Produced by the Technology Transfer Information Center of the
National Agricultural Library (ARS/USDA).
For information on ARS research related to invasive species, see the TEKTRAN invasive species page.
More information on the U.S. government's efforts to combat invasive species may be found on the Invasivespecies.gov website.
Descriptors: United States, Animal and Plant Health Inspection Service, APHIS, Rules and practice, Plant inspection, United States, Biological invasions.
Descriptors: Alien plants, Hawaii, Congresses, Alien plants control, Plant invasions, Plant-introduction.
Descriptors: acacia cyclops, allelopathy, leachates, phytotoxicity, nutrients, inhibition, growth.
Abstract: Aqueous leachates derived from canopy phyllodes of invasive Acacia cyclops affected growth of a range of shrub species independently of nutrient input effects. All plants showed a sublethal phytotoxic response. Root mass was general
ly less adversely affected than shoot mass and, while decreasing significantly in response to the 10% concentration, showed no such response to the 1% solution. Root-shoot biomass ratios increased, except in Euphorbia burmannii, which may recognize
intrinsic root architecture limitations on extensive exploitation of toxin-free soil. Application of surface plant litter from under A. cyclops canopies stimulated the production of basal stems in Protasparagus capensis and Eriocephalus racemosus but w
as insufficient to significantly reduce root-shoot ratios. Plant growth inhibition was maximized by canopy leachate compounded by surface litter effects in Anthospermum spathulatum. The net effect of leachate at high concentration on biomass allocat
ion in certain shrub species may help explain their patterns of association and disassociation with A. cyclops.
Descriptors: ceratitis-capitata, sterile-insect-release spread, mathematical-models.
Abstract: One of the most common methods of studying insect dispersal is the recapture of members of a population released at a single time from a single location. This procedure especially lends itself to quantitative analysis. Quantitative s
tudies of the dispersal of insects released in this manner may be divided into the following three general categories: (1) statistical studies in which certain dispersal parameters such as average distance flown are estimated without assuming any particul
ar model; (2) curve fits to an empirical model having a predetermined functional form, such as an exponential; and (3) fits to a fundamental biological model such as a diffusion-based model. Each of these methods of analysis serves a purpose. For example,
the first and second methods are often useful in developing control strategies for invasive pest species, whereas the third is useful for understanding the biological process driving dispersal. The article presents a quantitative analysis of the dispersa
l of irradiated Mediterranean fruit flies, Ceratitis capitata (Wiedemann) in a macadamia nut orchard near Hilo, Hawaii. All three of the methods described above are used in the analysis. The article had three primary objectives. The first was to review an
d contrast the three methods of analyzing data on the dispersal of insects from a point source. The second was to illustrate how these methods may be applied to insect recapture data using the example of released Mediterranean fruit flies. The third was t
o use the quantitative analysis to compare the results of the present release study with other studies on related species and to draw general conclusions about the nature of the dispersal of released sterile Mediterranean fruit flies. Results indicated th
at a population of irradiated flies released from a single point dispersed in a manner that may be modeled as if the population consisted of two subpopulations, one of which was dispersing in a diffusionlike pattern and the other was not dispersing, and t
hat the fraction of the population in the nondispersing subpopulation increased. The dispersal pattern appeared to be little influenced by prevailing wind and to remain centered near the release point. The pattern had almost complete circular symmetry.
Descriptors: woody weeds, weed control, South Africa, invasive species.
Descriptors: pinus, banksia, invasion, fynbos, forest ecology, introduced species, mountain forests, plant communities, weed competition, weed control, literature reviews, South Africa.
Descriptors: Invasive plants, Control Invasive plants, Ecology Plant invasions, Plant-introduction
Descriptors: solidago, trirhabda, herbivores, plant communities,
community ecology, biomass production, leaves, roots, light-penetration, soil-water-content,
nitrate-nitrogen cycling, competitive-ability, Minnesota, solidago-missouriensis,
trirhabda-canadensis, herbivory, community-structure.
Descriptors: rhizoctonia-solani, plant-pathogenic-fungi, biological control agents, rhizoctonia, hypovirulence, colonization, survival, fungus control, disease control, efficacy.
Abstract: Despite research on biological control dating back to the early 1930s, reliable, economical biocontrols of diseases caused by Rhizoctonia solani are not generally available commercially. New approaches for detection and use of novel
agents and development of broadly applicable biological control management systems are needed, especially for field crops. During the past 10 years, new sources of agents from within the diverse groups of binucleate Rhizoctonia spp. and hypovirulent R. s
olani isolates have been demonstrated to be effective in biocontrol of a range of host--R. solani disease combinations. Although these agents include isoiates from several different binucleate Rhizoctonia anastomosis groups (AG) and hypovirulent R. solani
AG. neither mycoparasitism nor antibiosis is involved in biocontrol of R. solani by any of these isolates. Postulated mechanisms of biocontrol include induction of systemic host resistance, and/or competition for recognition and invasion sites or nutrien
ts. Tested collections of binucleate Rhizoctonia spp. and hypovirulent R. solani differ markedly in effectiveness as biocontrol agents for diseases caused by R. solani. Reportedly, plant surface-colonizing isolates (i.e. on or superficially within outer
tissues of roots, crowns, hypocotyls, stems or petioles) are effective biocontrol agents, whereas, non-colonizers are ineffective.
Descriptors: Weeds, control, Great Britain, Congresses.
Descriptors: solanum-sisymbriifolium, weed control, biological control, coleoptera, host-range, biological control agents, feeding behavior, fecundity, generation-interval, life-cycle, adults, longevity, survival, oviposition, host-preferences h
ost-specificity, datura, nicandra, physalis, solanum, brassica, spinacia, lactuca, solanaceae, South Africa.
Abstract: A leaf-feeding tortoise beetle (Gratiana spadicea) was screened as a potential biological control agent for the invasive exotic weed Solanum sisymbriifolium in South Africa. Favorable biological characteristics of G. spadicea include
a high rate of increase, long-lived and mobile adults, several generations per year, and a high per capita feeding rate. Host range was investigated in larval survival tests and adult choice tests under laboratory conditions. Larvae were successfully rea
red on 8 of 11 indigenous Solanum species, on 4 of 5 exotic Solanum species (apart from S. sisymbriifolium), and on economically important S. melongena (eggplant) but not on any of the species of Datura, Nicandra, and Physalis tested. Very limited adult f
eeding and oviposition occurred on several of the indigenous Solanum species and on eggplant. These trials were conducted under quarantine conditions with the potential for laboratory artifacts. The poor larval survival on nonhosts and the inability of th
e agent to recognize nonhosts as oviposition sites supported a request for release of this agent, which was subsequently granted.
