Activities of some defense proteins associated with age or plant family in larch needles of <Emphasis Type="Italic">Larix olgensis</Emphasis> and <Emphasis Type="Italic">L. kaempferi</Emphasis> × <Emphasis Type="Italic">L. gmelinii</Emphasis>

Defence proteins are a kind of chemical defence compounds. They play a key role in plant restraining biotic and abiotic harm. To illuminate activities of some defense proteins associated with age or plant family of larch, the larch needles were collected from two different families of Korean larch, Larix olgensis and a hybrid larch, L. kaempferi × L. gmelinii, respectively, and then the activities of defence proteins in those were tested using a UV spectrophotometry. The results showed that the activities of protective enzymes at the16-/17- and 19-year-age groups were higher than those at the other age groups in the both larch species. While the activities of polyphenol oxidase (PPO) at the 16-/17-year-age group and phenylalanine ammonia-lyase (PAL) and protease inhibitors at the 19-year-age group were the highest among all age groups. Then, compared with L. olgensis, the hybrid larch had significant effects on the activities of protective enzymes. The effects of plant family on the activities of PAL and chymotrypsin inhibitor were significantly different, and then those on the activities of PPO were not significantly different. The effects of the two families in L. olgensis on the activities of trypsin inhibitor (TI) were significantly different, while those in the hybrid larch on the activities of TI were contrary. To conclusions showed that the different age and plant family significantly affected the activities of defence proteins in the needles of two larch species, and then enhanced the larch resistance to pests. These could play a key function in forestry tree genetic improvement and management in future.     

Differences in leaf functional traits between red and green leaves of two evergreen shrubs <Emphasis Type="Italic">Photinia</Emphasis> × <Emphasis Type="Italic">fraseri</Emphasis> and <Emphasis Type="Italic">Osmanthus fragrans</Emphasis>

Leaf functional traits are adaptations that enable plants to live under different environmental conditions. This study aims to evaluate the differences in leaf functional traits between red and green leaves of two evergreen shrubs Photinia × fraseri and Osmanthus fragrans. Specific areas of red leaves are higher than that of green leaves in both species. Thus, the material investment per unit area and per lamina of red leaves is significantly lower than that of green leaves, implying an utmost effort of red leaves to increase light capture and use efficiency because of their low leaf-chlorophyll concentration. The higher petiole length of green leaves compared with that of red leaves indicates that adult green leaves may have large fractional biomass allocation to support the lamina structures in capturing light with maximum efficiency and obtaining a high growth rate. The high range of the phenotypic plasticity of leaf size, leaf thickness, single-leaf wet and dry weights, and leaf moisture of green leaves may be beneficial in achieving efficient control of water loss and nutrient deprivation. The high range of phenotypic plasticity of leaf chlorophyll concentration of red leaves may be advantageous in increasing resource (especially light) capture and use efficiency because this leaf type is juvenile in the growth stage and has low leaf-chlorophyll concentration.     

AFLP fingerprinting of <Emphasis Type="Italic">Populus deltoides</Emphasis> and <Emphasis Type="Italic">Populus </Emphasis>×<Emphasis Type="Italic"> canadensis</Emphasis> elite accessions

Amplified fragment length polymorphism (AFLP) was used in genetic fingerprinting of 22 elite Chinese Populus deltoides and Populus × canadensis accessions. The results indicated that each of the nine AFLP primer pairs selected generated fingerprint profiles that were unique to each of the accessions. Therefore, each accession was definitively identified by any of the nine primer pairs. Furthermore, the inter-accession genetic relationships inferred based on 461 polymorphic fragments from the nine AFLP primer pairs were largely consistent with phylogenetic relationships based on morphologic traits. Bootstrap analysis showed that three AFLP primer pairs were required to obtain genetic similarity values with a maximum CV of 10% while 10 AFLP primer pairs could give a maximum CV of 5%. Thus, AFLP can readily be applied for a rapid and accurate evaluation of the degree of similarity between poplar cultivars. In this study, the number of AFLP fragments used was sufficient to establish a reliable estimate of genetic similarity among accessions, with a maximum CV of 5.12%. Therefore, the information on the genetic relationships among the poplar accessions generated in this study in connection with knowledge on agronomic traits may have an impact on poplar breeding and planting in China.     

