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1.
Factors affecting the production of conidia of Peronosclerospora sorghi , causing sorghum downy mildew (SDM), were investigated during 1993 and 1994 in Zimbabwe. In the field conidia were detected on nights when the minimum temperature was in the range 10–19°C. On 73% of nights when conidia were detected rain had fallen within the previous 72 h and on 64% of nights wind speed was < 2.0 m s−1 . The time period over which conidia were detected was 2–9 h. Using incubated leaf material, conidia were produced in the temperature range 10–26°C. Local lesions and systemically infected leaf material produced 2.4–5.7 × 103 conidia per cm2 . Under controlled conditions conidia were released from conidiophores for 2.5 h after maturation and were shown to be well adapted to wind dispersal, having a settling velocity of 1.5 × 10−4 m s−1 . Conditions that are suitable for conidia production occur in Zimbabwe and other semi-arid regions of southern Africa during the cropping season. 相似文献
2.
A wind tunnel was designed to study the effect of wind, relative humidity, leaf movement and colony age on dispersal of conidia of Uncinula necator . Wind speed as low as 2.3 m s−1 instantaneously triggered dispersal of conidia from fixed leaf discs of 18-day-old infections. Conidia were observed on sporulating leaf discs even after exposure to 17 m s−1 wind. The fraction of conidia dispersed at a given wind speed increased with colony age from 12 to 24 days. Conidia of 27-day-old colonies were less easily dispersed. No gradient of maturation of conidia along the conidial chain was observed, suggesting that even newly formed conidia were able to germinate after dispersal. Germination of dispersed conidia decreased slightly with greater colony age. Both wind and simulated rain drops caused dispersal of conidia from infected leaves. Leaf movement at wind speed of 3.5–4 m s−1 increased dispersal, and the first impact of three simulated raindrops caused release of 53% of the total conidia dispersed. Relative humidity had no effect on dispersal of conidia at different wind speeds. 相似文献
3.
A study was carried out to demonstrate that Rice yellow mottle virus (RYMV), a virus known to be transmitted by beetles, can spread between rice plants by direct leaf contact caused by wind. Almost all healthy plants surrounding an infected plant became infected when exposed to a fan blowing for 15 min at a distance of 50 cm. Spread of RYMV by plant contact, mediated by wind, was also demonstrated in field experiments, the extent of spread depending on plant density. Infection was almost 10 times higher in plots with a density of 33 plants m−2 than in plots with 16 plants m−2 . Less spread was observed in plots protected by 1·5 m high windscreens. It is suggested that wind-mediated spread of RYMV may result from abrasive contact between leaves of plants. 相似文献
4.
Development of sorghum downy mildew, incited by Peronoscleospora sorghi (Weston and Uppal) C.G. Shaw, on maize, sorghum and Johnson grass was investigated at two locations in Uganda during three seasons (1994 and 1995). More sorghum downy mildew developed on the Johnson grass and sorghum than on the maize at all locations and in all seasons. No significant differences were observed in sporulation of P. soghi on the three hosts. Leaf shredding occurred on the three hosts but was the least on maize. Cross-inoculation with both conidia and oospores was achieved on the three hosts. Since the fungal population formed oospores and sporulated readily on the three hosts, which is typical of the sorghum strain, the disease in Uganda is attributed to the sorghum strain. 相似文献
5.
Application of Pythium oligandrum to a soil-based compost as a mycelial suspension (5 × 102 CFU g−1 of dry compost) and oospore alginate pellets (105 oospores/g of dry compost) controlled pre- and postemergence damping-off of sugar beet caused by Pythium ultimum to a level similar to metalaxyl seed treatment. Oospore seed treatments and aqueous suspensions of oospores applied to compost failed to control disease. Problems in the use of P. oligandrum oospore inocula for the control of damping-off were highlighted. It was shown that treatment of oospores with cellulase (20 g L−1 ) increased germination approximately three-fold in comparison to untreated spores. Untreated and cellulase pretreated oospores were subsequently evaluated as seed treatments for their ability to control damping-off of sugar beet. The highest rate of pretreated oospores (104 oospores/seed) gave levels of emergence and establishment in infested compost that were not significantly different from the uninfested controls, whereas seed treatment with untreated oospores gave no significant reduction in disease. In a trial carried out in a controlled environment to assess the effect of pH (4.5–8.0), P. oligandrum (104 cellulase pretreated oospores/seed) was shown to control pre- and postemergence damping-off of sugar beet at pH 7.0 and 7.5 only. 相似文献
6.