Descriptors: eupatorium-odoratum, introduced-specie,s invasion, biological control, weed control, pareuchaetes, larvae, host-range, host-specificit,y interactions, formicidae, argentina, South Africa.
Descriptors: brassica-campestris, seedlings, xanthomonas-campestris-pv -campestris, bacterial diseases, infections, monitoring, plant disease control, chemical control, fosetyl, timing, efficacy, luminescence, environmental temperature.
Abstract: Autophotography of a bioluminescent transconjugant of Xanthomonas campestris pv. campestris provided a reliable means to quantify the extent of bacterial invasion into cabbage (Brassica campestris). A single prophylactic treatment of
fosetyl-Al at 4,800 mg kg-1 a.i. as a spray and drench reduced the invasiveness of Xanthomonas campestris pv. campestris on inoculated cabbage seedlings. Multiple treatments did not reduce invasiveness further. The effect of fosetyl-AI was immediate (wit
hin 1 h) and persisted for at least 21 days. The efficacy of fosetyl-Al treatments was more pronounced at 20 degrees C and decreased as temperature increased; however, the data indicated a separate effect of temperature on disease development and no direc
t interaction between temperature and fosetyl-Al treatment.
Descriptors: steppes, fire control, bromus-tectorum, fire effects, plant ecology, Idaho.
Descriptors: streptomyces, biological control, biological control agents, fungal antagonists, metabolites, antibiotics, antifungal properties, antagonism, pythium-ultimum, rhizoctonia-solani, aphanomyces-euteiches, phymatotrichopsis-omnivora, rhiz
octonia solani, fusarium, biological control, fungal diseases, root rots, seed inoculation, soil inoculation, pisum sativum.
Abstract: The actinomycete Streptomyces lydicus WYEC108 showed strong in vitro antagonism against various fungal plant pathogens in plate assays by producing extracellular antifungal metabolites. When Pythium ultimum or Rhizoctonia solani was
grown in liquid medium with S. lydicus WYEC108, inhibition of growth of the fungi was observed. When WYEC108 spores or mycelia were used to coat pea seeds, the seeds were protected from invasion by P. ultimum in an oospore-enriched soil. Results showed th
at WYEC108 was capable not only of destroying germinating oospores of P. ultimum but also of damaging the cell walls of the fungal hyphae. These results show that S. lydicus WYEC108 is potentially a potent biocontrol agent for use in controlling Pythium s
eed and root rot.
Descriptors: Plant ecology, Plants, Cultivated, Urban-plants, Fallow land plants, Hybridization, Vegetable.
Descriptors: plant-pests, insect control, biological control agents, entomophilic-nematodes, pathogenicity, strain differences.
Abstract: Five bioassays were compared for their usefulness to determine the virulence of four nematode strains. The objective of this study was to develop standard assays for particular nematode species. In all assays, the nematodes Steinerne
ma feltiae (strain UK), S. riobravis, S. scapterisci Argentina and Heterorhabditis bacteriophora HP88 were exposed to Galleria mellonella larvae. All bioassays except the sand column assay were conducted in multi-well plastic dishes. The present study d
emonstrated the variation in entomopathogenic nematode performance in different bioassays and supports the notion that one common bioassay cannot be used as a universal measure of virulence for all species and strains because nematodes differ in their beh
avior. Furthermore, particular assays should be used for different purposes. To select a specific population for use against a particular insect, assays that are more laborious but which simulate natural environmental conditions (e.g. the sand column assa
y) or invasion by the nematode (e.g. the penetration rate assay) should be considered. In cases where commercial production batches of the same nematode strains are compared, simple and fast assays are needed (e.g. the one-on-one and exposure time assays)
. Further studies are needed to determine the relationships between data obtained in each assay and nematode efficacy in the field.
Descriptors: cunoniaceae, invasion, introduced-species, pittosporum, plant-water-relations, riparian forests, weed control, South Africa.
Descriptors: Manihot esculenta.
Abstract: Cassava is a food crop of increasing importance for the rapidly growing rural population in Africa. Easy to grow even under harsh agronomic conditions, cassava is the primary source of carbohydrates for more than 200 million people,
including the poorest on the continent, and provides food security to most subsistence farmers. Several pests including phytophagous arthropods, plant pathogens and weeds constrain cassava production on the continent. The exotic species introduced acciden
tally from the Neotropics constitute the largest group of pests. The long cropping cycle exposes cassava to relatively few additional pests in Africa, and enhances sustainable pest management interventions such as biological control, host plant resistance
and cultural practices. Historically, cassava plant protection focused on resistance breeding, but since the invasion of several devastating exotic pests in the 1970s, a wider range of pest management solutions are now being pursued. Plant protection int
erventions that are developed and tested by teams of multi-disciplinary scientists with input from extension agents and client farmers are urgently needed. Appropriate technology development requires an understanding of key pest-host-agroecosystem interac
tions in the context of the agronomic practices of the farmer and the socio-economic importance of the crop. A regional project to develop, test and implement ecologically sustainable cassava plant protection in West Africa is presented as a general model
for developing appropriate pest management in Africa.
Descriptors: alnus-glutinosa frankia, complementary-dna, multigene families, cysteine proteinases, nucleotide sequences, amino-acid-sequences, gene expression, messenger rna, root nodules, molecular sequence data, genbanku13940.
Abstract: Nodules formed on the roots of actinorhizal plants as a consequence of nitrogen-fixing symbioses with the actinomycete Frankia appear to result from modification of the developmental pathway that leads to lateral root formation. Pres
ently no information exists about factors that control this developmental switch or, until now, about genes that are differentially expressed as a result of an altered developmental pathway. Differential screening of an Alnus glutinosa nodule cDNA library
revealed altered levels of gene expression in nodules as compared with roots and allowed isolation of host plant nodule-specific cDNA sequences. The deduced amino acid sequence of one full-length cDNA, AgNOD-CP1, represents a nodule-specific cysteine pro
teinase similar to cysteine proteinases of the papain superfamily. Residues critical to catalysis, active site, and disulfide bridges are conserved. Suggested roles for this enzyme are as a defense response to Frankia invasion, as a component of tissue re
modeling in root and nodule tissues, as a cell cycle component, or as an element of protein turnover. Complexity of hybridization patterns revealed by Southern blot analysis suggests that the gene for AgNOD-CP1 is a member of a multigene family. Northern
hybridization results indicate that this gene may have been recruited for a role specific to this symbiosis, a phenomenon observed in the rhizobium-legume symbioses, perhaps common to many microbe-plant interactions.
Descriptors: Weeds control, Riparian plants, Ecology, Plant invasions.