Quantitative genetics of cold hardiness and growth in <Emphasis Type="Italic">Eucalyptus</Emphasis> as estimated from <Emphasis Type="Italic">E.</Emphasis><Emphasis Type="Italic">urophylla</Emphasis> × <Emphasis Type="Italic">E. tereticornis</Emphasis> hybrids

Interspecific hybrids of Eucalyptus urophylla S. T. Blake × E. tereticornis Smith were used for quantitative genetic analysis of cold hardiness (CH) and growth traits height (H), diameter at breast height (D) and volume (V) at 0.5, 1.5, 2.5 and 4 years of age. The effect of E. tereticornis male variance was significant (P < 0.05) for CH as well as 2.5- and 4-year-old growth except for H ₄, and E. urophylla female × E. tereticornis male interaction was significant for 0.5- and 1.5-year-old growth and CH except for CH _0.5, whereas E. urophylla female effect was not significant for the majority of traits analyzed. Both additive and dominance gene action were present in the genetics of all the traits measured at most ages, indicating that those traits may be improved by hybrid breeding. The σ _D ²/σ _A ² ratios tended to decline after 1.5 years of age in CH and growth traits, implying that breeding value predictions derived from older performance might be more reliable. Estimates of narrow-sense heritability (h ² ) for CH and growth ranged from 0.03 ± 0.05 to 0.28 ± 0.13, depending on trait and age. Additive genetic correlations between CH and V were 0.28 ± 0.48 and 0.69 ± 0.30 at ages 1.5 and 2.5, respectively, suggesting that selection for growth would cause a favorable increase in cold hardiness in E. urophylla × E. tereticornis hybrids.     

Soil microorganisms alleviate the allelopathic effect of <Emphasis Type="Italic">Eucalyptus grandis</Emphasis> × <Emphasis Type="Italic">E</Emphasis>. <Emphasis Type="Italic">urophylla</Emphasis> leachates on <Emphasis Type="Italic">Brassica chinensis</Emphasis>

Soil microbes may be critical players in determining the allelopathic potential of some plants. Low levels of plant community biodiversity in Eucalyptus plantations have been attributed to the allelopathic potential of these tree species. The role of soil microbes in the allelopathic effect of leaf leachates of the hybrid tree Eucalyptus grandis × E. urophylla, was tested in Petri dish assays with Brassica chinensis as a receiver plant. Soils were collected from either a local garden (soil A) or a Eucalyptus plantation (soil B) and half of each soil was sterilized to remove microbes. These soils were then treated with E. grandis × E. urophylla leachates for 0–72 h. Seed germination of B. chinensis was significantly inhibited in soils treated with leaf leachates relative to untreated soils. The inhibitory effect of the leaf leachates was more pronounced in sterilized soils. Total phenolic content was obvious lower in nonsterile leachate-treated soils than in sterile soils. Biomass of B. chinensis was negatively correlated with the total phenolic content in soils. Our findings suggest that soil microbes can alleviate the allelopathic potential of Eucalyptus and thereby its negative impact on plant growth.     

The effects of phenolic acid on nitrogen metabolism in <Emphasis Type="Italic">Populus</Emphasis> × <Emphasis Type="Italic">euramericana</Emphasis> ‘Neva’

