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1.
A muscarinic acetylcholine receptor (mAChR) has been demonstrated and partially characterized in larvae of the cattle tick Boophilus microplus. Its properties are compared with mAChR from an epithelial cell line from the dipteran insect Chironomus tentans. Competition studies with cholinergic ligands of different specificity revealed the muscarinic nature of the cholinergic receptors investigated in both species. In homogenates from tick larvae, specific binding sites for [3H]quinuclidinyl benzilate (QNB) with high affinity (1·2±(0·13) nM ; Bmax 22·5 pmol mg protein−1) were detected that do not bind nicotinic compounds specifically. The estimated IC50 values for nicotine, imidacloprid and α-bungarotoxin were all in the mM range. Additionally, with tick larvae, high-affinity nicotinic binding sites were detected with [3H]nicotine which could be displaced by high concentrations of imidacloprid or QNB. The estimated IC50 values for nicotine, α-bungarotoxin, imidacloprid and QNB were 43(±8) nM , 0·8(±0·2) μM , 2·8(±0·6) μM and 78(±1·9) μM , respectively. With homogenates of the non-neuronal insect cell line from C. tentans, only high-affinity binding sites for [3H]QNB were found. Muscarinic antagonists selectively displaced [3H]quinuclidinyl benzilate (QNB) binding to tick larvae homogenates. The mAChR of B. microplus preferred pirenzepine (IC50 2·13(±1·02) μM ) among different subtype-specific mAChR antagonists (4-DAMP had IC50 49·9(±9·13) μM and methoctramine had IC50 121(±14·2) μM ) indicating a type of binding site similar to the vertebrate M1 mAChR subtype. The tick muscarinic receptor seems to be a G-protein-coupled receptor, as concluded from the 4·8-fold reduction in receptor affinity for binding of the muscarinic agonist oxotremorine M upon treatment with the non-hydrolysable GTP-analogue γ-S-GTP. Binding data for the agonists oxotremorine M (IC50 71·3(±19·6) μM ) and carbachol (IC50 253(±87·1) μM ) parallel the biological efficacy of these compounds, in that, while oxotremorine M showed some activity against ticks, carbachol was ineffective.  相似文献   

2.
The molecular weight pattern and the stage-specific activities of chitinases from the blowfly Lucilia cuprina, the tick Boophilus microplus and the intestinal nematode Haemonchus contortus were examined. Chitinolytic enzymes could be detected in all parasite species tested, but the activity was different between the stages. Highest chitinolytic titers were found in blowfly pupae (83 kDa, 118 kDa), hatching larvae of ticks (58 kDa, 94 kDa) and nematode eggs (43 kDa). Leaves from ethylene-treated bean plants Phaseolus vulgaris expressed two basic Class I chitinases (Ia, Ib) of 34 kDa, differing in their amino acid sequences at residue 33 and 34 (Ia: glycine, proline; Ib: lysine, aspartic acid). Inhibitor studies with blowfly pupae revealed that allosamidin (IC50=0·32 (±0·02) μM ) was by far the best inhibitor when compared with various amino sugar derivatives. This compound also inhibited chitinases from tick larvae (IC50=0·69(±0·10) μM ) and nematode eggs (IC50=0·048(±0·0045) μM ) specifically. Whereas Class Ia chitinase from bean leaves was inhibited only up to 18% by 10 μM allosamidin, it had an IC50 of 1(±0·14) μM for the Ib type, which is the first plant chitinase described to be highly sensitive to allosamidin.  相似文献   