Descriptors: taeniatherum-caput-medusae, fire ecology, plant competition, plant ecology, plant succession, taxonomy, weed control, invasion, wildfires.
Descriptors: brassica napus var, oleifera transgenics, genetic engineering, ecology, invasiveness.
Abstract: Concerns about genetically engineered crop plants centre on three conjectural risks: that transgenic crop plants will become weeds of agriculture or invasive of natural habitats; that their engineered genes will be transferred by pol
len to wild relatives whose hybrid offspring will then become more weedy or more invasive; or that the engineered plants will be a direct hazard to humans, domestic animals or beneficial wild organisms (toxic or allergenic, for example). Here we describe
an experimental protocol for assessing the invasiveness of plants. The object is to determine whether genetic engineering for herbicide tolerance affects the likelihood of oilseed rape becoming invasive of natural habitats. By estimating the demographic p
arameters of transgenic and conventional oilseed rape growing in a variety of habitats and under a range of climatic conditions, we obtain a direct comparison of the ecological performance of three different genetic lines (control, kanamycin-tolerant tran
sgenics and herbicide-tolerant transgenic lines). Despite substantial variation in seed survival, plant growth and seed production between sites and across experimental treatments, there was no indication that genetic engineering for kanamycin tolerance o
r herbicide tolerance increased the invasive potential of oilseed rape. In those cases in which there were significant differences (such as seed survival on burial), transgenic lines were less invasive and less persistent than their conventional counterpa
rts.
Descriptors: acer-saccharum, fraxinus americana, gleditsia triacanthos, prunus serotina, poa-pratensis, solidago, interspecific competition, seedlings, leaf water potential, leaves, nitrogen-content, leaf-area, photosynthesis, community ecology, i
nvasion, water use efficiency, leaf-conductance, seedling growth, survival, plant competition, old-fields, light-intensity, Illinois.
Abstract: 1. The performance of seedlings of Acer saccharum, Fraxinus americana, Gleditsia triacanthos and Prunus serotina was examined in eight old-field vegetation patch types and in control plots with no competition. Measurements of seedlin
g gas exchange, water potential, foliar N, and specific leaf area were related to microenvironmental conditions and to seedling growth and survival. 2. Among vegetated patch types, predawn leaf water potentials and midday photosynthetic rates of the tree
seedlings were highest in the short-statured and shallow-rooted patches of Poa pratensis, and lowest under established trees and shrubs where both soil moisture and subcanopy irradiance are reduced. 3. For seedlings of all tree species, photosynthetic rat
es per unit leaf area averaged 21-28% of that measured in control seedlings free of competition. Irradiance and photosynthesis both varied significantly among patch types, and photosynthesis was more strongly correlated with irradiance than with other var
iables. 4. In all species, photosynthesis under full light was strongly correlated with photosynthesis measured under ambient light. Ambient photosynthesis most closely approached photosynthetic capacity in late-successional species (Acer > Fraxinus &g;
t; Prunus > Gleditsia). Shade-tolerance thereby enhances the potential for late-successional species to invade established plant communities. 5. The ratio of net photosynthesis to stomatal conductance in tree seedlings was decreased in competitive envi
ronments dominated by Solidago and other fast-growing herbs. Reduced water use efficiency appears to be caused by competitively induced nitrogen limitations. Some competitive environments thus reduce both soil moisture and. photosynthetic water use effic
iency of tree seedlings. 6. Measurements of photosynthesis and foliar nitrogen are good indicators of long-term seedling growth, but not of survival. The complex interaction of light, moisture and nitrogen availability varies distinctively among old-field
vegetation patches, and invading tree species differ in their ability to cope with these compound stresses. Such differences can explain differential tree seedling growth rates in old-field vegetation, but the densities of trees found germinating and sur
viving from year to year depend on other factors.
Descriptors: coccinellidae, communities, species diversity, population density, interspecific competition, coccinella septempunctata, introduced species, biological control agents, agricultural land, medicago sativa, zea mays, field crops, South D
akota, native-species, species abundance, small grain crops.
Abstract: Seven native coccinellid species inhabited alfalfa, corn, and small grain fields in eastern South Dakota prior to invasion and establishment of Coccinella septempunctata L. Six species occurred in all crops, however, Adalia bipunctat
a (L.) occurred only in corn. The structure of native coccinellid communities differed significantly for years prior to compared with years after establishment of C. septempunctata in fields of the three agricultural crops. Differences in community struct
ure were accounted for mainly by reduced abundance of two species, C. transversoguttata richardsoni Brown and Adalia bipunctata (L.). Annual abundance of C. transversoguttata richardsoni averaged 20-32 times lower during post-invasion years than in years
prior to invasion, depending on crop; while annual abundance of A. bipunctata averaged 20 times lower in corn after invasion. Addition of C. septempunctata to the community did not result in a significant increase in total abundance of coccinellids in the
crops. Coccinellid abundance in agricultural crops may be limited by the total abundance of prey or by the availability of other requisites in the landscape as a whole. Therefore, introduction of a new species, while resulting in reductions in native spe
cies populations, may not increase total coccinellid abundance, and may therefore have no net effect on biological control of aphid pests.
Descriptors: forest-trees, forests, herbage, seedlings, ecosystems, invasion, lonicera-tatarica, plant communities, plant ecology, weed control, Massachusetts, Vermont, facultative-weeds.
Descriptors: oryza-sativa, rhizobiaceae, endophytes, nitrogen-fixation, tumors, induction, 2,4-d, colonization, root nodules, nodulation, histology, plant anatomy, plant-tissues, para-nodules, para-nodulation.
Abstract: Rice seedlings developed nodule-like tumors (pare-nodules) along primary and secondary roots when treated with the auxin 2,4-dichlorophenoxy-acetic acid (2,4-D). Histologically, these tumors appeared as cancerous out-grown lateral-ro
ot primordes and were thus comparable with stem nodules of the legume Sesbania rostrata. Azorhizobium caulinodans (a diazotroph known as a specific endophyte of Sesbania rostrata) was introduced and became established inside rice pare-nodules and in root
tissues around tumor bases. The infection with A. caulinodans followed a typical "crack-entry" invasion at places where paranodule tumors had emerged through the root cortex and epidermis. The bacteria settled with high cell densities in interce
llular spaces of the induced tumors and between root cortical cells. Infection of plant cells took place both in the epidermis and in cortical tissue. Intracellularly established A. caulinodans was found inside the cytoplasm, surrounded by membrane-like s
tructures. N2 fixation by tumor-inhabiting Azorhizobium sp. was increased at low O2 tensions (1.5-3 kPa) compared with an untreated control. Only a little activity remained at O2 tensions of 5 kPa and above. The present results confirm that root-tumor ind
uction offers a suitable method of establishing diazotrophs endophytically in the roots of gramineous crops.
