Phytotoxic activity of pethoxamid in soil under different moisture conditions

The phytotoxic activity of soil-applied pethoxamid [2-chloro- N -(2-ethoxyethyl)- N -(2-methyl-1-phenyl-1-propanyl) acetamide], (TKC-94), on the plant growth of rice ( Oryza sativa cv. Kiyohatamochi ) seedlings as an assay plant in soil was investigated under different soil moisture conditions. The phytotoxic activity of pethoxamid mixed with soil on the shoot and root growth of rice seedlings was uppermost under the highest soil moisture condition and it decreased with declining soil moisture content, while the inhibition was greater on the root growth than the shoot growth. The amount of pethoxamid adsorbed on soil solid and the concentration of pethoxamid in soil water from soil applied with this herbicide were not influenced by the soil moisture content. In addition, the phytotoxic activity on the growth of rice seedlings in sea sand culture applied with the soil water from the herbicide-applied soil was not influenced by the soil moisture content. In the sea sand culture, the phytotoxic activity of pethoxamid was significantly reduced in negative water potential as the concentration of polyethylene glycol-6000 added to the water increased. It is suggested that the phytotoxic activity of pethoxamid in the soil primarily depends on the concentration in soil water, but the phytotoxic activity was affected by soil moisture through the effect on absorption of this herbicide by rice seedlings.     

Residual thenylchlor concentration in soil water and its phytotoxic activity in soil

The phytotoxic activity of soil-applied thenylchlor (2-chloro- N -[3-methoxy-2-thenyl]-2',6'-dimethylacetanilide) on the growth of rice seedlings and its behavior in two different types of soil, Ryugasaki soil and Tsukuba soil, after application was investigated with emphasis on the concentration in the soil water. The greatest inhibition of thenylchlor on the growth of rice seedlings was found immediately after application to both the Ryugasaki and Tsukuba soils. The phytotoxic activity decreased with time in both soils. However, the rate of decrease in phytotoxic activity was slower in the Ryugasaki soil than in the Tsukuba soil. The concentration of thenylchlor in soil water, the amount adsorbed on the soil solid, and the amount in the total soil reduced with time after application to both soils. The amount of thenylchlor adsorbed on the soil solid phase was more persistent than that in the soil water in both soils and the concentration in the soil water was higher in the Ryugasaki soil than in the Tsukuba soil at any given time. The residual phytotoxic activity of thenylchlor on the growth of the rice seedlings in the soil was highly correlated with its concentration in the soil water but not with the amount in the total soil. These results suggested that the residual phytotoxic activity of thenylchlor in the soil is determined by its concentration in the soil water after application.     

Residual phytotoxic activity of pethoxamid in soil and its concentration in soil water under different soil moisture conditions

The relationship between the residual phytotoxic activity of pethoxamid (2-chloro- N -[2-ethoxyethyl]- N- [2-methyl-1-phenyl-1-propenyl] acetamide) on rice ( Oryza sativa cv. Kiyohatamochi) seedlings and its behavior in soil was investigated under different moisture conditions. The phytotoxic activity of pethoxamid on the shoot growth of rice seedlings in soil was higher in 80% soil moisture content than in 70% and 60% soil moisture contents. The phytotoxic activity in soil in 70% and 80% soil moisture conditions decreased with the increasing time after application, but the phytotoxic activity was slight in 50% soil moisture conditions at any given time after application. The residues of pethoxamid in soil water, the amount adsorbed on soil solid, and the amount in total soil was reduced with the time after application in a similar manner among these soil moisture conditions. The residual phytotoxic activity of pethoxamid on the shoot growth of rice seedlings in soil was more highly correlated with the concentration in soil water than with the amounts adsorbed on soil solid and in total soil. The partition coefficients between the amounts of pethoxamid adsorbed on soil solid and its concentration in soil water were similar among the soils with different moisture conditions at each day, and the partition coefficient increased with the time after application. These results suggested that the residual phytotoxic activity of pethoxamid in soil depends on the decreasing concentration of pethoxamid in soil water with time, except in low soil-moisture conditions, which were insufficient for seedling growth.     