3.
The calcium channel and the ‘calcium release channel’ of muscle membrane of the cockroach Periplaneta americana have been characterized. Biological assays with calcium channel blockers and ryanodine on different insects and acari revealed pronounced insecticidal effects with ryanodine, but not with calcium channel blockers, at concentrations between 0·1 and 300 μg ml−1. Skeletal muscle membranes derived either from the tubular network or from the sarcoplasmatic reticulum of P. americana were characterized with respect to the binding of the dihydropyridine (DHP) [3H]isradipine (PN 200-110), the phenyl-alkylamine [3H]verapamil and the alkaloid [3H]ryanodine. Preliminary binding studies with the benzothiazepine [3H]diltiazem suggest a low-affinity binding site with a IC50 value of 3·3 μM . All binding sites tested were sensitive to treatment with proteinase K. Optimal conditions for binding of the radioligand ryanodine revealed the highest specific binding at pH 8 and at calcium chloride concentrations between 100 and 500 μM . EGTA at 10 μM abolished 95% of the ryanodine binding. Binding studies with calcium channel binding sites revealed a pronounced effect of low Ca2+ concentrations on specific isradipine binding, whereas verapamil and diltiazem binding were only reduced by the presence of 200 μM EGTA. With respect to high Ca2+ concentrations, specific binding of diltiazem, isradipine and verapamil was reduced by 73, 40 and 20%, respectively, at 5 mM Ca2+. Radioligand binding experiments showed high-affinity binding sites for ryanodine and isradipine. KD values of 0·95 nM (Bmax=550 fmol mg−1 protein) and 0·75 nM (Bmax=213 fmol mg−1 protein) were determined respectively. A lower-affinity binding site was identified in binding studies with verapamil (KD=7·4 nM and Bmax=27 fmol mg−1 protein). [3H]isradipine displacement studies with several dihydropyridines revealed the following ranking of affinity: nitrendipine>isradipine>Bay K8664≪nicardipine. Displacement of [3H]verapamil binding by effectors of the phenylalkylamine binding site showed that bepridil and S(-)verapamil had the highest affinities of the compounds tested followed by (±)verapamil, nor-methylverapamil and R(+)verapamil.  相似文献   

4.
Alternaria leaf blight (ALB), caused by Alternaria dauci, is one of the most damaging foliar diseases of carrot worldwide. The aim of this study was to compare different methods for evaluating levels of carrot resistance to ALB. Three techniques were investigated by comparison with a visual disease assessment control: in vivo conidial germination, a bioassay based on a drop‐inoculation method, and in planta quantification of fungal biomass by quantitative PCR (Q‐PCR). Three carrot cultivars showing different degrees of resistance to A. dauci were used, i.e. a susceptible cultivar (Presto) and two partially resistant genotypes (Texto and Bolero), challenged with an aggressive or a very aggressive isolate of A. dauci. Both partially resistant genotypes produced a higher mean number of germ tubes per conidium (up to 3·42±0·35) than the susceptible one (1·26±0·18). The drop‐inoculation results allowed one of the partially resistant genotypes (Bolero, log10(S+1) = 1·34±0·13) to be distinguished from the susceptible one (1·90±0·13). By contrast, fungal growth measured by Q‐PCR clearly differentiated the two partially resistant genotypes with log10(I) values of 2·77±0·13 compared to the susceptible cultivar (3·65±0·13) at 15 days post‐inoculation. This result was strongly correlated (r2 = 0·91) with the disease severity index scored at the same date. Data obtained with the different assessment methods strongly suggest that the Texto and Bolero genotypes have different genetic resistance sources.  相似文献   

5.
The pharmacokinetics of total radioactivity and of intact fenvalerate were determined in sheep treated intravenously with radiolabelled or non-radiolabelled fenvalerate. Mean residence times (MRT) of total radioactivity and intact fenvalerate in plasma were 910 (±75) and 39 (±3) min, while harmonic mean elimination-phase half-lives (TMβ) were 990 and 82 min, each respectively. Systemic clearance values (ClS) of total radioactivity and intact fenvalerate were 2·8 (±0·3) ml min−1 kg−1 and 51·3 (±5·9) ml min−1 kg−1, respectively. Volumes of distribution at steady state (VSS) were each near 2500 ml kg−1. Elimination of radioactivity occurred, in part (33·3 (±3·3)% of dose), by renal excretion, at a rate (0·9 (±0·1) ml min−1 kg−1), similar to that of glomerular filtration. These data are consistent with a disposition model according to which intact fenvalerate was rapidly distributed into a peripheral compartment, where metabolism occurred. In addition, since the elimination half-life of fenvalerate from plasma was less than 90 min after intravenous injection, ‘flip-flop’ kinetics should be considered when longer elimination half-lives are observed after oral or dermal exposures.  相似文献   

