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1.  Infection Behavior and Overwintering Survival of Foliar Nematodes, Aphelenchoides fragariae, on Hosta 
Journal of nematology  2006;38(1):130-136.
We studied the pathogenicity and overwintering survival of the foliar nematode, Aphelenchoides fragariae, infecting Hosta spp. Nematodes applied to either lower or upper sides of noninjured and injured hosta leaves were able to infect and produce typical symptoms on nine cultivars. Leaves of only four cultivars (Borschi, Fragrant Blue, Patomic Pride, and Olive Bailey Langdon) showed no symptoms of nematode infection. The nematodes overwintered as juveniles and adults in soil, dry leaves, and dormant buds, but not in roots. Nematode winter survival was higher in dormant buds and soil from the polyhouse than in an open home garden. Of the nematodes found in the dormant buds, 35% to 79% were located between the first two outside layers of the buds. The nematodes tolerated 8 hr exposure to 40°C and −80°C in leaf tissues. Relative humidity influenced nematode migration from soil to leaves. The presence of nematodes only on the outer surface of foliage (leaves and petioles) confirmed the migration of A. fragariae on the surface of the plants. Of the total number of nematodes found on the foliage, 25% to 46% and 66% to 77% were alive at 90% and 100% relative humidity, respectively, suggesting that high moisture is required for the survival and upward movement of nematodes. We conclude that A. fragariae can overwinter in soil, infected dry leaves, and dormant buds and migrate in films of water on the outer surface of the plant during spring to leaves to initiate infection.
PMCID: PMC2586432  PMID: 19259438
Aphelenchoides fragariae; dormant buds; foliar nematode; Hosta spp.; overwintering; pathogenicity; temperature tolerance
2.  Effectiveness of a Hot Water Drench for the Control of Foliar Nematodes Aphelenchoides fragariae in Floriculture 
Journal of Nematology  2004;36(1):49-53.
Effectiveness of a hot water drench for the control of Aphelenchoides fragariae infesting hosta (Hosta sp.) and ferns (Matteuccia pensylvanica) was studied. Drenching with hot water at 70 °C and 90 °C in October reduced (P < 0.05) A. fragariae in the soil but not in the leaves relative to the control (25 °C) 300 days after treatment (DAT). Plants drenched with 90 °C water had lower numbers of nematode-infected leaves per plant than those treated with 25 °C and 70 °C water (P < 0.05). Hot water treatments had no adverse effect on the growth parameters of hosta. Boiling water (100 °C) applied once a month for 3 consecutive months (April, May, June) consistently reduced the number of infected leaves and the severity of infection relative to the control 150 DAT in hosta but not in ferns (P < 0.05). Boiling water (100 °C) caused a 67% reduction in A. fragariae population in hosta leaves, 50% in fern fronds, and 61% to 98% in the soil over the control 150 DAT. A boiling water drench had no effect on the fern growth but caused 49% and 22% reduction in the number and size of hosta leaves, respectively, over the control in 2002. We conclude that 90 °C water soil drench in the autumn or early spring could prove effective in managing foliar nematodes on hosta in nurseries and landscapes.
PMCID: PMC2620739  PMID: 19262787
Aphelenchoides fragariae; fern; foliar nematode; Hosta spp; hot water; Matteuccia pensylvanica
3.  Conventional and PCR Detection of Aphelenchoides fragariae in Diverse Ornamental Host Plant Species 
Journal of Nematology  2007;39(4):343-355.
A PCR-based diagnostic assay was developed for early detection and identification of Aphelenchoides fragariae directly in host plant tissues using the species-specific primers AFragFl and AFragRl that amplify a 169-bp fragment in the internal transcribed spacer (ITS1) region of ribosomal DNA. These species-specific primers did not amplify DNA from Aphelenchoides besseyi or Aphelenchoides ritzemabosi. The PCR assay was sensitive, detecting a single nematode in a background of plant tissue extract. The assay accurately detected A. fragariae in more than 100 naturally infected, ornamental plant samples collected in North Carolina nurseries, garden centers and landscapes, including 50 plant species not previously reported as hosts of Aphelenchoides spp. The detection sensitivity of the PCR-based assay was higher for infected yet asymptomatic plants when compared to the traditional, water extraction method for Aphelenchoides spp. detection. The utility of using NaOH extraction for rapid preparation of total DNA from plant samples infected with A. fragariae was demonstrated.
PMCID: PMC2586516  PMID: 19259510
Aphelenchoides fragariae; detection; diagnosis; foliar nematode; ITS1; method; NaOH; ornamental host; PCR; rDNA
4.  Refinement of Hot Water Treatment for Management of Aphelenchoides fragariae in Strawberry 
Journal of Nematology  1993;25(4S):795-799.
