Acacia Dealbata Link Research Articles

First Report of Phytophthora taxon niederhauserii Causing Root and Stem Rot of Mimosa in Italy.

Mimosa [Acacia dealbata Link, syn. Acacia decurrens (Wendl. F.) Wild. var. dealbata (Link) F. Muell., Fabaceae] is an evergreen shrub native to southeastern Australia that is cultivated as an ornamental plant in warm temperate regions of the world. In spring 2010, in a commercial nursery in Liguria (northern Italy), 6- to 10-month-old potted plants of A. dealbata showed symptoms of sudden collapse, defoliation, and wilt associated with root and basal stem rot. An abundant gum exudate oozed from the basal stem. A Phytophthora species was consistently isolated from roots and stem on BNPRAH selective medium (4). On V8 agar (V8A), axenic cultures obtained by single hyphal transfers formed stellate to radiate colonies with aerial mycelium whereas on potato dextrose agar (PDA) the colonies grew more slowly than on V8A and showed stoloniform mycelium and irregular margins. Minimum and maximum growth temperatures on PDA were 10 and 35°C, with the optimum at 30°C. In water, all isolates produced catenulate or single fusiform hyphal swellings and ellipsoid, nonpapillate, persistent sporangia. Dimensions of sporangia were 46.1 to 65.4 × 23.1 to 30.8 μm (mean l/b ratio 2.1). All isolates were A1 mating type and produced spherical oogonia with amphyginous antheridia when paired with A2 mating type of P. drechsleri Tucker on V8A plus β-sytosterol (4). Internal transcribed spacer (ITS) regions of rDNA of the representative Phytophthora isolate IMI 500394 from A. dealbata were amplified and sequenced in both directions with primers ITS6/ITS4. The consensus sequence (GenBank Accession No. JF900371) was 99% similar to sequences of several isolates identified as Phytophthora taxon niederhauserii Z.G. Abad and J.A. Abad (e.g., GQ848201 and EU244850). Pathogenicity tests were performed on 1-year-old potted plants of A. dealbata with isolate IMI 500394. Twenty plants were transplanted into pots (12-cm-diameter) filled with soil infested (4% v/v) with the inoculum of IMI500394 produced on kernel seeds. Plants were kept in a greenhouse with natural light at 25 ± 2°C and watered to field capacity weekly. All inoculated plants showed symptoms of wilt, leaf chlorosis, and basal stem rot within 3 to 4 weeks. Twenty control plants transplanted in autoclaved soil mix remained healthy. P. taxon niederhauserii was reisolated solely from inoculated plants, thus fulfilling Koch's postulates. Since 2003, this pathogen has been found on bottlebrush and rock rose grown in a nursery in Sicily (southern Italy), as well as on Banksia in a nursery in Liguria (2,3). To our knowledge, this is the first report of P. taxon niederhauserii on A. dealbata. P. taxon niederhauserii, recently described as P. niederhauserii sp. nov. (1), is a polyphagous pathogen that was originally reported on arborvitae and ivy in North Carolina in 2001.

Differential impact on soil microbes of allelopathic compounds released by the invasive Acacia dealbata Link

Acacia dealbata Link, an Australian tree legume, is one of the most invasive species in south-eastern Europe. The invasive success of A. dealbata is partially attributed to its ability to release allelopathic compounds that affect native plant species, but the allelopathic effect on soil microbes has been little explored. Here, we used natural leachates to assess the bioactivity of these allelochemicals on soil microorganisms in native Mediterranean pine and mixed forests. Soil samples were treated either with acacia canopy leachate or the corresponding canopy leachate. Soil microbial communities were analyzed using Biolog Ecoplates™ and PCR–DGGE. Allelochemicals naturally released by A. dealbata clearly modified soil bacterial functional diversity in the pine forest where acacia leachate significantly increased the consumption of carbohydrates and amino acids and reduced the utilization of carboxylic acids. Acacia leachates also lead to a significant reduction in bacterial richness and diversity in the pine forest soil. However, the soil microorganisms of mixed oak forest were insensitive to allelochemical activity. Our results show that the allelopathic effects of A. dealbata on soil microbes depend on ecosystem type and that soil bacteria are more sensitive than soil fungi to the allelochemicals released by A. dealbata. We conclude that the higher sensitivity of pine forest soil microbiota to allelochemicals introduced by A. dealbata can contribute to the process of invasion.

