A fungal endophyte of black spruce (Picea mariana) needles is also an aquatic hyphomycete

An aquatic hyphomycete, Dwayaangam sp., was isolated from superficially sterilized black spruce (Picea mariana) needles submerged in aerated water in a small glass chamber (microcosm). The internal transcribed spacer (ITS) sequence of this fungus and of a commonly encountered foliar endophyte isolated from P. mariana showed a high degree of similarity. When sporulation was induced in the microcosm, both the aquatic hyphomycete and the endophyte isolate produced similar aquatic conidia after 30 days, which is longer than previously documented in similar studies. Without the use of molecular tools, the link between the aquatic and endophytic phases of the fungus would have gone unnoticed. This is the first time that a fungal endophyte of conifer needles has been shown to have an aquatic phase. Its presence both as a foliar endophyte and a sporulating aquatic fungus suggests an alternating life cycle between the two environments.     

Dark septate endophyte and arbuscular mycorrhizal status of vegetation colonizing a bottomland hardwood forest after a 100 year flood

Levels of arbuscular mycorrhizal (AM) colonization and dark septate endophyte (DSE) colonization were assessed in the vegetation recolonizing a remnant bottomland hardwood forest in north central Texas following a 100 year flood. Thirty seven plant species representing 21 dicotyledonous and 2 montocotyledonous families established following floodwater recession. AM and/or DSE were found in all species. AM colonization was found in 31 out of the 37 species assessed including both monocotyledonous families (Poaceae and Cyperaceae) and 17 out of 21 dicotyledonous families (Acanthaceae, Asteraceae, Boraginaceae, Cucurbitaceae, Euphorbiaceae, Lamiaceae, Loganiaceae, Lythraceae, Malvaceae, Onagraceae, Pedaliaceae, Ranunculaceae, Sapindaceae, Scrophulariaceae, Solanaceae, Verbanaceae and Violaceae). DSE were found in 31 out of 37 species assessed including both monocotyledonous families and 15 out of 21 dicotyledonous families (Amaranthaceae, Asteraceae, Boraginaceae, Brassicaceae, Cucurbitaceae, Euphorbiaceae, Lamiaceae, Lythraceae, Malvaceae, Pedaliaceae, Phytolaccaceae, Polygonaceae, Ranunculaceae, Sapindaceae, Scrophulariaceae and Violaceae). There were no detectable differences in AM or DSE colonization levels among wetland indicator groups (p > 0.05). Levels of DSE colonization were negatively correlated with vesicular colonization and hyphal colonization for the obligate wetland species. There were no other significant relationships between AM and DSE colonization detected. Spearman rank order correlation coefficients did not differ significantly among wetland indicatory category for any level of AM or DSE colonization.     

Inter-annual variation in above- and belowground herbivory on a native,annual legume

The relative importance of subterranean versus aboveground insect damage to plants is not well understood. In particular, the simultaneous effects of above- and belowground herbivory, and the importance of highly variable abiotic factors such as rainfall, have received little attention in diverse natural ecosystems. We investigated the influence of both above- and belowground herbivory on Lupinus nanus (Fabaceae), an annual plant native to coastal California. A number of insect species damage L. nanus aboveground, and a weevil larva consumes nodules belowground. To manipulate herbivory in the field, we employed a combination of insecticides and simulated herbivory during two different years. In 1997, simulated belowground damage reduced L. nanus survival, and insecticide application to roots increased seed production and seed mass. By contrast, in 1998, only aboveground folivory significantly reduced L. nanus reproduction, and, in combination, above- and belowground insecticides did not affect flower or seed number relative to controls. A growth chamber experiment conducted in the absence of herbivory revealed that the aboveground insecticide marginally reduced flower production and the belowground insecticide marginally increased flower production compared to controls; these non-target effects made our field experiments for aboveground herbivory conservative. Finally, ambient levels of herbivory differed among years (1997, 1998, and 2000), which varied greatly in rainfall due to the effects of El Nino. The results suggest that the impacts of herbivores are temporally variable and that abiotic factors, particularly those related to large-scale changes in weather patterns, may be more important than insect herbivory to L. nanus in some years. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic diversity of photosynthetic characters in native populations of Triticum dicoccoides

