THE ADSORPTION OF LINURON, ATRAZINE AND EPTC BY MODEL ALIPHATIC ADSORBENTS AND SOIL ORGANIC PREPARATIONS

Summary. Model adsorbents were prepared by treating cellulose phosphate powder with a series of alkyltrimethylammonium compounds in which the size of the alkyl group was varied from C₈to C₁₈. The adsorption of linuron, atrazine and EPTC by these materials was found to increase logarithmically with increasing chain length. The extent of the adsorption was large compared with the adsorption of these herbicides by a humic acid and by a preparation made by removing the bulk of the inorganic constituents of a peat soil with a mixture of HCl and HF. Since soil organic matter is thought to contain alkyl groups, it is concluded that the possible influence of such groups should be considered in any discussion of the mechanisms involved in the adsorption of organic molecules by soils.
Adsorption du linuron, de I'atrazine de l'EPTC par des adsorbants de la série aliphatique et des préparations organiques de sol     

Synthesis of the solanapyrone phytotoxins by Ascochyta rabiei in response to metal cations and development of a defined medium for toxin production

The phytotoxic solanapyrones A, B and C, were produced by Ascochyta rabiei when grown on Czapek Dox nutrients supplemented with an aqueous extract of chickpea seed but not when grown on Czapek Dox nutrients alone. Addition of amino acids, vitamins and inorganic ions to Czapek Dox nutrients allowed the production of the solanapyrones in good yields. By systematic elimination of components of this medium, the constituents essential for toxin production were identified as the divalent metal cations Zn²⁺, Ca²⁺, Mn²⁺ and Cu²⁺. When these ions were added to Czapek Dox nutrients in the same concentrations as those found in chickpea extract, concentrations of the phytotoxins similar to those found in Czapek Dox nutrients supplemented with chickpea extract were detected. Removal of cations from the chickpea supplement by a cation exchange resin did not affect the growth of the fungus compared with growth on the medium containing the complete supplement, but no toxin was produced. A defined medium and cultural conditions suitable for solanapyrone production by A. rabiei are described.     

SOME PHYSICO-CHEMICAL INTERACTIONS OF PARAQUAT WITH SOIL ORGANIC MATERIALS AND MODEL COMPOUNDS

Summary. The adsorption equilibria of paraquat were investigated on a range of organic materials including an organic soil, various humic fractions of that soil, model polymers prepared by the oxidative coupling of benzoquinone, ion-exchange resins (Zeo-Karb 216 and 226) and a polystyrene resin (Amberlite XAD-2). Isotherms were prepared for adsorption on the H⁺ and on some of the Ca²⁺ saturated materials. Measurement of the counter-ion in solution at equilibrium, and correlation of the adsorption with exchange capacity for H⁺ adsorbents showed that ion exchange was the primary adsorption mechanism. Significant amounts of non-exchange adsorption were also detected, especially at low concentrations, but generally the results followed the Rothmund-Kornfeld isotherm equation fairly accurately. The Rothmund-Kornfeld plots for the Ga²⁺ forms were complicated by the hydrolysis by water of some of the exchange sites. Other types of isotherm equations were tested and found to be unsatisfactory.
Desorption of paraquat with HCl from organic soil preparations was less than expected, and the isotherms did not conform to the Rothmund-Kornfeld or to the mass action equations. The probable reasons for this behaviour arc discussed.
Quelques interactions physico-chimiques du paraquat avec des matériaux de sol organique et des composés modèles
II. Adsorption, désorption et équilibre dans les suspensions aqueuses     

Response of black, cranberry, kidney, and white bean to linuron

Dry bean producers in Ontario, Canada, have few herbicide options available for annual broad-leaved weed management and there is little information on the tolerance of dry bean to linuron. The tolerance of black, cranberry, kidney, and white bean to the pre-emergence (PRE) application of linuron at the rates of 0, 500, 1000, 1500, 2000, and 2500 g ai ha⁻¹ was evaluated in field studies conducted in 2005 and 2006 at Exeter and in 2006 at Ridgetown, Ontario. The four market classes differed in their response to linuron. Cranberry and kidney bean were more tolerant to the PRE application of linuron than black and white bean. Linuron applied PRE caused as much as 12% injury in cranberry and kidney bean, 47% injury in black bean, and 56% injury in white bean. Linuron applied PRE at 500–2500 g ai ha⁻¹ had no effect on the height of cranberry and kidney bean but decreased the height by 7, 8, and 15% in black bean and by 10, 13, and 23% in white bean at 1500, 2000, and 2500 g ai ha⁻¹, respectively. Linuron applied PRE at the rates evaluated did not cause any adverse affect on the yield of cranberry, kidney, and white bean but black bean yield was reduced by 16% at 2500 g ai ha⁻¹. Based on these results, there is not an adequate margin of crop safety for the PRE application of linuron in black and white bean at rates >1000 g ai ha⁻¹. However, there is a potential for the use of linuron PRE for weed management in cranberry and kidney bean at the rates evaluated.     