The effects of hot water treatments on a California population of the foliar nematode, Aphelenchoides fragariae, and on five strawberry cuttivars ('Chandler', 'Douglas', 'Fern', 'Pajaro', and 'Selva') were assessed in laboratory and greenhouse tests. Nematodes extracted from fern leaves were placed in water maintained at 44.4, 46.1,47.7, or 49.4 C for different time periods. Exposure periods of 15, 5, 4, and 2 minutes were required to produce 100% mortality at 44.4, 46.1, 47.7, and 49.4 C, respectively. In a water bath, 4 minutes were required for strawberry crowns initially at 25 C to equilibrate with temperatures ranging from 44.4-54.4 C. The maximum exposure periods that did not significantly reduce subsequent plant growth and flowering were 30, 15, and 10 minutes, at 44.4, 46.1, and 47.7 C, respectively. Survival of Selva was lower (P = 0.05) than for the other cultivars. Treatment at 49.4 C for 5 minutes significantly reduced plant growth and flowering of all cultivars. The minimum-maximum exposure periods that killed A. fragariae without damaging the cultivars tested were 20-30 minutes at 44.4 C, 10-15 at 46.1 C, or 8-10 at 47.7 C.
PMCID: PMC2619442  PMID: 19279842
Aphelenchoides fragariae; foliar nematode; Fragaria chiloensis; hot water treatment; nematode; strawberry
5.  Efficacy of Insecticides for Control of Aphelenchoides fragariae and Ditylenchus dipsaci in Flowering Perennial Ornamentals 
Journal of Nematology  1999;31(4S):644-649.
The effects of abamectin B1, diazinon, and methiocarb insecticides on Aphelenchoides fragariae and Ditylenchus dipsaci in Lamium maculatum, Phlox subulata, Rhododendron indicum, and Begonia × tuberhybrida were determined in a series of greenhouse experiments. Abamectin at 0.005 or 0.011 g a.i./liter (0.3 or 0.6 ml/liter Avid 0.15 EC), diazinon at 0.62 or 1.87 g a.i./liter (2.6 or 7.8 ml/liter KnoxOut GH), or methiocarb at 3.5 g a.i./liter (4.7 g/liter Mesurol) were applied in two to six weekly or biweekly applications to foliage until runoff. Diazinon and abamectin reduced both A. fragariae and D. dipsaci populations in Lamium and Phlox, especially after repeated applications. Diazinon was generally more effective than abamectin. While methiocarb reduced A. fragariae densities in Lamium, it was not as efficacious as diazinon or abamectin. Nematode populations varied widely between host plant species and over time. Management of high nematode populations was difficult, and none of the materials tested was effective against A. fragariae in azalea or begonia. Both abamectin and diazinon are currently registered for insect control in ornamentals and may be combined with cultural control tactics to manage foliar nematodes.
PMCID: PMC2620411  PMID: 19270930
abamectin; Aphelenchoides fragariae; avid; azalea; begonia; diazinon; Ditylenchus dipsaci; KnoxOut; Lamium maculatum; Mesurol; methiocarb; nematicide; nematode; Phlox subulata; stem and bulb nematode
6.  Induction of Glutaredoxin Expression in Response to Desiccation Stress in the Foliar Nematode Aphelenchoides fragariae 
Journal of Nematology  2012;44(4):370-376.
Desiccation tolerance plays an important role in the overwinter survival of the foliar nematode Aphelenchoides fragariae. Survival rates of A. fragariae were compared with those of the anhydrobiotic soil-dwelling nematode Aphelenchus avenae after desiccation (90% RH), cold (4°C) and osmotic (500 mM sucrose) stress treatments. A. fragariae formed aggregates during desiccation and showed higher survival rates than A. avenae under desiccation and osmotic stress. Analysis of transcripts with Illumina RNA-seq indicated that glutaredoxin and other antioxidant-related genes were up-regulated under desiccation stress. Quantitative RT-PCR demonstrated 2.8 fold and 1.3 fold up-regulation of a glutaredoxin gene under desiccated and osmotic stress, respectively, suggesting the participation of antioxidant mechanisms in desiccation tolerance of A. fragariae.
PMCID: PMC3592362  PMID: 23483835
Aphelenchoides fragariae; desiccation; cold stress; osmotic stress; glutaredoxin; survival rate
7.  Epidemiology and Control of Strawberry Bacterial Angular Leaf Spot Disease Caused by Xanthomonas fragariae 
The Plant Pathology Journal  2016;32(4):290-299.
Strawberry bacterial angular leaf spot (ALS) disease, caused by Xanthomonas fragariae has become increasingly problematic in the strawberry agro-industry. ALS causes small angular water-soaked lesions to develop on the abaxial leaf surface. Studies reported optimum temperature conditions for X. fragariae are 20°C and the pathogen suffers mortality above 32°C. However, at the nursery stage, disease symptoms have been observed under high temperature conditions. In the present study, results showed X. fragariae transmission was via infected maternal plants, precipitation, and sprinkler irrigation systems. Systemic infections were detected using X. fragariae specific primers 245A/B and 295A/B, where 300-bp and 615-bp were respectively amplified. During the nursery stage (from May to August), the pathogen was PCR detected only in maternal plants, but not in soil or irrigation water through the nursery stage. During the cultivation period, from September to March, the pathogen was detected in maternal plants, progeny, and soil, but not in water. Additionally, un-infected plants, when planted with infected plants were positive for X. fragariae via PCR at the late cultivation stage. Chemical control for X. fragariae with oxolinic acid showed 87% control effects against the disease during the nursery period, in contrast to validamycin-A, which exhibited increased efficacy against the disease during the cultivation stage (control effect 95%). To our knowledge, this is the first epidemiological study of X. fragariae in Korean strawberry fields.
doi:10.5423/PPJ.OA.01.2016.0007
PMCID: PMC4968639  PMID: 27493604
epidemiology; oxolinic acid; validamycin-A; Xanthomonas fragariae
8.  Interaction of Pratylenchus penetrans and Rhizoctonia fragariae in Strawberry Black Root Rot 
Journal of Nematology  2003;35(1):17-22.