Wild emmer wheat (Triticum dicoccoides Korn) has shown wide genetic diversity for disease resistance and morpho-physiological traits of economic importance. Our objectives were to test for genetic variation (V_G) in photosynthetic characteristics residing within and between native populations sampled from three ecogeographical regions of Israel, and to identify potential sources of high photosynthetic efficiency for future wheat improvement. Accessions sampled in the center of wild emmer distribution (upper Jordan Valley) in a relatively narrow geographical range showed the greatest diversity in CO₂-assimilation rate per unit leaf area (A) or per unit chlorophyll (A/Chl). Genetic variation was absent for internal CO₂ concentration (Ci) and water-use efficiency (WUE) and generally lacking for stomatal conductance (gs). Leaf area, although quite variable, was not a significant cofactor in assessing genetic potential for photosynthesis. Accessions within a given population showed 10-times more variation in A and A/Chl than populations sampled from different locations in a region. Accessions with the highest photosynthetic efficiency were derived from upland steppic populations located in marginal habitats extending southward into Israel. Some accessions having high photosynthetic capacity (A=32 mol m^-2 s^-1) with no significant reduction in leaf size constitute a potentially valuable genetic resource yet untapped for genetic improvement of hexaploid (T. aestivum L.) wheat.Abbreviations LA total leaf area - V_G total genetic variance - PPFD photosynthetic photon flux density - WUE water-use efficiency     

Effects of colonization of a bacterial endophyte,Azospirillum sp. B510, on disease resistance in tomato

A plant growth-promoting bacteria, Azospirillum sp. B510, isolated from rice, can enhance growth and yield and induce disease resistance against various types of diseases in rice. Because little is known about the interaction between other plant species and this strain, we have investigated the effect of its colonization on disease resistance in tomato plants. Treatment with this strain by soil-drenching method established endophytic colonization in root tissues in tomato plant. The endophytic colonization with this strain-induced disease resistance in tomato plant against bacterial leaf spot caused by Pseudomonas syringae pv. tomato and gray mold caused by Botrytis cinerea. In Azospirillum-treated plants, neither the accumulation of SA nor the expression of defense-related genes was observed. These indicate that endophytic colonization with Azospirillum sp. B510 is able to activate the innate immune system also in tomato, which does not seem to be systemic acquired resistance.     

Phytochemical correlates of herbivory in a community of native and naturalized cruciferae

Oviposition and larval feeding behaviors of the crucifer specialist Pieris napi macdunnoughii correlate with leaf glucosinolate profils of plant species in a natural community. Profiles are species-specific in this group of eight Cruciferae, but particular glucosinolates are shared by subsets of the community. Pieris accepts two lethal naturalized weeds whose glucosinolate profiles resemble that of an indigenous foodplant. The results suggest that specific glucosinolates constitute insect behavioral cues which are only loosely linked evolutionarily to foodplant suitability, and further suggest that allelochemically similar community associates influence the coevolution of individual plant species with insect herbivores.     

Comparison of five strains of a parthenogenetic species,Macrotrachela quadricornifera (Rotifera,Bdelloidea)

Five clonal populations belonging to the parthenogenetic species Macrotrachela quadricornifera were analyzed electrophoretically. The populations stemmed from samples collected from different environments paired geographically: water bodies (C, P, F) and terrestrial mosses (Ml, M2). The six enzymes considered were: leucine amino peptidase (LAP), arginine phosphokinase (APK), glucose phosphate isomerase (PGI), and esterases (EST) and malic enzyme (ME). The results are interpreted under the assumption that bdelloid rotifers have a diploid chromosome set. A genetic interpretation of the banding patterns was attempted. A relatively high degree of enzymatic polymorphism among the strains was found. Only 27% of alleles are shared by all strains. The relationship among the strains was examined by single-link cluster analysis: we can distinguish moss and water populations, regardless of their geographic origins, and in accord with the results of a life-history traits study on the same strains. The differences in life-history parameters among the five strains may be due not only to phenotypic plasticity induced by the environment, but to real genetic divergence.     

Isolation of Bacillus pumilus from in vitro grapes as a long-term alcohol-surviving and rhizogenesis inducing covert endophyte

AIMS: To isolate and characterize the alcohol-surviving covert bacterium associated with grape tissue culture. METHODS AND RESULTS: Single colony was isolated by plating the spent rectified spirit used during grape culturing and the organism was identified as Bacillus pumilus using partial 16S rDNA sequence data. Spotting tests (1 microl) using 3-day-old broth culture having a spore content of 20-30% showed similar bacterial survival in 25-90% (v/v) aqueous ethanol for 14 days. Survival in 90% ethanol and 90% rectified spirit appeared affected thereafter with no colony growth from 1 microl samples after 4 months. Plating the samples at this stage gave similar CFU ml(-1) for 25, 50 and 70% ethanol, a significant reduction in 80% ethanol and very few colonies in 90% ethanol and rectified spirit. B. pumilus-inoculated grape microcuttings showed substantial endophytic colonization of original cuttings (7.4 x 10(6) CFU g(-1)) followed by the sprout (5.9 x 10(5)) and roots (2.0 x 10(4)). The bacterium although a poor root colonizer, induced early rooting and more roots in vitro. Inoculation at ex vitro planting resulted in significantly more roots, root weight and shoot growth. CONCLUSIONS: Bacillus pumilus could remain as a covert endophyte in grape tissue cultures and survive in aqueous ethanol for extended periods. 90% ethanol was the most effective bactericidal concentration. The bacterium showed endophytic colonization and root and shoot growth promotion. SIGNIFICANCE AND IMPACT OF THE STUDY: The revelation that general recommendation of 70-80% ethanol may not be the most effective bactericidal concentration for all bacteria, elucidation of the possibility of covert bacterial survival in vitro plant cultures and isolation of a potential plant growth promoting endophyte in grape.     