Descriptors: diaphania-hyalinata heterorhabditis-bacteriophora steinernema, neoaplectana, entomophilic-nematodes insect control, species-differences efficacy, pathogenicity, infectivity, larvae, susceptibility, mortality, cucurbita-pepo florida-<
i>
Abstract: Laboratory bioassays were conducted to determine pathogenicity of five entomopathogenic nematodes from the genera Steinernema and Heterorhabditis against melon-worm, Diaphania hyalinata (L.). S. carpocapsae (Weiser) (Mexican strain)
was the most pathogenic nematode species, followed by H. bacteriophora (Poinar), S. feltiae (Filipjev), S. anomali (Kozodoi), and S. glaseri (Steiner), respectively. The LC50 for S. carpocapsae (Mexican) was 39.9 infective juveniles per milliter. The rate
of nematode invasion into insects was proportional to the overall pathogenic effect of the various nematodes. The level of insect mortality and infectivity (the number of nematodes invading the insect) were directly related to exposure time. First instar
s and pupae were significantly less susceptible to S. carpocapsae infection than older larvae and prepupae. The number of nematodes found in the hemocoel increased with larval age. Mortality and infectivity were inversely related to nematode size. In fiel
d trials, survival of S. carpocapsae (All strain) on squash plant foliage was reduced to 0.77% within 40 h in a trial under high humidity conditions and to 0.25% after 18 h in a trial under moderate humidity conditions. Field applications of 5 billion nem
atodes per hectare produced infection rates of 52-55%.
Descriptors: plant parasitic nematodes, heterodera schachtii, biological control, nematode control, hirsutella, nematophagous fungi, biological control agents, hyphae, pelleting, efficacy, release techniques, inoculum, fungistasis, inundative rele
ase.
Abstract: Research was conducted to determine whether pelletized hyphae of Hirsutella rhossiliensis suppressed invasion of roots by the sugarbeet cyst nematode Heterodera schachtii in field microplots. The loamy sand in the microplots was infe
sted with H. schachtii but not with H. rhossiliensis. Alginate pellets, with or without hyphae of H. rhossiliensis, were mixed into soil removed from the microplots (1 pellet/cm3 of soil). The soil was placed in cylinders positioned vertically in microplo
ts; cylinders (6/microplot) were 10.1 cm wide and 15.3 cm deep and contained 1200 cm3 of soil. Pellets and soil also were placed in soil observation chambers, which were buried in the cylinders or kept at 20 degrees C in moisture chambers in the laborator
y. After 12 days, cabbage seeds were planted in each cylinder, and after 10 days of growth, the seedlings were removed from the soil and H. schachtii in the roots were counted. The number of H. schachtii in roots was large and was unaffected by addition o
f H. rhossiliensis. In soil observation chambers, H. rhossiliensis grew vigorously from the pellets in heat-treated soil but not in nonheated soil, and enchytraeids and collembolans were observed near damaged pellets. We suspect that organisms, possibly i
ncluding enchytraeids and collembolans, fed upon or otherwise inhibited H. rhossiliensis.
Descriptors: weeds, invasion, characterization, weed control, Virginia.
Descriptors: melaleuca-quinquenervia botryosphaeria-ribis fungal-diseases histopathology, invasion, leaves, stems, callus, pathogenesis, defense-mechanisms weeds, mycoherbicides, biological control, -agents plant-anatomy histochemistry, lignin, su
berin, tannins, xylem, cambium, phloem-
Descriptors: lythrum-salicaria wetlands, weed control, biological control, biological control, -agents hylobius, host-specificity roots, boring-insects environmental-impact
Abstract: Introduction of purple loosestrife into North America and its spread into wetlands has led to the degradation of these important habitats for wildlife. Conventional control efforts are unsuccessful in providing long-term control. A c
lassical biological control program offers the best chance for reducing the numbers of this invasive plant and improving regeneration of the native flora and fauna. European studies demonstrated that the root boring weevil Hylobius transversovittus is hig
hly host specific to the target weed. Attack of two test plant species (winged lythrum and swamp loosestrife) during host range screening was most likely due to artificial test conditions. An environmental assessment of the potential effects of the releas
e of the purple loosestrife borer in North America indicated that benefits outweigh any potential negative impact. Therefore its field release was approved in 1992.
Descriptors: festuca-rubra dactylis-glomerata lotus-corniculatus coronilla-varia public-utilities rights-of-way vegetation-management brush control, trees, cultural control, plant-introduction plant-competition botanical-composition frequency-di
stribution cover-crops ground-cover-plants biomass-production species-diversity plant-communities power-lines electric-power ontario-
Descriptors: acacia-saligna uredinales, rust-diseases galls, woody-weeds weed control, stems, diameter, plant-density seed-banks biological control, -agents biological control, South Africa gall-rust
Abstract: The impact of an introduced, gall-forming rust fungus, Uromycladium tepperianum, on an invasive tree Acacia saligna was evaluated in the Western Cape Province. The number of infected trees, rust galls per tree, state of trees (dead o
r alive), stem diameter of trees, and number of seeds in the soil were recorded along transects at yearly intervals from 1991 to 1996 at eight sites where the fungus had been inoculated during 1988 or 1989. The levels of disease increased rapidly after 19
92 at all sites. By 1995, the mean number of galls per tree varied from 5 to approximately 1500 per tree depending on tree size. Tree density decreased by at least 80% at all sites over the period, although young seedlings started to grow at some sites. T
he seed number in the soil seed bank stabilized after 1992 at most sites, except where fires occurred which reduced the number of seeds. U. tepperianum therefore is proving to be a highly effective biological control agent, as shown by greatly reduced pop
ulation densities of A. saligna in South Africa.
Descriptors: vegetation-management weed control, forest-ecology herbicides, silviculture, plant-succession disturbance-
Abstract: Forest managers are under increasing pressure to decrease herbicide use throughout North America. Reducing herbicide use for stand tending, while maintaining or increasing reforestation success, will require greater knowledge of how
to minimize vegetation management problems in young stands. The type, intensity, timing, and frequency of silvicultural activities (especially harvesting and site preparation) interact with the autecological characteristics of forest weeds to affect their
survival or invasion. Autecological characteristics include 1) habitat requirements, 2) modes of reproduction, 3) growth habit, 4) phenology and 5) response to disturbance. Not considering these relationships often initiates successional pathways that fo
rce vegetation management into a "removal loop", where release treatments are required to remove or suppress forest weeds. Modifying silvicultural activities based on thorough analysis of site conditions and an understanding of plant autecology
can move vegetation management into a "prevention loop" thus reducing dependence on herbicides for stand tending.
