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1.
Phosphonic acid was more effective in inhibiting the production of sporangia of Phytophthora clandestina in sterile pond water (ED50= 1·4 p.p.m.) than it was in inhibiting the growth of mycelium of the fungus on either corn meal agar (ED50= 13·8p.p.m.) or lima bean agar (ED50= 236 p.p.m.). Experiments under controlled environmental conditions showed that better control of tap root rot of subterranean clover caused by P. clandestina was achieved by application of potassium phosphonate to a pasteurized soil mixture than by a spray on the foliage alone. However, in a soil from a pasture, foliar sprays were more effective than soil treatments. Application of superphosphate at a rate of 250 kg/ha or higher to the soil reduced the effectiveness of sprays. In three experiments in irrigated pastures a spray of potassium phosphonate at 300 or 313 ml/ha, applied to cotyledons of subterranean clover and to soil, reduced severity of Phytophthora root rot and increased the annual production of dry matter of the legume by 1·96 to 5·11 t/ha in comparison with untreated controls.  相似文献   

2.
Studies were carried out in controlled environment rooms reflecting field situations. In the presence of the devastating soilborne pathogen Phytophthora clandestina, subterranean clover (Trifolium subterraneum) seedling emergence was significantly affected by moisture, soil type, temperature and cultivar. The level of rotting of tap and lateral roots was significantly affected by nutrition, soil type, temperature and cultivar. There were significant interactions involving temperature, moisture, soil type and cultivar; cultivar resistance, high moisture, high or medium temperature, high nutrition and sand soil all contributed towards less pre‐emergence damping‐off and tap and lateral root disease and to greater clover productivity. Host resistance of subterranean clover cultivars was critical for reducing disease severity and increasing productivity, even when favourable environmental conditions for severe disease occurred. In the presence of P. clandestina, the most resistant cultivar, Seaton Park, performed best under a high temperature, high nutrition and high moisture combination, but showed lower productivity under conditions of low nutrition or lower temperature, even when moisture level was high. In contrast, less resistant cultivars Riverina and Meteora had less disease and greater productivity under low moisture conditions. Findings reflect field observations that pre‐emergence damping‐off and root disease from P. clandestina in subterranean clover is particularly severe under colder conditions and in nutritionally impoverished sandy soils, and demonstrate how variations in soil type, nutrition, moisture, temperature and cultivar have profound effects on the expression and severity of phytophthora pre‐emergence damping‐off and root disease and the productivity of subterranean clover forages.  相似文献   

3.
ABSTRACT Seed treatment with Trichoderma harzianum strain T22, which results in colonization of plant roots but little or no colonization of shoots or leaves, had substantial effects on growth of and disease expression in maize inbred line Mo17. Shoots and roots of 10-day-old seedlings grown in a sandy loam field soil were larger (roots were nearly twice as long) in the presence of T22 than in its absence. Both main and secondary roots were increased in size and area and the root hair area was greater with T22. However, root hair area per unit of root length was greater in control plants. Increased growth probably was due to direct stimulation of plant growth in addition to effects from biological control of deleterious microflora. Seedlings of Mo17 grown in autoclaved or mefenoxamtreated sandy loam field soil were larger than those produced in untreated soil. However, seedlings grown in the presence of T22, either in treated or untreated soil, were larger than those produced in its absence. Infestation of soil with Pythium ultimum had little effect upon growth of Mo17. The presence of T22 increased protein levels and activities of beta-1,3 glucanase, exochitinase, and endochitinase in both roots and shoots, even though T22 colonized roots well but colonized shoots hardly at all. With some enzymes, the combination of T22 plus P. ultimum gave the greatest activity. Plants grown from T22-treated seed had reduced symptoms of anthracnose following inoculation of leaves with Colletotrichum graminicola, which indicates that root colonization by T22 induces systemic resistance in maize.  相似文献   

4.
The seed potatoes used in these experiments had been grown in a slightly acid pleistocene sandy soil or in a marine, holocene sandy loam. They were free of sclerotia ofR. solani or lightly or moderately speckled with them. Seed potatoes from the sandy soil produced plants that suffered less fromRhizoctonia than plants from seed potatoes that had been grown on the marine sandy loam. Similarly harvested tubers had, in a non-conducive soil and in conducive soils with a (very) low inoculum density ofR. solani, fewer sclerotia when they came from seed potatoes grown in an acid sand. In each soil, the degree of infestation of the crop not only depended on the severity of infection of the seed potatoes, but also on their origin. With regard to sclerotia production on tubers, three types of soil were distinguished: suppressive, conducive with a high, and conducive with a very low inoculum density ofR. solani. The differences in infestation and in the amounts of sclerotia on tubers between the crop grown from seed potatoes from the sandy soil and that from seed potatoes from the marine sandy loam soil, is attributed to a richer load of antagonists on the former and possibly to a larger proportion of saprophyticRhizoctonia strains among their sclerotia. The antagonists seem to be inhabitants of the subterranean parts of the plant and to function independently of the soil. This implies possibilities for their use in biological control.  相似文献   

