Alba Clone Research Articles

Five Year Field Evaluation of Prosopis alba Clones on pH 9–10 Soils in Argentina Selected for Growth in the Greenhouse at Seawater Salinities (45 dS m−1)

Prosopis alba seedlings, that grew at the 45 dS m−1 salinity level in a previous study of growth and survival of Argentine and Peruvian Prosopis, were propagated by rooting cuttings and established in a seed orchard/long term evaluation trial on soils with low salinity (EC 5.1–7.5 dS m−1) but high pH (8.9 to 10.2). A pH gradient occurred in the field with values ranging from pH 9.4 in block 1 to pH 10.3 in block 5. After five years growth, almost all of the clones had a mean height greater than 4 m and one clone was more than 5 m. Ten of the 21 tested clones had significantly greater biomass growth than the three seed propagated check varieties. The broad-sense (i.e., clone mean) heritability was estimated to be 0.45 for biomass, 0.53 for diameter and 0.59 for height indicating that strong genetic gains should be possible by selecting and vegetatively propagating the best genotypes. In the block with the highest pH values, two clones that appear to be P. alba × P. ruscifolia hybrids (i.e., P. vinallilo) had the greatest biomass. Correlations between growth during the last two months in the high salinity hydroponic greenhouse selection system and growth in the field were significant (R2 = 0.262) and positive, although the relationship was negative for putative P. vinallilo clones (R2 = 0.938). The several fold increase in biomass of some of the clones over the three check varieties, suggests that the greenhouse screen was successful in identifying superior salt tolerant clones. Apparently whether the greenhouse seedlings had lesser (~1 cm) to greater (~3 cm) height growth was not as important as just having a healthy live apical meristem. The observed salt tolerance of the putative P. vinalillo clones may prove useful as rootstocks for recently described high pod producing P. alba clones.

Arbuscular mycorrhizal fungi restore normal growth in a white poplar clone grown on heavy metal-contaminated soil, and this is associated with upregulation of foliar metallothionein and polyamine biosynthetic gene expression.

It is increasingly evident that plant tolerance to stress is improved by mycorrhiza. Thus, suitable plant-fungus combinations may also contribute to the success of phytoremediation of heavy metal (HM)-polluted soil. Metallothioneins (MTs) and polyamines (PAs) are implicated in the response to HM stress in several plant species, but whether the response is modulated by arbuscular mycorrhizal fungi (AMF) remains to be clarified. The aim of the present study was to check whether colonization by AMF could modify growth, metal uptake/translocation, and MT and PA gene expression levels in white poplar cuttings grown on HM-contaminated soil, and to compare this with plants grown on non-contaminated soil. In this greenhouse study, plants of a Populus alba clone were pre-inoculated, or not, with either Glomus mosseae or G. intraradices and then grown in pots containing either soil collected from a multimetal- (Cu and Zn) polluted site or non-polluted soil. The expression of MT and PA biosynthetic genes was analysed in leaves using quantitative reverse transcription-PCR. Free and conjugated foliar PA concentrations were determined in parallel. On polluted soil, AMF restored plant biomass despite higher Cu and Zn accumulation in plant organs, especially roots. Inoculation with the AMF caused an overall induction of PaMT1, PaMT2, PaMT3, PaSPDS1, PaSPDS2 and PaADC gene expression, together with increased free and conjugated PA levels, in plants grown on polluted soil, but not in those grown on non-polluted soil. Mycorrhizal plants of P. alba clone AL35 exhibit increased capacity for stabilization of soil HMs, together with improved growth. Their enhanced stress tolerance may derive from the transcriptional upregulation of several stress-related genes, and the protective role of PAs.

Exploring the metal phytoremediation potential of three Populus alba L. clones using an in vitro screening