Invasion by the leguminous tree Acacia dealbata (Mimosaceae) reduces the native understorey plant species in different communities

Acacia dealbata Link (Mimosaceae) is a woody leguminous tree introduced to Europe from Australia that has become a serious environmental problem in north-western Spain, where it forms dense monospecific patches threatening native-plant biodiversity. We describe the effects of invasion by A. dealbata on understorey plant composition in shrubland, oak- and pine-forest communities in north-western Spain. Plant species richness and composition, plant density and total plant cover were measured and compared among patches with different invasion status (invaded, transition and non-invaded patches) in each studied community. A clear effect of the community type and invasion on the understorey vegetation was observed. In general, composition of shrubland was different from that of oak and pine forests. We found significant effects of invasion status on species richness, plant density and total plant cover; values were significantly lower in invaded than non-invaded patches. Invasion by A. dealbata also was associated with changes in species composition. In total, eight native species, including the endemic Daboecia cantabrica (thuds) K. Koch, were confined to non-invaded patches and were replaced by other natives in invaded and transition patches. Our results suggest that although A. dealbata represented a serious threat to all of the study communities, the severity of the impact depended on the community type.

Metal (Al, Mn, Pb and Zn) soils extractable reagents for available fraction assessment: Comparison using plants, and dry and moist soils from the Braçal abandoned lead mine area, Portugal

Eleven composite soil samples, developed either on schist materials or fine heterogeneous waste materials and coarse metallurgical slags, were collected in the Braçal (Portugal) abandoned lead mine. Plants growing in each sampling area were identified. A total of 49 plant samples of eight species –Acacia dealbata Link, Acacia melanoxilon R. Br., Cistus inflatus Pourr. ex Demoly, Erica arborea L., Eucalyptus globulus Labill., Pinus pinaster Aiton, Quercus robur L., and Ulex minor Roth – were collected. This study intends to evaluate the available fraction of aluminium, lead, manganese, and zinc in the soils using dry and moist samples in contact with five extractant solutions, degasified distilled water, and calcium chloride, calcium nitrate, ammonium acetate and DTPA aqueous solutions, and to compare together these results with the total elemental amounts in the aboveground part of the plant species. The available fraction is higher in moist than in the dry soil samples. The correlations between the soil available fraction of the elements and its concentration in the plants suggest that DTPA is not the best extractant for lead bioavailability evaluation. Variable results were observed for the bioavailable fraction of the elements evaluation suggesting that, in multielemental contaminated soils, calcium chloride seems to be a good extractant medium, once it correlates with the higher number of plant species.

Parasitoids of the painted apple moth Teia anartoides Walker (Lepidoptera: Lymantriidae) in Australia

Painted apple moth Teia anartoides Walker (Lepidoptera: Lymantriidae), a native to Australia, was discovered in Auckland, New Zealand in late 1999 and eradicated by 2006. It was recognised in 2002 that biological control would be the most effective long-term control strategy if eradication was unsuccessful, and a search was initiated for potential biocontrol agents in Australia. In 2003, autumn and spring surveys were undertaken in Victoria, Tasmania and South Australia of the guild of parasitoid natural enemies of T. anartoides. Eggs, larvae and pupae were collected and held to rear out any parasitoids. In addition, localised searches were made in Queensland in late 2003 early 2004 and laboratory-reared juvenile stages of T. anartoides were released for recapture in both Victoria and Queensland. Acacia dealbata Link (Fabales: Fabaceae) was the main plant from which T. anartoides was recovered, followed by apple. Most T. anartoides samples were collected from Victoria and Tasmania. Eighteen species from 13 genera of egg, larval and pupal parasitoids were reared and included Diptera (Tachinidae) and Hymenoptera (Braconidae, Encyrtidae, Eulophidae and Ichneumonidae). Of the seven Hymenopteran genera recovered from the larval stage, the most common in Victoria and Tasmania was a previously unidentified larval parasitoid Cotesia Cameron (Hymenoptera: Braconidae) sp. Echthromorpha intricatoria (Fabricius) (Hymenoptera: Ichneumonidae) was the dominant pupal parasitoid. The survey showed that the parasitoid complex associated with T anartoides is structurally very similar to that on other pest Lymantriidae in the northern hemisphere such as gypsy moth (Lymantria dispar L.) (Lepidoptera: Lymantriidae). Meteorus pulchricornis (Wesmael) (Hymenoptera: Braconidae) was recorded for the first time in Australia.