The declines in soil fertility and productivity in continuously cropped poplar plantations are related to phenolic acid accumulation in the soil. Nitrogen is a vital life element for poplar and whether the accumulation of phenolic acid could influence nitrogen metabolism in poplar and thereby hinder continuous cropping is not clear. In this study, poplar cuttings of Populus × euramericana ‘Neva’ were potted in vermiculite, and phenolic acids at three concentrations (0X, 0.5X and 1.0X) were added according to the actual content (1.0X) in the soil of a second-generation poplar plantation. Each treatment had eight replicates. We measured gas exchange parameters and the activities of key enzymes related to nitrogen metabolism in the leaves. Leaf photosynthetic parameters varied with the concentration of phenolic acids. The net photosynthetic rate (P_N) significantly decreased with increasing phenolic acid concentration, and non-stomatal factors might have been the primary limitation for P_N. The activities of nitrate reductase (NR), glutamine synthetase (GS) and glutamate synthase (GOGAT), as well as the contents of nitrate nitrogen, ammonium nitrogen, and total nitrogen in the leaves decreased with increasing phenolic acid concentration. This was significantly and positively related to P_N (P < 0.05). The low concentration of phenolic acids mainly affected the transformation process of NO₃^? to NO₂^?, while the high concentration of phenolic acids affected both processes, where NO₃^? was transferred to NO₂^? and NH₄⁺ was transferred to glutamine (Gln). Overall, phenolic acid had significant inhibitory effects on the photosynthetic productivity of Populus × euramericana ‘Neva’. This was probably due to its influence on the activities of nitrogen assimilation enzymes, which reduced the amount of amino acids that were translated into protein and enzymes. Improving the absorption and utilization of nitrogen by plants could help to overcome the problems caused by continuous cropping.     

Comparative analysis of diterpene composition in the bark of the hybrid larch F<Subscript>1</Subscript>, <Emphasis Type="Italic">Larix gmelinii</Emphasis> var. <Emphasis Type="Italic">japonica × L. kaempferi</Emphasis> and their parent trees

The diterpene compositions in the bark of branches were investigated for two families of the F₁ hybrid, Kurile larch (Larix gmelinii var. japonica Pilg.) × Japanese larch [Larix kaempferi (Lamb.) Carr.] (hereafter F₁) and their parents clones. 13-Epimanool, larixol, larixyl acetate, 13-epitorulosyl acetate (not detected in L. gmelinii var. japonica), isopimaric acid, abietic acid, dehydroabietic acid, and neoabietic acid were detected. Larixol and abietic acid represented more than 50% of the diterpene content in L. gmelinii var. japonica and L. kaempferi, respectively. Larixol and abietic acid were the predominant diterpene components in the F₁, and the proportions of these diterpenes were between those of the parental species. Therefore, the diterpene compositions in the F₁ were hereditarily infl uenced by their parents. The ratios of labdane, pimarane, and abietane diterpenes suggested that the main diterpene biosynthesis pathway in L. gmelinii var. japonica was from copalyl diphosphate (CDP) to labdane-type diterpenes, and that in L. kaempferi was from CDP to abietane-type diterpenes via pimarane type. Furthermore, linear discriminant analysis suggested that the diterpene contents are effective indices for the discrimination of the hybrid seedlings. Part of this article was presented at the Annual Meetings of the Japan Society for Bioscience, Biotechnology, and Agrochemistry in Kyoto, March 2006, and in Tokyo, March 2007     

5<Emphasis Type="Italic">Α</Emphasis>-Reductase inhibitory tannin-related compounds isolated from <Emphasis Type="Italic">Shorea laeviforia</Emphasis>

Five tannin-related compounds – gallic acid, flavogallonic acid dilactone, valoneic acid dilactone, gallagyldilactone, ellagic acid – were isolated from the heartwood of Shorea laeviforia, and the inhibitory activity of each against rat liver 5-reductase was evaluated. Valoneic acid dilactone and gallagyldilactone exhibited positive inhibitory activity, but gallic acid and ellagic acid did not. Flavogallonic acid dilactone stimulated 5-reductase activity, even though this compound is structurally similar to valoneic acid dilactone. The kinetic study of valoneic acid dilactone and gallagyldilactone indicated that the inhibitory behavior of 5-reductase were not competitive against the substrate (testosterone) and were partially competitive against the cofactor (NADPH). Additionally, double inhibition analysis of valoneic acid dilactone and NADP⁺ showed synergetic inhibition. These results suggested that neither valoneic acid dilactone nor gallagyldilactone can affect the binding of testosterone but that either compound could interact with an enzyme–NADP⁺ complex to inhibit 5-reductase.     