Plant sensitivity to atrazine and chlorsulfuron residues in a soil-free system

The sensitivity of 22 major crops, pastures and weeds from the north-east grain region of Australia to atrazine and chlorsulfuron residues was determined in a glasshouse using a soil-free bioassay system. A logistic equation was fitted to the seedling fresh weights as a function of the logarithm of herbicide concentration by non-linear regression and used to calculate the doses for 10%, 30% and 50% inhibition of seedling growth (ID₁₀, ID₃₀ and ID₅₀). The ID₅₀ for atrazine ranged from 0.03 to 0.04 mg a.i. L^–1 for Salvia reflexa Hornem. and barley to 1.47 mg a.i. L^–1 for sorghum. The ID₅₀ for chlorsulfuron ranged from 0.19 to 0.21 μg a.i. L^–1 for lucerne and snail medic to 102 μg a.i. L^–1 for wheat. Based on ID₅₀ values measured, the predicted responses of each species to a range of concentrations of atrazine and chlorsulfuron were classified into four categories ranging from no damage to severe damage. These sensitivity data will assist in planning cropping sequences in soils previously treated with atrazine or chlorsulfuron.     

Effect of the fungal pathogen Bipolaris sorokiniana toxin prehelminthosporol on barley root plasma membrane vesicles

The effects of the phytotoxin prehelminthosporol from the fungal pathogen Bipolaris sorokiniana on the activities of the plasma membrane H⁺-ATPase, Ca²⁺- ATPase, and 1, 3-β-glucan synthase in barley roots were investigated in vitro. Plasma membranes were isolated by aqueous polymer two-phase partitioning. Proton pumping by the H⁺-ATPase was drastically reduced in a dose-dependent manner, with complete inhibition at 500 μM prehelminthosporol, while inhibition of ATP hydrolysis was less drastic, with a 35% inhibition at 500 μM toxin. Ca²⁺ uptake was also reduced, although to a lesser extent than proton pumping, with a maximal inhibition of 60% at 500 μM toxin. The 1, 3-β-glucan synthase activity was weakly stimulated at toxin concentrations below 100 μM, with higher concentrations being inhibitory. Taken together, our results indicate that prehelminthosporol exerts its effect in at least two ways. First, it appears to disrupt the membrane barrier and thus seriously interfere with establishment of the proton gradient that drives ion and nutrient uptake and affect the efflux of Ca²⁺ to maintain the low cytoplasmic concentration of Ca²⁺ essential for the function of Ca²⁺ as a messenger in signal transduction. Secondly, it appears to inhibit the enzyme activities. The 1, 3-β-glucan synthase is activated by Ca²⁺ and can operate in the presence of low concentrations of prehelminthosporol (which may induce Ca²⁺ leakage into the cytoplasm and hence activate the enzyme), to produce callose to seal leaky membranes.     

Application of a flowing solution culture technique to study the parasitic fitness of the nematode Radopholus similis on banana plantlets under two different nitrogen nutrient regimes

A flowing solution culture technique was used to study the effects of N nutrition on banana root infestation by the burrowing nematode Radopholus similis . Paired groups of banana plants were grown in separate compartments containing coarse sand (2–5 mm diameter). Input nutrient solutions had fixed compositions and identical total N concentrations. The two compartments differed in their NH₄⁺/total N concentrations, one receiving 0% NH₄⁺/total N (100% NO₃⁻/total N) and the other 60% NH₄⁺/total N (40% NO₃⁻/total N). The compartments were connected by a inverted T-shaped tube containing fine sand (200–250  μ m diameter) through which nematodes were inoculated. The pH and N concentrations of the output solution were determined at regular intervals. The pH of the output solution differed markedly between the two compartments, with values of 6.8 and 3.6 in the 0% and 60% NH₄⁺ compartments, respectively. In the compartment receiving 0% NH₄⁺, the number of nematodes in the roots and the growth of banana plants was significantly higher than in the compartment receiving 60% NH₄⁺. Even though they were more infested by nematodes, banana plants receiving 100% NO₃⁻ developed better than the less infested plants grown in the medium containing 40% NO₃⁻.     