Survival and growth of Acacia dealbata vs. native trees across an invasion front in south-central Chile

Tree invasions cause important conservation problems, such as changes in plant community composition, reduced regeneration rates of native species, and alteration in landscape structures. One of the most invasive tree genera in the world is Acacia (Fabaceae). In Chile, Acacia dealbata Link is distributed in the mediterranean zone, mostly associated with roadsides and anthropogenic disturbances. In this paper we address the following questions: How does A. dealbata perform across a gradient of native forest and invasive stands? Will it be capable of establishing itself in non-invaded native forests and regenerating under its own canopy in the absence of disturbances? From a contrasting viewpoint, will native species such as Cryptocarya alba (Molina) Looser and Nothofagus obliqua (Mirb.) Oerst be able to survive in an A. dealbata stand, allowing re-colonization of the invaded area? We conducted survival and growth experiments on A. dealbata seedlings in three sites near Concepción, Chile (36°S–72°W) under three conditions: under Acacia stand, in a close native forest and on an intermediate matrix between these two conditions. We compared this to the performance of two native trees ( Cryptocarya alba and Nothofagus obliqua). Results showed that A. dealbata and C. alba have high growth and establishment capacities within the native forest, but on the intermediate matrix only A. dealbata can grow and survive. C. alba survives at significantly higher rates than A. dealbata within Acacia stand. Nothofagus obliqua only survive at a very low rate in the native forest. Without disturbances, A. dealbata would be successful on the intermediate matrix and within native forest, while C. alba seems capable of surviving and establishing itself in invaded areas, thereby contributing to recovery and restoration of natural spaces. The interplay between Acacia dealbata and the native vegetation may show us a larger picture of how invasive species are capable of expanding even into forested ecosystems and, furthermore, how we can restore native vegetation and avoid further invasion.

Allelopathic interference of invasive Acacia dealbata Link on the physiological parameters of native understory species

The tree Acacia dealbata Link is an Australian woody legume that has become a serious environmental problem in Northwest Spain, where its expansion is assumed to reduce populations of native species and threaten local plant biodiversity. In order to investigate the potential involvement of allelopathic mechanisms in this process, net photosynthetic and respiration rates of four test native understory species (Hedera hibernica (G. Kirchn.) Bean, Dicranum sp., Dactylis glomerata L. and Leucobryum sp.) were evaluated using a Clark-type electrode in the presence of canopy leachate collected under A. dealbata stands at four times of the year for 2 years and macerate from their apical branches at the same sites and times. The first two test species were present both inside and outside of A. dealbata stands, while the last two were only located outside the stands. We found that there were significant differences in respiration and net photosynthetic rates between the control and A. dealbata extracts in all test species. The respiration rate was increased by both canopy leachate and macerate extracts on certain collection dates, but net photosynthetic rate was stimulated by macerate and inhibited by canopy leachate on other dates. The main phenological stages of A. dealbata in which respiration and net photosynthetic rates were more affected were blossoming, inflorescence formation and in periods after severe drought, in this decreasing order. Our results also showed that Dicranum sp., Leucobryum sp. and D. glomerata were more affected by aqueous extracts than other species during a 2-year period. We suggest that the observed inhibitory or stimulatory effects on the physiological parameters studied could have an adverse effect on the understory species, and that allelopathic interference seems to participate in this process.

Effect of invasive Acacia dealbata Link on soil microorganisms as determined by PCR-DGGE