Effect of major inorganic nutrients on <Emphasis Type="Italic">β</Emphasis>-thujaplicin production in a suspension culture of <Emphasis Type="Italic">Cupressus lusitanica</Emphasis> cells

 The optimum conditions for β-thujaplicin production in a Cupressus lusitanica cell suspension culture were investigated. The conditions required for β-thujaplicin production were clearly different from the conditions for cell growth. The initial phosphate concentration and pH did not affect β-thujaplicin production. A total nitrogen source concentration higher than 3.2 mM suppressed production due to the presence of the ammonium ion. β-Thujaplicin production was observed at 95 mg/l without adding the ammonium ion to the medium. Strict control of major inorganic nutrients was not necessary to produce β-thujaplicin. This finding seems to be favorable for future automated production of β-thujaplicin in commercial cell culture plants.     

Effect of silvicultural treatments on growth,fertility and capsule traits in seedling seed orchards of <Emphasis Type="Italic">Eucalyptus camaldulensis</Emphasis> and <Emphasis Type="Italic">E. tereticornis</Emphasis>

The effects of nutritional treatments and the flowering promoter Paclobutrazol™ on tree growth and fertility were studied in unpedigreed seedling seed orchards (SSOs) of Eucalyptus camaldulensis and E. tereticornis at two locations in southern India. At Pudukkottai, a semi-arid site in Tamil Nadu State, five treatments were applied: (1) untreated control, (2) nitrogen (two doses of urea at 217 g N/tree), (3) nitrogen plus phosphorus (two doses of 312 g single superphosphate), potassium (two doses of 83 g muriate of potash) and trace elements (two doses of 10 g sodium borate and 25 g zinc sulphate), (4) pollarding trees at 4 m height with application of N, P, K and trace elements, (5) drenching with the flowering promoter Paclobutrazol (0.25 ml active ingredient per cm of stem girth) along with N, P, K and trace elements. At Panampalli, a higher-rainfall site in Kerala State, only treatments 1, 2 and 3 were applied. Four replicates of treatment plots sized 18 m × 18 m, with 22–32 trees per plot were set up in each orchard in randomized complete block designs. Untreated plots of E. camaldulensis and E. tereticornis at Pudukkottai displayed 12 and 21% fertile trees, respectively, in the first year of monitoring, while at Panampally the percentage of fertile trees in untreated E. camaldulensis plots was higher at 72%, and that of E. tereticornis similar at 23%. Both species attained greater stem diameter at breast height at age 9 years at the higher-rainfall location but there was no significant impact of fertilizer application on 9-year diameter at either site. Diameter was reduced by pollarding and Paclobutrazol application at Pudukkottai. Only Paclobutrazol produced a significant increase in fertility in both species for four successive years, increasing the percentage of fertile trees to 59 and 71%, respectively, for E. camaldulensis and E. tereticornis 1 year after application. The number of capsules produced per tree also increased significantly with Paclobutrazol application, although the difference was comparatively less by the fourth year. The number of capsules per umbel did not differ significantly between locations, whereas the germination rate varied between treatments although no consistent trends were observed.     

Seasonal variation of selected trace elements in rare endemic species <Emphasis Type="Italic">Thuriferous Juniper</Emphasis> growing in the <Emphasis Type="Italic">Aurès</Emphasis> Mountains of Algeria

We used energy dispersive X-ray fluorescence (EDXRF) to determine the seasonal variation of selected trace elements (Cr, Mn, Zn, Cu, Se and Fe) and some potential toxic elements (Cd, Pb and Br) in Juniperus thurifera subsp. africana Maire (Cupressaceae) a rare medicinal tree, growing indigenously in Aurès Mountains of Algeria. The precision of the results was assessed by analyzing the certified reference material IPE44 (WEPAL) grass leaves. Results showed J. thurifera was characterized by high Cr and Mn contents. During autumn and winter mineral concentrations were higher in general. The levels of Cr, Se and Mn were higher during autumn and winter than during spring and summer. Zn contents were higher during summer than in other seasons. Cu content did not vary by season. The potential toxic elements in J. thurifera (Pb > Cd > Br) were below the permissible limits recommended by the Joint WHO/FAO guidelines except for Pb in autumn and winter.     