Phytotoxic activity of clomeprop in soil and concentration of its hydrolysed metabolite DMPA in soil water

The relationship between the fate of clomeprop in soil and its phytotoxic activity on the growth of radish (Raphanus sativus) seedlings was investigated in the laboratory. The phytotoxic activity of clomeprop in sea sand was much higher than in non-autoclaved soil, and the phytotoxic activity in non-autoclaved soil was higher than in autoclaved soil. The phytotoxic activity of 2-(2,4-dichloro-3-methylphenoxy)propionic acid (DMPA), a hydrolysed metabolite of clomeprop, was higher than that of the latter under both soil conditions. Clomeprop was adsorbed on soil to a greater extent than DMPA. The concentration of clomeprop in soil water of non-autoclaved soil decreased with increase of the DMPA concentration in the soil water in a time-dependent manner. It is suggested that the phytotoxic activity of clomeprop applied to soil is induced mostly by the DMPA concentration in soil water after hydrolytic degradation by soil microbes. © 1999 Society of Chemical Industry     

Allelopathic potential of itchgrass (Rottboellia exaltata L. f.) powder incorporated into soil

Itchgrass ( Rottboellia exaltata L. f.) is a widespread weed in northern Thailand. The farmers in this area have been using itchgrass as a mulching material in order to control other weeds in vegetable fields. Laboratory experiments were undertaken to investigate the phytotoxic activity of itchgrass powder incorporated into soil in order to evaluate the allelopathic activity in the field. The phytotoxic activity on the growth of radish seedlings ( Raphanus sativa L. var. radicula ), used as a test plant, was more pronounced in the root than in the shoot growth. The phytotoxic activity was found to be similar for the soils incorporated with the shoot or the root powder of itchgrass. The growth of the radish seedlings grown in sea sand and watered with soil water obtained from the soil previously incorporated with itchgrass powder showed a similar inhibition to those planted in the treated soil. The phytotoxic activity on the growth of the radish seedlings in the soil incorporated with the powder decreased over time. It is suggested that itchgrass releases phytotoxic compound(s) into soil water and the concentration of the active compound(s) in the soil water decreases over time.     

Residual activity of clomeprop and its downward movement under laboratory conditions

The relationship between the behavior of clomeprop ([ RS ]-2-[2,4-dichloro- m -tolyloxy]propionanilide) and its residual phytotoxic activity in the soil was investigated in the laboratory with special emphasis on the concentration in the soil water. The phytotoxic activity of clomeprop on radish seedlings ( Raphanus sativus L. var. radicula cv. Akamaruhatsukadaikon), as the test plant, became greater with time after application but the inhibition was different between the two soils, which had different properties. The amount of 2-(2,4-dichloro-3-methylphenoxy)propionic acid (DMPA), a hydrolyzed and active metabolite of clomeprop, in the soil water and total soil increased with time, corresponding to the decrease in the amount of clomeprop under non-water leakage conditions. The residual phytotoxic activity of clomeprop in the soil was more highly correlated with the concentration of DMPA in the soil water than with the amount of DMPA in the total soil. In addition, a leaching column test was conducted with clomeprop and DMPA. The DMPA easily moved downward and the concentration in the soil water in the upper layer decreased with time after application. It is supposed that the downward movement of DMPA was one of the factors influencing the lasting effect of clomeprop in the field.     

Establishing targeted control of creeping perennial weeds with soil‐active chemical injections: Assessment of subterranean bud responses in contact

Increased infestation of aggressive creeping perennial weeds is a significant problem in urban vegetation management programs. These weeds produce vigorous biomass and extensive underground networks of either rhizomes or creeping roots that easily regrow from numerous buds. Foliar application of proper systemic herbicides has been a most effective way to suppress regrowth from underground creeping organs; however, killing the mature plants has disadvantages from aesthetic, economic, and ecological viewpoints. Therefore, we intended to test the possibility of soil‐injection of soil‐active herbicides for effective control of the perennial weeds which develop underground network systems. A pot experiment using combinations of seven species (seven rhizomatous and two having creeping roots) and five chemicals (four herbicides and a plant growth regulator) was conducted to assess whether and how chemicals diffused in soil affect the sprout and growth of buds on creeping organs. All the tested herbicides completely inhibited bud sprouting in one and more species when applied at median or high rates, while most of the flurprimidol‐applied segments sprouted but shoot elongation was significantly reduced. Characteristics of each herbicide were also reflected in the selectivity and features of new outgrowth. The results indicated that chemicals existing in soil were undoubtedly absorbed and affected bud activities. It is concluded that soil injection that delivers the probable soil‐active chemicals to subterranean creeping systems could be a promising technology for controlling noxious creeping perennials.     