6.
The present study reports on the insecticidal and acaricidal potentials of dibenzyltrisulfide (DBTS) isolated from the roots of Petiveria alliacea L. using thin layer and high performance liquid chromatography. The 96-h LD50 value (μg per tick) obtained for adult Boophilus microplus (Canestrini) topically treated with DBTS was 0·920. The LD50 values obtained for three commercial acaricides dimethoate, lindane and carbaryl were 4·6, 9·3 and 6·9 μg per tick respectively. The IOD50 and IHD50 (concentrations inhibiting egg laying and hatching by 50% respectively) in μg per tick doses for DBTS were 0·22 and 0·24 respectively. The 24-h LD50 dose (μg per insect) obtained for DBTS on adult Cylas formicarius elegantulus (Summer) was 0·193 μg per insect. The vapour from a stock solution of 5 g litre-1 of DBTS was highly toxic to adult Hypothenemus hampei Ferr. inside coffee berries, inflicting 89% mortality within 24 h. © 1997 SCI.  相似文献   

7.
Effective treatment with juvenile hormone analogues (JHAs) of early penultimate or early last-instar locust hoppers induces a supernumerary ‘extra’ nymphal instar. These ‘extra’ nymphs, also termed ‘adultoids’, die in the course of, or shortly after, an ‘extra’ moult. Less effective treatment results in imperfect adults with crumpled twisted wings which presumably limit their flight and migratory abilities. Extremely effective treatment leads to death in the next moult. Comparing dose-response relations of (7S)-methoprene, fenoxycarb, pyriproxyfen and a new JHA, R70-1 (ethyl cis-N-{2-[4-(2-hydroxycyclohept-1-ylmethyl)phenoxy]ethyl}carbamate), we revealed that route of administration, instar of the recipient hopper, and species may alter over 1000-fold the ED50 for the same JHA. Locusta migratoria migratorioides is much more susceptible to JHAs than Schistocerca gregaria. The lowest ED50 found to induce adultoids and subsequent death in the ‘extra’ moult was 0·12 μg pyriproxyfen injected in olive oil to early penultimate instar hoppers of L. m. migratorioides (about 0·5 μg g-1 fresh weight). R70-1 was more active than pyriproxyfen following the more practical topical application to early last-instar hoppers of L. m. migratorioides, 5·9 μg and 46 μg per hopper, respectively (about 10 μg g-1 and 78 μg g-1 fresh weight). The high susceptibility of last-instar L. m. migratorioides nymphs to topically applied R70-1 is promising from the practical standpoint. ©1997 SCI  相似文献   

8.
Downy blight, caused by Peronophythora litchii, is an important disease of lychee (litchi) plants in China. The in vitro sensitivities of various asexual stages of P. litchii to the three carboxylic acid amide (CAA) fungicides dimethomorph, flumorph and pyrimorph were studied with four single‐sporangium isolates. None of the three fungicides affected zoospore discharge from sporangia, but they strongly inhibited mycelial growth (mean EC50 values of 0·075, 0·258 and 0·115 mg L?1, respectively); sporangial production (mean EC50 values of 0·085, 0·315 and 0·150 mg L?1, respectively); germination of cystospores (mean EC50 values of 0·140, 0·150 and 0·645 mg L?1, respectively); and germination of sporangia (mean EC50 values of 0·203, 0·5 and 0·743 mg L?1, respectively). As mycelial growth was the most sensitive stage to dimethomorph and pyrimorph, it was chosen to test baseline sensitivities to the three fungicides. In 2007, from 131 isolates collected in Fujian, Guangdong and Guangxi provinces, 127, 116 and 113 isolates were used to establish baseline sensitivity for dimethomorph, flumorph and pyrimorph respectively. Isolates from different provinces exhibited similar baseline sensitivity to the same fungicide. Baseline sensitivities to dimethomorph, flumorph and pyrimorph were distributed as unimodal curves, with mean EC50 values of 0·082 (± 0·01), 0·282 (± 0·047), and 0·115 (± 0·032) mg L?1, respectively. This information will serve as a baseline for tracking future changes in sensitivities of P. litchii populations to these three CAA fungicides.  相似文献   

9.
The biological action of citruspeel oils was shown to depend on a strong fumigant action. Bioassays conducted in air-tight glass chambers showed that all the six citrus oils tested had vapour toxicity towards adults of Callosobruchus maculatus F., Sitophilus zeamais Motsch. and Dermestes maculatus Deg. The 24-h LC50 value of limepeel oil (a typical citrus oil) vapour against C. Maculatus was 7·99 μl litre−1 which made it 1·5 and 1·6 times less toxic against the smaller S. zeamais and the larger D. maculatus adult insects. When immature stages were fumigated, limepeel oil vapour had 24-h LC50 values of 7·8 and 21·5 μl litre−1 against eggs of C. maculatus and D. maculatus respectively, and 9·1, 17·8 and 23·1, 23·9 μl litre−1 against early larvae, pupae of C. maculatus and late larvae, pupae of D. maculatus respectively. X-ray studies showed that fumigated C. maculatus larvae within cowpea grains died immediately without further development. The bioactivities of five other citruspeel oils were similar to that of limepeel oil. Bioassays showed that sorption of citruspeel oil fumes occurred in the presence of grains or strips of dried fish, and that this tended to reduce the amount available for fumigant action outside the materials. The problems presented by sorption may hinder the development of citrus oils into practical fumigants for large-scale treatments of stored commodities.  相似文献   