Comparative microsporogenesis and flower development in <Emphasis Type="Italic">Eucalyptus urophylla</Emphasis> × <Emphasis Type="Italic">E. grandis</Emphasis>

Microsporogenesis and flower development in Eucalyptus urophylla × E. grandis were examined using chromosome tableting to provide a method to predict the meiotic stages in this species. Although microsporogenesis was normal, cytokinesis during meiosis of pollen mother cells occurred simultaneously, with strong asynchronism observed in the two different lengths of stamens in a flower bud. In a single flower, the developmental period of microsporogenesis in anthers on the longer stamens was always ahead of those on the shorter stamens. Flower development was also asynchronous at different locations on a branch. Flower buds on the upper side of the branch were larger in diameter than those on the lower side. In addition, a correlation was observed between microsporogenesis development and flower bud diameter growth. The pachytene stage was first observed when the diameter of the flower buds increased to 3.0 mm, and the majority of the meiotic stages were observed when bud diameters ranged from 3.5 to 5.0 mm. This study showed that the developmental stages of microsporogenesis in Eucalyptus urophylla × E. grandis could be distinguished readily, which may be applicable to future breeding studies.     

Influence of stem rot pathogen <Emphasis Type="Italic">Fomitiporia</Emphasis> sp. on “Sanbu-sugi” cultivar of the Japanese cedar <Emphasis Type="Italic">Cryptomeria japonica</Emphasis>

An unidentified Fomitiporia sp. causes severe white-rot on stems of a cultivar “Sanbu-sugi” of the Japanese cedar, Cryptomeria japonica. The influence of the fungus on tree health and wood properties was determined. Bark from dead branches and xylem from living branches contained more glucose than bark from living branches and xylem from dead branches. Tree heights at which annual rings were disconnected were 2, 4 and 6 m at ages 37, 15 and 24 years old, respectively. The pH values of damaged parts were lower than those of non-damaged parts, and the damaged parts were clearly identified using bromocresol green solution. Weight loss of sapwood during 60 days of fungal degradation was 1.4 %, which was less than that by a saprophyte, Trametes versicolor. The amount of polyphenols in the heartwood from damaged tree stems was less than that from non-damaged stems. Degraded parts were less stiff than the non-degraded sapwood as measured with a wood-decay tester, Pilodyn. Our observations indicate that damaged stems are chemically and physically inferior to non-damaged stems.     

Can drought tolerance of Norway spruce (<Emphasis Type="Italic">Picea abies</Emphasis> (L.) <Emphasis Type="Italic">Karst</Emphasis>.) be increased through thinning?

To investigate whether drought tolerance of individual trees can be increased through the provision of more growing space, trees from a thinning experiment were analysed for reductions in radial growth during drought years and their subsequent recovery. Tree-ring widths were quantified on increment cores as well as stem discs of 32 trees from stands of a thinning trial established in 1974 in 27-year-old spruce stands in the Alpine Foreland of Southwest Germany. Three different thinning regimes of the trial were selected for this study: unthinned control (8 trees), moderate (13 trees) and heavy thinning (11 trees) intensities. All trees sampled were of a co-dominant to dominant canopy status. The standardisation of growth data was carried out using the software program ARSTAN (University of Arizona). For the year 1976—a widespread and severe drought year in Germany—we found year ring widths were not reduced compared to those of the pre-drought years for all treatments. However, we observed the formation of false year rings and resin ducts for this year in all trees investigated. The drought events in 1992 and 2003 led to severe growth depressions in the year of the drought event in all trees, regardless of previous thinning regimes. However, the resilience—the recovery of basal area growth in subsequent years—was significantly more rapid in trees from heavily thinned stands, even if the drought event occurred more than 10 years after the last thinning intervention. This indicates a shorter stress period for trees with more growing space, which may reduce the susceptibility to secondary pathogens or pest species such as bark beetles.     