This work was planned for providing a useful screening tool for the selection of Populus alba clones suitable for phytoremediation techniques. To this aim, we investigated variation in arsenic, cadmium, copper, and zinc tolerance, accumulation and translocation in three poplar clones through an in vitro screening. Poplars have been widely proposed for phytoremediation, as they are adaptable to grow on contaminated areas and able to accumulate metals. The investigation of possible differences among poplar clones in metal tolerance and accumulation deserves to be deeply studied and exploited for the selection of the more suitable tool for phytoremediation purposes. In vitro multiplied microshoots of a commercial and two autochthonous P. alba clones were subcultured on hormone-free WPM medium for 1month and then transferred for 2weeks onto media containing different concentrations of the metals investigated. At the end of the treatments, plantlets were sampled, weighed, and mineralised by wet ashing. Metal concentrations were determined by ICP-OES. For the metal concentration used in the experiments, our clones of P. alba showed variation in metal tolerance, metal accumulation and content. The fast-growing commercial clone, even if rarely showing the highest plant metal concentration, displayed the highest metal content, suggesting biomass production as the key factor in evaluating the phytoextraction capacity of P. alba clones for the metals studied. Data demonstrated that in vitro screening of cuttings represents a valuable way of assessing the ability of different poplar clones to take up, tolerate and survive metal stress.

A comparison of pod production and insect ratings of 12 elite Prosopis alba clones in a 5-year semi-arid Argentine field trial

Semi-arid adapted nitrogen fixing trees of the genus Prosopis have been extensively used in Argentina for soil improvement, luxury quality lumber production and sweet (35% sucrose) pods for humans and livestock. Due to the great demand of Prosopis alba for lumber, erect, tall, high pod producing trees of this species have been greatly overharvested, leading to erosion of the gene pool. A previous progeny trial with 57 half sib families identified 12 trees with promise for rapid growth, high production of pods and sweet pods. This trial, on a site with a salinity of 8.6 dS m −1 EC and a pH of 7.7, examined clones of these 12 trees in a randomized complete block trial with 8 single tree replications for height, basal diameter, canopy height and diameter, production of pods, sensory characteristics of the pods, disease resistance and insect resistance. In the 5th year of production and 7th year from planting, three clones produced more than 50 kg pods per tree versus 32 kg for check. At this 10 m × 10 m spacing, this yield of 5000 kg/ha compares favorably to many other semi-arid crops, especially given the unfavorable salinity and pH. In contrast to genetic improvement in pod production, the clones had lower diameter, height and canopy growth than the check. The lower biomass production may be due to fibrous root system produced from cuttings, since some of the clones blew over in high winds but none of the checks produced from seed blew over. Companion seed orchards of salt tolerant clones may provide rootstock for these high pod production clones. Significant differences in insect and disease resistance of the clones were observed and full sib crosses were made to study the genetics of the resistance. All clones had good sensory properties for use in human food. This is the first replicated trial with multipurpose clones useful for lumber and human food. The annual diameter growth rates ranged from 2.8 to 4.1 cm year −1 which was estimated to produce an internal return of approximately 20% from lumber alone.

Sheep preference for and effect of browsing on regrowth of two <i>salix</i> species and <i>chamaecytisus palmensis</i> (H. Christ) Hutch

To evaluate the usefulness of two Salix species in pastoral systems, two experiments were conducted to determine 1) the effects of browsing intensity and frequency on the regrowth of the Salix species andChamaecytisus palmensis (H. Christ) Hutch and 2) sheep preference for them. The species responded well to browsing but the mean regrowth of S. kinuyanagi Kimura and C. palmensis was higher than that for S. matsudana x alba clone ‘Tangoio’. Across species, browsing twice during summer-autumn yielded more edible dry matter (DM) than browsing once and seemed the most practical management for the farmer. Heavy browsing increased woody stem DM in S. kinuyanagi but did not influence regrowth in S. matsudana x alba and C. palmensis. S. matsudana x alba was the most preferred species by sheep but declined dramatically in preference during autumn. It is suggested that C. palmensis must be grown alone to enhance its use while the Salix spp. could be mixed.

Mating patterns, genetic composition and diversity levels in two seed orchards with few clones—Impact on planting crop

