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1.
ABSTRACT The root-knot nematode Meloidogyne incognita is a major pathogen of a range of important crops. Currently, control is typically achieved by the use of nematicides. However, recent work suggests that manipulating the ability of roots to slough off border cells, which then act as a decoy to the nematode, can significantly decrease damage to the roots. We investigated the attractiveness of border cells to M. incognita and the response of the nematode to border cells in close proximity. We found very limited attraction, in that nematodes did not preferentially alter direction to move toward the border cells, but a large and significant increase in nematode speed was observed once they were in the immediate vicinity of border cells. We discuss the results in the context of physical and biological mechanisms in relation to the control of pathogenic nematodes.  相似文献   

2.
Many animals obtain reliable information about potential mates, including whether they are parasitised or not, mostly from olfactory cues in urine. Previous experiments with rodents have shown that females can detect parasites in males that are potentially transmissible during copulation, so that females can directly avoid infection by discriminating against parasitised males. Here, using choice tests, we examine whether female rats can distinguish males infected with the tapeworm Hymenolepis diminuta Rudolphi, 1819, a parasite with a complex life cycle and thus not directly transmissible among rats. Female rats tended to spend more time investigating the urine of non-parasitised males than that of parasitised males. The magnitude of the parasite burden in the infected males had no effect on the females' preference for the non-parasitised males. We also found that parasitised males had lover testosterone levels in their blood than non-parasitised males. These results suggest that females use cues in male urine reflecting either the presence of the parasite and/or lower testosterone levels to avoid parasitised males and possibly secure resistance genes for their offspring.  相似文献   

3.
The northeastern coast of the Caspian Sea is one of the youngest territories for plant colonization in Kazakhstan,and the flora of the most recent portion of this coastal area,the New Caspian marine plain,was chosen to study phytogeographical characteristics of plant species,especially as related to alien origin and invasive potential.Because of the recent formation of this flora,I expected that a large proportion of the species may be alien and invasive.After compiling a comprehensive species list from previous research,I identified the taxonomic,life form,ecological,and geographical structures of the flora.The area belongs to the northern type of deserts with continental climate and low annual precipitation.Taxonomic and life form structures show that the flora is specific to Central Asian deserts.Ecological structure demonstrates a high percentage of halophytes,which resulted from their adaptation to soil salinity and shallow ground waters that occur throughout the study area.Geoelements of the flora indicate allochtonous properties of the flora(i.e.species derived from areas outside the study area) with a low proportion of native(Caspian) plants.Alien species are estimated to comprise 12%-19% of the flora.Although some species have invasive features,severe arid environmental conditions and high salinity of soils and ground waters decrease invasive capacity of exotic plants.However,a threat of expansion of potentially invasive plants exists in the New Caspian marine plain due to the fast growth of anthropogenic habitats associated with recent oil developments.  相似文献   

4.
Precipitation, a natural feature of weather systems in the Earth, is vitally important for the environment of any region. Under global climate change condition, the characteristics of precipitation have changed as a consequence of enhanced global hydrological cycle. The source region of the Yellow River(SRYR), locating within the Qinghai-Tibet Plateau, is sensitive to the global climate change due to its complex orography and fragile ecosystem. To understand the precipitation characteristics and its impacts on the environment in the region, we studied the characteristics of rainy days and precipitation amount of different precipitation classes, such as light(0–5 and 5–10 mm), moderate(10–15, 15–20 and 20–25 mm) and heavy(≥25 mm) rains by analyzing the precipitation data of typical meteorological stations in the SRYR during the period 1961–2014, as well as the trends of persistent rainfall events and drought events. Results showed that annual average precipitation in this area had a non-significant(P>0.05) increasing trend, and 82.5% of the precipitation occurred from May to September. Rainy days of the 0–5 mm precipitation class significantly decreased, whereas the rainy days of 5–10, 10–15, and 20–25 mm precipitation classes increased and that of ≥25 mm precipitation class decreased insignificantly. The persistent rainfall events of 1-or 2-day and more than 2-day showed an increasing trend, with the 1-or 2-day events being more frequent. Meanwhile, the number of short drought periods(≤10 days) increased while long drought periods(>10 days) decreased. Since the 0–5 mm precipitation class had a huge impact on the grasslands productivity; the 5–10, 10–15, and 20–25 mm precipitation classes had positive effects on vegetation which rely on the deep soil water through moving nutrients and water into the root zone of these vegetation or through the plant-microbe interactions; the ≥25 mm precipitation class contributed to the floods; and more persistent rainfall events and fewer long drought events inferred positive effects on agriculture. Thus, these results indicate grassland degradation, less risk of floods, and the upgrading impact of climate change on agriculture. This study may provide scientific knowledge for policymakers to sustain the eco-environmental resources in the SYSR.  相似文献   