Effects of Thidiazuron,basal medium and light quality on adventitious shoot regeneration from <Emphasis Type="Italic">in vitro</Emphasis> cultured stem of <Emphasis Type="Italic">Populus alba</Emphasis>×<Emphasis Type="Italic">P. berolinensis</Emphasis>

The effect of Thidiazuron （TDZ）, basal media and light quality on adventitious shoot regeneration from in vitro cultured stem of Populus albaxP berolinensis were determined to establish a high efficiency shoot regeneration system from stem explants of P. alba~P berolinensis. Stems ofPopulus alba~P berolinensis were collected from cultured shoots in vitro derived from dormancy buds of 3-year-old seedlings. The stem explants were cultured on MS medium containing 0.02-mg·L-1NAA （naphthaleneacetic acid）, and 0.1, 0.3, 0.5 and 1.0 mg·L-1 concentrations of TDZ to determine the effect of TDZ on shoot regeneration. Three basal media, i.e. MS, woody plant medium （WPM） and B5, were used to test their influences of different media on adventitious shoot regeneration. Green, red, blue and yellow plastic films in comparison with florescent light as control were used to observe their effects on shoot regeneration. The results showed that differ- ent concentrations of TDZ had an evident influence on shoot regeneration. Lower concentration of TDZ （0.1 mg·L-1） resulted in more ad- ventitious shoot regeneration and higher concentration of TDZ （〉0.1 mg·L-1） inhibited shoot regeneration. Among different media, MS medium exhibited a high efficiency for shoot regeneration, followed by WPM medium, while B5 medium inhibited shoot regeneration. Normal light and yellow light exhibited better effects on shoot regeneration, compared with other light.     

Micropropagation of <Emphasis Type="Italic">Eucalyptus grandis</Emphasis> × <Emphasis Type="Italic">E. urophylla</Emphasis> AEC 224 clone

Genetic transformation systems require protocols that allow regenerating transgenic plants from transformed tissues. This study aimed to establish a protocol for indirect organogenesis in leaf explants of a Eucalyptus grandis  ×  E. urophylla AEC 224 clone. During callogenesis stage, several concentrations of NAA and then NAA or 2,4-D combined with TDZ were tested in JADS culture medium for 30 days, followed by subculture of the explants in the regeneration medium, containing 5.0 µM BA and 0.5 µM NAA for another 30 days. In these media, the explant oxidation rate was high (95 %). Thus, in order to reduce oxidation, different culture media were compared: WPM, MS, JADS and modified QL, followed by explant transfer onto regeneration medium. The highest percentage of regeneration and the lowest oxidation rate were achieved on WPM medium. Then, NAA and 2,4-D were tested in combination with TDZ and also TDZ and BA combined with NAA in WPM medium. The most efficient culture media in terms of shoot regeneration were WPM supplemented with 0.25 µM TDZ and 0.1 µM NAA during 30 days for callus induction and then with 5.0 µM BA and 0.5 µM NAA for another 30 days. This protocol yielded a regeneration rate of 43 %, with a low oxidation of tissues. A rooting experiment was conducted using half strength MS medium and comparing three concentrations of IBA (2.46, 4.90 and 7.35 µM). The highest rooting percentage (35 %) was obtained on medium containing 2.46 µM IBA. Once the shoots were rooted, acclimatization in a greenhouse was not challenging and plant survival reached 100 %.     

Two novel eukaryotic translation initiation factor 5A genes from <Emphasis Type="Italic">Populus simonii</Emphasis> × <Emphasis Type="Italic">P. nigra</Emphasis> confer tolerance to abiotic stresses in <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