Paternity analyses using microsatellites were conducted in two conifer clonal seed orchards (CSOs). The aim was to study mating patterns and potential dysfunctions such as unbalanced male contribution, and how these factors influence genetic diversity. The effect of unequal male contribution was quantified by the status number ( N S), which reflects build up of coancestry in the seed orchard crop due to low number of clones and unequal male contribution. This approach was also used to quantify the effect of clonal differences in germination percentages on effective population sizes. Furthermore the genetic diversity of the Abies alba and Larix kaempferi CSOs was compared to other alternative seed sources via observed heterozygosity and allelic richness. Both CSOs had a low pollen contamination rate (1.4% and 2.8%). The CSO with 12 A. alba clones showed a very skewed distribution of paternal contributions, where four clones (25%) sired more than 80% of the offspring, resulting in a status number of ( N S) = 4.6. The CSO with 10 L. kaempferi clones showed a much more equal distribution of paternal contributions, with ( N S) = 10.2. For both CSOs the paternal contributions varied significantly with sampling site within the seed orchards. The amount of selfing in the CSO seed crops was 4.7% in A. alba and 3.1% in L. kaempferi and selection against selfing could be observed. The relative self-fertility was estimated to 59% in A. alba and 33% in L. kaempferi. A study of early versus late germinating seedlings in two L. kaempferi clones indicated no increased proportion of selfed individuals in late germinating individuals. Clonal differences in germination percentages in the two CSOs had little impact on effective population sizes. The level of heterozygosity was not significantly different between CSOs and the alternative seed sources. Fixation indices ( F is) were significantly negative in the seed crops from both CSOs, indicating heterozygote excess. There were substantial differences in allelic richness between CSO seed crops and alternative seed sources. The number of alleles was 57% higher in the alternative A. alba seed source Mt. Gariglione and 25% higher in the alternative L. kaempferi seed source F410 Frøslev.

SPE-HPTLC of procyanidins from the barks of different species and clones of Salix

A SPE-HPTLC method was developed for the qualitative and quantitative analysis of procyanidin B 1 in willow barks. The chromatography was performed on HPTLC silica gel layer with the mobile phase chloroform–ethanol–formic acid (50:40:6 v/v/v), in the Automatic Developing Chamber—ADC 2. The methanol extracts from willow barks were purified by SPE method on RP-18 silica gel columns with methanol–water (7:93 v/v) as the eluent. The presence of procyanidin B 1 was revealed in the majority of investigated willow barks. The content of procyanidin B 1 varied from 0.26 mg/g in the extract of Salix purpurea clone 1067–2.24 mg/g in the extract of Salix alba clone 1100. The method was validated for linearity, precision, LOD, LOQ and repeatability.

Distribution and concentration of cadmium in root tissue of Populus alba determined by scanning electron microscopy and energy-dispersive x-ray microanalysis

In a polluted environment with potentially toxic elements, plants may play a relevant role on contaminant absorption or stabilization. The aim of this study was to discriminate two poplar clones in their tolerance to high Cd concentrations (50 μM) in the growth solution and to show the potential of poplar in the cleaning-up of Cd-contaminated substrate. Chemical analyses to determine the content of heavy metals in biological samples involve their destruction by digestion with concentrated acids, preventing the localization of potentially toxic elements in situ. In contrast, scanning electron microscopy equipped with energy-dispersive x-ray microanalysis may provide information on element localization and chemical composition of biological samples. Scanning electron microscopy allows for the observation of samples in a dry or wet state, at high magnifications and good field depth with a minimum preparation, and the possibility to combine structural and analytical information by energy-dispersive x-ray microanalysis and digital images. Although, energy-dispersive x-ray microanalysis has relatively low detection limits, it is useful in establishing distribution maps of potentially toxic elements inside cells and tissues. Tissue concentration and localization of Cd (and other elements) in root tips of Populus alba clones (6K3 and 14P11) were investigated, using two different types of scanning electron microscope (ambient temperature and low temperature) both coupled with energy-dispersive x-ray microanalysis. These techniques were useful to investigate structural modifications and to identify in situ concentration and distribution of Cd in poplar roots, establishing indirect correlations between accumulation and localization of the metal. Overall, observations suggested differential patterns between 6K3 and 14P11 clones in accumulating Cd within the root profile, though overall concentration and content of Cd in the root system, determined by atomic absorption spectrophotometry, did not differ between clones. The possibility that these accumulation patterns arise from differences in uptake processes and structural properties is discussed and related to tolerance mechanisms.

Chromatographic analysis of salicylic compounds in different species of the genus Salix