10.
The toxicity of ryanodine ( 1 ) and 9,21-didehydroryanodine ( 2 ) (the principal active ingredients of the botanical insecticide ryania) to adult female house flies (Musca domestica L.) is attributable to binding to the ryanodine receptor (ryr) and thereby disrupting the Ca2+-release channel. These ryanoids, assayed in house flies with piperonyl butoxide (PBO) to suppress cytochrome P450-dependent detoxification, give injected KD50 values of 0·07–0·11 μg g-1, injected LD50 values of 0·39–0·45 μg g-1 and topical LD50 values of 12– 50 μg g-1. They inhibit the [3H]ryanodine binding site of house fly and rabbit muscle with IC50 values of 3–10 nM . This study examines the effect of structure on potency, with 15 variants of the cyclohexane substituents, two 4,6-cyclic boron and two methylated derivatives, and four modifications of the isopropyl and ester substituents. The most effective compound examined was 10-deoxy- 2 ( 3 ) which was more potent than 2 by 2–4-fold on injection and 29-fold applied topically following PBO (LD50 0·41 μg g-1). Additional high-potency compounds were 10-oxo- 1 and the cyclohexane variants with lactam, 21-nor-9-oxo and 21-nor-10-deoxy substituents. Other modifications usually reduced toxicity. The injected knockdown potency of the ester ryanoids was generally related to their effectiveness in competing with [3H]ryanodine at the ryr of rabbit skeletal muscle. Two non-ester ryanoids, ryanodol and 9,21-didehydroryanodol, were found to be more toxic than predicted from their potency at the ryr and may therefore act in a different manner such as at a K+ channel, as suggested by Usherwood and Vais. Clearly ryanoids are challenging prototypes for a potential new generation of insecticides. © 1997 SCI.  相似文献   

11.
水稻稻瘟病菌对烯肟菌胺的抗性风险评估及抗性机制初探   总被引：2，自引：0，他引：2  
 采用菌丝生长速率法测定了100株采自我国主要水稻产区的水稻稻瘟病菌对烯肟菌胺的敏感性, 结果表明, 其EC50分布于0.011 1~0.295 6 μg·mL-1, 平均EC50=(0.078 6±0.056 1) μg·mL-1。供试菌株对烯肟菌胺的敏感性分布呈单侧峰曲线, 未出现抗药性亚群体, 可将该曲线作为稻病瘟菌对烯肟菌胺的敏感性基线。通过室内药剂驯化获得了7株抗药突变体, 突变频率为1.11×10-4, 其中2株高抗突变体NJ0811-I和A10的抗性水平大于1 000倍, 抗药性性状能稳定遗传, 致病力显著弱于其亲本菌株;5株低抗突变体抗性水平在2.05～4.55倍之间, 抗药稳定性差, 适合度与亲本无显著性差异。交互抗药性结果表明, 烯肟菌胺与嘧菌酯存在正交互抗药性, 与田间防治稻瘟病常用药剂稻瘟灵、异稻瘟净无交互抗药性。综合分析表明, 稻瘟病菌对烯肟菌胺可能存在低到中等抗性风险。进一步克隆了抗药突变体及其亲本的cytb基因, CYTB氨基酸序列比对结果表明, 2株高抗突变体均在143位由甘氨酸突变为丝氨酸(G143S), 建立了高抗菌株的AS-PCR分子检测方法;而5株低抗突变体cytb基因未发生点突变, 推测可能存在其他的抗性分子机制。  相似文献   