This study investigated conidial dispersal in the field, and effects of simulated wind and rain on the dispersal of A. brassicicola on Chinese cabbage ( Brassica pekinensis ). Spores were sampled using a Burkard volumetric spore sampler and rotorod samplers in a Chinese cabbage crop. Disease incidence in the field was well fitted by a Gompertz curve with an adjusted r 2 of >0·99. Conidia of A. brassicicola were trapped in the field throughout the growing season. Peaks of high spore concentrations were usually associated with dry days, shortly after rain, high temperature or high wind speed. Diurnal periodicity of spore dispersal showed a peak of conidia trapped around 10·00 h. The number of conidia trapped at a height of 25 cm above ground level was greater than that at 50, 75 and 100 cm. Conidial dispersal was also studied under simulated conditions in a wind tunnel and a rain simulator. Generalized linear models were used to model these data. The number of conidia caught increased significantly at higher wind speeds and at higher rain intensities. Under simulated wind conditions, the number of conidia dispersed from source plants with wet leaves was only 22% of that for plants with dry leaves. Linear relationships were found between the number of conidia caught and the degree of infection of trap plants. 相似文献
7.
Single and combined effects of smoke pollution and the root-knot nematode, Meloidogyne incognita race 1, were studied on eggplant in 1988 and 1989 at two sites (K1 and K2) 1 and 2 km respectively away from a coal-fired thermal power plant, and a control site at the Department of Botany, Aligarh Muslim University (AMU). Mean concentrations of SO2 , NO2 and suspended particulate matter (SPM) were respectively 172, 95 and 626 μg/m3 in 1988 and 144, 97 and 556 μg/m3 in 1989 at K1; and 258, 150 and 344 μg/m3 in 1988 and 226, 113 and 293 μg/m3 in 1989 at K2. Peak levels of the gases and SPM were recorded in the early (12.00–15.00) and late (15.00–18.00) afternoon respectively. Concentrations of the pollutants at a control site were very low. Marginal browning appeared on the leaves of eggplants grown at site K2 whether or not they were infected by the nematodes. The galling caused by nematodes was severe at both polluted sites but egg mass production was inhibited at K2. Egg laying was significantly reduced at both polluted sites. M. incognita significantly reduced plant growth, yield and leaf pigment production of eggplant at the control and polluted sites. Most non-infected plants also showed significant reductions in these plant varieties i.e. from the effects of pollution at K2. Foliar concentrations of sulphur were significantly increased at both polluted sites, being greater in infected plants. The interaction of smoke pollution and M. incognita infection led to greater suppressions at the polluted sites, which were mostly significant at K1. At the polluted sites, leaves had more and longer trichomes; also the number and size of stomata were decreased but their openings were wider especially in infected plants at the two polluted sites. 相似文献
8.
KOICHI SHOJI 《Weed Biology and Management》2007,7(1):14-22
Tillage for the "complete inversion" of soil, that is, overturning soil slices 180° was proposed, a "spot plow" was developed and tested to accomplish the task, and a simulation model was evaluated to demonstrate the efficacy of the plow on weed control. A 360 mm wide spot plow was designed to operate at a speed of 1.9 m s−1 for the spot plowing with the least possible lateral displacement of the soil slice by utilizing the inertia of the soil slice and securely rotating it. In field experiments, complete spot inversion required an operating speed of at least 1.6 m s−1 ; at lower speeds, a portion of the soil block was left half-inverted and further lowering led to considerable lateral displacement. The displacement in the forward and lateral directions was minimal, implying that spot plowing is suitable for potential application to and verification of the weed population dynamics model in the field. A simple linear matrix model of the population dynamics of annual weeds was proposed, whereby four layers of soil were set to describe tillage and other ecological events. The effect of tillage on weed control was evaluated by the equilibrium reproduction rate allowed to sustain a stable population of weeds. The simulation model showed that alternately changing the depth of spot plowing had a significant effect on controlling weeds of low-survival-rate seeds, even when some incomplete inversion of the soil slice was taken into account. 相似文献
9.