Descriptors: pinus-monophylla pinus-edulis juniperus-osteosperma brush control, invasion, rangelands, chemical control, tebuthiuron, application-rates placement, utah, woody-plant-invasion
Abstract: Tebuthiuron [N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]N,N'-dimethylurea] controls small trees in regrown pinyon-juniper woodland chainings. Precise applications by hand minimize cost and damage to forage plants. Little informat
ion exists on the applicability of local trials to varying Intermountain sites slated for reinvestment. We conducted 2 balanced factorial experiments at well-separated sites in the Great Basin and Colorado Plateau. Four rates (0.12, 0.25, 0.50, and 0.75 g
m a.i. per 130 dm3 crown volume) of tebuthiuron boluses were applied to tree stembase, mid-crown, or dripline placements. Four size classes (12-99, 100-299, 300-599, and 600-1099 dm3 crown volume) of Utah juniper [Juniperus osteosperma (Torr.) Little] and
single needle (Pinus monophylla Torr. and Frem.), and Rocky Mountain (P. edulis Engelm.) pinyon trees were treated in September 1985. Defoliation and mortality levels were estimated 24 and 36 months following treatments. Both sites received highly simila
r amounts of herbicide and cumulative precipitation. Analysis of variance showed that the presence and strength of main effects and first order interactions was largely site-specific. Pinyon was more susceptible than juniper at tither site. Medium-sized a
nd large saplings were apparently more readily defoliated than seedlings and small saplings. Dosage effects were generally nonlinear for both species. The highest, most rapid and most uniform defoliation and mortality of trees resulted from application of
tebuthiuron at the stem bases. This placement option has strong operational advantages and minimizes damage to forage plants beneath trees.
Descriptors: plant-pests parasites-of-insect-pests biological control, -agents insect control, hyperparasitism-
Abstract: Aphelinid parasitoids have an outstanding record of success in programmes of classical biocontrol against whiteflies and scale insects. Heteronomous hyperparasitoids are aphelinids in which the sexes develop on or in different hosts.
The female always develops as a primary endoparasitoid of Homoptera. The male develops as a secondary parasitoid (hyperparasitoid) of his own or another species of homopteran endoparasitoid. Caged experiments were performed with the cabbage whitefly, Ale
yrodes proletella to examine the invasion of a population of a conventional parasitoid, Encarsia inaron (both sexes primary endoparasitoids) by a heteronomous hyperparasitoid, E. tricolor. In all cages the heteronomous hyperparasitoid successfully invaded
an established population of the conventional parasitoid and the conventional species population declined to very low levels within 8 weeks of the introduction of the heteronomous hyperparasitoid. The patterns of invasion were different in each cage. In
two cages, high levels of male production by E. tricolor were observed, indicating that hyperparasitism of the conventional species was probably an important factor in causing the decline in the E. inaron population. In a reciprocal experiment in which E.
inaron was introduced to an established population of E. tricolor the conventional species failed to invade or persist. A survey of published references to complexes of parasitoids containing a heteronomous hyperparasitoid and one or more conventional sp
ecies indicated that, in the majority of cases, the heteronomous hyperparasitoid was the most important species in the complex. There are clear implications for the use of these parasitoids in. programmes of classical biocontrol. This is because high com
petitive ability against other parasitoids is not necessarily a good indicator of the ability of a species to maintain high levels of pest control, especially when hyperparasitic behaviour is involved.
Descriptors: Invasive plants, North-America Invasive plants, Control-North-America
Descriptors: ceratitis-capitata insect-pests plant-pests insect control, biological control, control-programs quarantine, history, life-cycle california-
Abstract: Classical biological control is suggested as a tool worth developing now for possible future use in the integrated pest management of the Mediterranean fruit fly (Medfly), Ceratitis capitata (Wiedemann), in California. Three factors
that impact broadly on developing and implementing such a biological control program are: (1) the question of Medfly establishment, (2) quarantine considerations, and (3) agricultural and urban concerns. Each of these factors and their combined effects mu
st be considered when discussing biological control of Medfly in California as shaped by historical perspectives on Medfly invasions, methods of Medfly eradication, and past biological control efforts against Medfly. We believe that biological control res
earch should play a foundational role in any future Medfly management programs in California. Development of biological control should involve life history studies of Medfly and its natural enemies in their area of endemicity in sub-Saharan, southeast Afr
ica. Medfly has been studied and should continue to be studied in areas it has invaded, because information derived from such studies provides insights into the potential distribution, abundance, and impact of Medfly populations in California. A plan for
a biological research program on Medfly and its relatives and a biological control strategy are presented.
Descriptors: pastures, botanical-composition plant-colonization plant-succession community-ecology zero-grazing sheep, hill-grasslands hill-land long-term-experiments microtus-agrestis herbivores, wales-
Abstract: 1. From 1957 to 1968 a series of nine experiments was established to determine the effects of excluding sheep from hill pasture in Snowdonia. Each experiment consisted of three ungrazed plots and six grazed control plots. Species abu
ndance was recorded non-destructively by cover pins during 1958-81. In autumn 1982, two of the experiments were completely fenced; vegetation changes in the formerly grazed plots were recorded by herbage sampling from 1981 to 1990. 2. Successional changes
depended strongly on the soil and initial vegetation of the site. Compositional change in grasslands initially dominated by Agrostis capillaris and Festuca ovina was smaller than in vegetation initially dominated by Nardus stricta and Festuca ovina, and
was less obviously driven by coarser plants overtopping short ones. 3. There was almost no invasion of new plant species, the only exceptions being Sorbus aucuparia, which was associated with bird perches on fences, Dryopteris dilatata, which emerged in t
ussocky grassland, and Solidago virgaurea, which may have spread to one site from nearby cliffs. The invaders played no important part in the succession. 4. Early changes were relatively rapid, with the character of the vegetation altering markedly over a
bout 7 years. Low-growing plants such as Danthonia decumbens, Juncus squarrosus, Trifolium repens and Polytrichum commune declined consistently, as did the biennial Cirsium palustre. 5. Longer-term changes in the herbaceous vegetation were few. Suppressed
shrubs of Calluna vulgaris and Erica cinerea grew into full-sized bushes, which at one site flourished for 20 and 12 years, respectively, before degenerating, but at other sites coalesced to achieve local dominance. 6. In the absence of sheep, voles beca
me the dominant herbivore and caused large year-to-year variation in herbage biomass. Agrostis vinealis and Holcus mollis were less damaged by voles than A. capillaris. Established tussocks of Molinia caerulea were also little affected. In years of high v
ole abundance the pleurocarpous mosses Hylocomium splendens and Pleurozium schreberi increased greatly among mats of dead grass.