12.
Fundamental to the development of models to predict the spread of cucurbit downy mildew is the ability to determine the escape of Pseudoperonospora cubensis sporangia from infected fields. Aerial concentrations of sporangia, C (sporangia m?3), were monitored using Rotorod samplers deployed at 0·5 to 3·0 m above a naturally infected cucumber canopy in two sites in central and eastern North Carolina in 2011, where disease severity ranged from 1 to 40%. Standing crop of sporangia was assessed each morning at 07·00 h EDT and ranged from 320 to 16 170 sporangia m?2. Disease severity and height above the canopy significantly (P < 0·0001) affected C with mean concentration (Cm) being high at moderate disease. Values of Cm decreased rapidly with canopy height and at a height of 2·0 m, Cm was only 7% of values measured at 0·5 m when disease was moderate. Daily total flux (FD) was dependent on disease severity and ranged from 5·9 to 2242·3 sporangia m?2. The fraction of available sporangia that escaped the canopy increased from 0·028 to 0·171 as average wind speed above the canopy for periods of high C increased from 1·7 to 3·6 m s?1. Variations of Cm and FD with increasing disease were well described (P < 0·0001) by a log‐normal model with 15% as the threshold above which Cm and FD decreased as disease severity increased. These results indicate that disease severity should be used to adjust sporangia escape in spore transport simulation models that are used to predict the risk of spread of cucurbit downy mildew.  相似文献   

13.
The mobility and retention of atrazine and dicamba in six Atlantic Coastal Plain soils were estimated by soil thin-layer chromatography (soil-TLC). The soils studied were representative of the major agricultural regions in Delaware and were sampled, by horizon, to the water table. Four horizons from each profile were leached simultaneously with distilled water on one soil-TLC plate. Two values were obtained from each plate: the ratio of the distance traveled by the herbicide center of mass over that traveled by the solvent front (Rm), and a sorption distribution coefficient (Kd). The Rm values ranged from 0·06 to 0·94 for atrazine and from 0·80 to 0·94 for dicamba. Herbicide mobility was found to be greatest in coarse-textured soil horizons that contained low levels of organic matter, clay, and Fe and Al oxides. Correlation analysis indicated that effective cation exchange capacity, exchangeable acidity, exchangeable aluminum, and clay were useful predictive variables or both atrazine mobility and sorption. Organic matter was not useful for predicting soil-TLC derived sorption estimates; however, it was correlated to Kd-batch estimates. Distribution coefficients calculated from soil-TLC data were found to be in general agreement with Kd values obtained for the same soils by batch equilibrium techniques. The average Kd-soil-TLC values for atrazine and dicamba were 2·09(±2·24) and 0·03(±0·02), respectively. The ratio of the batch Kd to the soil-TLC Kd ranged from 0·1 to 19 (x̄=1·6, SD=3·8) for atrazine and from 2·9 to 38 (x̄=12·6, SD=8·7) for dicamba. Thus, although for some horizons agreement between the two methods was good, for other horizons significant discrepancies existed. It is suggested that the soil-TLC gives results under non-equilibrium conditions, whereas the batch procedure is, by definition, at quasi-equilibrium. These fundamental differences may account for the observed differences between the two methods. It is also suggested that, due to this difference, the soil-TLC procedure can provide additional information relevant to herbicide partitioning in the field environment that is not provided by traditional batch equilibrium techniques. © 1998 Society of Chemical Industry  相似文献   

14.
The dissipation of mecoprop in wheat (Triticum aestivum L.) and oat (Avena sativa L.) was monitored over a growing season following post-emergence application of the dimethylamine salt of mecoprop to each crop at 1·1 kg ha?1. Residues of mecoprop, as its methyl ester, were determined gas chromatographically using electrolytic conductivity detection. Initial residues in wheat (119 (±20) mg kg?1) and oat (95·3 (± 10·0) mg kg?1) on the day of application (four-leaf stage of wheat and four- to five-leaf stage of oat) decreased to 0·1 to 0·2 mg kg?1, respectively, within six weeks. Residues were non-detectable in the mature seed of both crops. Recoveries of mecoprop were in the order of 90% from the green tissue and seed of both crops fortified at 0·05 mg kg?1.  相似文献   