The separation of nine phenol glycosides--salicin, salicortin, 2'-acetylsalicortin, populin, tremulacin, salidroside, triandrin, picein and helicin--by normal phase (NP), reversed phase (RP) HPLC techniques and a coupling of NP and RP monolithic silica columns was studied. Among the above nine compounds only five--salicin, populin, tremulacin, salidroside and triandrin--were resolved in an NP system with a mobile phase comprising hexane/isopropanol/methanol (87:12:1, v/v/v). Optimized separation was performed with two coupled monolithic silica columns of different polarity (bare silica and RP-18). The method was applied to verify the presence of salicylic compounds and other phenolic derivatives in the bark of six species from the genus Salix, namely S. purpurea, S. daphnoides clone 1095, S. alba clone 1100, S. triandra, S. viminalis, and S. herbacea. Gradient elution with a mobile phase composed of acetonitrile and water containing 0.05% of trifluoroacetic acid, with increasing acetonitrile concentration from 3% to 48%, was chosen as optimal. For the selective detection of the salicylic compounds, an evaporative light scattering detector was employed along with a UV detector. The differences in the composition of phenols in the different plant materials were confirmed. Additionally, it must be emphasized that for the first time the presence of 2'-acetylsalicortin was revealed in S. alba clone 1100. Furthermore, an SPE-HPLC method was developed for the rapid analysis of the salicin content, analyzed as free and total fraction, in willow barks. The determined concentrations of total salicin varied from 25.4 mg/g in S. alba clone 1100 to 96.47 mg/g in S. daphnoides clone 1095.

Cadmium and zinc accumulation in willow and poplar species grown on polluted soils

AbstractWoody plant species that produce high biomass have been proposed for use in phytoremediation technology. We investigated the accumulation of cadmium (Cd) and zinc (Zn) in Salix babylonica, S. caprea, S. dasyclados, S. matsudana × alba, S. purpurea, S. smithiana, Populus tremula, and P. nigra clones grown in a pot experiment on a Calcaric and a Eutric Cambisol (pH 7.2 and 6.4) of different levels of contamination (total metal concentrations in mg kg–1 in soil A: 32.7 Cd, 1760 Zn; soil B: 4.34 Cd, 220 Zn).Generally, the tested clones tolerated large metal concentrations in soils and had larger Cd and Zn concentrations in leaves compared to the roots. The largest Cd concentrations in leaves were found in two clones of S. smithiana (440 mg kg–1 on soil A; 70 mg kg–1 on soil B). One of the S. smithiana clones had also the largest Zn concentrations (870 mg kg–1) on soil B but accumulated slightly less Zn than a S. matsudana × alba clone (2430 mg kg–1) on soil A. The Cd concentrations in leaves of both S. smithiana clones on soil A are the largest ever reported for soil‐grown willows. The bioconcentration factors of the best performing clone reached 15.9 for Cd and 3.93 for Zn on the less contaminated soil B. Also based on the metal contents in leaves, this clone was identified as the most promising for phytoextraction.The metal concentrations in leaves observed in the pot experiment do not reflect those found in a previous hydroponic study and the leaf‐to‐root ratios are clearly underestimated in hydroponic conditions. This demonstrates the need for testing candidates for phytoextraction crops on soils rather than in hydroponics. Our data also show that the phytoextraction potential should be tested on different soils to avoid misleading conclusions.

Comparison of genetic transformation in Morus alba L. via different regeneration systems

Three different regeneration systems, viz. direct regeneration of adventitious shoot buds from explant, regeneration through callus cultures and somatic embryos were compared to see their effect on transfer of neomycin phosphotransferase (nptII) and beta-glucuronidase (GUS) reporter gene (gus) to Morus alba clone M5, through Agrobacterium tumefaciens mediated transformation. Pre-conditioning and co-cultivation durations had a marked effect on transformation frequency. The highest transformation frequency of 18.6% was obtained using direct induction of adventitious shoot buds. Expression and presence of transgene were assayed histochemically and through polymerase chain reaction. Southern analysis of GUS and PCR positive transformants confirmed stable integration of transgenes with two to four copy numbers. The selected transformants showed normal phenotype under in vitro and field conditions.

Assessment of salt tolerance in Populus alba clones using chlorophyll fluorescence

Cuttings of five Populus alba clones (S18 F1-26, Al29 F8-35, J3 F1-4, GU1 F16-36, PO9 F21-88), Populus euphratica, and Populus×euramericana (I-214) were submitted during 45 d to regular watering with NaCl solutions of electrical conductivity of 7 and 14 dS m−1. Chlorophyll a fluorescence in response to the salinity stress was assessed, using F0 and Fv/Fm. Differences in reaction to the salt were found in P. alba clones, F0 and Fv/Fm being the fluorescence parameters used to check out this stress. Minimal constant fluorescence of dark-adapted plants (F0) showed a better correlation with the disease index exhibited by plants and also with salinity dose than the parameter Fv/Fm. Some of the P. alba clones showed the same behaviour, assessed through fluorescence parameters, as P. euphratica, which was previously defined as salt tolerant, while the rest exhibited the same characteristics as I-214, which was very sensitive.