Descriptors: woodlands, flora, forest-ecology, introduced-species, invasion, plant-succession, undergrowth, vegetation-management, weed control, Scotland.
Descriptors: weeds, pinus, fynbos, environmental-impact simulation-models alien-plants
Descriptors: weeds, introduced-species non-crop-weed control, conservation-areas
Descriptors: plant-ecology plant-colonization plant-succession pioneer-species plant-communities botanical-composition riparian-vegetation tropical-rain-forests aquatic-plants floodplains, alluvial-land landforms, rivers, forest-ecology lakes, rip
arian-forests community-ecology peru-
Abstract: (1) The major proportion of western Amazon forests grow on fluvial deposits and thus originated in floodplain environment. The fluviodynamic character of the sites initially colonized by plants was studied along different river types
, and this information was combined with botanical observations from the same areas. Special emphasis was given to colonizing plant distribution and survival in relation to the abiotic environment. (2) Four frequently occurring landform types, each rich i
n microforms, were recognized in relation to the colonization process: fluvial bars, swales, abandoned channels and riverbanks. They are affected by seasonal fluctuations in the rivers and tend to be narrow, curved or linear patches. Local site and coloni
zing vegetation characteristics vary considerably between different river types (meandering or braided, rich or poor in suspended sediment). (3) The newly deposited fluvial sediments are poor in organic carbon and nitrogen. Colonization begins either with
immigrant propagules dispersed by wind or water, or with the invasion of species by vegetative means. Usually numbers of individuals are few, and the initial vegetation pattern is a reflection of the small-scale mosaic of microsites. The pioneer flora (1
25 species recorded) includes many widespread perennial herbs, and seeds of most forest species do not germinate in the dry sediments. Herbaceous colonist species are almost non-existent in suspension-poor rivers of low erosion rite. (4) The persistence o
f the initial plant assemblage is controlled by the evolution of fluvial landforms. Only a few species among the set of colonists are significant in later forest succession. These include Tessaria integrifolia and Gynerium sagittatum, which resist moderat
e flood damage and resprout after burial. Mature seed populations of these 10-15-m-tall species are abundant at the outermost margin of the successional forest just beyond the fluvial bars. The low representation of tree species in the colonizing phase su
ggests that the extreme environmental conditions at the river margins differ from other natural environments along the Amazon. (5) Aquatic succession on takes affected by suspension-rich waters starts with genuine floating species. The general habits of t
hese vegetation assemblages and their species composition are highly similar in the 'white-water' floodplains of the study area. An annual vegetation flush characteristically follows the flood period. On the other hand, macrophyte vegetation is almost non
-existent on the floodplain lakes of suspension-poor rivers. (6) The Amazon floodplain corridors provide a good opportunity for ecological studies of plant colonization because basically similar succession is present at each meander along the rivers. Furt
hermore, the basic physiographic processes which form the sites and control their further evolution are both well known and measurable.
Descriptors: coccoidea, parasitoids, defense-mechanisms encapsulation, host-parasite-relationships parasitism, age, environmental-temperature host-plants plant-effects parasites-of-insect-pests biological control, -agents biological control, lite
rature-reviews host-age superparasitism-
Abstract: Encapsulation is a common defense mechanism exerted by a host insect in response to invasion by a metazoan parasitoid or other foreign organisms. In the process of encapsulation, the host forms a capsule around the parasitoid egg or
larva, which is usually composed of host blood cells and the pigment melanin. The capsule may kill the parasitoid and thus prevent successful parasitism. Encapsulation may adversely affect the degree of biological control effected by parasitoids as it may
either prevent the establishment of exotic parasitoids in new regions or reduce parasitoid efficacy. A high incidence of encapsulation may also cause difficulties in mass rearing of parasitoids. In the Coccoidea (Homoptera), parasitoid encapsulation has
so far been recorded in three families: Coccidae (soft scale insects), Diaspididae (armored scale insects), and Pseudococcidae (mealybugs). Important factors that affect the frequency of parasitoid encapsulation in the Coccoidea include: Host and parasito
id species, the host's physiological age and physiological condition, the host origin (or strain), superparasitism, the rearing and/or ambient temperature, and the host plant. The effects of these factors on the incidence of parasitoid encapsulation in th
e Coccidae, Diaspididae, and Pseudococcidae are described.
Descriptors: flora, introduced-species invasion, nature-conservation public-parks weed control, usa-
Descriptors: Invasive plants, South Africa-Transvaal-Identification Plant-competition-South Africa-Transvaal Plant-introduction-South Africa-Transvaal Botany-South Africa-Transvaal
Descriptors: Invasive plants, Control Invasive-plants, Plant invasions, Plant conservation.
Descriptors: Invasive plants, Plant invasions, Congresses, Invasive plants.
Descriptors: Weeds, Australia.
Descriptors: Invasive plants, Control, Biological control, Biological invasions.
Descriptors: Invasive plants, Control.
Abstract: Outlines a nationwide effort to stem the tide of potentially invasive plants arriving in the United States; to control or eradicate those that are already a problem; and to restore full function to our degraded agricultural lands, ra
ngelands, forests, and ecosystems. Proposes three national goals: prevention, control, and restoration.
Descriptors: prosopis-glandulosa-var, glandulosa, brush control, chemical control, fenuron, manual-weed control, plant-density, seedlings, survival, grasslands, deserts, rangelands, arid-zones, New Mexico, shrub-invasion.
Abstract: Honey mesquite (Prosopis glandulosa Torr. var. glandulosa populations continue to expand and become more dense, even on areas once "successfully" treated either with herbicides or by bulldozing in southern New Mexico. Areas
treated from 1958-1964 for mesquite control on the USDA-ARS Jornada Experimental Range and the New Mexico State University College Ranch were sampled to determine mesquite density changes. On herbicide treated areas sampled in 1976 and again in 1988, mes
quite densities increased 10% to 128% and had densities from 67 to 494 plants/ha. Two areas treated by either bulldozing or fenuron in 1959-60, and with original kills near 100%, had an average density of 377 plants/ha by 1988, with an establishment rate
of 13.5 plants/ha/year. On the College Ranch, mesquite densities increased 11%, from 130 (1982) to 147 (1988) plants/ha. Only 19% of a cohort of mesquite seedlings which germinated in 1989 were still alive in May 1990. Even though only a small percentage
of the mesquite that germinated survived into the second year, this is enough to change former grasslands into mesquite-dominated rangelands.
