An experimental test of the evolution of increased competitive ability hypothesis in goldenrod, <Emphasis Type="Italic">Solidago gigantea</Emphasis>

The mechanisms that allow introduced plants to become invasive are poorly understood. Here, we present a test of the evolution of increased competitive ability hypothesis, which holds that because specialized natural enemies may be absent from the introduced range, exotic plants may evolve to invest less in anti-herbivore defenses and thereby gain a competitive advantage over native plants. We grew Solidago gigantea plants derived from both the native range (North America) and the invasive range (Europe) in a common garden in the native range for 2 years. Half the plants were treated with insecticide to protect them from insect herbivores and the other half were exposed to insects that colonized the garden from nearby fields. Insect herbivore biomass was significantly higher on European plants than US plants in the first year but not the second. European plants were more heavily attacked by pathogens in both years of the study. When exposed to insect herbivores, US plants produced more seed than European plants, but when plants were protected from herbivores, seed production was equivalent between US plants and European plants. The presence of insect herbivores suppressed seed production of European plants much more than that of US plants, even though the level of herbivory experienced by European and US plants was similar in the second year, suggesting that the ability to tolerate herbivory was diminished in European plants. These results partially support the EICA hypothesis: plants from the introduced range were more susceptible to some natural enemies and benefited more from insect removal than plants from the native range. The prediction that European plants would perform better than US plants in the absence of insect herbivores was not supported. Electronic Supplementary Material Supplementary material is available for this article at     

Biological control of <Emphasis Type="Italic">Musca domestica</Emphasis> and <Emphasis Type="Italic">Stomoxys calcitrans</Emphasis> by mass releases of the parasitoid <Emphasis Type="Italic">Spalangia cameroni</Emphasis> on two Norwegian pig farms

House flies (Musca domestica L.) and stable flies (Stomoxys calcitrans (L.)) (Diptera: Muscidae) are nuisance pests on livestock farms. In the present study we tested the effect of biweekly mass release of Spalangia cameroni Perkins (Hymenoptera: Pteromalidae), the most common parasitoid of house flies and stable flies in southern Norway, on pig premises with scattered fly breeding sites. The study spanned two successive summer periods, with two control and two release units each year. Spalangia cameroni suppressed both house flies and stable flies in one release unit during the first year, and stable flies in one release unit the second year. The apparent lack of success in fly control in the other release units was likely due to immigration of flies in two of the trials and high temperatures in one trial. Recommendations concerning release of S. cameroni in similar pig production premises are given. Handling editor: Torsten Meiners.     

Predation by <Emphasis Type="Italic">Nesidiocoris tenuis</Emphasis> on <Emphasis Type="Italic">Bemisia tabaci</Emphasis> and injury to tomato

Tomato is the most important vegetable crop in Spain. The mirid bug Nesidiocoris tenuis (Reuter) commonly appears in large numbers in protected and open-air tomato crops where little or no broad-spectrum insecticides are used. Nesidiocoris tenuis is known to be a predator of whiteflies, thrips and several other pest species. However, it is also considered a pest because it can feed on tomato plants, causing necrotic rings on stems and flowers and punctures in fruits. Our objectives were to evaluate predation by N. tenuis on sweetpotato whitefly Bemisia tabaci Gennadius under greenhouse conditions and establish its relationship to N. tenuis feeding on tomato. Two different release rates of N. tenuis were compared with an untreated control (0, 1 and 4 N. tenuis plant⁻¹) in cages of 8 m². Significant reductions of greater than 90% of the whitefly population and correspondingly high numbers of N. tenuis were observed with both release rates. Regression analysis showed that necrotic rings on foliage caused by N. tenuis were best explained by the ratio of B. tabaci nymphs:N. tenuis as predicted by the equation y = 15.086x − 0.6359.