Monitoring the spatial and temporal dynamics of a community of the tree-root endophyte Phialocephala fortinii s.l

Phialocephala fortinii sensu lato was isolated from Picea abies roots that had been collected from the same 3 x 3-m forest plot in 2001 and 2004, to examine the spatial and temporal dynamics of this fungal community. RFLP analysis was used to define the multilocus haplotype (MLH) of each isolate. Pielou's measure of association and chi(2) tests of independence were employed to examine the randomness of patterns of spatial distribution of MLH observed in 2001 and 2004. Population differentiation between the two samplings was tested using the G(ST) statistic. In 2001, 144 strains of 28 MLH were isolated; in 2004, 139 strains of 29 MLH. Abundant MLH in 2001 also prevailed in 2004, and the same two cryptic species were dominant in both collections. The probability of being isolated in both years increased with increasing frequency of an MLH. The patterns of spatial distribution of most MLH did not differ between years. The G(ST) values indicated identity of the two collections. Communities of P. fortinii sensu lato remain spatially and genetically stable for at least 3 yr.     

Associational effects and the maintenance of polymorphism in plant defense against herbivores: review and evidence

Many plant species have evolved defense traits against herbivores. Associational effects (AEs) refer to a kind of apparent interaction where the herbivory risk to a focal plant species depends on the composition of other plant species in a neighborhood. Despite ample evidence for AEs between different plant species, this point of view has rarely been applied to polymorphism in defense traits within a plant species. The purpose of this review is to highlight an overlooked role of conspecific AEs in maintaining polymorphism in antiherbivore defense. First, I present a general review of AE between plant species and its role in the coexistence of plant species. This viewpoint of AE can be applied to genetic polymorphism within a plant species, as it causes frequency‐ and density‐dependent herbivory between multiple plant types. Second, I introduce a case study of conspecific AEs in the trichome‐producing (hairy) and glabrous plants of Arabidopsis halleri subsp. gemmifera. Laboratory and semi‐field experiments illustrated that AEs against the brassica leaf beetle Phaedon brassicae mediate a minority advantage in defense and fitness between hairy and glabrous plants. Combined with a statistical modeling approach, field observation revealed that conspecific AEs can maintain the trichome dimorphism via negative frequency‐dependent selection in a plant population. Finally, I discuss spatial and temporal scales at which AEs contribute to shaping genetic variation in antiherbivore defense in a plant metapopulation. Based on the review and evidence, I suggest that AEs play a key role in the maintenance of genetic variation within a plant species.     

The biogeochemistry of a north-temperate grassland with native ungulates: Nitrogen dynamics in Yellowstone National Park

Nutrient dynamics of large grassland ecosystems possessing abundant migratory grazers are poorly understood. We examined N cycling on the northern winter range of Yellowstone National Park, home for large herds of free-roaming elk (Cervus elaphus) and bison (Bison bison). Plant and soil N, net N mineralization, and the deposition of ungulate fecal-N were measured at five sites, a ridgetop, mid-slope bench, steep slope, valley-bottom bench, and riparian area, within a watershed from May, 1991 to April, 1992.Results indicated similarities between biogeochemical properties of Yellowstone grassland and other grassland ecosystems: (1) landscape position and soil water affected nutrient dynamics, (2) annual mineralization was positively related to soil N content, and (3) the proportion of soil N mineralized during the year was negatively related to soil C/N.Grazers were a particularly important component of the N budget of this grassland. Estimated rates of N flow from ungulates to the soil ranged from 8.1 to 45.6 kg/ha/yr at the sites (average = 27.0 kg/ha/yr), approximately 4.5 times the amount of N in senescent plants. Rates of nitrogen mineralization for Yellowstone northern range grassland were higher than those measured in other temperate grassland ecosystems, possibly due to grazers promoting N cycling in Yellowstone.