Spatial biology of weed populations is the study of weed patches and their relevant patch-level processes. In this context, a patch was defined as an area in which individuals are aggregated into discrete subdivided populations. Four Abutilon theophrasti seedling patches in two continuous maize production fields were surveyed using a contiguous grid of quadrats between 1995 and 1997. Surveyed area was dependent on patch size and ranged from 96 m2 to 1134 m2 . Within each area, all seedlings were counted in each 1 m × 0.75 m quadrat in June, just before post-emergence weed control, and in mid-July after all weed control practices were completed. The spatial pattern observed in the seedling distribution maps was single or multiple focal points of high seedling density that decreased with distance from the focal point. Two-directional correlograms corroborated this visual observation, such that A. theophrasti seedling density in neighbouring quadrats was spatially autocorrelated, and correlation strength decreased with distance separating quadrats. Autocorrelation coefficients decreased at a greater rate across crop rows than parallel to crop rows. Visually, patch shape was elliptical and oriented in the direction of field traffic. Factors affecting patch-level processes of spatial aggregation, stability and edge dynamics were considered. 相似文献
10.
Host–parasite relationships and pathogenicity of Meloidogyne javanica on potatoes (newly recorded from Malta) were studied under glasshouse and natural conditions. Potato cvs Cara and Spunta showed a typical susceptible reaction to M. javanica under natural and artificial infections, respectively. In potato tubers, M. javanica induced feeding sites that consisted of three to four hypertrophied giant cells per adult female. Infection of feeder roots by the nematode resulted in mature large galls which usually contained at least one mature female and egg mass. In both tubers and roots, feeding sites were characterized by giant cells containing granular cytoplasm and many hypertrophied nuclei. Cytoplasm in giant cells was aggregated alongside the thickened cell walls. Stelar tissues within galls appeared disorganized. The relationship between initial nematode population density ( P ) [0–64 eggs + second-stage juveniles (J2s) per cm3 soil] and growth of cv. Spunta potato seedlings was tested under glasshouse conditions. A Seinhorst model [ y = m + (1 − m ) z ( P − T ) ] was fitted to fresh shoot weight and shoot height data of nematode-inoculated and control plants. Tolerance limits ( T ) for fresh shoot weight and shoot height of cv. Spunta plants infected with M. javanica were 0·50 and 0·64 eggs + J2s per cm3 soil, respectively. The m parameter in that model (i.e. the minimum possible y -values) for fresh shoot weight and shoot height were 0·60 and 0·20, respectively, at P = 64 eggs + J2s per cm3 soil. Root galling was proportional to the initial nematode population density. Maximum nematode reproduction rate was 51·2 at a moderate initial population density ( P = 4 eggs + J2s per cm3 soil). 相似文献
11.
Regression equations used as empirical models to predict rice blast caused by Pyricularia grisea on cv. Jinheung at Icheon, South Korea, and on cvs. IR50 and C22 at Cavinti, Philippines, were generated, using weather factors identified by the WINDOW PANE program to be highly correlated with disease. Consecutive days with RH≥80% (CDRH80), number of days with RH≥80% (NDRH80), consecutive days with precipitation, and number of days with precipitation ≥ 84 mm day−1 were important variables predicting blast at Icheon. Total precipitation, precipitation frequency, mean maximum and minimum temperatures, number of days with wind speed above 3.5 m s−1 , CDRH80, and NDRH80 were important predictors of blast at Cavinti. The Allen's predicted error sum of squares (PRESS) criterion and a cross-validation procedure were used to evaluate the models using data that were not included in model development. Validation test showed that all models developed for the two sites, except the models predicting maximum lesion number and panicle blast incidence at Icheon, and panicle blast severity on IR50 at Cavinti, predicted blast reasonably well based on low PRESS values and close to zero average prediction errors. These models can be applied in actual rice production systems, but future validation is needed to further improve their predictive ability. 相似文献
12.