Acacia dealbata Link is an Australian woody legume that has become a serious environmental problem in Northwest Spain where it forms dense monospecific patches modifying the structure of different native ecosystems and threatening native aboveground biodiversity. In spite of the dramatic changes observed in the vegetation of invaded sites little is known about the consequences of invasion for soil microorganisms. To investigate the effect of A. dealbata invasion on the structure of soil fungi and bacteria communities, samples were taken from invaded and non-invaded areas from three different ecosystems in Northwest Spain: pine forest, shrubland and grassland. In each ecosystem type, soil samples were taken in areas of native vegetation, areas invaded by A. dealbata and in the transition zone between native and invaded vegetation. Soil microorganisms were analyzed in the different samples by PCR-DGGE using general primers for eubacteria and fungi. Soil analyses were also performed to evaluate the effect of A. dealbata invasion on soil fertility. The invasion by A. dealbata consistently increased soil N, C, organic matter and exchangeable P content in the three studied ecosystems. A clear effect of the invasion on the overall structure of microorganism communities was only observed in the shrubland where soil fungal communities in the invaded and transition areas clustered together and apart from the native soil. Significant differences in soil microorganisms richness and diversity between invaded and not invaded soils were only found in the grassland. Grassland invasion by A. dealbata lead to a significant increase of bacterial richness and to a significant reduction in fungal richness and diversity. Our results show that although the changes on soil chemistry due to A. dealbata invasion are consistent among the studied ecosystems, the effect on soil microorganisms depends on the ecosystem type affected by the invasion.

Differential responses to allelopathic compounds released by the invasive Acacia dealbata Link (Mimosaceae) indicate stimulation of its own seed

Invasion by exotic species constitutes a major threat to natural ecosystems. One of the most invasive species of current concern in Europe is Acacia dealbata Link (Mimosaceae), the expansion of which is reducing populations of native species, and hence biodiversity. To investigate the potential involvement of allelopathic mechanisms in this process, we evaluated the germination and seedling growth performance of Lactuca sativa L. (Compositae), Zea mays L. (Gramineae), Dactylis glomerata L. (Gramineae), Arabidopsis thaliana (L.) Heynh. (Cruciferae) and A. dealbata, in the presence of mixtures of throughfall and litter leachate and of aqueous soil extracts collected under A. dealbata at different times of the year. Each test species responded differently to the solutions being assayed suggesting that A. dealbata allelochemicals may affect a variety of physiological growth parameters. In most cases the observed effects were stimulatory rather than inhibitory, which may have long-term deleterious effects on native plant populations since premature growth during periods of poor resources can be detrimental. Interestingly, increased radical growth of A. dealbata was detected with either extract suggesting a positive autoalleloapthy effect.

The genus Acacia as invader: the characteristic case of Acacia dealbata Link in Europe

• We review current knowledge about the biology of the genus Acacia, and Acacia dealbata Link (silver wattle) in particular, as an invader in Europe, focusing on (i) the biology of the genus Acacia; (ii) biological attributes that are important for the invasiveness of the genus and A. dealbata; (iii) possible hypotheses for the invasion success; and (iv) control methods. • Several Australian wattles have been recorded as naturalized in Europe. Acacia has attained pest proportions in certain habitats and protected sites (notably coastal dunes, river courses, natural parks and biosphere reserves). • The spread of Acacia dealbata seems to be assisted by human interference such as soil disturbance and severe fires. The biological attributes favoring invasion by A. dealbata include tolerance of changing soil conditions, the ability to take advantage of environmental disturbance, phenotypic plasticity, vegetative reproduction, fire tolerance and allelopathic potential. • Different hypotheses explaining invasiveness and transition between invasion steps related to biological attributes as the key factor for A. dealbata invasion are discussed. Effects on the biodiversity of native flora are little understood and studies of suppression of autochthonous species are needed. It is desirable that further studies comparing Acacia at field sites in their native and exotic range should be done. • Understanding the biology of invasive wattles in Europe is the first step to an effective control method. Studies comparing plant invaders at field sites in their native and invaded areas seem to be most appropriate in order to be able to attack the most vulnerable stages.

Natural and induced polyploidy in Acacia dealbata Link. and Acacia mangium Willd.

Seeds were obtained from seven natural populations of Acacia dealbata, three natural populations of A. mangium and a seed orchard of A. mangium, representing the natural range of the two species. Polyploids were discovered in two of the seven populations of A. dealbata. The 2C DNA amount for diploid A. dealbata (2n = 2x = 26) was 1.74 pg, and for diploid A. mangium (2n = 2x = 26) was 1.30 pg. A naturally occurring tetraploid of A. dealbata (2n = 4x = 52) had a 2C DNA amount of 3.41 pg and a naturally occurring triploid genotype had a 2C DNA amount of 2.53 pg. The use of colchicine and oryzalin was investigated as a means of producing higher frequencies of tetraploids of both A. mangium and A. dealbata for incorporation into breeding programmes. Colchicine treatment gave tetraploid frequencies up to 29% for A. dealbata seedlings, and up to 18% for A. mangium seedlings. In contrast, no tetraploid A. mangium was detected following oryzalin treatment, and the low frequencies of tetraploids observed in A. dealbata could be attributed to their natural occurrence.