5.
ABSTRACT Soil receptivity as a quantifiable characteristic ranging from conduciveness to suppressiveness to soilborne pea pathogens Thielaviopsis basicola and Aphanomyces euteiches was determined by analysis of differences in disease response curves obtained by artificial introduction of inoculum into natural field soil samples. Several parameters, including maximum root rot severity, the area under the health index curve, scores on the first axis of a principal component analysis (PCA) on dose responses, and Weibull model fitting were used to describe the disease responses. In all cases, the Weibull model gave satisfactory fits. PCA yielded a first axis that comprised 86% of the variance found when using Weibull predicted responses for T. basicola and 74% of the variance found for A. euteiches. This PCA axis essentially represented the average increase in disease severity due to the addition of increasing doses of inoculum to the soil. The Weibull scale parameter B, which represents the amount of inoculum necessary to increase root rot severity by 63% with respect to the level caused by pathogens naturally present in the soil, is another means of quantifying the receptivity of soils to these plant pathogens. Weibull parameter B, maximum root rot severity, the areaunder the health index curve, and the scores on the first PCA axis were strongly correlated for each of the pathogens tested individually. To compare the extent and behavior of soil receptivity responses to different pathogens, Weibull parameters B and C (slope at dose B) were chosen because of their universal definition, in contrast to PCA scores. Comparison of the average levels of Weibull parameters B and C indicated significant differences between the pathogens. Yet, no significant similarity in the ranking of the soils was found for the three pathogens, demonstrating that individual soils may interact with different pathogens in totally different ways. In general, soils were suppressive to T. basicola but conducive to A. euteiches, whereas their response to Fusarium solani f. sp. pisi ranged from conducive to suppressive. Therefore, risk assessment of soils prior to planting may require different strategies for each pathogen. Bioassays with soil samples taken before the last pea crop in 1987 and 1991 revealed a significant increase in the natural inoculum potential of soils that mainly was accounted for by A. euteiches and Pythium spp. These results strongly indicate that A. euteiches must be considered one of the most threatening pathogens to pea crops in the Netherlands.  相似文献   

6.
 Rice seedling growth, estimated by plant height and root development and discoloration, was better in pasteurized soil than in unpasteurized soil obtained from a flooded rice field. Rice seedlings also grew better in sterilized soil modified by adding roots harvested from the pasteurized soil than in soil modified by adding roots harvested from the unpasteurized soil. The results demonstrate that seedling growth in the rice field soil was inhibited by soil microorganisms, even though no typical symptoms such as seedling blight or damping-off appeared. Pythium aristosporum is suggested to be involved in the inhibition. Thus, it appears that inconspicuous restraint of rice seedling growth could occur in soils of rice paddy fields. Received: May 20, 2002 / Accepted: October 16, 2002 Acknowledgments The authors thank Dr. T. Ichitani, former professor at Osaka Prefectural University, for providing an isolate of Pythium aristosporum for comparison, and Mr. Mitsuaki Sato of Akita Prefectural College of Agriculture for technical assistance.  相似文献   

7.
Subterranean clover ( Trifolium subterraneum L.) appears to be a suitable winter legume cover crop for Japan because the subterranean clover stands maintain themselves by reseeding in autumn and the large seeds facilitate establishment and enable early fall production. However, there is little information on the relationship between reseeding and tillage systems for subterranean clover under Japanese climatic conditions. A weed-tillage population dynamics model was developed to investigate the effects of the tillage method and timing on the reseeding of subterranean clover. The field experiments were conducted in a silage corn and subterranean clover rotation system. The life cycle of subterranean clover was modeled to describe the seed production competing with weed growth, seasonal changes in the buried seeds' viability, and the movement of seeds by tillage treatments. In the numerical simulation, the effect of the tillage method on the seedling population of reseeded subterranean clover was investigated and the simulation results showed good agreement with the experimental results. Rotary tilling immediately after subterranean clover seed maturation successfully produced a good subterranean clover stand the following spring. However, rotary tillage conducted 2 months after seed maturation killed the emerging subterranean clover seedlings and the field was dominated by winter weeds. These simulation results suggest that a suitable tillage system can maintain successful subterranean clover re-establishment from year to year.  相似文献   