HERSHENHORN GOLDWASSER PLAKHINE ALI BLUMENFELD BUCSBAUM HERZLINGER GOLAN CHILF EIZENBERG DOR & KLEIFELD 《Weed Research》1998,38(5):343-349
Field experiments were conducted from 1994 to 1997 at two locations to study the effectiveness of chlorsulfuron and triasulfuron applied through different irrigation methods (chemigation) for control of Orobanche aegyptiaca Pers. in tomato ( Lycopersicon esculentum Mill). Three split applications of chlorsulfuron at 2.5 g a.i. ha−1 and of triasulfuron at 7.5 g a.i. ha−1 , through conventional sprinkler irrigation systems, 10–14 days apart followed immediately by sprinkling with water, controlled O. aegyptiaca by about 90% and 80% and increased crop yield 25–47% and 30%, respectively, without any crop injury symptoms. Repeated applications of the same herbicides at half rates resulted in slightly higher O. aegyptiaca control and crop yield than only one herbicide application at double rate. Chemigation by the sprinkler systems (microsprinklers, 60 m3 ha−1 ) slightly increased the herbicide efficiency as compared with the high volume spray (800 m3 ha−1 ). O. aegyptiaca control from sulfonylureas applied by drip chemigation was poor, as this probably requires very accurate timing and the herbicide distribution in the soil was not uniform. 相似文献
13.
M. Novo C. M. Gayoso F. Pomar M. M. Lucas A. Ros Barceló F. Merino 《Plant pathology》2007,56(6):998-1004
Elemental sulphur levels, sulphur localization in stems, and levels of sulphate, glutathione and cysteine were studied in pepper ( Capsicum annuum ) cvs Yolo Wonder (higher resistance) and Luesia (lower resistance) after inoculation with Verticillium dahliae , the cause of vascular wilt. Accumulation of elemental sulphur (S0 ) was first detected 10 days after inoculation in Yolo Wonder (mean S0 level 7·3 µ g g−1 DW), and 15 days after inoculation in Luesia (mean S0 level 3·3 µ g g−1 DW). The maximum level was reached 21 days after inoculation in Yolo Wonder (14·1 µ g g−1 DW). In control plants, elemental sulphur was not detected. SEM-EDX (scanning electron microscopy-energy dispersive X-ray microanalysis) indicated that the sulphur was not restricted to a specific location, but was dispersed throughout the vascular tissue. Sulphate levels showed a decline at the end of the experiment in inoculated plants, possibly related to the increase in sulphur levels seen in the two cultivars. The differences in sulphate levels between the two cultivars may be due to faster sulphate breakdown in cv. Yolo Wonder. 相似文献
14.
Z. Karolewski B. D. L. Fitt A. O. Latunde-Dada S. J. Foster † A. D. Todd K. Downes N. Evans 《Plant pathology》2006,55(3):387-400
Methods to assess light leaf spot ( Pyrenopeziza brassicae ) on winter oilseed rape cultivars were compared in laboratory, controlled-environment and field experiments. In controlled-environment experiments with seedling leaves inoculated at GS 1,4, the greatest differences in percentage area affected by P. brassicae sporulation were observed with inoculum concentrations of 4 × 103 or 4 × 104 spores mL−1 , rather than 4 × 102 or 4 × 105 spores mL−1 , but older leaves had begun to senesce before assessment, particularly where they were severely affected by P. brassicae . In winter oilseed rape field experiments, a severe light leaf spot epidemic developed in 2002/03 (inoculated, September/October rainfall 127·2 mm) but not in 2003/04 (uninoculated, September/October rainfall 40·7 mm). In-plot assessments discriminated between cultivars best in February/March in 2003 and June in 2004, but sometimes failed to detect plots with many infected plants (e.g. March/April 2004). Ranking of cultivar resistance differed between seedling experiments done under controlled-environment conditions and field experiments. The sensitivity of detection of P. brassicae DNA extracted from culture was greater using the PCR primer pair PbITSF/PbITSR than using primers Pb1/Pb2. P. brassicae was detected by PCR (PbITS primers) in leaves from controlled-environment experiments immediately and up to 14 days after inoculation, and in leaves sampled from field experiments 2 months before detection by visual assessment. 相似文献
15.