Overexpression of <Emphasis Type="Italic">SsDGAT2</Emphasis> from <Emphasis Type="Italic">Sapium sebiferum</Emphasis> (L.) Roxb Increases Seed Oleic Acid Level in <Emphasis Type="Italic">Arabidopsis</Emphasis>

Sapium sebiferum (L.) Roxb is one of the most important oil trees in China. Diacylglycerol acyltransferases (DGATs) esterify sn-1, 2-diacylglycerol with a long-chain fatty acyl-CoA, the last step and the rate-limiting step of triacylglycerol (TAG) biosynthesis in prokaryotic and eukaryotic organisms. At least 74 DGAT2 sequences from 61 organisms have been identified, but the SsDGAT2 gene had not been reported to date. To clarify the function of SsDGAT2, we cloned the CDS (rapid amplification of cDNA end) of SsDGAT2 by RACE technology. The full-length CDS of SsDGAT2 contains 1011 bp and encodes a protein of 336 amino acids. Recombinant SsDGAT2 restored TAG biosynthesis to the yeast strain Saccharomyces cerevisiae H1246 TAG-deficient mutant and preferentially incorporated unsaturated C18 fatty acids into lipids. To investigate the biotechnological potential of SsDGAT2, it was expressed under the control of the 35S promoter in Arabidopsis Col-4. The oleic acid content increased by 50 % in transgenic plants relative to the control. The results indicated that most of the oleic acid increase was at the expense of linolenic acid (18:3) content, which suggests that high-oleic-acid-content seeds can be created by the overexpression of SsDGAT2 in S. sebiferum (L.) Roxb.     

Environmental and developmental factors influencing aflatoxin production by <Emphasis Type="Italic">Aspergillus flavus</Emphasis> and <Emphasis Type="Italic">Aspergillus parasiticus</Emphasis>

Aflatoxins are carcinogenic mycotoxins formed by a number of fungi in the genus Aspergillus. The major fungi responsible for aflatoxin formation in crop seeds in the field and in storage are Aspergillus flavus and A. parasiticus. This review emphasizes developmental, environmental, biological, and chemical factors that influence aflatoxin formation by A. flavus and A. parasiticus.     

Population genetics of an invasive riparian species,<Emphasis Type="Italic"> Impatiens glandulifera</Emphasis>

We assess the population genetic structure of the invasive riparian weed Impatiens glandulifera, and where possible, determine whether natural or anthropogenic dispersal best explains the observed patterns. Results are compared with a similar contemporary analysis for Heracleum mantegazzianum undertaken in the same catchments, and we suggest that some of the observed differences in genetic structure could be because of life history differences between these species. Our results confirm the importance of at least occasional dispersal events mediated by human activity in the colonisation and subsequent spread of invasive plants in river catchments. However, processes related to river structure, dispersal range and genetic drift also appear to be structuring these populations over short temporal scales. The implication is that local populations can be established as small founders, and therefore eradication programs need to be thorough and undertaken at the catchment scale. Effective management needs to consider the natural spread of riparian species along rivers, but also prevent long-distance dispersal from sources outside the catchment. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

<Emphasis Type="Italic">Trichoderma harzianum</Emphasis>: a biocontrol agent against <Emphasis Type="Italic">Bipolaris oryzae</Emphasis>

Rice brown spot, caused by Bipolaris oryzae, can be a serious disease causing a considerable yield loss. Trichoderma harzianum is an effective biocontrol agent for a number of plant fungal diseases. Thus, this research was carried out to investigate the mechanisms of action by which T. harzianum antagonizes Bipolaris oryzae in vitro, and the efficacy of spray application of a spore suspension of T. harzianum for control of rice brown spot disease under field conditions. In vitro, the antagonistic behavior of T. harzianum resulted in the overgrowth of B. oryzae by T. harzianum, while the␣antifungal metabolites of T.␣harzianum completely prevented the linear growth of B. oryzae. Light and scanning electron microscope (SEM) observations showed no evidence that mycoparasitism contributed to the aggressive nature of the tested isolate of T. harzianum against B. oryzae. Under field conditions, spraying of a spore suspension of T. harzianum at 10⁸ spore ml⁻¹ significantly reduced the disease severity (DS) and disease incidence (DI) on the plant leaves, and also significantly increased the grain yield, total grain carbohydrate, and protein, and led to a significant increase in the total photosynthetic pigments (chlorophyll a and b and carotenoids) in rice leaves.     