5.
To elucidate the early epidemic stages of septoria tritici blotch, especially the relationship between the onset of epidemics, the local availability of primary inoculum, and the presence of wheat debris, the early disease dynamics and airborne concentration in Zymoseptoria tritici ascospores were concomitantly assessed at a small spatiotemporal scale and over two years, using spore traps coupled with a qPCR assay. One plot, with the crop debris left, provided a local source of primary inoculum, while the other plot, without debris, lacked any. According to the assay's limits of detection, daily spore trap samples were classified as not detectable or not quantifiable, detectable, and quantifiable. The proportions of samples assigned to the different classes and numbers of spores in samples classified as quantifiable were significantly different between years, time periods (from November to March) and spore trap location (field with or without debris). The effect of year on the airborne ascospore concentration was high: 22 daily peaks with more than 230 ascospores m?3 day?1 were identified in the autumn of 2012/13, but none in the autumn of 2011/12. The local presence of wheat debris had no obvious effect on the amount of airborne ascospores or on the earliness of the two epidemics, especially in the year with high inoculum pressure (2012/13). These results suggest that the amount of primary airborne inoculum available in a wheat crop is not a limiting factor for the onset of an epidemic.  相似文献   

6.
Journal of Plant Diseases and Protection - We show here that the disodium salt of 2-acetyl-5-chloro-4- hydroxycarbonylmethylthiocyclopent-4-ene-1,3-dione (salt 2) inhibits tobacco mosaic virus...  相似文献   

7.
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8.
It is widely accepted that hydrogeochemistry of saline springs is extremely important to understand the water circulation and evolution of saline basins and to evaluate the potential of potassium-rich evaporites.The Kuqa Basin,located in the northern part of the Tarim Basin in Northwest China,is a saline basin regarded as the most potential potash-seeking area.However,the origin and water circulation processes of saline springs have yet to be fully characterized in this saline basin.In this study,a total of 30 saline spring samples and 11 river water samples were collected from the Qiulitage Structural Belt(QSB)of the Kuqa Basin.They were analyzed for major(K^+,Ca2^+,Na^+,Mg2^+,SO42-,Cl-and HCO3-)and trace(Sr2^+and Br-)ion concentrations,stable H-O-Sr isotopes and tritium concentrations in combination with previously published hydrogeochemical and isotopic(H-O)data in the same area.It is found that the water chemical type of saline springs in the study area belonged to the Na-Cl type,and that of river water belonged to the Ca-Mg-HCO3-SO4 type.The total dissolved solid(TDS)of saline springs in the QSB ranged from 117.77 to 314.92 g/L,reaching the brine level.On the basis of the general chemical compositions and the characteristics of the stable H-O-Sr isotopes of saline springs,we infer that those saline springs mainly originated from precipitation following river water recharging.In addition,we found that saline springs were not formed by evapo-concentration because it is unlikely that the high chloride concentration of saline springs resulted in evapo-concentration and high salinity.Therefore,we conclude that saline spring water may have experienced intense evapo-concentration before dissolving the salty minerals or after returning to the surface.The results show that the origin of salinity was mainly dominated by dissolving salty minerals due to the river water and/or precipitation that passed through the halite-rich stratum.Moreover,there are two possible origins of saline springs in the QSB:one is the infiltration of the meteoric water(river water),which then circulates deep into the earth,wherein it dissolves salty minerals,travels along the fault and returns to the surface;another is the mixture of formation water,or the mixture of seawater or marine evaporate sources and its subsequent discharge to the surface under fault conditions.Our findings provide new insight into the possible saltwater circulation and evolution of saline basins in the Tarim Basin.  相似文献   