The tree row volume (TRV) model was adapted for use in stone-fruit orchards. The number of leaves, leaf area and TRV were determined in apricot, peach, cherry and plum orchards in France and Switzerland. The number of leaves per tree ranged from 2500 to 25900, and TRV values ranged from 5400 to 28600 m3 ha−1 . Trees were sprayed with a fluorescent tracer, according to TRV, in order to determine the quantity and distribution of tracer deposition in the crown of the trees. For large trees with TRV values above 15000 m3 ha−1 , tracer deposits on leaves were lower in the upper half of the crown than in the lower half. The TRV formula developed for pome-fruit trees was accordingly used for spraying stone-fruit trees, but with a 15% increase in spray volume for large trees. Under these conditions, disease control was efficient, and residues of difenoconazole, penconazole and dithianon were below the maximum residue limit. The TRV method was thus found to allow adaptation of spray dosage and volume to the volume of the trees, on condition that sprayers are carefully calibrated and adjusted for each orchard. The TRV concept can be applied to a wide range of pome and stone-fruit orchards and can help to harmonize registration protocols for fungicides and insecticides. 相似文献
16.
A HUSSNER 《Weed Research》2009,49(5):506-515
Crassula helmsii , Hydrocotyle ranunculoides , Ludwigia grandiflora and Myriophyllum aquaticum are four well known invasive aquatic plants in European waters. In this study, plant growth at different nutrient availabilities, regeneration capacity and photosynthesis were investigated. Results show high relative growth rates (RGR) of the species of up to 0.132 ± 0.008 g g−1 dry weight (dw) day−1 ( H. ranunculoides ) and a significant increase in RGR with increasing nutrient availability. All species show a high regeneration capacity and the ability to form new shoots from single nodes, even though it differs between the species. Ludwigia grandiflora and M. aquaticum also show regeneration from single leaves. Species differed in maximal amounts, and in temperature and light optima of net assimilation rates: H. ranunculoides leaves reach maximum photosynthetic rates of up to 3500 μmol CO2 × h−1 g−1 dw, L. grandiflora (leaves) up to 2200 μmol CO2 × h−1 g−1 dw, M. aquaticum (shoots) 400 μmol CO2 × h−1 g−1 dw and C. helmsii (shoots) up to 200 μmol CO2 × h−1 g−1 dw. Hydrocotyle ranunculoides , L. grandiflora and M. aquaticum preferred high light intensity and high temperatures, whilst C. helmsii was negatively affected by intense sunlight. Summarising, it can be assumed that at least H. ranunculoides , L. grandiflora and M. aquaticum can grow well under current and likely future central European climate conditions. 相似文献
17.
The effects of the density and proportion of both volunteer barley ( Hordeum vulgare L.) and Stellaria media (L.) Vill. (common chickweed) on the seed yield of both species was investigated in linseed ( Linum usitatissimum L.) and autumn-sown field bean ( Vicia faba L.). A model was created to estimate these effects. It was a combination of two models. The first was a simple linear model relating weed seed number m2 to weed dry weight m2 . The second was an inverse linear model relating weed dry weight per plant to weed density. A very good relationship existed between barley dry weight and number of seeds m2 and between S. media dry weight and number of seed capsules m2 . This relationship was relatively consistent between experiments. The inverse linear model provided a good estimation of the relationship between weed density and weed dry weight per plant for both barley and S. media . Model variables, however, differed between experiments. Using the combined model it was estimated that, in the absence of other weed species and at a density of 800 plants m2 , S. media would produce between 4000 and 48 000 seeds m2 , whereas volunteer barley, at a density of 400 plants m2 , would produce between 2000 and 8000 seeds m2 . The presence of barley always reduced S. media seed yield and a barley population of 100 plants m2 could reduce S. media seed yield by up to 79%. The presence of S. media reduced barley seed yield in only one of three experiments, in which a S. media density of 800 plants m2 reduced barley seed yield by up to 68%. It was concluded that interspecific weed competition should not be ignored as a factor in models of weed population dynamics 相似文献
18.