Herbivory and population dynamics of invasive and native <Emphasis Type="Italic">Lespedeza</Emphasis>

Some exotic plants are able to invade habitats and attain higher fitness than native species, even when the native species are closely related. One explanation for successful plant invasion is that exotic invasive plant species receive less herbivory or other enemy damage than native species, and this allows them to achieve rapid population growth. Despite many studies comparing herbivory and fitness of native and invasive congeners, none have quantified population growth rates. Here, we examined the contribution of herbivory to the population dynamics of the invasive species, Lespedeza cuneata, and its native congener, L. virginica, using an herbivory reduction experiment. We found that invasive L. cuneata experienced less herbivory than L. virginica. Further, in ambient conditions, the population growth rate of L. cuneata (λ = 20.4) was dramatically larger than L. virginica (λ = 1.7). Reducing herbivory significantly increased fitness of only the largest L. virginica plants, and this resulted in a small but significant increase in its population growth rate. Elasticity analysis showed that the growth rate of these species is most sensitive to changes in the seed production of small plants, a vital rate that is relatively unaffected by herbivory. In all, these species show dramatic differences in their population growth rates, and only 2% of that difference can be explained by their differences in herbivory incidence. Our results demonstrate that to understand the importance of consumers in explaining the relative success of invasive and native species, studies must determine how consumer effects on fitness components translate into population-level consequences. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Biological control of <Emphasis Type="Italic">Septoria tritici</Emphasis> blotch on wheat by <Emphasis Type="Italic">Trichoderma</Emphasis> spp. under field conditions in Argentina

Biological control is an additional tool available for the design of more sustainable control strategies of wheat diseases. Trichoderma spp. have previously been used as biocontrol agents to protect wheat plants against leaf spots diseases in Argentina, but the information from field assays is scarce. The effectiveness of four Trichoderma harzianum strains and one T. koningii strain in reducing the incidence and severity of the leaf blotching of wheat caused by Septoria tritici blotch (STB) under two formulation conditions, spore suspension and the coated-seed technique, was studied under field conditions. Significant differences between wheat cultivars, formulation types and growth stages were found. In 2003, at the tillering stage, all of the treatments tested (except SST1 for incidence) effectively reduced the incidence or the severity of the disease compared to the control. Similarly, in 2004, ten of the treatments reduced the severity at tillering. At the heading stage, none of the treatments tested caused a significant decrease of the disease. These results indicated, therefore, that the antagonism was effective at an early stage of the disease only. Comparing both formulations, spraying spore suspension onto leaves and the coated-seed application technique, both were effective in decreasing the disease. Some isolates, such as CST4 and CST2, reduced the incidence value of STB to 40% and the severity value to 70% of the control values applied as coated-seed formulation. On the other hand, isolates T4 and T2 showed the greatest effectiveness for controlling STB, with similar reduction values to that shown by the fungicide (Folicur^®) application treatment. The results of this study indicated that, although the immediate impact of Trichoderma isolates may be seen as reduced incidence and severity on the first stages of STB, in the long term, the same disease levels as found in untreated sites may be attained. This study also demonstrated that the incorporation of Trichoderma as a biocontrol preparation may be a promising step towards reducing STB disease in the field and the levels of fungicide residues in the context of a more integrated approach to the problem.     

Mutation in <Emphasis Type="Italic">cyaA</Emphasis> in <Emphasis Type="Italic">Enterobacter cloacae</Emphasis> decreases cucumber root colonization

Strains of Enterobacter cloacae show promise as biological control agents for Pythium ultimum-induced damping-off on cucumber and other crops. Enterobacter cloacae M59 is a mini-Tn5 Km transposon mutant of strain 501R3. Populations of M59 were significantly lower on cucumber roots and decreased much more rapidly than those of strain 501R3 with increasing distance from the soil line. Strain M59 was decreased or deficient in growth and chemotaxis on most individual compounds detected in cucumber root exudate and on a synthetic cucumber root exudate medium. Strain M59 was also slightly less acid resistant than strain 501R3. Molecular characterization of strain M59 demonstrated that mini-Tn5 Km was inserted in cyaA, which encodes adenylate cyclase. Adenylate cyclase catalyzes the formation of cAMP and cAMP levels in cell lysates from strain M59 were approximately 2% those of strain 501R3. Addition of exogenous, nonphysiological concentrations of cAMP to strain M59 restored growth (1 mM) and chemotaxis (5 mM) on synthetic cucumber root exudate and increased cucumber seedling colonization (5 mM) by this strain without serving as a source of reduced carbon, nitrogen, or phosphorous. These results demonstrate a role for cyaA in colonization of cucumber roots by Enterobacter cloacae.     

