01 mm accuracy and seed weight was estimated by electronic balance with 0,01 g accuracy. d) Pollen fertility: spikes were picked up in early morning from three trees which were chosen to research on floral characteristics above, then dried and sieved. Pollen viability was assessed on agar medium (10% agar, 20% sucrose and 0,01% boric acid) at ambient temperature. Germination of pollen was observed and recorded under light microscopy after 4 hours. A polyad was scored as having germinated when the length of at least one pollen tube was longer than the polyad diameter. e) Pod set 10
On three trees which were used to collect inflorescence sample above, tagging to assess and count flower at anthesis (least 2000 spikes per ramet). Pods which matured were counted and harvested and pod set calculated as the ratio pods harvested to estimated total number of hermaphrodite flower at anthesis. f) Viability of progenies of triploid acacia + Estimating ratio of seed germination: Seeds were soaked in 100oC water in 30 seconds, then stopped fire and kept seeds in the water in 24 hours. Seeds let in petri with wet filter paper in ambient temperature. Seed usually begin to germinate after 2 days. + Assessing growth performance of triploid acacia: Germinating seeds were transplanted into pots with 89% surface soil + 9% coconut fibre + 1% organic fertilizer. Counting survival ratio was took place at 3 months after transplanting. Survival trees were planted in the field in order to assess growth and morphology after 12 months planting. g) Ploidy level of progenies of triploid acacia Ploidy level was estimated by counting and classifying cells by flow cytometry (FCM) using a CyFlow Ploidy Analyzer (Partec, Munster, Germany). 2.2.2.4. Data analysis For each trial, using ANOVA analysis for mean value of each variable in order to estimate difference between treatments. In case there was significant difference among treatments, using method of Tukey multiple range test for ranking treatments according to descending order. Calculation and ANOVA analysis were implemented on Excel 2016 and Genstat 12th (VSN International) software. Chapter 3 RESULTS AND DISCUSSION 3.1. Growth characteristics and stem quality of triploid acacias 3.1.1. Growth characteristics of clones in the 10-tree-plot trial a) At Yen The The average survival rate of the trial after 3 years of age was relatively low, only 70.8%, because some strains had very low survival rates. Two triploid Acacia Acacia strains (X31 and X41) had very low 11
survival rates (15%), triploid X11 and BV10 diploid Acacia hybrids also had relatively low survival rates (75.0 respectively. % and 72.5%. The remaining triploid acacia hybrid lines all had high survival rates (82.5- 92.5%). The difference between lines in terms of survival was statistically significant (Fpr < 0.001). X201, X102 and X101 were three promising triploid A. hybrid clones, yielding higher or equivalent to two control diploid A. hybrid clones BV10 and BV16 (24.5 - 29.9 m3/ha/year compared with 17.5 - 23.4 m3/ha/year). The triploid A. hybrid clone X204, although being as ful- sibling with the X201, had a very slow growth rate. There were significant differences in growth traits among clones (Fpr < 0.001). b) At Cam Lo At the age of 3, the average survival rate for the whole trial was 90%, most of the clones had a survival rate of over 80%, except for the X1201 (77.5%). The difference in survival among clones was not statistically significant (Fpr = 0.246). Growth among the clones had a clear difference in all the studied traits (Fpr < 0.001). Clones X101, X102, X201, X205 and X1100 were promising triploids, yielding from 19.4 to 29.4 m3/ha/year, higher or equivalent to the control A. hybrid clones BV16 and AH7 (19.4 – 27.2 m3/ha/year in terms of yield). The remaining triploid A. hybrid clones grew slower than the control, especially X1201 and X204 had very slow growth. The A. auriculiformis clones X41, X42 (triploids) and Ctl18(diploid) had relatively slow