The infection process of Septoria nodorum was studied on the flag and second leaves of wheat plants at the flag-leaf emergence growth stage (GS 39), after pre-inoculative fumigation with different doses of ozone (0, 80, 180 or 240 μg/m3 ) for 7 h daily over 7 days. On ozone-treated plants, formation of appressoria occurred earlier, leading to a greater number and density of appressoria and faster growth of superficial infection hyphae than on plants grown without ozone amendment. Additionally, on leaves treated with 180 and 240 μg/m3 ozone, the percentage of papillae per appressorium was only half that on control plants. The number of germ tubes per conidium was not significantly affected by any treatment. Effects of increasing leaf age on the infection process were similar to those obtained with ozone. These results provide further evidence for similarities in the physiological effects of ozone and leaf ageing, which support the hypothesis that disease alterations due to ozone are strongly determined by the senescing effects of the pollutant. 相似文献
19.
Nematicidal activity of essential oils and organic amendments from Asteraceae against root-knot nematodes 总被引：1，自引：0，他引：1
M. P. Pérez J. A. Navas-Cortés M. J. Pascual-Villalobos P. Castillo † 《Plant pathology》2003,52(3):395-401
The essential oil of Chrysanthemum coronarium flowerheads showed strong nematicidal activity in vitro and in growth-chamber experiments. Essential oil concentrations of 2, 4, 8 and 16 µ L mL−1 , significantly reduced hatch, J 2 survival (determined by final value and area under curves of cumulative percentage hatch or mortality) and reproduction rate of Meloidogyne artiellia in vitro , with the lowest values occurring at 16 µ L mL−1 . In pot trials with chickpea cv. PV 61, essential oil concentrations of 10–40 µ L per 500 cm3 soil, applied on sterile cotton pellets, also significantly reduced the nematode's reproduction rate. The biological processes of mortality and hatching/reproduction were adequately described by the monomolecular and expanded negative exponential models, respectively. Effectiveness of soil amendment with either flowers, leaves, roots or seeds of C. coronarium , and flowers from several species of Asteraceae ( Chrysanthemum segetum , Calendula maritima , Calendula officinalis and Calendula suffruticosa ) at 5 g per 500 cm3 soil was tested for suppression of M. artiellia and growth of chickpea cv. PV 61 under growth-chamber conditions. In these tests, flowers of all five Asteraceae species and various parts of C. coronarium significantly reduced reproduction rates of M. artiellia , by 83·0–95·9%, with the minimum rates occurring in infected chickpea plants amended with flowers of C. officinalis and C. suffruticosa . The in vitro and in planta results suggest that the essential oil of C. coronarium and organic amendments from Asteraceae species may serve as nematicides. 相似文献
20.
Urediniospore production by Puccinia striiformis on wheat per unit leaf area infected was much lower at low light intensities than at high light intensities. The number of pustules per unit area of infected leaf and the daily sporulation rate per pustule increased linearly with increasing light over the range 10–50 W/m2 . Increasing temperature between 7 and 20°C shortened latent period and reduced the longevity of sporulating leaves. Colonization rate and the frequency of pustules per unit area of infected leaf increased between 7 and 15°C but declined markedly at 20°C. Spore production reached its peak earlier and declined more rapidly with increasing temperature between 7 and 15°C. this decline being less marked in the highly susceptible cultivar Maris Beacon than in the more resistant Maris Nimrod and Maris Huntsman. 相似文献