Response to sodium chloride in different species and clones of genus Populus L.

A greenhouse study was undertaken to evaluate the response to sodium chloride (control, 68 mM and 137 mM) of different species and genotypes of genus Populus L. (P. × euramericana (Dode) Guinier clones: ‘I-214’, ‘Flevo’, ‘I-MC’ and ‘Triplo’; P. deltoides × P. alba clones: ‘M30’ and ‘M31’; P. alba L. clones: ‘Jalón-F-1–22’, ‘Jalón F-1–4’, ‘Guadalquivir F-21–38’,‘Guadalquivir F-21–39’, ‘Guadalquivir F-21–40’ and ‘Montañana F-2–9’; and P. euphratica Oliv.). Survival, visual symptomatology, height growth, dry weight both in shoots and roots, photosynthesis rate and leaf concentrations of Na+, K+ and Ca2+ were evaluated. There were differences in survival between clones (0 per cent for the most sensitive and 100 per cent for the most tolerant) but growth was significantly reduced in all cases except for dry weight of P. euphratica at 68 mM. The photosynthesis rate was significantly reduced in all clones at the end of the experiment (60 days) but not in the same way in the middle (30 days). The leaf levels of Na+, K+ and Ca2+ were also significantly different between clones. Intra- and interspecific variability have been detected in the genus, especially in P. alba.

A survey of environmental and biological factors ( Azospirillum spp, Agrobacterium rhizogenes, Pseudomonas aurantiaca) for their influence in rooting cuttings of Prosopis alba clones

To improve the rooting percentages of recently identified multi-purpose clones of Prosopis alba (algarrobo blanco), a survey was conducted of various plant growth promoting rhizobacteria and environmental factors. Four strains of Agrobacterium rhizogenes were examined as previous reports indicated this bacterium had stimulated rooting of difficult to root woody species, both by genetically transforming the tissue around the pericycle to induce roots, and without transforming the roots by secretion of growth promoting substances. Azospirillum brasilense was examined as this bacterium has been shown to stimulate growth in legumes by secretion of growth promoting substances, especially auxins. Pseudomonas aurantiaca was examined as a biocontrol agent for Fusarium, which we believe is an important pathogen in rooting Prosopis. The effect of the root temperature was examined by comparing mist benches with and without bottom heat. The influence of age of the stock plant on the rooting was examined by comparing the rooting of 21-1 year old plants vs. 4 clones from 4-year-old stock plants. Great variability was encountered in the experiments, which precluded definitive conclusions. Nevertheless, the most important effect in stimulating rooting was obtained by increasing the root temperature of the cuttings to about 33 °C, even when daily maximum air temperatures were 40 °C. The second most important factor seemed to be the age of the stock plant. Future research should be aimed at methods to rejuvenate the tissue, possibly by grafting onto immature seedlings. Of the rhizobacteria, the Pseudomonas seemed to have the greatest potential. Azospirillum, which often serves as “a helper bacterium”may have stimulated rooting in a synergistic way that is difficult to measure. The Tiger 232 strain of A. rhizogenes was selected from among the 4 A. rhizogenes strains as giving some of the most consistent results. When indolebutyric acid, napthaleneacetic acid, thiamine HCl, 33 °C root temperatures were combined with A. rhizogenes and Azospirillum, the mean rooting percentage and number of roots per cutting for 21-year old P. alba plants were 80% and 30, respectively. In contrast, 50% rooting was observed for four, 4-year-old stock plants. The rooting parameters for the young stock plants are much greater than obtained in earlier work on Prosopis (80% rooting with a maximum of 12 roots/cutting) and suggests that in spite of lack of significant treatment effects, these rhizobacteria may stimulate rooting.

Agrobacterium tumefaciens mediated genetic transformation and regeneration of Morus alba L.

Abstract An efficient method was established for genetic transformation of Morus alba clone M5 using Agrobacterium tumefaciens mediated gene transfer. Cotyledon explants from in vitro grown seedlings were co-cultivated with disarmed strain LBA 4404 harbouring the binary vector pBI121 carrying chimeric β-glucuronidase (GUS) and neomycin phosphotransferase (npt II) genes. Maximum transformation frequency of 18.60% was recorded with 48 h of pre-conditioning followed by co-cultivation for the same duration. Expression and presence of transgene was confirmed by histochemical test and polymerase chain reaction. The transgenic plants were micropropagated and successfully acclimatised.