A split-root technique was used to examine the interaction between Pratylenchus penetrans and the cortical root-rotting pathogen Rhizoctonia fragariae in strawberry black root rot. Plants inoculated with both pathogens on the same half of a split-root crown had greater levels of root rot than plants inoculated separately or with either pathogen alone. Isolation of R. fragariae from field-grown roots differed with root type and time of sampling. Fungal infection of structural roots was low until fruiting, whereas perennial root colonization was high. Isolation of R. fragariae from feeder roots was variable, but was greater from feeder roots on perennial than from structural roots. Isolation of the fungus was greater from structural roots with nematode lesions than from non-symptomatic roots. Rhizoctonia fragariae was a common resident on the sloughed cortex of healthy perennial roots. From this source, the fungus may infect additional roots. The direct effects of lesion nematode feeding and movement are cortical cell damage and death. Indirect effects include discoloration of the endodermis and early polyderm formation. Perhaps weakened or dying cells caused directly or indirectly by P. penetrans are more susceptible to R. fragariae, leading to increased disease.
PMCID: PMC2620604  PMID: 19265969
black root rot; Fragaria × ananassa; interaction; lesion nematode; Pratylenchus penetrans; Rhizoctonia fragariae; strawberry
9.  Long-Term Environmental Correlates of Invasion by Lantana camara (Verbenaceae) in a Seasonally Dry Tropical Forest 
PLoS ONE  2013;8(10):e76995.
Invasive species, local plant communities and invaded ecosystems change over space and time. Quantifying this change may lead to a better understanding of the ecology and the effective management of invasive species. We used data on density of the highly invasive shrub Lantana camara (lantana) for the period 1990–2008 from a 50 ha permanent plot in a seasonally dry tropical forest of Mudumalai in southern India. We used a cumulative link mixed-effects regression approach to model the transition of lantana from one qualitative density state to another as a function of biotic factors such as indicators of competition from local species (lantana itself, perennial grasses, invasive Chromolaena odorata, the native shrub Helicteres isora and basal area of native trees) and abiotic factors such as fire frequency, inter-annual variability of rainfall and relative soil moisture. The density of lantana increased substantially during the study period. Lantana density was negatively associated with the density of H. isora, positively associated with basal area of native trees, but not affected by the presence of grasses or other invasive species. In the absence of fire, lantana density increased with increasing rainfall. When fires occurred, transitions to higher densities occurred at low rainfall values. In drier regions, lantana changed from low to high density as rainfall increased while in wetter regions of the plot, lantana persisted in the dense category irrespective of rainfall. Lantana seems to effectively utilize resources distributed in space and time to its advantage, thus outcompeting local species and maintaining a population that is not yet self-limiting. High-risk areas and years could potentially be identified based on inferences from this study for facilitating management of lantana in tropical dry forests.
doi:10.1371/journal.pone.0076995
PMCID: PMC3805544  PMID: 24167555
10.  The effects of Brassica green manures on plant parasitic and free living nematodes used in combination with reduced rates of synthetic nematicides 
Journal of Nematology  2011;43(2):119-121.
Brassica plants once incorporated into soil as green manures have recently been shown to have biofumigant properties and have the potential of controlling plant-parasitic nematodes. In Washington State, plant-parasitic nematodes are successfully managed with synthetic nematicides. However, some of the synthetic nematicides became unavailable recently or their supply is limited leaving growers with few choices to control plant-parasitic nematodes. The objective of this project was to evaluate the effects of Brassica green manures on their own and in combination with reduced rates of synthetic nematicides on plant-parasitic nematodes and free living nematodes. In a greenhouse experiment and field trials in three seasons, Brassica green manures in combination with half the recommended rate of 1,3-dichloropropene (1,3-D, Telone) reduced root knot nematode, Meloidogyne chitwoodi to below detection levels, and reduced lesion nematodes, Pratylenchus penetrans and stubby root nematodes, Paratrichodorus allius, to below economic thresholds. The combination treatments did not affect the beneficial free-living nematode populations and the non-pathogenic Pseudomonas. The total cost of growing and soil-incorporating Brassica crops as green manures in combination with reduced rates of 1,3-D was approximately 35% lower than the present commercial costs for application for the full rate of this fumigant. Integrating conventional management practices with novel techniques fosters sustainability of production systems and can increase economic benefit to producers while reducing chemical input.
PMCID: PMC3380464  PMID: 22791922
Plant parasitic nematodes; free living nematodes; Brassicaceae green manures; Telone
11.  Effects of Pratylenchus penetrans and Rhizoctonia fragariae on Vigor and Yield of Strawberry 
Journal of Nematology  1999;31(4):418-423.