SHOOT ZONE UPTAKE OF SOIL-APPLIED HERBICIDES IN PISUM SATIVUM L.

Summary. The effects of localized herbicide placement at different internodes of pea ( Pisum sativum L. cv. Alaska) shoots below the soil surface after plant emergence were studied by removing the soil from around the shoots and replacing with herbicide-treated soil. The first internode proved insensitive to linuron, diuron, atrazine and simazine at 4·5 kg/ha, while treatment of the second and third internodes markedly reduced plant growth 4–6 days after treatment. Separate exposure of the first internode alone, and the second and part of the third together to ¹⁴C-labelled atrazine indicated no difference in herbicide metabolism. However, a two- to threefold increase in ¹⁴C uptake and movement to the foliar parts occurred when the second and part of the third internode was treated, as compared to first internode treatment. Thus the differential sensitivity of the internodes to atrazine, and possibly to the other herbicides, may be because the more mature first internode allows less uptake and subsequent movement to the foliar parts.
Absorption dans la zone des tiges des herbicides appliqués dans le sol chez Pisum sativum L.     

阳离子对黄瓜苗期猝倒病菌果胶酶活性的影响

 本文首次从寄主-寄生物相互关系角度系统研究了阳离子对黄瓜苗期猝倒病菌Pythium aphanidermatum产生的果胶酶活性的影响,胚轴胞壁Ca²⁺含量很大,而且随苗龄增加,其含量也有规律的增加。细胞壁Ca³⁺含量变化与胚轴抗病菌果胶酶能力密切相关。不同阳离子对病菌在寄主体内、外产生的PG活性有明显影响,并随反应时间而变化。病菌在寄主体内和体外合成的PG对阳离子敏感程度不同。低浓度Ca²⁺有激活PG的作用,高浓度Ca²⁺则抑制PG活性。Na⁺超过一定浓度时有抑制PG活性的作用。PGTE比PMTE对Ca³⁺抑制作用敏感。     

Effects of salt stress on ion accumulation and antioxidative enzyme activities of Oryza sativa L. and Echinochloa oryzicola Vasing

The effects of salt stress on physiological factors, such as inorganic ion absorption and antioxidative enzyme activities, of rice ( Oryza sativa L. cv. Anapurna) and Echinochloa oryzicola Vasing were investigated. Although having similar morphology, rice and E. oryzicola possessed considerably different salt-tolerance mechanisms. Echinochloa oryzicola was more salt-tolerant than rice. When exposed to salt stress (100 mmol L⁻¹ sodium chloride, NaCl; six days), E. oryzicola had the ability to limit the accumulation of sodium ions (Na⁺), maintained high potassium ion (K⁺) content and had a constantly higher K⁺/Na⁺ ratio than rice. Rice was not effective in limiting Na⁺ absorption but had a higher antioxidative capacity than E. oryzicola . The constitutive activities of superoxide dismutase (SOD) and catalase of rice were three and five times higher than that of E. oryzicola, respectively. Induced activities of SOD, ascorbate peroxidase and glutathione reductase were also higher in rice than in E. oryzicola . The high antioxidative capacity was one of the tolerance mechanisms used by rice to cope with salt stress. Therefore, the salt tolerant-mechanisms are different between the two plants.     

The effect of nutrients on the decomposition of the herbicides atrazine and linuron incubated with soil

The rates of disappearance of atrazine and linuron when incubated at 22°C with soil or soil containing added nutrient materials were determined with 2 contrasting soils. Inorganic salts, straw or a combination of both increased atrazine degradation in both soils. None of the treatments influenced linuron breakdown greatly. It is concluded that in these soils the rate limiting step in atrazine degradation could be microbiological, not chemical.     

Weeds resistant to chlorsulfuron and atrazine from the north-east grain region of Australia