9.
Barley yellow dwarf virus (BYDV)-PAV isolates from USA have been separated into two distinct clusters (Chay et al. (1996) Virology 219: 57–65; Chay et al. (1996) Phytopathology 86: 370–377). Following this finding we have shown that BYDV-PAV is divided into two groups cpA and cpB based on their coat protein gene sequence, and distinct host preferences (Mastari et al. (1998) Phytopathology 88: 818–821). We have sequenced the complete 3 half of the genomes of two lethal and two mild cpA isolates and compared them with those of several known PAV cpA isolates to assess variability and locate potential determinants of severity. Open reading frames (ORFs) 3, 4, 5, 6 and the 3 untranslated regions had different percent homologies between isolates: ORF5 (92–97%), ORF3 (88–98%) 3-translational enhancer (87–100%) ORF4 (85–99%), 3 untranslated region (72–97%) and ORF6 (61–99%). In contrast to the mild isolates, the field-lethal isolates (FHv1 and FHv2) fell into the same cluster, regardless of the genomic region analysed. The isolates FHv1 and FHv2 differed from mild isolates by eight amino acid substitutions in ORFs 3 and 4, and insertions in ORF5. Four amino acid substitutions in the 17-kDa protein encoded by ORF4 caused a change in local net charge in the field-lethal isolates. Two insertions of four amino acids were identified in the C-terminal half of ORF5 of the field-lethal isolates, but were not present systematically in all lethal isolates analysed. The potential relationships of these differences in predicted amino acid sequences to disease severity are discussed.  相似文献   

10.
Journal of Plant Diseases and Protection - The red palm mite Raoiella indica Hirst attacks coconut, banana and açai trees. In 2007, the mite was recorded for the first time in South America....  相似文献   

11.
Drought-prone grasslands provide a critical resource for the millions of people who are dependent on livestock for food security.However,this ecosystem is potentially vulnerable to climate change(e.g.,precipitation)and human activity(e.g.,grazing).Despite this,the influences of precipitation and grazing on ecological functions of drought-prone grasslands in the Tianshan Mountains remain relatively unexplored.Therefore,we conducted a systematic field investigation and a clipping experiment(simulating different intensities of grazing)in a drought-prone grassland on the northern slopes of the Tianshan Mountains in China to examine the influences of precipitation and grazing on aboveground biomass(AGB),soil volumetric water content(SVWC),and precipitation use efficiency(PUE)during the period of 2014–2017.We obtained the meteorological and SVWC data using an HL20 Bowen ratio system and a PR2 soil profile hydrometer,respectively.We found that AGB was clearly affected by both the amount and seasonal pattern of precipitation,and that PUE may be relatively low in years with either low or excessive precipitation.The PUE values were generally higher in the rapid growing season(April–July)than in the entire growing season(April–October).Overall,moderate grazing can promote plant growth under water stress conditions.The SVWC value was higher in the clipped plots than in the unclipped plots in the rapid growing season(April–July),but it was lower in the clipped plots than in the unclipped plots in the slow growing season(August–October).Our findings can enhance the understanding of the ecological effects of precipitation and grazing in drought-prone grasslands and provide data that will support the effective local grassland management.  相似文献   