Microplot and small field-plot experiments were conducted to determine the effects of Pratylenchus penetrans on strawberry yield over several seasons and to evaluate the effects of nematode control on strawberry vigor and yield. Pratylenchus penetrans alone or in combination with the black root rot pathogen, Rhizoctonia fragariae, reduced strawberry yield in microplots over time. There were no differences in effects on yield among R. fragariae anastomosis groups A, G, or I. The interaction of the two pathogens appeared to be additive rather than synergistic. In field plots infested with P. penetrans alone, plant vigor and yield were increased by the application of carbofuran and fenamiphos nematicides. Nematode control was transitory, as P. penetrans populations were initially suppressed but were not different in samples taken 10 months after treatment. These data highlight the error in associating causality between plant damage and nematode populations based on a correlation of root disease with nematode diagnostic assays from severely diseased plants. These findings may help to explain how nematode numbers can sometimes be higher in healthy plants than in severely diseased plants that lack sufficient roots to maintain nematode populations. Because nematode populations from up to a year before harvest are better correlated with berry yield, preplant nematode diagnostic assays taken a year in advance of harvest may be superior in predicting damage to perennial strawberry yield.
PMCID: PMC2620392  PMID: 19270914
black root rot; disease complex; Fragaria × ananassa; lesion nematode; nematode; Pratylenchus penetrans; Rhizoctonia fragariae
12.  Strawberry Cultivars Vary in their Resistance to Northern Lesion Nematode 
Journal of Nematology  1998;30(4S):577-580.
The genetic diversity of commercial cultivars of strawberry Fragaria x ananassa from various parentages, as expressed by their resistance to the northem lesion nematode Pratylenchus penetrans, was evaluated in nematode-infested field plots for two growing seasons. Data taken for each plant in each season included soil nematode Pi and Pf, end-of-season nematode numbers in each entire root system, and end-of-season fresh and dry top weight and whole root system weight. Resistance was estimated using an index of the nematode load on the plant: Nematode load = {n(root) + (200 × n[soil])}/{root dry weight} where n (root) = number of nematodes in the root, n [soil] = number of nematodes in 50 g of nonfumigated soil, and 200 is a multiplier to convert the soil nematode count to a 10-kg basis. Nineteen strawberry cultivars varied in their resistance to the northern lesion nematode, from a mean load of 382 nematodes/plant for Pajaro to 1,818 nematodes/plant for Veestar. This variability could be related to the original family groupings, with the most resistant cultivars related to Lassen and the least resistant to Sparkle x Valentine.
PMCID: PMC2620340  PMID: 19274249
Fragaria x ananassa; nematode; nematode load; northern lesion nematode; Pratylenchus penetrans; resistance; strawberry; tolerance
13.  Foliar Sprays with Steinernema carpocapsae against Early-season Apple Pests 
Journal of Nematology  1998;30(4S):599-606.
Persistence and field efficacy of the entomopathogenic nematode Steinernema carpocapsae A11 strain applied by foliar sprays were evaluated against the apple sawfly Hoplocampa testudinea and the plum curculio Conotrachelus nenuphar, two early-season pests in Quebec apple orchards. From 1992 to 1995, bioassays with Galleria mellonella larvae were conducted to assess the persistence of S. carpocapsae on leaves, flower clusters, and twigs up to 4 days after evening application. S. carpocapsae juveniles remained infective on apple leaves 24, 42, 98, and 24 hours after application in 1992, 1993, 1994, and 1995, respectively. In bioassays, the percentage of G. mellonella mortality was consistently higher on leaves (average = 84%), intermediate on flower clusters (73%), and lower on twigs (43%) for all application dates. In 1992 and 1993, single nematode sprays applied every 2 to 3 days from early May to mid-June on apple tree limbs reduced primary damage caused by H. testudinea by 98% and 100%, respectively, but none of the treatments was effective in 1994. In 1993 and 1994, multiple border-row sprays were applied against C. nenuphar adults with a commercial hand-gun applicator in an insecticide-free orchard. At harvest, plum curculio damage in the nematode-treated orchard reached 5% and 55% in 1993 and 1994, respectively, as compared to 80% and 85% in an adjacent insecticide-free orchard. In a second experiment performed in 1994, multiple broadcast sprays with a commercial orchard sprayer caused no significant effect on plum curculio damage (nematode = 28%; control = 31%). Although some efficacy of canopy sprays of nematodes was detected against early-season apple pests, the inconsistent results and high application costs preclude their use as a sole control tactic against these pests in commercial apple orchards.
PMCID: PMC2620325  PMID: 19274253
apple; biological control; Coleoptera; Conotrachelus nenuphar; Curculionidae; European apple sawfly; field persistence; foliar application; Hoplocampa testudinea; Hymenoptera; nematode; plum curculio; Steinernema carpocapsae; Tenthredinidae
14.  Infection of Narcissus Roots by Aphelenchoides subtenuis 
Journal of Nematology  1993;25(3):476-479.