Relationships between stem diameter, sapwood area, leaf area and transpiration in a young mountain ash forest.

We examined relationships between stem diameter, sapwood area, leaf area and transpiration in a 15-year-old mountain ash (Eucalyptus regnans F. Muell.) forest containing silver wattle (Acacia dealbata Link.) as a suppressed overstory species and mountain hickory (Acacia frigescens J.H. Willis) as an understory species. Stem diameter explained 93% of the variation in leaf area, 96% of the variation in sapwood area and 88% of the variation in mean daily spring transpiration in 19 mountain ash trees. In seven silver wattle trees, stem diameter explained 87% of the variation in sapwood area but was a poor predictor of the other variables. When transpiration measurements from individual trees were scaled up to a plot basis, using stem diameter values for 164 mountain ash trees and 124 silver wattle trees, mean daily spring transpiration rates of the two species were 2.3 and 0.6 mm day(-1), respectively. The leaf area index of the plot was estimated directly by destructive sampling, and indirectly with an LAI-2000 plant canopy analyzer and by hemispherical canopy photography. All three methods gave similar results.

Nitrogen Fixation Associated With Acacia dealbata Link. Seedlings as Estimated by the Acetylene Reduction Assay

Seedlings of Acacia dealbata were grown in pots containing a sandy loam and inoculated with a suspension of homogenized nodules collected from naturally occurring A. dealbata trees. Plants were maintained in a controlled environment growth room. The rate of acetylene reduction by intact plants was determined by placing pots inside 1 25 litre jars. Experiments were conducted after 12 weeks of growth when the plants had attained a steady acetylene reduction activity. The rate of ethylene production was linear for at least 3 h, and the Michaelis-Menten constant (Km) value was 3 87 kPa acetylene. The seedlings showed little diurnal variation in acetylene reduction activity when day and night lengths were 12 h, but activity declined when the dark period was extended to 15 h. Acetylene reduction activity was markedly affected by soil moisture, the optimum rate occurring between 25 and 50% of field capacity (33 kPa). A rapid decline in the rate of acetylene reduction occurred when 8 mg nitrate-N was added per pot. Acetylene reduction activity, dry matter yield and nitrogen uptake were adversely affected by induced soil salinity. The loss in acetylene reduction activity was highly correlated with the degree of soil salinization.

Nitrogen mineralization and nitrate reduction in forests

The mineralization of soil nitrogen was studied in four forests growing on krasnozem soils. Soils from Silver Wattle ( Acacia dealbata Link.) and Mountain Ash ( Eucalyptus regnans F. Muell.) forests showed considerable nitrification in laboratory incubations. Messmate ( Eucalyptus obliqua L'Herit) and Monterey Pine ( Pinus radiata D. Don) forest soils were predominantly ammonifiers. Forests having significant soil nitrification were found to have considerable nitrate reductase activity (NRA) in root or leaf tissue or both. NRA may therefore be useful as an indication of soil nitrification in natural ecosystems. The occurrence of nitrification in Australian forests appears to be predominantly related to the amount of N present and its rate of turnover rather than to inhibitory effects.

Studies on the Fireblight Beetle,Pyrgoides orphana(Erichson) (Coleoptera: Chrysomelidae) and its Effect on the Growth of Silver Wattle in Tasmania

SUMMARY Pyrgoides orphana (Erichson) severely defoliates large areas of silver wattle (Acacia dealbata Link) in Tasmania, particularly in the Florentine Valley region. Attacked trees are often completely stripped of all foliage during the winter months by the larval stages of this beetle. The life history of P. orphana is described and an account of the effect of defoliation on growth of silver wattle over an 18 year period is presented. There is a marked reduction in height increment following P. orphana outbreaks and repeated defoliation has killed many trees. Diameter growth has been retarded and no increment has occurred in the period 1974–77. The significance of P. orphana is discussed in relation to its direct effect on the growth of silver wattle and the possible secondary effects of reducing competition of wattle with other commercial forest species.