growth compared to the A. hybrid clones. c) At Xuan Loc The average survival rate of the trial was relatively low, only 71%. However, most of the fast growing clones have high survival rates (over 80%). The difference in survival among clones was statistically significant (Fpr < 0.001). The two triploi A. hybrid clones X201 and X101 had yields of 39.0 m3/ha/year and 38.6 m3/ha/year, respectively, the difference was not significant with the control diploid A. hybrid BV73 (30.0 m3/ha/year) but significantly higher than the other control diploid A. hybrid clone AH7 (21.0 m3/ha/year). Two other triploid A. hybrid clones X102 and X1100 also showed good growth potential in this trial, yielding 28.9 m 3/ha/year and 24.3 m3/ha/year, respectively. The remaining triploid A. hybrid clones all had slow growth, the yield is less 17 m3/ha/year, especially the three 12
triploid A. hybrid clones X1200, X1201 and X204 had very poor growth (under 10 m3/ha/year). A. auriculiformis X21, X41, X42 (triploid) and AA1 (diploid) all grew relatively slowly in this trial, yielding only 2.7 - 10.4 m3/ha/year. The difference in growth and yield traits among clones was statistically significant (Fpr < 0.001). 3.1.2. Growth characteristics of clones in 49-tree-plot trial at 3 study sites The results obtained in 49-tree plot trials at all 3 study sites showed similarity with the results obtained in the respective 10-tree plots by site. Most of the promising clones in the 10-tree plot trials also showed promise in the 49-tree plot trials. The average survival rate after 3 years of age in all 3 study sites was high (90.4% in Yen The, 87.5% in Cam Lo and 83.1% in Xuan Loc). The difference in survival among clones was not statistically significant at Yen site, but very significant (Fpr < 0.001) in the other 2 sites. Growth and yield were significantly different among clones in all 3 study sites (Fpr < 0.001). In particular, the triploid A. hybrid X201 showed superiority in all three study sites, yielding 30.6 m3/ha/year in Yen The, 26.0 m3/ha/year in Cam Lo and 32.6 m3/ha/year in Xuan Loc; two other triploid A. hybrid X101 and X102 showed good prospects at Yen The and Xuan Loc sites, yielding 23.0 m3/ha/year and 24.4 m3/ha/year respectively for Yen The; 27.9 m3/ha/year and 33.1 m3/ha/year; and X205 also showed good growth in both tested locations (Cam Lo and Xuan Loc). All four fast-growing triploid A. hybrid clones (X101, X102, X201 and X205) have good resistance to pink disease and wind resistance, except for the X205, which had a relatively high percentage of bent trees (29.9%). 3.1.3. Growth characteristics of triploid A. hybrid clones according to crossing direction Initial research results showed that, at age 3, the survival rate did not differ significantly among crossing directions, as well as crossing direction and control group in all 3 study locations (Fpr > 0.05). Growth (D1.3 and Hvn) and yield among the triploid crossing directions were not significantly different in Yen The (Fpr > 0,05) but is very significant in the other 2 sites. The productivity of crossing direections in Yen The reached from 19.1 to 20.8 m3/ha/year after 3 years of age; In Cam Lo, crossing direction AM (A. auriculiformis 2x × A. 13
mangium 4x) had a yield of 20.9 m3/ha/year, significantly higher (Fpr < 0.001) than group MA (A. mangium 4x × free pollen) and MA* (A. hybrid 2x × A. hybrid 4x), 16.0 m3/ha/year and 15.0 m3/ha/year, respectively; Similarly, the yield of AM in Xuan Loc was also superior (Fpr = 0.005) compared with MA and MA* (35.5 m3/ha/year versus 14.7 m3/ha/year and 11.5 m3/ha/year respectively). Initially, results have shown a good prospect of the crossing direction AM. The rate of promising clones of this crossing direction was high in all 3 study sites (3/4 clones in Yen The, 2/5 clones in Cam Lo and 4/5 clones in Xuan Loc). 