8.
黑龙江省大豆疫霉根腐病调查与病原分离   总被引：10，自引：0，他引：10  
１９９６年对黑龙江省东部和中部大豆产区２３个市、县的大豆苗期疫霉根腐病进行了调查、研究,应用ＰＢＮＩＣ疫霉选择性培养基分离大豆疫霉根腐病病原菌,从牡丹江、穆棱、林口和佳木斯豆田具疫霉根腐症状的大豆植株上分离到大豆疫霉根腐病菌,并从根腐病株上单独或与大豆疫霉菌同时分离到终极腐霉菌,研究进一步证实我国黑龙江省有大豆疫霉根腐病。调查发现,大豆疫霉根腐病和终极腐霉根腐病主要发生在土质粘重、土壤含水量高或易积水的田块。  相似文献   

9.
Persistence of ethofumesate [(±)2-ethoxy-2.3-dihydro-3,3-dimethylbenzofuran-5-yl-methansulphonate] in soil was associated with soil temperature. Ethofumesate applied at 4.5 kg/ha in November persisted about twice as long in soil as that applied the following March. In another field study, 88–91% of the herbicide had dissipated after 24 weeks in sandy loam soil, compared to 72–77% in loam soil when it was applied at rates of 2.2, 3.4, 4.5, and 9.0 kg/ha. The rate of degradation was independent of the initial rate of chemical applied. The time required for 50% of the herbicide to dissipate in sandy loam and loam soils was 7.7 and 12.6 weeks, respectively. The movement of ethofumesate in these two soils over a 24-weeks sampling period was confined mainly to the upper 7.5 cm of the soil profile.  相似文献   

10.
ABSTRACT Six herbicides were evaluated for their effects on Pythium root rot and growth of sugarcane in greenhouse experiments and on in vitro mycelial growth rate of Pythium arrhenomanes. Pendimethalin and atrazine were most inhibitory to mycelial growth, but neither reduced root rot severity. Asulam, atrazine, and metribuzin were not phytotoxic to sugarcane and did not affect root rot symptom severity in clay loam or silt loam field soils. Atrazine and metribuzin increased shoot number, and atrazine increased total shoot weight for treated plants in silt loam soil. Glyphosate, pendimethalin, and terbacil were phytotoxic to sugarcane. These herbicides increased root rot severity, but the extent to which growth reductions resulted from increased disease severity or from direct herbicide injury was not clear. Adverse effects on plant growth and root rot severity were greater in clay loam than in silt loam soil. The results suggest that sugarcane injury from some herbicides is compounded by increased severity of root rot.  相似文献   

11.
The colonization of the roots of four cultivars of subterranean clover by isolates representing four races of Phytophthora clandestina was studied. There was a highly significant race × cultivar interaction in the growth of inoculated tap roots and the degree of colonization of roots by the pathogen. While all races were able to infect the roots of all cultivars tested, roots of the susceptible cultivars were colonized more rapidly and extensively than those of the resistant cultivars. In compatible combinations, fungal colonization extended for a few centimetres in the tap root and lateral roots in the moderately susceptible cultivars Trikkala and Meteora, or throughout the whole root system leading to the death of the host in the very susceptible cultivar Woogenellup. In contrast, limited fungal colonization of the tap root and lack of extension of the fungus into lateral roots was typical of incompatible combinations. In all cultivars, lateral roots were as susceptible to infection as tap roots. The number of lateral roots of Woogenellup was significantly reduced by infection. However, neither the rate of lateral root formation nor the total number of lateral roots of Seaton Park, Meteora and Trikkala was reduced by infection with virulent or avirulent races of the pathogen.  相似文献   

12.
Eleftherohorinos  I.  Dhima  K.  Vasilakoglou  I. 《Phytoparasitica》2004,32(3):274-285
Petri dish bioassays, based on root response of corn grown in soil or in perlite, were used to study the activity, adsorption, mobility and field persistence of sulfosulfuron in a silty clay loam and a sandy loam soil. Both bioassays indicated that activity of sulfosulfuron increased with increasing herbicide concentration, and to a slightly greater degree in sandy loam soil than in silty clay loam soil. More sulfosulfuron was adsorbed on the sandy loam (not biologically available) than on the silty clay loam soil. Consequently, slightly greater amounts of sulfosulfuron were leached through the silty clay loam than through the sandy loam soil. Biologically available sulfosulfuron was not detected at depths below 40 cm after application in sandy loam, but this was not the case for the silty clay loam soil. In 2002, all sulfosulfuron rates showed field persistence of less than 5 months. On the other hand, in 2003, biologically available sulfosulfuron was detected in the 0–10-cm soil depth 150 days after application. http://www.phytoparasitica.org posting May 6, 2004.  相似文献   