12.
The fungal pathogen Stagonospora avenae f. sp. avenaria infects oat leaves, which contain the saponins avenacoside A and B. The avenacosides are glycosylated steroidal saponins that occur within oat leaves in a non-fungitoxic form and are converted upon damage or pathogen invasion to their antifungal form by a plant enzyme. It has previously been shown that oat-attacking isolates of S. avenae are able to hydrolyse the sugar chain at the C3 position of the avenacosides. This carbohydrate moiety is a branched chain that consists of one -{scL}-rhamnose and two or three -{scD}-glucose residues in avenacosides A and B, respectively. Removal of the -{scL}-rhamnose residue is sufficient to detoxify the avenacosides. This work describes the purification of the avenacoside-degrading -{scL}-rhamnosidase–and determination of peptide sequence from the protein which represents the first -{scL}-rhamnosidase thus characterised in a fungal plant pathogen.  相似文献   

13.
A total of 74 mass isolates of cucumber powdery mildew fungus (Podosphaera xanthii) were collected from commercial greenhouses with a history of boscalid use in Ibaraki Prefecture, Japan, and tested in a leaf disk assay for their sensitivity to boscalid. The mildew development of 40 of 74 isolates and five sensitive reference isolates on the disks was completely suppressed at 5 μg boscalid/ml. The minimum inhibitory concentrations (MIC) for the remaining 34 isolates were 50 μg/ml or higher, and 21 of these isolates also grew well at 500 μg/ml. Six single-spore isolates were resistant to boscalid with MIC values higher than 500 μg/ml; four of these were moderately resistant (MR), and two were very highly resistant (VHR) isolates. The growth of MR isolates was almost completely suppressed at 500 μg/ml, whereas two VHR isolates grew vigorously at 500 μg/ml. In foliar inoculation tests of potted cucumber plants, the efficacy of boscalid (500 μg/ml) against both MR and VHR isolates was very low. Partial DNA fragment of the iron–sulphur protein subunit (SdhB) gene of succinate dehydrogenase was PCR-amplified from five sensitive and five resistant isolates and directly sequenced, revealing that VHR isolates possess a substitution from a highly conserved histidine (CAT) to tyrosine (TAT) in a third cysteine-rich center of a putative SdhB, whereas MR isolates so far have not been found to have such substitution in SdhB.  相似文献   

14.
Slugs are major pests of many crops, including winter wheat, in temperate climates, yet current methods of control are often unreliable. The aim of this study is to investigate the potential for common legume species to act as an alternative source of food, or trap crop, for the most damaging agricultural pest species, the grey field slug, Deroceras reticulatum Müller, thereby reducing damage to the wheat crop. A series of three controlled-environment experiments were designed to assess this aim. Individual slugs were fed leaves of one of ten legume species together with winter wheat leaves for a 72-h period. A clear hierarchy of acceptability was shown, with red clover, lucerne, lupin and white clover showing significantly higher Acceptability Indices than the other six species tested. Red clover produced the greatest reduction in mean wheat consumption (78%) from day 1 to day 3. When species were fed individually, red clover was consumed in significantly greater quantities than any of the other treatments: 40% more than white clover and 56% more than wheat. Furthermore, when fed with red clover the amount of wheat consumed was some 50% less than when the latter was fed alone. The results indicate that legumes vary greatly in their acceptability to D. reticulatum and it is essential that a legume with a high Acceptability Index is chosen, which results in the least amount of wheat consumed.  相似文献   