3.1.4. Stem quality a) At Yen The At 3 years, results achieved at 10-tree-plot and 49-tree-plot trials were equal. Triploid A. hybrid clone X201 showed highest stem quality index (Icl) and diploid A. hybrid clone BV10 was the lowest. Two triploid A. hybrid clones X101 and X102 had stem straight (Dtt) superior to others. b) At Cam Lo Two prospect triploid A. hybrid clones (X201 and X205) had Icl in the top group thank for having Ptn (top development) and Sk (health) superior to other clones at both trials. X101 and X102 still revealed best Dtt, however other parameters (Ptn and Sk) were poorer. Both diploid A. hybrid clones AH7 (at 10-tree-plot trial) and BV16 (at both trials) had good Icl, belonged to top group while BV10 (at 49-tree-plot trial) showed lowest Icl inspite having highest Sk. Remain triploid A. hybrid clones which grew inferior growth had poor Icl for both trials. c) At Xuan Loc Similar to above sites, prospect triploid A. hybrid clones (X101, X102, X201 and X205) had high Icl at both trials. X101 and X102 also proposed superior Dtt while X201 and X205 had superior Ptn and Sk compared with remain clones. Diploid A. hybrid clone as control (BV73) had poor Ptn because of being affected by high rate of pink disease trees. 3.1.5. Monthly at-breast diameter increment (Z) and leaf area index (LAI) at Xuan Loc Research results have shown that Zd trend and seasonal variation of LAI were similar among clones. All of them (including fast growing or slow growing clones) almost stopped growing in 4 months of dry season (from January to April). This was period when the LAI of clones was the lowest of the year. The differences among clones in terms of Zd were only 14
evident in some months of the rainy season. In particular, the most obvious difference was between the triploid A. hybrid clone X205 and the diploid A. hybrid BV73. The X205 showed a slower growth trend in the early months of the rainy season but faster during the peak of the rainy season. The diploid A. hybrid clone BV73 had very slow growth in the last 3 months of the rainy season (October - December). The regularity of Zd and LAI of the clones was clearly shown over 2 years of follow-up. The LAI was not significantly different between the A. hybrid clones (both triploid and diploid) but there was a very clear difference between the A. auriculiformis and A. hybrid clones during the follow-up period. However, the difference tends to decrease over time. The study showed that monthly rainfall (related to soil moisture) was the key factor determining the growth of acacia plantations in the Southeast region. 3.2. Properties of triploid acacia wood 3.2.1. Wood denisity a) At Cam Lo At 3.8 years old (46 months), triploid A. hybrid clones (X101, X102 and X201) had similar wood density (358.9 - 377.7 kg/m3), significantly lower than with two control A. hybrid clones BV10 and BV16 (407.4 - 447.1 kg/m3). The triploid A. auriculiformis X41, although growing significantly slower than A. hybrid (D1.3 was only 9.6 cm compared to 10.8 - 13.4 cm) but has the highest density (462.5 kg/m3). The difference in density among clones was statistically significant (Fpr < 0.001). b) At Vinh Cuu Wood density at 3.8 years old was not significantly different between the two ploidy groups, but there was a significant difference (Fpr < 0.001) between the two clones in the same ploid group. X101 had a significantly higher wood density than X102 clone (484.7 kg/m3 vs 434.3 kg/m3) in triploid group, while BV10 was significantly higher than BV16 (490.4 kg/m3 compared with 444.4 kg/m3) in the diploid group. Compared with Cam Lo site, all 4 clones in this study site had higher density of wood respectively. c) At Xuan Loc At the age of 3.0 years, most of the triploid A. hybrid clones had a lower wood density than the diploid A. hybrid clones (378.5 – 427.0 kg/m3 compared with 440.8 – 455.6 kg/m3), except for the X11 (448.6 kg/m3). However, only 2 clones (X201 and X102) were significantly lower (Fpr < 15