Increased tolerance to salt stress in the phosphate-accumulating <Emphasis Type="Italic">Arabidopsis</Emphasis> mutants <Emphasis Type="Italic">siz1</Emphasis> and <Emphasis Type="Italic">pho2</Emphasis>

High salinity is an environmental factor that inhibits plant growth and development, leading to large losses in crop yields. We report here that mutations in SIZ1 or PHO2, which cause more accumulation of phosphate compared with the wild type, enhance tolerance to salt stress. The siz1 and pho2 mutations reduce the uptake and accumulation of Na⁺. These mutations are also able to suppress the Na⁺ hypersensitivity of the sos3-1 mutant, and genetic analyses suggest that SIZ1 and SOS3 or PHO2 and SOS3 have an additive effect on the response to salt stress. Furthermore, the siz1 mutation cannot suppress the Li⁺ hypersensitivity of the sos3-1 mutant. These results indicate that the phosphate-accumulating mutants siz1 and pho2 reduce the uptake and accumulation of Na⁺, leading to enhanced salt tolerance, and that, genetically, SIZ1 and PHO2 are likely independent of SOS3-dependent salt signaling.     

Overexpression of a <Emphasis Type="Italic">Panax ginseng</Emphasis> tonoplast aquaporin alters salt tolerance,drought tolerance and cold acclimation ability in transgenic <Emphasis Type="Italic">Arabidopsis</Emphasis> plants

Water movement across cellular membranes is regulated largely by a family of water channel proteins called aquaporins (AQPs). Since several abiotic stresses such as, drought, salinity and freezing, manifest themselves via altering water status of plant cells and are linked by the fact that they all result in cellular dehydration, we overexpressed an AQP (tonoplast intrinsic protein) from Panax ginseng, PgTIP1, in transgenic Arabidopsis thaliana plants to test its role in plant’s response to drought, salinity and cold acclimation (induced freezing tolerance). Under favorable conditions, PgTIP1 overexpression significantly increased plant growth as determined by the biomass production, and leaf and root morphology. PgTIP1 overexpression had beneficial effect on salt-stress tolerance as indicated by superior growth status and seed germination of transgenic plants under salt stress; shoots of salt-stressed transgenic plants also accumulated greater amounts of Na⁺ compared to wild-type plants. Whereas PgTIP1 overexpression diminished the water-deficit tolerance of plants grown in shallow (10 cm deep) pots, the transgenic plants were significantly more tolerant to water stress when grown in 45 cm deep pots. The rationale for this contrasting response, apparently, comes from the differences in the root morphology and leaf water channel activity (speed of dehydration/rehydration) between the transgenic and wild-type plants. Plants overexpressed with PgTIP1 exhibited lower (relative to wild-type control) cold acclimation ability; however, this response was independent of cold-regulated gene expression. Our results demonstrate a significant function of PgTIP1 in growth and development of plant cells, and suggest that the water movement across tonoplast (via AQP) represents a rate-limiting factor for plant vigor under favorable growth conditions and also significantly affect responses of plant to drought, salt and cold stresses.     

Pathogenicity of <Emphasis Type="Italic">Beauveria bassiana</Emphasis> and <Emphasis Type="Italic">Metarhizium anisopliae</Emphasis> to the tobacco spider mite <Emphasis Type="Italic">Tetranychus evansi</Emphasis>