15.
Yuling HU 《干旱区科学》2017,9(6):924-937
Based on daily precipitation data from 163 meteorological stations, this study investigated precipitation changes in the mid-latitudes of the Chinese mainland(MCM) during 1960–2014 using the climatic trend coefficient, least-squared regression analysis, and a non-parametric Mann-Kendall test.According to the effects of the East Asian summer monsoon on the MCM and the climatic trend coefficient of annual precipitation during 1960–2014, we divided the MCM into the western MCM and eastern MCM. The western MCM was further divided into the western MCM1 and western MCM2 in terms of the effects of the East Asian summer monsoon. The main results were as follows:(1) During the last four decades of the 20~(th) century, the area-averaged annual precipitation presented a significant increasing trend in the western MCM, but there was a slight decreasing trend in the eastern MCM, where a seesaw pattern was apparent. However, in the 21~(st) century, the area-averaged annual precipitation displayed a significant increasing trend in both the western and eastern MCM.(2) The trend in area-averaged seasonal precipitation during 1960–2014 in the western MCM was consistent with that in the eastern MCM in winter and spring. However, the trend in area-averaged summer precipitation during1960–2014 displayed a seesaw pattern between the western and eastern MCM.(3) On an annual basis,both the trend in rainstorms and heavy rain displayed a seesaw pattern between the western and eastern MCM.(4) The precipitation intensity in rainstorms, heavy rain, and moderate rain made a greater contribution to changes in the total precipitation than precipitation frequency. The results of this study will improve our understanding of the trends and differences in precipitation changes in different areas of the MCM. This is not only useful for the management and mitigation of flood disasters, but is also beneficial to the protection of water resources across the MCM.  相似文献   

16.
Dothistroma needle blight (DNB) emerged in France in the past 15 years. This disease is induced by two closely related species: Dothistroma septosporum and D. pini. Although both species are currently present in France, only D. septosporum was reported in the past. We investigated whether a recent arrival of D. pini in France could be a cause of the DNB emergence. We analyzed herbarium specimens of pine needles with DNB symptoms using polymerase chain reaction techniques to study the past frequency of D. pini in France. We also determined the present distribution within the country of D. septosporum and D. pini and compared it with the spatial pattern of DNB reported in the Département de la Santé des Forêts (DSF; French forest health monitoring agency) database. Although D. pini was detected on herbarium specimens from 1907 and 1965, it was not frequent in France in the past. Today, it is frequent, although not present throughout the country, being absent from the north and the east. There is no relationship between the D. pini distribution in France and the spatial pattern of DNB reported in the DSF database. Thus, the emergence of DNB in France cannot be explained by a recent arrival of D. pini.  相似文献   

17.
Qinghai Lake is the largest saline lake in China.The change in the lake volume is an indicator of the variation in water resources and their response to climate change on the Qinghai-Tibetan Plateau(QTP)in China.The present study quantitatively evaluated the effects of climate change and land use/cover change(LUCC)on the lake volume of the Qinghai Lake in China from 1958 to 2018,which is crucial for water resources management in the Qinghai Lake Basin.To explore the effects of climate change and LUCC on the Qinghai Lake volume,we analyzed the lake level observation data and multi-period land use/land cover(LULC)data by using an improved lake volume estimation method and Integrated Valuation of Ecosystem Services and Trade-offs(InVEST)model.Our results showed that the lake level decreased at the rate of 0.08 m/a from 1958 to 2004 and increased at the rate of 0.16 m/a from 2004 to 2018.The lake volume decreased by 105.40×108 m3 from 1958 to 2004,with the rate of 2.24×108 m3/a,whereas it increased by 74.02×108 m3 from 2004 to 2018,with the rate of 4.66×108 m3/a.Further,the climate of the Qinghai Lake Basin changed from warm-dry to warm-humid.From 1958 to 2018,the increase in precipitation and the decrease in evaporation controlled the change of the lake volume,which were the main climatic factors affecting the lake volume change.From 1977 to 2018,the measured water yield showed an"increase-decrease-increase"fluctuation in the Qinghai Lake Basin.The effects of climate change and LUCC on the measured water yield were obviously different.From 1977 to 2018,the contribution rate of LUCC was -0.76% and that of climate change was 100.76%;the corresponding rates were 8.57% and 91.43% from 1977 to 2004,respectively,and -4.25% and 104.25% from 2004 to 2018,respectively.Quantitative analysis of the effects and contribution rates of climate change and LUCC on the Qinghai Lake volume revealed the scientific significance of climate change and LUCC,as well as their individual and combined effects in the Qinghai Lake Basin and on the QTP.This study can contribute to the water resources management and regional sustainable development of the Qinghai Lake Basin.  相似文献   