0.001) compared with diploid A.hybrid clone (AH7, BV73, TB12). Wood density of all clones in all 3 study sites tended to decrease with sampling height. 3.2.2. Heartwood ratio a) At Cam Lo At 3.8 years of age (46 months), the percentage of heartwood of the three triploid A. hybrid clones X101, X102 and X201 was equivalent to that of the two diploid A. hybrid clones BV10 and BV16 (34 - 37.4%) compared to 33.7 – 35.2%). The triploid A. auriculiformis clone X41 had the lowest percentage of heartwood (18.0%). However, the difference among clones in the percentage of heartwood was not statistically significant (Fpr = 0,100). b) At Vinh Cuu Two triploid A. hybrid clones (X101 and X102) had a significantly higher percentage of heartwood (Fpr < 0.001) compared with the two control clone BV10 and BV16 (44.7 – 47.0% vs 24.7 – 31.3%). Comparing with Cam Lo, the two triploid A. hybrid clones X101 and X102 here had a significantly higher percentage of heartwood, while the two diploid A. hybrid clones BV10 and BV16 were equivalent. Thereby, the interaction between the environmental conditions by the clones (genotypes) to the percentage of heartwood was significant. c) At Xuan Loc After 3 years of planting, the three triploid A. hybrid clones X11, X101 and X102 had a high percentage of heartwood (45.9%, 44.5% and 37.6%, respectively). The remaining triploid A. hybrid clones X201, X205 and X1100 have the same proportion of heartwood as the diploid A. hybrid clones AH7, BV73 and TB12. The difference in the percentage of heartwood among clones was statistically significant (Fpr < 0.001). Regarding height variation, the percentage of heartwood tended to decrease with tree height and was clearly seen in all clones (both triploid and diploid) at the 3 study sites. 3.2.3. Length of wood fiber a) At Cam Lo At 3.8 years of age, the wood fiber of the three triploid A. hybrid clones X101, X102 and X201 were significantly longer (Fpr < 0.001) compared with the two diploid A. hybrid clones BV10 and BV16 (899.7 – 919.8 µm vs. with 825.1 – 855.3 µm). The triploid A. auriculiformis X41 16
had the longest wood fiber (969 µm) but the difference was not significant compared with the three triploid A. hybrid clones. b) At Vinh Cuu The two triploid A. hybrid clones X101 and X102 had superior wood fiber length (Fpr < 0.001) compared with the two diploid A. hybrid clones BV10 and BV16 (1030.2 µm and 981.7 µm compared to 821.8 µm and 847 µm respectively). Compared with Cam Lo, the wood fiber length of the two triploid A. hybrid clone X101 and X102 was significantly longer, while the two diploid A. hybrid clones BV10 and BV16 were similar. This showed that the interaction between the environmental conditions by the clones to the wood fiber length was significant. c) At Xuan Loc The triploid A. hybrid clones also had longer wood fiber than the diploid A. hybrid clones (954.3 – 1009.9 µm compared with 933.6 – 948.7 µm). However, the difference was not significant compared with BV73 (948.7 µm) and only X201 and X205 were significantly different (Fpr < 0.001) compared with the two control lines AH7 and TB12. . Wood fiber length tended to increase steadily from the pith to the bark direction and was clearly seen in all clones at the 3 study sites. This also means that the length of the wood fiber increases with the age of the tree. 3.2.4. Wood shrinkage a) At Cam Lo  Tangential shrinkage The total linear shrinkage of the wood in the tangent direction of the clones was not significant difference (Fpr = 0.100). The range of variation between clones was relatively small (5.8 – 6.4%). The coefficient of variation among individual trees in a clone was moderate (5.9 – 13.2%).  Radial shrinkage The total linear shrinkage of wood in the radial direction was only significant (Fpr < 0.001) between the triploid X201 A. hybrid (2.9%) compared with the diploid BV10 A. hybrid clone (2.4%) and A. auriculiformis X41 (2.4%). The remaining clones were in the same group. Compared to the tangent direction, the coefficient of variation among individual trees in the each clone was somewhat larger here (11.6 - 14.9%). The ratio between the total linear shrinkage of wood in the tangential 17