The role of plant eIF5A proteins in multiple biological processes, such as protein synthesis regulation, translation elongation, mRNA turnover, programmed cell death and stress tolerance is well known. Toward using these powerful proteins to increase stress tolerance in agricultural plants, in the present study, we cloned and characterized PsneIF5A2 and PsneIF5A4 from young poplar (P. simonii × P. nigra) leaves. The deduced amino acid sequences of PsneIF5A2 and PsneIF5A4 were 98 % similar to each other, and they are orthologs of eIF5A1 in Arabidopsis. In a subcellular localization analysis, PsneIF5A2 and PsneIF5A4 proteins were localized in the nucleus and cytoplasm. qRT-PCR analysis showed that PsneIF5A2 and PsneIF5A4 were transcribed in poplar flowers, stem, leaves, and roots. In addition, they were also induced by abiotic stresses. Transgenic yeast expressing PsneIF5A2 and PsneIF5A4 had increased salt, heavy metal, osmotic, oxidative tolerance. Our results suggest that PsneIF5A2 and PsneIF5A4 are excellent candidates for genetic engineering to improve salt and heavy metal tolerance in agricultural plants.     

Genetic parameters for growth and wood chemical properties in <Emphasis Type="Italic">Eucalyptus urophylla</Emphasis> × <Emphasis Type="Italic">E. tereticornis</Emphasis> hybrids

Key message

Growth and wood chemical properties are important pulpwood traits. Their narrow-sense heritability ranged from 0.03 to 0.49 in Eucalyptus urophylla × E. tereticornis hybrids, indicating low to moderate levels of genetic control. Genetic correlations were mostly favorable for simultaneous improvement on growth and wood traits. Additive and non-additive genetic effects should be considered in making a hybrid breeding strategy.

Context

Eucalypt hybrids are widely planted for pulpwood production purposes. Genetic variations and correlations for growth and wood chemical traits remain to be explored in Eucalyptus interspecific hybrids.

Aims

Our objectives were to clarify the heritability of growth and wood chemical traits and determine the genetic correlations between traits and between trials in E. urophylla × E. tereticornis hybrids.

Methods

Two trials of 59 E. urophylla × E. tereticornis hybrids derived from an incomplete factorial mating design were investigated at age 10 for growth (height and diameter) and wood chemical properties (basic density, cellulose content, hemi-cellulose content, lignin content, and syringyl-to-guaiacyl ratio). Mixed linear models were used to estimate genetic parameters.

Results

Narrow-sense heritability estimates were 0.13?0.22 in growth and 0.03?0.49 in wood traits, indicating low to moderate levels of additive genetic control. Genetic correlations were mostly positively significant for growth with basic density and cellulose content but negatively significant with hemi-cellulose and lignin contents, being favourablefavorable for pulpwood breeding purpose. Type-B correlations between sites were significant for all the traits except diameter and lignin content.

Conclusion

Hybrid superiority warrants the breeding efforts. An appropriate breeding strategy should be able to capture both additive and non-additive genetic effects.

     

Factors Affecting Small-Scale Farmers’ Land Allocation and Tree Density Decisions in an <Emphasis Type="Italic">Acacia decurrens</Emphasis>-Based <Emphasis Type="Italic">taungya</Emphasis> System in Fagita Lekoma District,North-Western Ethiopia

The development of woodlots as an additional source of livelihood and as a land management option for small-scale farmers is a challenging issue in the cereal-based subsistence farming systems of north-western Ethiopia. There is a need to understand why and which factors determine the decisions of small-scale farmers to grow short-rotation woodlots on their land. Data used in this study were collected from a survey of 200 randomly selected households in the region. A Tobit regression model was used to determine predictor variables for farmers’ decisions to allocate land to planting Acacia decurrens (J.C. Wendl.) Willd. and at what density trees are planted on the respective plots. The most important motivations for planting A. decurrens were income, soil fertility management, and soil and water conservation. Having a male head of household, long distance to markets and plots being on marginal land, among other factors, increased the allocation of land to A. decurrens woodlots. Having a male head of household, access to credit and plots being on marginal land, among other factors, increased tree planting density. Age had a negative effect on both allocation of land to woodlots and tree density, whereas farm size had an inverted U-shaped relationship with both decisions. These results suggest that wider expansion of A. decurrens-based plantation systems could be achieved through improving extension, credit access and road infrastructure to connect small-scale farmers to markets and finance.