The widespread destruction of commercially grown bulbs of Narcissus tazetta papyraceus (Paper White) has been reported in Israel. This phenomenon is usually characterized by a premature yellowing of the foliage, accompanied by root rot and dark, sunken basal plates. This study confirmed thatAphelenchoides subtenuis is the main cause of the basal plate disease of Narcissus. In contrast to other Aphelenchoides species, which feed on stems or leaves, A. subtenuis penetrates Narcissus roots. In our experiments, in winter (6 to 8 weeks after penetration), nematodes laid their eggs in the root parenchymal cells without inducing obvious symptoms on foliage or roots. Toward spring, juveniles became numerous throughout the parenchymal cells of the root cortex. Consequently, the root system collapsed rapidly, at the usual peak of bulb and foliage production. Bulbs of infected plants were small and weighed less than those of uninfected plants, and foliage became necrotic prematurely. At that time, in field conditions, secondary elements like Fusarium penetrate the bulb and cause it to rot, given this syndrome the common name of basal plate disease. To our knowledge, this is the first report of an Aphelenchoides species as a root pathogen.
PMCID: PMC2619407  PMID: 19279798
Aphelenchoides subtenuis; Fusarium; Narcissus; nematode; pathogenicity
15.  Comparison of Pratylenchus penetrans Infection and Maladera castanea Feeding on Strawberry Root Rot 
Journal of Nematology  2005;37(2):131-135.
The interaction of lesion nematodes, black root rot disease caused by Rhizoctonia fragariae, and root damage caused by feeding of the scarab larva, Maladera castanea, was determined in greenhouse studies. Averaged over all experiments after 12 weeks, root weight was reduced 13% by R. fragariae and 20% by M. castanea. The percentage of the root system affected by root rot was increased by inoculation with either R. fragariae (35% more disease) or P. penetrans (50% more disease) but was unaffected by M. castanea. Rhizoctonia fragariae was isolated from 9.2% of the root segments from plants not inoculated with R. fragariae. The percentage of R. fragariae-infected root segments was increased 3.6-fold by inoculation with R. fragariae on rye seeds. The presence of P. penetrans also increased R. fragariae root infection. The type of injury to root systems was important in determining whether roots were invaded by R. fragariae and increased the severity of black root rot. Pratylenchus penetrans increased R. fragariae infection and the severity of black root rot. Traumatic cutting action by Asiatic garden beetle did not increase root infection or root disease by R. fragariae. Both insects and diseases need to be managed to extend the productive life of perennial strawberry plantings.
PMCID: PMC2620957  PMID: 19262852
asiatic garden beetle; black root rot; Fragaria × ananassa; interaction; lesion nematode; Maladera castanea; Pratylenchus penetrans; Rhizoctonia fragariae; scarab; strawberry
16.  Effect of RotyIenchulus reniformis on Reflectance of Cotton Plant Leaves 
Journal of Nematology  1975;7(4):368-374.
Differences between light reflectance from leaves of cotton (Gossypiurn hirsutum) plants grown with a low- or no-nematode (Rotylenchulus reniformis) population (nonstressed), and from leaves grown with a high nematode population (stressed) were measured in field and greenhouse experiments. Reflectance was measured spectrophotometrically in the laboratory on single leaves and spectroradiometrically in the field on plant canopies. Nematode-stressed cotton plants were stunted with fewer, smaller, and darker-green leaves than nonstressed plants. Over the 0.5- to 2.5-/μm waveband, stressed leaves had lower reflectance than nonstressed leaves of the same chronological age for both field- and greenhouse-grown plants. Reflectance differences between stressed and nonstressed leaves in the visible (0.5 to 0.75 μm), near-infrared (0.75 to 1.35 μm) and infrared water absorption (1.35 to 2.5 μm) regions were primarily caused by differences in leaf chlorophyll concentration, mesophyll structure, and water content, respectively. Results indicate the potential for remotely sensing nematode-infested plants to distinguish them from normal plants.
PMCID: PMC2620127  PMID: 19308184
stressed and nonstressed leaves; remote sensing; chlorophyll content
17.  Climate Warming May Facilitate Invasion of the Exotic Shrub Lantana camara 
PLoS ONE  2014;9(9):e105500.
Plant species show different responses to the elevated temperatures that are resulting from global climate change, depending on their ecological and physiological characteristics. The highly invasive shrub Lantana camara occurs between the latitudes of 35°N and 35°S. According to current and future climate scenarios predicted by the CLIMEX model, climatically suitable areas for L. camara are projected to contract globally, despite expansions in some areas. The objective of this study was to test those predictions, using a pot experiment in which branch cuttings were grown at three different temperatures (22°C, 26°C and 30°C). We hypothesized that warming would facilitate the invasiveness of L. camara. In response to rising temperatures, the total biomass of L. camara did increase. Plants allocated more biomass to stems and enlarged their leaves more at 26°C and 30°C, which promoted light capture and assimilation. They did not appear to be stressed by higher temperatures, in fact photosynthesis and assimilation were enhanced. Using lettuce (Lactuca sativa) as a receptor plant in a bioassay experiment, we also tested the phytotoxicity of L. camara leachate at different temperatures. All aqueous extracts from fresh leaves significantly inhibited the germination and seedling growth of lettuce, and the allelopathic effects became stronger with increasing temperature. Our results provide key evidence that elevated temperature led to significant increases in growth along with physiological and allelopathic effects, which together indicate that global warming facilitates the invasion of L. camara.
doi:10.1371/journal.pone.0105500
PMCID: PMC4153567  PMID: 25184224
18.  The Influence of Pratylenchus penetrans on the Incidence and Severity of Verticillium Wilt of Potato 
Journal of Nematology  1978;10(1):95-99.