18.
The ability of o,p′DDT to bind to the 8S moiety in the uterine cytosol or to interfere with the binding of 3H-estradiol-17β (3H-E2) to that binding component was investigated utilizing a 10–30% sucrose gradient sedimentation analysis. Attempts to demonstrate the binding of radiolabeled o,p′DDT to the 8S receptor in the mouse and rabbit were not successful, presumably due to the relatively low specific activity of the radiolabeled o,p′DDT, however, binding to the “nonspecific” 4S site(s) was detected. On the other hand, the addition of nonlabeled o,p′DDT inhibited the binding of 3H-E2 to the 8S receptor. Thus, o,p′DDT (2 μM) suppressed by 58% the binding of 3H-E2 (2 nM) in the 8S region in ovariectomized adult mice. Similarly, in immature rats three concentrations of o,p′DDT (16, 32, and 96 μM) inhibited by 39.5, 52.9, and 59.7% respectively, the binding of 3H-E2 (2.8 nM). Similar results were obtained with uterine preparations from mature rats. However, the suppression of binding of 3H-E2 in the 8S region resulted in an increased binding in the 3–4S region.A Scatchard plot analysis of the binding of 3H-E2 in the presence of o,p′DDT revealed the same number of binding sites as in the absence of o,p′DDT, indicating that o,p′DDT did not “destroy” the binding capacity. Also, this analysis revealed that o,p′DDT merely caused a decrease in the ratio of the bound to free E2, indicating that o,p′DDT binds to the receptor and thus interferes with E2 binding.In addition, our observations that the administration of o,p′DDT to immature female rats causes a marked increase in the levels of the uterine nuclear binding sites (nuclear estogren receptor) is a further indication that o,p′DDT acts as a typical estrogenic compound. However, whether o,p′DDT has antiestrogenic activity as well has not been established.  相似文献   

19.
Microclimates play important roles in controlling water budgets and water vapor transportation, as well as vegetation growth characteristics. In order to understand the differences in meteorological parameters under different vegetation cover (VC) and terrain conditions, wind velocity, air temperature, relative humidity (RH), photosynthetically active radiation (PAR), and solar radiation were simultaneously monitored on shifting, semi-fixed and fixed sandy lands, and an oasis. The air temperature and RH differences among the four landscape types were obvious in the period from May to October. It was found that the higher elevations of semi-fixed sandy land can influence PAR and solar radiation during sand-blowing weather. The differences of air temperature and RH among the four sites during the dust-storm and rainy days were not obvious, but their differences during sand-blowing weather were greater than during rainy weather and less than during floating-dust and sunny weather. The differences of PAR and solar radiation among the four landscape types were most obvious during the dust-storm event. During most of the weather types studied, significant positive correlations were found between wind velocity and temperature, PAR, and solar radiation, as well as between temperature and PAR, and solar radiation. Meanwhile, significant negative correlations were found between RH and wind velocity, temperature, PAR, and solar radiation. VC and topography were found to be the main factors influencing the changes in meteorological parameters between desert–oasis ecotone and oasis.  相似文献   

20.
ABSTRACT

The aim of this study was to evaluate whether foraging decisions of Acromyrmex lundi in the field are affected by the extract of Aristolochia argentina. A free choice test was performed using Rosa x hybrida leaves treated with the extract and control with acetone. Two leaves (treated and control) were presented on either side of a foraging trail. The percentage of removed material was recorded for 90 minutes of observation on two consecutive days. Dry weight and repellency index were calculated. Ant activity, the percentage of carried leaves and weight data were analyzed using a “t”-test for paired data, and a General Linear Mixed Model test was used to evaluate the different variables and their interactions. A. argentina extract (1%) did not affect the foraging activity of A. lundi, whereas the 5% dose caused significant differences in foraging activity as well as between the factors and the interactions. A repellency index of above 95% was obtained at the 5% dose. The extract of A. argentina could be considered for future management of this insect.  相似文献   

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