Potential of commercial hardwood forestry plantations in arid lands—an economic analyses of Prosopis lumber production in Argentina and the United States

Prosopis has one of the world’s most dimensional stable lumbers. More than 100,000 t of Prosopis alba logs are being harvested annually in the Chaco Province, Argentina for the furniture industry. A growing luxury furniture industry has developed in southwestern USA with wholesale prices of US$ 1600 m −3. As the production arises from unmanaged, non-certified native stands it will be important to initiate plantations to guarantee the sustainability of this resource. This economic analyses was developed to quantify the profitability of Prosopis plantations and was based on published values for basal diameter growth of unmanaged and managed native Prosopis stands, and plantations derived from seed and improved clones. The economic model assumed that the rotation lengths necessary to achieve 100 trees ha −1 with 40 cm diameters containing 15.4 m −3 of sawn lumber per hectare were: 100 years for unmanaged native forests at 707 mm rainfall, 24 year in plantations with improved seed at 707 mm rainfall, 15 year with clones at 734 mm rainfall, 17 year from seed at 1000 mm rainfall and 11 year using clones at 1000 mm rainfall. Using a lumber price of US$ 800 m −3 and after deducting a custom sawing rate of US$ 107 m −3, and when the land value was not included in the economic analysis, the internal rate of returns (IRRs) were 5.3 and 3.1% for the unmanaged native stand and ranged from 11.8% (24 years, 707 mm rainfall) to 34.8% (11 years, clones, 1000 mm rainfall) and from 11.0% (24 years, 707 mm rainfall) to 32.5% (11 years, clones, 1000 mm rainfall) for the plantations in Argentina and the United States, respectively. The corresponding values when the land value was included were: 3.5 and 10.0–27.8% (Argentina), and 1.9 and 7.0–18.5% (USA). To simulate the scenario of selling logs and not custom sawing the timber, the price for logs in Argentina was used (US$ 33 t −1). Under these conditions the IRR of the plantations was found to range from 1.3 to 10.0%, when land value was not included in the analysis. Thus, due to the lower productivity of semi-arid forests, it is necessary to convert logs into sawn lumber to achieve economically viable IRRs. Shortening the rotation from 24 to 15 years with clones (even with a 3-fold increase in planting stock cost) doubled the IRR while nearly a 4-fold increase in price was necessary to double the IRR. Clones cannot be commercially produced by rooted cuttings, but can be by grafting. High variability exists in P. alba clones for rooting ability and research is needed to develop systems for rooting cuttings. Inclusion of complimentary grazing, commercial wildlife, intercropping and pod production showed little increase in the IRR over plantations alone. Prosopis plantations had IRRs equivalent to many other commercial hardwood and softwood plantations suggesting that for the first time, commercial forestry may be possible in the world’s arid zones that are in urgent need of reforestation and economic development.

The potential of mini-grafting for large-scale production of Prosopis alba clones

With the objective to develop rapid, cost-effective asexual propagation methods for elite clones of Prosopis alba, grafting treatments were examined on small (2 mm diameter) seedlings that are easier and more rapid to graft than larger stems. Three techniques were evaluated to seal the wedge graft union (black plastic electrical tape, clear plastic grafting tape, and Parafilm™ as used in biochemical laboratories) and two treatments (black plastic tape and water-soluble mastic) were evaluated to seal the distal end of the scion. These graft union/distal end-sealing techniques were examined under and outside a plastic tunnel with intermittent mist to maintain high humidity. All of the treatments were examined under a 65% shade cloth in which the mean and 95% confidence interval of light intensity was 329±53 μmol m −2 s −1 and the mean and 95% confidence interval noon temperatures under and outside the tunnel were 28.8±1.23°C and 26.4±1.19°C, respectively. The maximum percentage grafting of 70% was obtained under the tunnel with a combination of parafilm for the graft union and black mastic to seal the distal end of the scion. Lower successes were obtained from grafts with individual plastic bags outside the tunnel. The maximum rate of 20 graft h −1 (two people) would represent an additional cost of about $33 ha −1 for the recommended planting density of 100 trees ha −1 which would be almost insignificant in the total cost over a 30-year rotation of about $2000. This is the only technique currently available that is sufficiently rapid and reliable for use in establishing commercial clonal plantations of Prosopis alba.