The influence of Pratylenchus penetrans on the incidence and severity of Verticillium wilt was examined in the potato cultivars 'Kennebec', 'Katahdin', and 'Abnaki'. Single-stem plants were grown in soil maintained at a temperature of 22 ± 1 C. Axenically cultured nematodes were suspended in water and introduced to the soil, at a rate of ca 5,000/25.4-cm pot, through holes made around each stem. Ten days after infestation with nematodes, conidial suspensions of Verticillium albo-atrum were introduced into the soil at a rate of ca 1,000,000/pot. Among Katahdin plants, the severity of foliar symptoms was increased in the presence of both pathogens 2 and 3 weeks after soil intestation. During the remaining 5 weeks, severity of foliar symptoms was not different between plants infected by both pathogens and those infected by Verticillium alone. Within the wilt-susceptible cultivar Kennebec and the resistant eultivar Abnaki, no effects on foliar symptom severity were observed. When plant heights, shoot weights, and tuber yields were analyzed, a Pratylenchus-Verticillium interaction was not evident within any of the cultivars tested. Nematode populations in roots and rhizosphere were suppressed in Kennebec and Katahdin plants in the presence of Verticillium.
PMCID: PMC2617862  PMID: 19305819
Lesion nematode; nematode-fungus interaction; Solanum tuberosum; Verticillium albo-atrum
19.  Seasonal Fluctuations of Soil and Tissue Populations of Ditylenchus dipsaci and Aphelenchoides ritzemabosi in Alfalfa 
Journal of Nematology  1999;31(1):27-36.
Population dynamics of A. ritzemabosi and D. dipsaci were studied in two alfalfa fields in Wyoming. Symptomatic stem-bud tissue and root-zone soil from alfalfa plants exhibiting symptoms of D. dipsaci infection were collected at intervals of 3 to 4 weeks. Both nematodes were extracted from stem tissue with the Baermann funnel method and from soil with the sieving and Baermann funnel method. Soil moisture and soil temperature at 5 cm accounted for 64.8% and 61.0%, respectively, of the variability in numbers of both nematodes in soil at the Big Horn field. Also at the Big Horn field, A. ritzemabosi was found in soil on only three of the 14 collection dates, whereas D. dipsaci was found in soil on 12 dates. Aphelenchoides ritzemabosi was found in stem tissue samples on 9 of the 14 sampling dates whereas D. dipsaci was found on all dates. Populations of both nematodes in stem tissue peaked in October, and soil populations of both peaked in January, when soil moisture was greatest. Numbers of D. dipsaci in stem tissue were related to mean air temperature 3 weeks prior to tissue collection, while none of the climatic factors measured were associated with numbers of A. ritzemabosi. At the Dayton field, soil moisture plus soil temperature at 5 cm accounted for 98.2% and 91.4% of the variability in the soil populations of A. ritzemabosi and D. dipsaci, respectively. Aphelenchoides ritzemabosi was extracted from soil at two of the five collection dates, compared to extraction of D. dipsaci at three dates. Aphelenchoides ritzemabosi was collected from stem tissue at six of the seven sampling dates while D. dipsaci was found at all sampling dates. The only environmental factor that was associated with an increase in the numbers of both nematodes in alfalfa stem tissue was total precipitation 1 week prior to sampling, and this occurred only at the Dayton field. Numbers of A. ritzemabosi in stem tissue appeared to be not affected by any of the environmental factors studied, while numbers of D. dipsaci in stem tissue were associated with cumulative monthly precipitation, snow cover at time of sampling, and the mean weekly temperature 3 weeks prior to sampling. Harvesting alfalfa reduced the numbers of A. ritzemabosi at the Big Horn field and both nematodes at the Dayton field.
PMCID: PMC2620350  PMID: 19270872
alfalfa; alfalfa stem nematode; Aphelenchoides ritzemabosi; chrysanthemum foliar nematode; climate; distribution; Ditylenchus dipsaci; Medicago sativa; nematode; sampling; seasonal fluctuations
20.  Distribution in the Western United States on Alfalfa and Cultivar Reaction to Mixed Populations of Ditylenchus dipsaci and Aphelenchoides ritzemabosi 
Journal of Nematology  1994;26(4S):705-719.
Ditylenchus dipsaci and Aphelenchoides ritzemabosi were extracted from 29 of 40 plant samples (72.5%) collected from Arizona, California, Colorado, Idaho, Montana, Oregon, South Dakota, Utah, Washington, and Wyoming. Percentages of A. ritzemabosi in tissue of the 29 samples ranged from 1.77 to 67.82%. Only Ditylenchus dipsaci was recovered from the remaining 11 samples. All of the 16 fields sampled in Wyoming contained both nematodes. Percentages of A. ritzemabosi in the Wyoming samples ranged from 0.7-30.0%, with an overall mean of 10.3%. Individual plants collected from a field in Big Horn, Wyoming, all contained both nematodes. Percentages of A. ritzemabosi in tissue ranged from 5-70%. Alfalfa stem nematode symptomatic plants in 17 of 18 alfalfa cultivars collected from a screening nursery in California contained both nematodes, of which 10-94% were A. ritzemabosi. Only one cultivar had D. dipsaci only, and no entries had A. ritzemabosi only. Under environmentally controlled conditions, A. ritzemabosi reproduced in all nine alfalfa cultivars tested at 6 weeks of age with a mean reproductive factor (final population/initial population) of 4.1. There were more (P ≤ 0.05) A. ritzemabosi in stem and bud tissue of the susceptible cultivars at harvest than in the resistant cultivars with combined cultivar means of 238, 42, 78, and 4 A. ritzemabosi/g tissue for the susceptible, moderately resistant, resistant, and highly resistant cultivars, respectively. Percentage A. ritzemabosi in tissues decreased over time in seedlings but increased in older plants.