Seventeen isolates of Metarhizium anisopliae (Metschnikoff) Sorokin and two isolates of Beauveria bassiana (Balsamo) Vuillemin were evaluated for their pathogenicity against the tobacco spider mite, Tetranychus evansi Baker & Pritchard. In the laboratory all the fungal isolates were pathogenic to the adult female mites, causing mortality between 22.1 and 82.6%. Isolates causing more than 70% mortality were subjected to dose–response mortality bioassays. The lethal concentration causing 50% mortality (LC₅₀) values ranged between 0.7×10⁷ and 2.5×10⁷ conidia ml⁻¹. The lethal time to 50% mortality (LT₅₀) values of the most active isolates of B. bassiana and M. anisopliae strains varied between 4.6 and 5.8 days. Potted tomato plants were artificially infested with T. evansi and treated with B. bassiana isolate GPK and M. anisopliae isolate ICIPE78. Both fungal isolates reduced the population density of mites as compared to untreated controls. However, conidia formulated in oil outperformed the ones formulated in water. This study demonstrates the prospects of pathogenic fungi for the management of T. evansi.     

Analysis of a <Emphasis Type="Italic">LEA</Emphasis> gene promoter via <Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated transformation of the desiccation tolerant plant <Emphasis Type="Italic">Lindernia brevidens</Emphasis>

An Agrobacterium tumefaciens-based transformation procedure was developed for the desiccation tolerant species Lindernia brevidens. Leaf explants were infected with A. tumefaciens strain GV3101 harbouring a binary vector that carried the hygromycin resistance gene and an eGFP reporter gene under the control of a native dehydration responsive LEA promoter (Lb2745pro). PCR analysis of the selected hygromycin-resistant plants revealed that the transformation rates were high (14/14) and seeds were obtained from 13/14 of the transgenic lines. A combination of RNA gel blot and microscopic analyses demonstrated that eGFP expression was induced upon dehydration and ABA treatment. Comparison with existing procedures used to transform the well studied resurrection plant and close relative, Craterostigma plantagineum, revealed that the transformation process is both rapid and leads to the production of viable seed thus making L. brevidens a candidate species for functional genomics approaches to determine the genetic basis of desiccation tolerance.     

Heterologous expression of <Emphasis Type="Italic">Arabidopsis</Emphasis><Emphasis Type="Italic">NPR1</Emphasis> (<Emphasis Type="Italic">AtNPR1</Emphasis>) enhances oxidative stress tolerance in transgenic tobacco plants

In Arabidopsis, NPR1 (non-expressor of pathogenesis related genes 1, AtNPR1) functions downstream of salicylic acid (SA) and modulates the SA mediated systemic acquired resistance. It is also involved in a cross talk with the jasmonate pathway that is essential for resistance against herbivores and necrotrophic pathogens. Overexpression of AtNPR1 in transgenic plants resulted in enhanced disease resistance. Recently, tobacco transgenic plants expressing AtNPR1 were shown to be tolerant to the early instars of Spodoptera litura (Meur et al., Physiol Plant 133:765–775, 2008). In this communication, we show that the heterologous expression of AtNPR1 in tobacco has also enhanced the oxidative stress tolerance. The transgenic plants exhibited enhanced tolerance to the treatment with methyl viologen. This tolerance was associated with the constitutive upregulation of PR1, PR2 (glucanase), PR5 (thaumatin like protein), ascorbate peroxidase (APX) and Cu²⁺/Zn²⁺ superoxide dismutase (SOD). This is the first demonstration of the novel function of heterologous expression of AtNPR1 in oxidative stress tolerance in transgenic tobacco.     

<Emphasis Type="Italic">Ty</Emphasis>1<Emphasis Type="Italic">/copia</Emphasis>- and <Emphasis Type="Italic">Ty</Emphasis>3<Emphasis Type="Italic">/gypsy</Emphasis>-like DNA sequences in <Emphasis Type="Italic">Helianthus </Emphasis>species