Behavior of pyriftalid in soil and its phytotoxic activity on Echinochloa oryzoides seedlings emerging from various soil depths

The phytotoxic activity of pyriftalid ([RS]‐7‐[4,6‐dimethoxypyrimidin‐2‐ylthio]‐3‐methyl‐2‐benzofuran‐1[3H]‐one) on barnyard grass (Echinochloa oryzoides) seedlings emerging from various depths in the soil was investigated in relation to its behavior in the soil. The growth of the barnyard grass seedlings in the soil mixed with pyriftalid was inhibited, depending on the concentration of the herbicide in the soil water but not on the amount in the total soil. A topmost pyriftalid‐treated layer was formed by applying the herbicide to the soil surface under water‐leakage conditions. The concentration of pyriftalid in the soil water and the amount that was adsorbed on the soil solid decreased with time, but the decrease was more marked in the pyriftalid concentration in the soil water than in the amount that was adsorbed on the soil solid. The emergence time of barnyard grass in the soil was faster in the seeds that were located in the shallower soil layer, compared to the deeper soil layer. The growth inhibition of the barnyard grass seedlings emerging from the shallower soil layer was greater than that of the barnyard grass seedlings emerging from the deeper soil layer after the soil surface application of pyriftalid. It is suggested that the emergence timing from the different soil depths is an important factor affecting the herbicidal activity of pyriftalid when it is applied to the soil surface under paddy field conditions.     

Role of underground parts of barnyardgrass (Echinochloa crus-galli (L.) Beauv. var. formosensis Ohwi) in its sensitivity to thenylchlor in soil

In the present study, the phytotoxic activity of top-soil applied with thenylchlor [2-chloro- N -(3-methoxy-2-thieny)-2',6'-dimethylacetanilide] on the growth of rice ( Oryza sativa L.) was dependent on the emergence depth in soil but its activity on barnyardgrass ( Echinochloa crus-galli (L.) Beauv. var. formosensis Ohwi) was only slightly affected by the emergence depth. However, the phytotoxic activity on barnyardgrass and rice was similar irrespective of the different emergence depths in its treatment to all soil layers. Thenylchlor treatment to the mesocotyl of barnyardgrass induced significant inhibition of shoot elongation, whereas the treatment to the coronal root only inhibited the coronal elongation without inhibiting shoot elongation. Absorption and translocation of ¹⁴C-thenylchlor in barnyardgrass were determined in water culture. The different amounts of radioactivity per plant among the treatments to the underground parts were due to the plant part that came in contact with ¹⁴C-thenylchlor. The radioactivity per dry weight was found to be higher in the basal part of the shoot than in its upper part in all treatments to the underground parts. It was suggested that the phytotoxic activity of thenylchlor on the growth of barnyardgrass in soil is induced by its accumulation in the basal part of the shoot through translocation. This primarily occurs after the absorption substantially by the mesocotyl from the herbicide-treated layer and additionally by other underground parts.     

Differential safening activity of dymron and fenclorim on pretilachlor injury in rice seedlings in soil

The safening activity of dymron [1-(α,α-dimethylbenzyl)-3-( p -tolyl)urea] and fenclorim [4,6-dichloro-2-phenylpyrimidine] on the phytotoxic activity of pretilachlor [2-chloro-2',6'-diethyl- N- (2-propoxyethyl)acetanilide] on rice seedlings was examined in both water and soil culture. The safening activity of fenclorim in water culture was greater than that of dymron, whereas the activity of fenclorim in soil was lower than that of dymron. The fenclorim concentration in soil water was lower than that of dymron at all times when determined after the application at the same concentrations. The phytotoxic activity of pretilachlor and the safening activities of dymron and fenclorim were well correlated with the concentration of each in soil water but not with the amount in total soil. The adsorption of fenclorim on soil solids was greater than those of dymron and pretilachlor. It was suggested that both the phytotoxic activity of pretilachlor and the safening activities of dymron and fenclorim were dependent on their concentrations in soil water, which were primarily dominated by the adsorption on soil.     

Herbicide Effects on Sugarcane Growth, Pythium Root Rot, and Pythium arrhenomanes

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.     

Allelopathic activity of Mexican sunflower [Tithonia diversifolia (Hemsl.) A. Gray] in soil under natural field conditions and different moisture conditions

The allelopathic activity of Mexican sunflower [ Tithonia diversifolia (Hemsl.) A. Gray] in soil under natural field conditions and the effect of water stress on the growth and allelopathic activity of this plant were investigated. Seed germination, shoot growth and root growth of tested plant species in soil collected from a field where Mexican sunflower had been grown for 5 years were less than those in soil from an area without the plant. Growth of young leaves, mature leaves, senescent leaves, stem and roots of Mexican sunflower was reduced with decrease in soil moisture level. The allelopathic activity of water extracts (per dry weight of starting material) from each part of the plants grown at low soil moisture levels was greater than that of the water extracts from the same part of the plants grown at high soil moisture levels. The allelopathic activity was found in the soil from the pots previously planted with Mexican sunflower to a similar extent (per plant) at different soil moisture levels. These results suggested that, in the field, under water stress conditions, the growth of Mexican sunflower was reduced but the plants contained a greater amount of allelopathic substance(s) per dry weight than in the absence of water stress. It was considered that allelopathic activity of Mexican sunflower in soil was maintained to a similar extent under various soil moisture conditions in natural fields.     