Descriptors: meloidogyne-incognita, hirsutella, nematophagous-fungi, hyphae, nematode control, biological control, biological control, -agents, pellets, alginates, repellency, attractants, carbon-dioxide, chemotaxis, meloidogyne-javanica, plant-pa
rasitic-nematodes, brassica-oleracea-var, capitata roots, monacrosporium-ellipsosporum.
Abstract: The responses of second-stage juveniles (J2) of Meloidogyne incognita race 3 to calcium alginate pellets containing hyphae of the nematophagous fungi Monacrosporium cionopagum, M. ellipsosporum, and Hirsutella rhossiliensis were exam
ined using cylinders (38-mm-diam., 40 or 72 mm long) of sand (94% <250-micrometers particle size). Sand was wetted with a synthetic soil solution (10% moisture, 0.06 bar water potential). A layer of 10 or 20 pellets was placed 4 or 20 mm from one end o
f the cylinder. After 3, 5, or 13 days, J2 were put on both ends, on one end, or in the center; J2 were extracted from 8-mm-thick sections 1 or 2 days later. All three fungal pellets were repellent; pellets without fungi were not. Aqueous extracts of all
pellets and of sand in which fungal pellets had been incubated were repellent, but acetone extracts redissolved in water were not. Injection of CO2 (20 microliters/minute) into the pellet layer attracted J2 and increased fungal-induced mortality. In vials
containing four randomly positioned pellets and 17 cm3 of sand or loamy sand, the three fungi suppressed the invasion of cabbage roots by M. javanica J2. Counts of healthy and parasitized nematodes observed in roots or extracted from soil indicated that,
in the vial assay, the failure of J2 to penetrate roots resulted primarily from parasitism rather than repulsion. Data were similar whether fungal inoculum consisted of pelletized hyphae or fungal-colonized Steinernema glaseri. Thus, the results indicate
that nematode attractants and repellents can have major or negligible effects on the biological control efficacy of pelletized nematophagous fungi. Factors that might influence the importance of substances released by the. pellets include the strength,
geometry, and duration of gradients; pellet degradation by soil microflora; the nematode species involved; and attractants released by roots.
Descriptors: chromolaena-odorata, weed control, integrated control, chemical control, cultural control, introduced species, spread, invasion, geographical-distribution, South Africa.
Descriptors: nicotiana tabacum, phytophthora cryptogea, phytophthora-nicotianae-var, parasitica, plant pathogenic fungi, disease resistance, induced-resistance, pathogenicity, symptoms, necrosis, leaves, hyphae, cell-growth inhibition, ribonucleas
es, enzyme activity, genetic regulation, genes, genetic code, gene expression, transcription, cryptogein.
Abstract: The hypersensitive response and systemic acquired resistance (SAR) can be induced in tobacco (Nicotiana tabacum L.) plants by cryptogein, an elicitin secreted by Phytophthora cryptogea. Stem application of cryptogein leads to the est
ablishment of acquired resistance to subsequent leaf infection with Phytophthora parasitica var nicotianae, the agent of the tobacco black shank disease. We have studied early events that occur after the infection and show here that a tobacco gene encodin
g the extracellular S-like RNase NE is expressed in response to inoculation with the pathogenic fungus. Upon induction of SAR with cryptogein, the accumulation of NE transcripts coincided with a rapid induction of RNase activity and with the increase in t
he activity of at least two different extracellular RNases. Moreover, exogenous application of RNase activity in the extracellular space of leaves led to a reduction of the fungus development by up to 90%, independently of any cryptogein treatment and in
the absence of apparent necrosis. These results indicate that the up-regulation of apoplastic RNase activity after inoculation could contribute to the control of fungal invasion in plants induced to SAR with cryptogein.
Descriptors: oryza-sativa, leptochloa, symbiosis, symbionts, roots, cortex, xylem, stele, immunohistochemistry, leptochloa-fusca.
Abstract: The invasive properties of Azoarcus sp. strain BH72, an endorhizospheric isolate of Kallar grass, on gnotobiotically grown seedlings of Oryza sativa IR36 and Leptochloa fusca (L.) Kunth were studied. Additionally, Azoarcus spp. wer
e localized in roots of field-grown Kallar grass. To facilitate localization and to assure identity of bacteria, genetically engineered microorganisms expressing beta-glucuronidase were also used as inocula. beta-Glucuronidase staining indicated that the
apical region of the root behind the meristem was the most intensively colonized. Light and electron microscopy showed that strain BH72 penetrated the rhizoplane preferentially in the zones of elongation and differentiation and colonized the root interi
or inter, and intracellularly. In addition to the root cortex, stelar tissue was also colonized; bacteria were found in the xylem. No evidence was obtained that Azoarcus spp. could reside in living plant cells; rather, plant cells were apparently destro
yed after bacteria had penetrated the cell wall. A common pathogenicity test on tobacco leaves provided no evidence that representative strains of Azoarcus spp. are phytopathogenic. Compared with the control, inoculation with strain BH72 significantly
promoted growth of rice seedlings. This effect was reversed when the plant medium was supplemented with malate (0.2 g/liter). N2 fixation was apparently not involved, because the same response was obtained with a nifK mutant of strain BH72, which has a
Nif, phenotype. Also, Western blot (immunoblot) analysis of protein extracts from rice seedlings gave no indication that nitrogenase was present. PCR and Western immunoblotting, using. primers specific for eubacteria and antibodies recognizing type-spe
cific antigens, respectively, indicated that strain BH72 could colonize rice plants systemically, probably mediated by longitudinal spreading through vessels.
Descriptors: kochia prostrata, bromus-tectorum, weed control, introduced species, plant-communities, sowing, seedlings, Idaho.
Descriptors: prosopis, introduced-species invasion, pods, seeds, weed control, feed-supplements, sheep, South Africa.
Descriptors: rust diseases, plant-pathogenic-fungi, surfaces, hyphae, haustoria, cell-membranes, host-plants, defense-mechanisms, active-transport, disease resistance, apoptosis, gene-expression, cell-wall-components, oxidation, host-parasite-rela
tionships, literature-reviews, uredinales, hypersensitive response.
Abstract: Rust fungi are obligately biotrophic plant parasites that obtain their nutrients from living host cells. The initiation of the two parasitic phases of these fungi generally requires topographic signals from the plant surface followed
, for the dikaryotic phase, by a successive sequence of signals to control further fungal development within the plant. During the fungal life cycle, three types of intracellular structures (invasion hyphae, M-, and D-haustoria) are formed and each may di
fferently affect the host membrane that surrounds it, as well as affecting other cellular components. Each intracellular structure also prevents non-specific plant defences triggered by fungal activities, possibly by interfering with the signalling system
rather than defence expression. In resistant host cultivars, cellular invasion triggers a rapid cell death (the hypersensitive response) that shares some features with developmentally programmed cell death in animal and plant tissues, and is controlled b
y parasite-specific resistance genes that resemble those that defend plants against other types of pathogens. Evidence from one system suggests that this response is specifically elicited by a fungal peptide and does not involve the oxidative burst typica
l of resistance expression in other plant-pathogen interactions. However, overall, few of the molecules involved in any of these plant-rust fungi interactions have been completely characterized and much is left to be discovered, particularly with respect
to how cellular susceptibility to rust fungi is conditioned.