PMCID: PMC2619569  PMID: 19279952
alfalfa stem nematode; Aphelenchoides ritzemabosi; chrysanthemum nematode; cultivar reaction; Ditylenchus dipsaci; geographic distribution; mixed population; nematode; red clover; Sonchus sp.; sow thistle; Trifolium pratense
21.  Effect of Agricultural Management on Nematode Communities in a Mediterranean Agroecosystem 
Journal of Nematology  2001;33(4):208-213.
The effects of agricultural management on the soil nematode community were investigated in a field study at depths of 0 to 10 cm and 10 to 20 cm during a peanut (Arachis hypogaea) growing season in Israel. Nineteen nematode families and 23 genera were observed. Rhabditidae, Cephalobus, Eucephalobus, Aphelenchus, Aphelenchoides, Tetylenchus, Tylenchus, Dorylaimus, and Discolaimus were the dominant family and genera. Ecological measures of soil nematode community structure, diversity, and maturity indices were assessed and compared between the managed (by fertilization, irrigation, and pesticide application) and unmanaged fields. The total number of nematodes at a 10-cm depth during peanut-sowing, mid-season, and harvest periods was higher in the treated (managed) plot than in the control (unmanaged) plot. Bacterivores and fungivores were the most abundant trophic groups in both plots and both depths. The relative abundance of each group averaged 60.8 to 67.3% and 11.5 to 19.6% of the nematode community, respectively. Plant parasites and omnivores-predators at the 0 to 10-cm depth were much less abundant than any other two groups in our experimental plots. During the growing season, except the harvest period, populations of plant parasites and omnivores-predators at the 10 to 20-cm depth were lower in the treated plot than in the control plot. Maturity index (MI), plant-parasite index (PPI), and ratio of fungivores and bacterivores to plant parasites (WI) were found to be more sensitive indicators than other ecological indices for assessing the response of nematode communities to agricultural management in an Israeli agroecosystem.
PMCID: PMC2620504  PMID: 19265883
agricultural management; agroecosystem; diversity; maturity index; nematode communities; peanut
22.  Bulk and Rhizosphere Soil Bacterial Communities Studied by Denaturing Gradient Gel Electrophoresis: Plant-Dependent Enrichment and Seasonal Shifts Revealed 
Applied and Environmental Microbiology  2001;67(10):4742-4751.
The bacterial rhizosphere communities of three host plants of the pathogenic fungus Verticillium dahliae, field-grown strawberry (Fragaria ananassa Duch.), oilseed rape (Brassica napus L.), and potato (Solanum tuberosum L.), were analyzed. We aimed to determine the degree to which the rhizosphere effect is plant dependent and whether this effect would be increased by growing the same crops in two consecutive years. Rhizosphere or soil samples were taken five times over the vegetation periods. To allow a cultivation-independent analysis, total community DNA was extracted from the microbial pellet recovered from root or soil samples. 16S rDNA fragments amplified by PCR from soil or rhizosphere bacterium DNA were analyzed by denaturing gradient gel electrophoresis (DGGE). The DGGE fingerprints showed plant-dependent shifts in the relative abundance of bacterial populations in the rhizosphere which became more pronounced in the second year. DGGE patterns of oilseed rape and potato rhizosphere communities were more similar to each other than to the strawberry patterns. In both years seasonal shifts in the abundance and composition of the bacterial rhizosphere populations were observed. Independent of the plant species, the patterns of the first sampling times for both years were characterized by the absence of some of the bands which became dominant at the following sampling times. Bacillus megaterium and Arthrobacter sp. were found as predominant populations in bulk soils. Sequencing of dominant bands excised from the rhizosphere patterns revealed that 6 out of 10 bands resembled gram-positive bacteria. Nocardia populations were identified as strawberry-specific bands.
doi:10.1128/AEM.67.10.4742-4751.2001
PMCID: PMC93227  PMID: 11571180
23.  Morphological and Molecular Characterization of Two Aphelenchoides Endophytic in Poplar Leaves 
Journal of Nematology  2016;48(1):28-33.