Environmental influences on grafting success of Prosopis ruscifolia (vinal) onto Prosopis alba (algarrobo blanco)

Prosopis ruscifolia, with its 15 cm long spines, has spread onto vast areas of Argentine grazing lands and formed dense impenetrable stands. We examined grafting the highly respected Prosopis alba (algarrobo blanco) onto Prosopis ruscifolia (vinal) rootstock, with the objective of converting undesirable stands of vinal into desirable stands of P. alba. This grafting experiment examined five dates and three light treatments (full-sunlight, half-shade and ‘tent’ treatment 30×40 cm black plastic shade). The full-sun, half-shade and tent treatments gave 2·4±2·02, 6·0±1·22 and 6·6±0·99 (mean±95% confidence interval) successful grafts out of 10, respectively. Future work should evaluate grafting of P. ruscifolia coppice resprouts with P. alba scions, after the P. ruscifolia trees have been harvested for fuelwood or lumber. EliteP. alba clones are now available for use in grafting.

Development of macrophytic vegetation in the Agmon Wetland of Israel by spontaneous colonization and reintroduction

The draining of the Lake Hula and swamps, northern Israel, during the late 1950s resulted in the loss of a very diverse and rare ecosystem. Oxidation of the peat soil resulted in ground surface subsidence, while heavy autumn winds have eroded the dry peat. Moreover, agriculture on the peat soils is restricted, because of a nitrate surplus. Predictions that the sinking would continue and that more areas would go out of agricultural production led authorities to re-flood a portion of the Hula Valley in 1994. The aim of the present study was to monitor the spontaneous establishment of vegetation in the re-flooded area, the Agmon wetlands, and to reestablish some of the major plant species lost from the valley when Lake Hula was drained. Within the first two years, 74 plant species colonized the wetland spontaneously. Five out of 11 species designated for reintroduction were successfully established. Cyperus papyrus and Cynodon dactylon demonstrated sustainable potential for lake-shore stabilization. Cyperus papyrus was reintroduced from seedlings and rapidly became the dominant riparian species, while Cynodon dactylon established spontaneously. Re-introduced Nymphaea alba clones were established only in enclosures protected from grazing by the semi-aquatic mammal Myocastor coypu. Nuphar lutea and Iris pseudacorus showed better resistance to grazing. These results demonstrate a high potential for successful re-establishment of much of the original Hula swamp macrophytic vegetation by either spontaneous colonization by extant species from the surrounding areas or by introduction of locally extinct species. As such, there is a good chance that the associated faunal components of the former Lake Hula and swamps that have returned to the region since the Hula rehabilitation project commenced will continue to flourish.

A novel lignin in poplar trees with a reduced caffeic acid/5‐hydroxyferulic acid O‐methyltransferase activity

SummaryLignin is a polymeric constituent of the cell wall that needs to be removed during the paper making process. Bi‐specific caffeic acid/5‐hydroxyferulic acid O‐methyltransferase (COMT) catalyses the O‐methylation of caffeic acid and 5‐hydroxyferulic acid to ferulic acid and sinapic acid, respectively. These compounds are intermediates in the biosynthesis of the lignin precursors. Therefore, COMTs are potential target enzymes for reducing the amount, or modifying the composition, of lignin in plants. Different antisense and sense constructs have been expressed of a gene encoding a COMT from poplar (Populus trichocarpa x P. deltoides) in a P. tremula x P. alba clone under the control of the cauliflower mosaic virus 35S promoter. From all analysed transformants, four lines transformed with an antisense construct had a reduced COMT activity. Two showed a 50% reduction of COMT activity, which altered only slightly the monomeric composition. In the two other transformants, the COMT activity was reduced by 95%. In the latter case, the syringyl/ guaiacyl ratio (S/G) was reduced by sixfold (due to a decrease of S and an increase of G), as analysed by thioacidolysis. A new component of lignin, the 5‐hydroxyguaiacyl residue, was detected among the thioacidolysis products. Moreover, in contrast to the white/yellow colour of wild‐type wood, the xylem of the transgenic lines with a 95% reduction of COMT activity was pale rose. A similar phenotype was observed in brown‐midrib mutants of maize and sorghum, known for their altered lignification. Although the lignin composition was consistently modified, the lignin content of the transgenic poplars was similar to that of the controls.