作物种类对根际土壤中丁草胺降解的影响

研究了根际和非根际土壤中除草剂丁草胺的降解。结果表明,棉花、水稻、小麦和玉米的种植明显促进丁草胺的降解,15 mg/kg丁草胺的降解半衰期缩短26.6%~57.2%,这种促进作用与作物种类有关,玉米、小麦、水稻、棉花依次增强。50 mg/kg丁草胺的降解有所受抑制,但作物种植仍显示良好的促进作用。作物根际丁草胺降解菌的测定结果显示,根际土壤中丁草胺降解菌的数量大于非根际土壤,作物种植对丁草胺降解的促进作用源于根际丰富的降解菌。     

土层水分非均匀供应下施锌对玉米植株中Ca、Fe、Mn、Cu吸收积累的影响

进行分层盆栽试验,模拟田间土壤剖面上下层水分不均匀分布条件,研究表层土壤施锌对玉米植株吸收Ca、Fe、Mn和Cu养分的影响。结果表明:上层土壤干旱抑制了苗期玉米植株生长,降低了地上部Ca、Fe、Mn分配比例。上层土壤干旱情况下,增加下层土壤水分供应,并没有提高植株生长和养分元素的吸收量。施锌明显促进了玉米地上部生长,在土壤水分充足时,施锌对植株生长效果更明显。不论土壤水分状况如何,施锌显著降低了植株中Ca、Fe、Mn、Cu浓度,对植株吸收积累Fe有拮抗作用;上层土壤干旱条件下,施锌还降低了地上部和整株中Mn以及根部Cu的积累量。施锌对植株体内Ca、Fe、Mn、Cu向上运输没有显著性影响。研究表明土壤表层干旱条件下,即使增加土壤水分,尚不能提高玉米植株生长和对Ca、Fe、Mn、Cu等养分的吸收利用。施用锌肥可以提高作物对土壤水分利用,但要注意对作物吸收Fe与Mn的拮抗作用,适当配合铁锰等养分供应。     

丛枝菌根菌丝桥传递作用对烟草抗病性相关酶活性的影响

为明确供体与受体植株间菌丝桥传递抗病信号对受体植株生长以及抗病性相关酶活性的影响,利用丛枝菌根真菌在供体与受体烟苗植株间建立菌根菌丝桥,对供体植株接种青枯菌的方法进行研究。结果表明:在供体烟苗接种丛枝菌根真菌条件下,再接种青枯菌,比只有菌丝连接的受体烟苗叶片内的过氧化物酶(peroxidase,POD)、多酚氧化酶(polyphenol oxidase,PPO)、苯丙氨酸解氨酶(phenylalanine ammonialyas,PAL)的活性分别提高了21%、29%和14%,地上部干重和植株磷含量也有相同的趋势;而在不接种丛枝菌根真菌条件下,供体烟苗接种青枯菌与否对酶的活性、植株干重及氮、磷含量均无显著影响。表明供体烟苗产生的抗病信号可以通过菌丝桥传递给受体烟苗,增强受体烟苗的抗病性。     

Plant growth inhibitory activity of Lycoris radiata Herb. and the possible involvement of lycorine as an allelochemical

Lycoris radiata Herb., a common medicinal plant of Far East Asia, was examined for its potential use in paddy weed control. The preliminary screening in greenhouse conditions indicated growth inhibitory activities. The emergence, root and shoot growth, and root dry weight of the bioassay species were reduced when grown in soil mixed with the leaves of L. radiata . Aqueous extracts of the fresh leaves at various concentrations inhibited the root and shoot growth of all tested plant species. To identify the active components, L. radiata ethanolic extract was subjected to bioassay-guided fractionation, purification, and spectroscopic analysis. This process led to the isolation of lycorine as a potential allelochemical. The concentration of lycorine in the dry leaves of L. radiata is estimated to be 0.08%. It is possible that lycorine is exuded from the roots or leaches from the living or decomposing leaves, along with other numerous inhibitors, and inhibits the growth of neighboring or successional plants. These results suggest that L. radiata has the potential to inhibit plant growth and lycorine acts as one of the most important plant growth inhibitors. This plant can be grown as a ground cover plant and its dead leaves could be applied as cover mulch.     