During a long-term, large network study of the ecology of plant endophytes in native habitats, various nematodes have been found. Two poplar species, Populus angustifolia (narrowleaf cottonwood) and Populus trichocarpa (black cottonwood), are important ecological and genomic models now used in ongoing plant–pathogen–endophyte interaction studies. In this study, two different aphelenchid nematodes within surface-sterilized healthy leaves of these two Populus spp. in northwestern North America were discovered. Nematodes were identified and characterized microscopically and molecularly with 28S ribosomal RNA (rRNA) and 18S rRNA molecular markers. From P. angustifolia, Aphelenchoides saprophilus was inferred to be closest to another population of A. saprophilus among sequenced taxa in the 18S tree. From P. trichocarpa, Laimaphelenchus heidelbergi had a 28S sequence only 1 bp different from that of a Portuguese population, and 1 bp different from the original Australian type population. The 28S and 18S rRNA trees of Aphelenchoides and Laimaphelenchus species indicated L. heidelbergi failed to cluster with three other Laimaphelenchus species, including the type species of the genus. Therefore, we support a conservative definition of the genus Laimaphelenchus, and consider these populations to belong to Aphelenchoides, amended as Aphelenchoides heidelbergi n. comb. This is the first report of these nematode species from within aboveground leaves. The presence of these fungal-feeding nematodes can affect the balance of endophytic fungi, which are important determinants of plant health.
PMCID: PMC4859615  PMID: 27168650
nematode ecology; phylogeny; ribosomal DNA; systematics; taxonomy
24.  Repellent Plants Provide Affordable Natural Screening to Prevent Mosquito House Entry in Tropical Rural Settings—Results from a Pilot Efficacy Study 
PLoS ONE  2011;6(10):e25927.
Sustained malaria control is underway using a combination of vector control, prompt diagnosis and treatment of malaria cases. Progress is excellent, but for long-term control, low-cost, sustainable tools that supplement existing control programs are needed. Conventional vector control tools such as indoor residual spraying and house screening are highly effective, but difficult to deliver in rural areas. Therefore, an additional means of reducing mosquito house entry was evaluated: the screening of mosquito house entry points by planting the tall and densely foliated repellent plant Lantana camara L. around houses. A pilot efficacy study was performed in Kagera Region, Tanzania in an area of high seasonal malaria transmission, where consenting families within the study village planted L. camara (Lantana) around their homes and were responsible for maintaining the plants. Questionnaire data on house design, socioeconomic status, malaria prevention knowledge, attitude and practices was collected from 231 houses with Lantana planted around them 90 houses without repellent plants. Mosquitoes were collected using CDC Light Traps between September 2008 and July 2009. Data were analysed with generalised negative binomial regression, controlling for the effect of sampling period. Indoor catches of mosquitoes in houses with Lantana were compared using the Incidence Rate Ratio (IRR) relative to houses without plants in an adjusted analysis. There were 56% fewer Anopheles gambiae s.s. (IRR 0.44, 95% CI 0.28–0.68, p<0.0001); 83% fewer Anopheles funestus s.s. (IRR 0.17, 95% CI 0.09–0.32, p<0.0001), and 50% fewer mosquitoes of any kind (IRR 0.50, 95% CI 0.38–0.67, p<0.0001) in houses with Lantana relative to controls. House screening using Lantana reduced indoor densities of malaria vectors and nuisance mosquitoes with broad community acceptance. Providing sufficient plants for one home costs US $1.50 including maintenance and labour costs, (30 cents per person). L. camara mode of action and suitability for mosquito control is discussed.
doi:10.1371/journal.pone.0025927
PMCID: PMC3192125  PMID: 22022471
25.  Belonolaimus longicaudatus: An Emerging Pathogen of Peanut in Florida 
Journal of Nematology  2015;47(2):87-96.
Sting nematode (Belonolaimus longicaudatus) is an economically important ectoparasitic nematode that is highly pathogenic on a wide range of agricultural crops in sandy soils of the southeastern United States. Although this species is commonly found in Florida in hardwood forests and as a soilborne pathogen on turfgrasses and numerous agronomic and horticultural crops, it has not been reported infecting peanut. In the summers of 2012 and 2013, sting nematode was found infecting three different peanut cultivars being grown on two separate peanut farms in Levy County, FL. The damage consisted of large irregular patches of stunted, chlorotic plants at both farms. The root systems were severely abbreviated and there were numerous punctate-like isolated lesions observed on pegs and pods of infected plants. Sting nematodes were extracted from soil collected around the roots of diseased peanut over the course of the peanut season at both farm sites. Peanut yield from one of these nematode-infested sites was 64% less than that observed in areas free from sting nematodes. The morphological characters of the nematode populations in these fields were congruous with those of the original and other published descriptions of B. longicaudatus. Moreover, the molecular analyses based on the sequences of D2/D3 expansion fragments of 28S rRNA and internal transcribed spacer (ITS) rRNA genes from the nematodes further collaborates the identification of the sting nematode isolates as B. longicaudatus. The sequences were deposited in GenBank (accession no. KF963097, KF963098 for ITS, and KF96399, KF963100 for D2-D3). The results of the phylogenetic analysis using the sequences of these isolates from peanut compared with those of other isolates from Florida suggests that the sting nematode from both peanut farms are genetically close to B. longicaudatus populations occurring in the state. Peanut plants inoculated with both nematode isolates showed punctate-like isolated lesions on pods and pegs, and an abbreviation of their root systems, whereas those symptoms were not observed on noninoculated peanut plants. To our knowledge, this is the first report of large-scale field damage caused by sting nematode infecting peanut grown under field conditions in Florida.
PMCID: PMC4492293  PMID: 26170470
Arachis hypogaea; Belonolaimus longicaudatus; emerging pathogen; morphology; pathogenicity; peanut; phylogenetics; sting nematode

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