13.
Diphenamid (N,N-dimethyl-2,2-diphenylacetamide) in an aqueous solution in plastic bottles was partially detoxified when exposed to sunlight for 1 week. Varying spray volumes from 300 to 1,800 I/ha did not have an appreciable effect on the phytotoxicity of diphenamid, sprayed on a coarse or fine soil surface. The marked dissipation of diphenamid which occurred from the soil surface was attributed to photodecomposition and volatilization. Diphenamid phytotoxicity was greater when the first irrigation after spraying was applied in four increments of 100 m3/ha or two increments of 200 m1/ha than when it was applied in a single 400 m1/h watering; the latter caused more leaching of the herbicide. The diphenamid fraction leached out of a 4-cm soil layer increased as the organic matter content in the soil decreased, from 25% in peat (22.3% o.m.) to >88% in sandy loam (0.9% o.m.). The herbicidal activity remaining after leaching was lower in sandy loam and in peat than in soil with medium organic matter content (11.6% and 6.2%). Diphenamid degradation rate in soil at 50% field capacity moisture level, increased when temperature was increased from 10° to 30°C. After 4 months of incubation at 10°C, 40-50% of the original herbicide was detoxified, while at 20° and 30°C the loss exceeded 90%. Within the range of day-temperatures of 10° to 40°C in soil and of 10° to 35°C in nutrient solution, diphenamid phytotoxicity to tomato seedlings increased with temperature.  相似文献   

14.
The leaching of aldicarb and thiofanox in soils (sandy loam, silt loam and sandy clay loam), and their uptake by sugarbeet plants were studied. Three irrigation levels were maintained: half, normal and double dose. The residues were determined as the sum of the insecticidal metabolites (parent compound + sulphoxide+ sulphone) for both pesticides. Leaching was greatly influenced by the amount of water added and the soil type. Under normal conditions, leaching seemed to proceed very slowly, keeping the chemicals available for uptake by the root systems for a long time. The concentration of insecticide in the leaves was highest in beets grown on sandy loam and lowest in those grown on sandy clay loam. The quantity of irrigation did not influence the residue concentration in the leaves greatly, although its influence was obvious on the total residue present (μg per plant). Increasing the water dose always resulted in a higher total residue, and a greater plant weight. The breakdown in the soils was directly related to the water dose. The experiments show that thiofanox was more stable than aldicarb and was taken up by sugarbeet to a greater extent.  相似文献   

15.
Analytical methods are described for the determination of residues of chlorfenvinphos, diazinon, fonofos and phorate in soils and carrots. The insecticides, applied in June 1969 at 2 kg (a.i.)/ha, persisted longer in peaty loam than in sandy loam. After 7 months, the sandy loam contained 1% of the applied diazinon and 20–30% of the applied chlorfenvinphos, fonofos and phorate, the latter as its sulphone; the corresponding figures for the peaty loam were 10, 40–50, 40–50 and 30–40% respectively. None of the residues showed any substantial change from October to January. Although high initial concentrations (up to 50 ppm) of the residues in carrots were diluted by plant growth, it is shown that concentrations >1 ppm could be present in marketable crops 12–14 weeks after application at recommended rates. Carrots harvested 26 weeks after sowing contained <0.2 ppm of all insecticides. In contrast, during the first 15 weeks of crop growth the weights of residues in the carrots increased and remained approximately proportional to the square root of the carrot mean weight. Rates of uptake declined as carrot growth declined and subsequently the amounts of chlorfenvinphos, diazinon and fonofos residues in the carrots changed very little, while phorate sulphone steadily declined.  相似文献   

16.
Incorporation into soil of dry mycelium ofPenicillium chrysogenum, a waste product of the pharmacological industry, enhanced plant growth and reduced root galling caused by the root-knot nematodeMeloidogyne javanica in cucumber and tomato plants. Incorporation into sandy loam soil in pots of dry mycelium at a concentration of 0.25% (w/w) resulted in complete protection of cucumber plants from the nematode. The number of juveniles recovered from soils containing dry mycelium was greatly reduced even at a concentration of 0.1% (w/w). In microplot studies conducted at two sites in two seasons, with three or four doses, dry mycelium caused a dose-dependent reduction in root galling index (GI) and promotion of plant growth of cucumber and tomato plants. Inin vitro studies, the water extract of dry mycelium immobilized nematode juveniles and reduced the egg hatching rate, but these effects were partly reversible after a rinse in water. Soil-drenching of cucumber and tomato seedlings with water extract of dry mycelium did not reduce GI or number of root-invading juveniles. The results show that dry mycelium promotes plant growth and protects plants against nematode infection. Protection, however, does not operatevia induced resistance. http://www.phytoparasitica.org posting April 6, 2003.  相似文献   