Descriptors: aquatic-weeds, eichhornia crassipes, hydrilla verticillata, myriophyllum spicatum, weed control, mycoherbicides, plant-pathogenic-fungi.
Abstract: For maintaining a stable ecosystem, the presence of a diverse community of aquatic plants is preferred to the absence of plants or the existence of one or two dominant species at nuisance levels. The dominant species tend to be exoti
c and invasive, and are justifiable targets for microbial control. However, control with microorganisms has proven difficult primarily due to the effective survival strategies of these plants. Indeterminate, rapid growth and vegetative proliferation enabl
e these plants to escape disease pressure by compensating for disease losses. Only a few pathogens capable of curtailing these aggressive weeds have been found. There are technical and environmental limitations to applying inoculum and maintaining its eff
icacy in water. Demand for quick and complete weed elimination discourages the use of biocontrols. Lack of etiological and epidemiological knowledge of diseases on submerged plants and the potential for adverse side-effects from using large doses of inocu
lum add to the problems. Despite these limitations, progress has been made towards controlling waterhyacinth (Eichhornia crassipes) with Cercospora rodmanii. Attempts at microbial control of hydrilla (Hydrilla verticillata) and eurasian watermilfoil (Myri
ophyllum spicatum) are promising.
Descriptors: wild-plants, introduced species, environmental protection, pest control, California.
Descriptors: globodera, nicotiana tabacum, solanum ptycanthum, lycopersicon esculentum, nematode control, cultural control, population density, biological development roots, plant parasitic nematodes, susceptibility, pest-resistance, Connecticut,
crop-destruction, nematode trap crops, trap cropping.
Abstract: Tobacco, eastern black nightshade, and tomato were grown for 3 to 13 weeks to assess differences in invasion, development, and soil density of Globodera tabacum tabacum (tobacco cyst nematode) in field plots and microplots over three
seasons. Tobacco cyst nematodes invaded roots of resistant and susceptible tobacco, nightshade, and tomato. Nematode development was fastest in nightshade and slowest in tomato, and few adults developed in roots of nematode-resistant tobacco. Soil popula
tions of tobacco cyst nematodes were reduced up to 80% by destroying nightshade or susceptible tobacco grown for 3 to 6 weeks. Nematode populations were reduced up to 96% by destroying tomato or resistant tobacco grown for 3 to 6 weeks. Timing of crop des
truction was less critical with tomato and resistant tobacco, as nematode populations did not increase after 13 weeks of growth. These studies demonstrate that trap cropping, through crop destruction, can significantly reduce G. t. tabacum populations.
Descriptors: plant pathogenic fungi, biological control.
Abstract: The interactions between microsclerotia (ms) of the fungal plant pathogen Verticillium dahliae and the mycoparasite Talaromyces flavus were followed in soil and on agar medium. Germinability of ms, which had been incubated for 14 day
s in soil treated with 0.5% of a T. flavus-wheat bran preparation, decreased from 84% to 17%, as compared with 81% and 74% in untreated soil and in soil treated with a sterilized biocontrol preparation respectively. Germinability of ms which had been buri
ed in treated soil for 4 days decreased to 70%, all ms being parasitized by T. flavus. Upon transfer of the ms to untreated soil for 10 more days, germinability decreased further to 20%, indicating that T. flavus continued to parasitize sclerotia in the u
ntreated soil. Scanning electron micrographs showed heavy fungal colonization and typical T. flavus conidia on the surface of the ms buried in the treated soil, but not in control soils. Transmission electron micrographs of ms incubated with T. flavus on
agar revealed parasitism involving invasion of some host cells by means of small penetration pegs; the host cell walls were mainly lysed at their site of contact with the parasite hyphal tips. Further colonization of the ms cells occurred simultaneously w
ith the degradation of the invaded host cell contents, rather than the cell walls. Mycoparasitism of V. dahliae ms by T. flavus hyphae may be involved in the biological control of verticillium wilt disease.
Descriptors: pinus-thunbergii, bursaphelenchus-xylophilus, pine-needles, plant-diseases, plant parasitic nematodes, xylem, water, potential virulence, xylem, tracheids, parenchyma, hydraulic-conductivity, discoloration, exudates, oleoresins, plant
-tissues, Japan, pine-wilt-disease, hydraulic-conductance.
Abstract: The development process of pine wilt disease caused by Bursaphelenchus xylophilus (Steiner and Buhrer) Nickle, pine wood nematode, was studied ecophysiologically and histologically in relation to pathogenicity of B. xylophilus. Judgi
ng from the predawn xylem pressure potential of needles, the heat pulse velocity, and the soil water potential, the control Pinus thunbergii Parl., used for the study, was not water-stressed. Virulent B. xylophilus isolate can kill non-water-stressed pine
s. In virulent B. xylophilus isolate-inoculated pines, the predawn xylem pressure potential of needles abruptly decreased when the colour of 1-year-old needles changed to brown and then the water conducting function of the xylem was lost completely. Aviru
lent B. xylophilus isolate does not affect the needle colour and the xylem pressure potential of pines. Avirulent B. xylophilus isolate-inoculated pines, however, responded to nematode invasion by decreasing hydraulic conductance of stem and root xylems.
In addition, oleoresin exudation slightly decreased. The decreased hydraulic conductance results from embolism of tracheids caused by cavitation in the central part of the xylem. From histological observation, all of the parenchyma cells in virulent B. xy
lophilus isolate-inoculated pines died. In contrast, the parenchyma cells, degenerated in avirulent B. xylophilus isolate-inoculated pines, were limited in the embolized region of the xylem. The difference between the response of pine to the virulent B. x
ylophilus isolate invasion and that to avirulent B. xylophilus isolate invasion indicates that nematode-induced death of pine relates to the death of parenchyma cells, as well as the decrease in xylem hydraulic conductance.
Descriptors: weeds, introduced species, invasions, weed competition, weed control, vegetation management, nature conservation, biodiversity, plant communities, rangelands.
Descriptors: Weeds control, Congresses, Invasive plants, Control, Biological control.
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Last Updated: May 18, 1999