Two repeated DNA sequences isolated from a partial genomic DNA library of Helianthus annuus, p HaS13 and p HaS211, were shown to represent portions of the int gene of a Ty3 /gypsy retroelement and of the RNase-Hgene of a Ty1 /copia retroelement, respectively. Southern blotting patterns obtained by hybridizing the two probes to BglII- or DraI-digested genomic DNA from different Helianthus species showed p HaS13 and p HaS211 were parts of dispersed repeats at least 8 and 7 kb in length, respectively, that were conserved in all species studied. Comparable hybridization patterns were obtained in all species with p HaS13. By contrast, the patterns obtained by hybridizing p HaS211 clearly differentiated annual species from perennials. The frequencies of p HaS13- and p HaS211-related sequences in different species were 4.3x10(4)-1.3x10(5) copies and 9.9x10(2)-8.1x10(3) copies per picogram of DNA, respectively. The frequency of p HaS13-related sequences varied widely within annual species, while no significant difference was observed among perennial species. Conversely, the frequency variation of p HaS211-related sequences was as large within annual species as within perennials. Sequences of both families were found to be dispersed along the length of all chromosomes in all species studied. However, Ty3 /gypsy-like sequences were localized preferentially at the centromeric regions, whereas Ty1/ copia-like sequences were less represented or absent around the centromeres and plentiful at the chromosome ends. These findings suggest that the two sequence families played a role in Helianthusgenome evolution and species divergence, evolved independently in the same genomic backgrounds and in annual or perennial species, and acquired different possible functions in the host genomes.     

Fitness and life history parameters of <Emphasis Type="Italic">Leptomastix epona</Emphasis> and <Emphasis Type="Italic">Pseudaphycus flavidulus</Emphasis>, two parasitoids of the obscure mealybug <Emphasis Type="Italic">Pseudococcus viburni</Emphasis>

Fitness and life table parameters of two endoparasitoids of the obscure mealybug Pseudococcus viburni (Signoret), the solitary Leptomastix epona (Walker) and the gregarious Pseudaphycus flavidulus (Brèthes), were examined in relation to temperature and host size with a view to determine the efficacy of the parasitoids as biocontrol agents of the pest. Three temperature levels (21°C, 26°C and 31°C) and two host sizes classes (small, which mostly comprised third instar nymphs and large, which consisted of female adults) were studied. The lower developmental threshold and thermal constant of the host and the parasitoids were found similar so the coincidence of pest and parasitoids is likely. The rate of development of the parasitoids increased with a linear trend as the temperature increased from 21°C to 31°C. Temperature had a significant effect on mummification in both parasitoid species and on successful parasitism by P. flavidulus. Host size had a significant effect on the mummification caused by L. epona and on the proportion of the male offspring which emerged as well as on the successful parasitism by P. flavidulus. Life table parameters of the parasitoids were estimated in small and large hosts at 26°C in the laboratory. Both parasitoids achieved a greater intrinsic rate of natural increase and gross reproductive rate in addition to a shorter generation and doubling time in large mealybugs compared with small ones. Consequently, large hosts are expected to have a higher impact on the rise of the parasitoids population and the potential of the parasitoids to control the mealybug population improves with the increase of host size. Handling Editor: Torsen Meiners.     

Overexpression of <Emphasis Type="Italic">Citrus junos</Emphasis> mitochondrial citrate synthase gene in <Emphasis Type="Italic">Nicotiana benthamiana</Emphasis> confers aluminum tolerance

Aluminum (Al) toxicity is one of the major factors that limit plant growth in acid soils. Al-induced release of organic acids into rhizosphere from the root apex has been identified as a major Al-tolerance mechanism in many plant species. In this study, Al tolerance of Yuzu (Citrus Junos Sieb. ex Tanaka) was tested on the basis of root elongation and the results demonstrated that Yuzu was Al tolerant compared with other plant species. Exposure to Al triggered the exudation of citrate from the Yuzu root. Thus, the mechanism of Al tolerance in Yuzu involved an Al-inducible increase in citrate release. Aluminum also elicited an increase of citrate content and increased the expression level of mitochondrial citrate synthase (CjCS) gene and enzyme activity in Yuzu. The CjCS gene was cloned from Yuzu and overexpressed in Nicotiana benthamiana using Agrobacterium tumefaciens-mediated methods. Increased expression level of the CjCS gene and enhanced enzyme activity were observed in transgenic plants compared with the wild-type plants. Root growth experiments showed that transgenic plants have enhanced levels of Al tolerance. The transgenic Nicotiana plants showed increased levels of citrate in roots compared to wild-type plants. The exudation of citrate from roots of the transgenic plants significantly increased when exposed to Al. The results with transgenic plants suggest that overexpression of mitochondrial CS can be a useful tool to achieve Al tolerance.