17.
Blackgrass (Alopecurus myosuroides Huds.) was controlled by 2 kg/ha of metoxuron in glasshouse trials while winter wheat, cultivar Cappelle Desprez, tolerated 4 kg/ha. Blackgrass was controlled by 1.2 kg/ha of chlortoluron. Winter wheat previously damaged by freezing was injured by 2.5 kg/ha of chlortoluron applied at an early stage. Seedlings not exposed to freezing were not damaged by 2.5 kg/ha applied at the 4- and 5-leaf stage. Breakdown of chlortoluron and metoxuron in the soil was attributed, in part, to microbial action. More than one-third of the chlortoluron applied at 2 kg/ha disappeared in 6 weeks when applied in early spring while one half disappeared in 3 weeks when applied 2 months later. The bioassay, used to determine the amount of chlortoluron or metoxuron in the soil, was found to be adequate for metoxuron in only one of three soils. The bioassay results, for both herbicides, were affected by the addition of calcium carbonate to the soil, by sterilization of the soil, and by leaching. In comparisons of results in two sandy loams and a clay loam, the observed differences could not be altogether accounted for by differences in pH nor by changes in adsorption of metoxuron. When perennial ryegrass was grown in sandy loam, and treated with metoxuron before or after emergence, different watering regimes did not give any difference in weight of top growth.  相似文献   

18.
Two 5-year trials were conducted in New South Wales on the control of broomrape (Orobanche minor Sm.), a plant parasite of subterranean clover (Trifolium subterraneum L.) and skeleton weed (Chondrilla juncea L.). Applications of superphosphate to two soils of low phosphorus status stimulated clover growth, which caused a reduction in the number of skeleton weed plants and a decrease in the broomrape population. Similar but less effective control was obtained when subterranean clover pasture was sprayed with 2,4-DB for skeleton weed control as soon as the clover seedlings had developed trifoliate leaves. In spring, sheep readily grazed the broomrape stems before flowering, causing death of the plants. Autumn application of super phosphate, coupled with grazing of the pasture by sheep, significantly reduced broomrape density.  相似文献   

19.
In a field trial, different doses of five herbicides applied in autumn and late winder were compared for the control of barley grass (Hordeum leporium Link) in dryland Lucerne. Diuron at 1·1, 2·2, and 4·5 kg/ha and atrazine at 1·1 kg/ha were more effective in increasing Lucerne production than linuron at 4·5 kg/ha and various rates of dalapon and paraquat. Autumn application generally resulted in greater Lucerne production than late winter application. Most treatments reduced the amount of barley grass in the Lucerne. Diuron and atrazine also eliminated reduced the amount of barley grass in the Lucerne. Atrazine, diuron and linuron had a strong residual effect and reduced the density of subterranean clover and barley grass in the autumn following treatment.  相似文献   

20.
Singh N 《Pest management science》2008,64(10):1057-1062
BACKGROUND: Metribuzin (4-amino-6-tert-butyl-4,5-dihydro-3-methylthio-1,2,4-triazin-5-one) is weakly sorbed in soils and therefore leaches easily to lower soil profiles and results in loss of activity. Soil amendments play an important role in the management of runoff and leaching losses of pesticides from agricultural fields. Therefore, the effect of biocompost from sugarcane distillery effluent on metribuzin degradation and mobility was studied in a sandy loam soil.RESULTS: Metribuzin was more persistent in biocompost-unamended (T-0) flooded soil (t(1/2) - 41.2 days) than in non-flooded (t(1/2) - 33.4 days) soil. Biocompost application at the rate of 2.5 and 5.0% (T-1 and T-2) in non-flooded soils increased metribuzin persistence, but no significant effect was observed on persistence in flooded soils. Freundlich adsorption constants (K(f)) for treatments T-0, T-1 and T-2 were 0.43, 0.64 and 1.13 respectively, suggesting that biocompost application caused increased metribuzin sorption. Leaching studies in packed soil columns indicated that biocompost application affected both metribuzin breakthrough time and maximum concentration in the leachate. Leaching losses of metribuzin were drastically reduced from 93% in control soil (T-0) to 65% (T-1) and 31% (T-2) in biocompost-amended soils.CONCLUSION: Biocompost from sugarcane distillery effluent can be used effectively to reduce downward mobility of metribuzin in low-organic-matter sandy loam soil. Copyright (c) 2008 Society of Chemical Industry.  相似文献   

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