The resistance of weeds to triazine and sulfonylurea herbicides has been recorded in several countries. The extent of the problem in the north-east grain region of Australia is uncertain. In an initial study, resistance to chlorsulfuron and atrazine in 15 weed species was investigated. The study showed that at least six of them have evolved resistance to one or other of these herbicides. Two collections of Rapistvum rugosum L., three of Sisymbrium orientale L., five of Sonchus oleraceus L., one of Fallopia convolvulus (L.) A. Love and one of Sisymbrium rhellungii O. Schultz were resistant to the recommended rate of chlorsulfuron (15 g a.i. ha^-1). Resistance to chlorsulfuron was not discovered in three collections of Sisymbrium L., two of Brassica tournefortii Gouan. three of Emex australis Steinh. and 11 of Phalaris paradoxa L. Two collections of Urochtoa panicoides Beauv. were resistant, and three collections possibly resistant, to the recommended rate of atrazine(1.8 kg a.i. ha^-1). Resistance to atrazine was not found in 12 collections of Hibiscus urionum L., nine of Salvia reflexa L., two of Parthenium hysterophorus L., two of Amaranthus viridis L. and 14 of Echinochloa colona (L) Link. The resistance status of four weeds ( R. rugosum. F. convolvulus, S. thellungii and U. panicoides was confirmed using a multiple dose-response screen and is the first report of resistance for these species. Herbicide usage records show that resistance has developed after 3-10 years of selection with chlorsulfuron and 2-15 years of selection with atrazine, with no correlation between the frequency of use and the degree of resistance for any of the species where eight or more collections were made.     

Triadimenol drenches and residues in tobacco seedbeds improve growth and disease control in transplants

Triadimenol residues in sandy and clay soils, following applications of up to 1 g/m² in previous seasons to tobacco seedlings 2 days before they were transplanted, had little effect on seedling emergence and growth. Residues were beneficial to transplants; they improved growth and controlled stem and root infection caused by Rhizoctonia solani and Fusarium solani. During the first 4 weeks after transplanting, stem infection was negatively correlated with log_e of the pre-sowing rate of triadimenol and with log_e of the soil concentration in seedbeds at pulling. Plant growth increased linearly according to the equation l/Y=a+b/(x-c), where Y = plant dry mass (g/plant), .x = triadimenol pre-sowing (mg/m²) and c= - 1 1, determined iteratively, r² = 0-94; P < 0.001. Triadimenol applications to bare soil increased the soil concentration by 1 μ/g per 50 mg/m² applied.     

THE DECOMPOSITION OF UREA HERBICIDES BY BACILLUS SPHAERICUS, ISOLATED FROM SOIL

Summary. The decomposition of seven urea herbicides by Bacillus sphaericus was studied. Experiments with ¹⁴C-labelled monolinuron demonstrated that monolinuron was degraded by removal of CO₂ from the ureido portion of the molecule and leaving the /Kchloroaniline moiety. Tests with monuron, diuron, monolinuron, linuron, metobromuron, fluometuron and methabenzthiazuron indicated that B. sphaericus was only able to decompose the methoxy compounds monolinuron, linuron and metobromuron in this way. All compounds were identified by infrared spectroscopy. A pathway for degradation of the herbicides by B. sphaericus is proposed.     

Chemical characteristics of precipitation and the indicative significance for sand dust events in the northern and southern slopes of Wushaoling Mountain,northwestern China

Precipitation chemistry analysis is essential to evaluate the atmospheric environmental quality and identify the sources of atmospheric pollutants. In this study, we collected a total of 480 precipitation samples at 6 sampling sites in the northern and southern slopes of Wushaoling Mountain from May 2013 to July 2014 to analyze the chemical characteristics of precipitation and to identify the main sources of ions in precipitation. Furthermore, we also explored the indicative significance for sand dust events in the northern and southern slopes of Wushaoling Mountain based on the precipitation chemistry analysis.During the sampling period(from May 2013 to July 2014), the p H values, EC(electrical conductivity)values and concentrations of cations(Ca~(2+), Mg~(2+), Na~+, K~+ and NH_4~+) and anions(SO_4~(2–), NO_3~–, Cl~–, NO_2~– and F~–) in precipitation were different in the northern and southern slopes at daily and seasonal time scales, with most of the values being higher in the northern slope than in the southern slope. The chemical type of precipitation in the southern and northern slopes was the same, i.e.,SO_4~(2–)-Ca~(2+)-NO_3~–-Na~+. The concentrations of ions in precipitation were mainly controlled by terrigenous material and anthropogenic activities(with an exception of Cl~–). The concentration of Cl~– in precipitation was mainly controlled by the sea salt fraction. The concentrations of Na+ and Cl~– showed an increasing trend after the occurrence of sand dust events both in the northern and southern slopes. In addition, after the occurrence of sand dust events, the concentrations of K~+, Mg~(2+), SO_4~(2–), NO_3~– and Ca~(2+) showed an increasing trend in the southern slope and a decreasing trend in the northern slope. It is our hope that the results may be helpful to further understand the atmospheric pollution caused by sand dust events in the Wushaoling Mountain and can also provide a scientific basis for the effective prevention of atmospheric pollution.     