Allelopathic effect of leaf debris, leaf aqueous extract and rhizosphere soil of Ophiopogon japonicus Ker-Gawler on the growth of plants

Laboratory and greenhouse experiments were conducted to evaluate the allelopathic potential of dwarf lily turf ( Ophiopogon japonicus Ker-Gawler) on lettuce, alfalfa, timothy and mustard plant growth. Dry leaf debris, aqueous extract of fresh leaves and O. japonicus grown soil were investigated. Emergence, dry weight, and root and shoot length of all bioassay species were inhibited when grown in soil incorporated with oven-dried leaves of O. japonicus. The inhibitory effects were often dependent on the concentration. However, the degree of inhibition varied among the test plant species. The aqueous leaf extract was highly phytotoxic and it significantly reduced germination, seedling growth, and the fresh weight of all the test species at all rates. The emergence and growth of all four tested plants were severely inhibited when planted in O. japonicus contaminated soil. These results indicate that O. japonicus incorporated leaf debris, leaf aqueous extract and its rhizosphere soil suppress seed germination, radicle growth, seedling emergence and seeding growth of certain weeds and suggest that these responses were attributed to an allelopathic effect.     

Potential of barnyard grass to remediate arsenic‐contaminated soil

The present study investigated the arsenic (As) remediation potential of barnyard grass (Echinochloa crus‐galli L. Beauv. var. formosensis Ohwi), with a special focus on the behavior of As in the soil in comparison with rice (Oryza sativa L. cv. Nipponbare). For both plants, very little growth inhibition was observed in the As‐contaminated soil. The amount of As in the soil was reduced by the plant's uptake and the level of As in the soil water from the rice‐growing pots was remarkably lower than that in the plant‐free soil water. In the soil with the barnyard grass, the amount of As in the soil water was higher than that in the plant‐free soil water, but the amount of As in the soil and the amount of As that was adsorbed on the soil solid were reduced by the plant's uptake. At the highest As level in the soil (100 mg kg^?1), 249.60 and 101.26 µg As pot^?1 were taken up by the rice shoot and barnyard grass shoot, respectively, and total amounts of 1468.65 and 1060.57 µg As pot^?1 were taken up by the barnyard grass and rice seedlings, respectively. At the same As level in the soil, the As concentrations were 14.99 and 37.76 µg g^?1 in the shoot of barnyard grass and rice, respectively, and 486.61 and 339.32 µg g^?1 in the root of barnyard grass and rice, respectively. Barnyard grass took up more As than rice, but the As concentration in the shoot of barnyard grass was lower than that in the shoot of rice. A considerable amount of As was taken up by both barnyard grass and rice, suggesting that the plant species have the potential to remediate As‐contaminated soil.     

Dry mycelium of<Emphasis Type="Italic">Penicillium chrysogenum</Emphasis> protects cucumber and tomato plants against the root-knot nematode<Emphasis Type="Italic">Meloidogyne javanica</Emphasis>

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.     

Litter-mediated allelopathic effects of kudzu (Pueraria montana) on Bidens pilosa and Lolium perenne and its persistence in soil

This study investigated the allelopathic effects of kudzu litter on the seed germination and early growth of Bidens pilosa and Lolium perenne . The bioassays, with various concentrations (10, 20, 30, 40, and 50 g L⁻¹) of aqueous kudzu litter leachate, significantly affected the germination percentages and radicle growth of both species. These parameters decreased progressively when the seedlings were exposed to increasing concentrations of leachate. The root and shoot length, dry weight, and chlorophyll concentration of the B. pilosa and L. perenne seedlings also were significantly affected when they were grown in leachate-amended soil. However, the chlorophyll fluorescence values of the seedlings subjected to different concentrations of aqueous kudzu litter leachate indicated that the mere presence of leachate in the soil was not stressful for the plants. The seedlings of both species were under stressful conditions only when they were grown in the soil that was treated with higher concentrations of leachate (30, 40, or 50 g L⁻¹). A 6 week decomposition study of the kudzu litter in soil was conducted to observe the retention of phenolic content in the soil. The results showed that, although the concentration of dissolved organic carbon decreased with increasing decomposition, the phenolic concentration was not significantly affected when the observation period ended. This suggests that the phytotoxic properties of kudzu litter remain stable in soil systems for a considerable amount of time after incorporation into the soil.