Contribution of host plant resistance and geographic distance to the structure of Potato virus Y (PVY) populations in pepper in northern Tunisia

The genetic structure of Potato virus Y (PVY) populations was investigated in naturally-infected pepper ( Capsicum annuum ) fields, collected at eight different localities in northern Tunisia, where 23% of the sampled plants were homozygous for the pvr2¹ recessive resistance allele, while the other plants carried the dominant susceptibility allele pvr2⁺ . Restriction fragment length polymorphism analysis at three PVY genome segments revealed a high level of viral diversity, with a majority of cases showing co-infection of individual plants by several PVY haplotypes and a strong genetic differentiation of viral populations collected in the different localities. Geographic distances affected the differentiation of PVY populations and isolation by distance among these populations was significant. However, the occurrence of the pvr2¹ resistance allele did not contribute to the structure of viral populations, suggesting that the virulence properties of the virus did not significantly affect its fitness. Consequently, greater deployment of the pvr2¹ gene would probably not be a suitable strategy to control PVY, and other resistance genes should be preferred.     

Resistance to Sphaerotheca pannosa in roses induced by 2,6-dichloroisonicotinic acid

The susceptible rose cv. Madelon and the partially resistant cv. Sonia both responded with reduced development of rose powdery mildew when they were treated with the synthetic inducer 2,6-dichloroisonicotinic acid (INA). The EC₅₀ for number of colonies cm⁻² was approximately 0.4 mg L⁻¹ in both cultivars when treated 4 days prior to inoculation. However, conspicuous differences were observed with respect to number of spores per cm². For sporulation, the EC₅₀ was 0.37 mg L⁻¹ in cv. Madelon and only 0.08 mg L⁻¹ in cv. Sonia. A comparison with the pathosystems cucumber/ Sphaerotheca fuliginea and red cabbage/ Peronospora parasitica is made and the importance of the observed phenomenon for the selection of parents in a breeding programme for (partial) resistance is discussed.     

Effect of the herbicides EPTC and linuron on cotton diseases caused by Rhizoctonia solani and Fusarium oxysporum f. sp. vasinfectum

The herbicides EPTC and linuron applied to soil in the field at three different concentrations X₂X, 1X, and 2X of recommended dose) decreased post-emergence, but not pre-emergence daraping-off in cotton incited by Rhizoctonia solani. Both herbicides at the two high concentrations significantly reduced wilt incited by Fusarium oxysporum f. sp. vasinfectum. Both herbicides reduced germination of chlamydospores of Fusarium in natural soil, but not in steamed soil. The 2X concentration of EPTC and linuron reduced the saprophytic activity of R. solani in soil. The effects of EPTC and linuron on post-emergence damping-off and wilt were attributed Ic their ability to suppress the saprophytic ability of R. solani and chlamydospore germinability of Fusarium in soil, respectively.     

Pathogenicity of the root-knot nematode Meloidogyne javanica on potato

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).     

Differences in physiological responses to NaCl between salt-tolerant Sesbania rostrata Brem. & Oberm. and non-tolerant Phaseolus vulgaris L.

Sesbania rostrata ( S. rostrata) Brem. & Oberm., a member of the Fabaceae family, has been used as a promising halophytic plant to ameliorate soil salinity in north-east Thailand. To obtain information regarding the mechanism of salt tolerance, the physiological responses of S. rostrata to NaCl was compared with those of the salt-susceptible species, kidney bean ( Phaseolus vulgaris L. cv. Meal). Seedlings were grown hydroponically with 0, 50, 100 and 150 m m NaCl for 10 days and their effects on growth, chlorophyll content, fluorescence yield ( F _v/ F _m), inorganic elements and amino acid content were determined. The results showed that tolerance to NaCl was clearly different between the two plants. At the highest concentration (150 m m ), the dry weight of S. rostrata was more than 50% greater than the control, whereas the kidney bean could not survive. Chlorophyll a content drastically reduced only in the kidney bean. The F _v/ F _m of S. rostrata did not change with increasing concentrations of NaCl, but that of kidney bean decreased. Greater percentages (≥80%) of absorbed Na⁺ and Cl^– were translocated and accumulated in the shoots of S. rostrata , but remained largely in the roots of kidney bean. The enhancement of contents of amino acids, including proline, with increasing NaCl was observed in both species. These results strongly suggest that the salt tolerance of S. rostrata is associated with the ability of the plant to translocate and sequester Na⁺ and Cl^– in the shoot cells.