15.
The relative importance of beetle species associated with Fusarium circinatum‐infected Monterey pines was investigated in three Monterey pine forests along the coast of central California, USA from April to November in 2004 and 2005. Fusarium circinatum was frequently isolated from Ips mexicanus and I. plastographus. The mean percentage isolation based upon numbers of I. mexicanus and I. plastographus carrying propagules of F. circinatum was 17·7 and 10·9% in 2004 and 16·7 and 17·3% in 2005, respectively. The mean percentage isolation was high in the spring and early summer and low in late summer and autumn in all three locations for both species. Isolation was higher from beetles emerging from harvested F. circinatum‐infected pine‐stems than for trapped beetles, 42·4% for I. mexicanus and 45·9% for I. plastographus. The mean (± SE) propagule load of trapped I. mexicanus was 269·5 (± 14·1) in 2004 and 281·7 (± 35·7) in 2005 and was 216·1 (± 28·9) in 2004 and 251·9 (± 28·4) in 2005 for I. plastographus. Mean propagule loads decreased from May to November in all locations for both species. Propagule loads of beetles emerged from infected stems were lower than that of trapped beetles, with means of 89·4 (± 23·2) and 93·0 (± 23·2) for I. mexicanus and I. plastographus, respectively. Thus beetles must acquire fungal propagules from more than one infected host. These results also suggest that higher contamination rates and propagule loads in spring and early summer may indicate a higher risk of pitch canker transmission, relative to late summer or autumn.  相似文献   

16.
Phytophthora austrocedrae is a recently discovered pathogen that causes severe mortality of Austrocedrus chilensis in Patagonia. The high level of susceptibility of the host tree, together with the distribution pattern of the pathogen, have led to the hypothesis that P. austrocedrae was introduced into Argentina. The aim of this study was to assess the population structure of P. austrocedrae isolates from Argentina in order to gain an understanding of the origin and spread of the pathogen. Genetic diversity was determined based on amplified fragment length polymorphisms (AFLPs). In total, 48 isolates of P. austrocedrae were obtained from infected A. chilensis trees, representing the geographical range of the host. Four primer combinations were used for the AFLP analysis. Of the 332 scored bands, 12% were polymorphic. Gene diversity (h) ranged from 0·01 to 0·03; the Shannon index (I) ranged from 0·01 to 0·04. A high degree of genetic similarity was observed among the isolates (pairwise S values = 0·958–1; 0·993 ± 0·009, mean ± SD). A frequency histogram showed that most of the isolate pairs were identical. Principal coordinate analysis using three‐dimensional plots did not group any of the isolates based on their geographical origin. The low genetic diversity (within and between sites) and absence of population structure linked to geographic origin, together with the aggressiveness of the pathogen and the disease progression pattern, suggest that P. austrocedrae might have been introduced into Argentina.  相似文献   

17.
Sikimi plant (also known as Japanese star anise), Illicium anisatium, is toxic to mammals. Extracts of Sikimi were studied for their insecticidal activity against the larvae of mosquito, Culex quinquefasciatus, and for their mechanism of action on ion channels. Crude methanol extract and its ethyl acetate-soluble fractions were insecticidally active, with EC50 values of 63·0 μg ml-1 and 43·7 μg ml-1, respectively. The ethyl acetate-soluble fraction was perfused through the bathing solution and the current induced by a brief (10 ms) application of GABA by pressure ejection through pipette electrode was recorded by the whole-cell patch clamp technique. The extract suppressed GABA-induced currents irreversibly with an EC50 value of 0·42 μg ml-1. The time constant of current fitted to the single exponential function was shortened by the ethyl acetate-soluble fraction at concentrations ranging from 0·1 μg ml-1 to 10 μg ml-1 in a concentration-dependent manner. It was concluded that Sikimi extracts decreased the affinity of GABA for its binding site on the GABA receptor, thereby suppressing GABA-induced currents. © 1998 SCI  相似文献   

18.
C. Zhang  H. Wu  X. Li  H. Shi  F. Wei  G. Zhu 《Plant pathology》2013,62(6):1378-1383
During 2009–2010, a total of 323 isolates of Xanthomonas oryzae pv. oryzae were obtained from rice with symptoms of bacterial leaf blight (BLB) in four provinces (Zhejiang, Jiangsu, Anhui and Hubei) in China. These isolates were tested for baseline sensitivity to zinc thiazole, a novel bactericide with strong antibacterial activity against Xanthomonas. The sampled pathogenic population had similar sensitivity to zinc thiazole (0·1–16·8 mg L?1) in all four regions and over the whole two‐year study period. The baseline sensitivity was distributed as a unimodal curve with a mean EC50 value of 6·79 ± 1·61 mg L?1. The risk of mutation to resistance of zinc thiazole in X. oryzae pv. oryzae was further evaluated in vitro and in vivo. Twelve zinc thiazole‐resistant mutants were obtained through ultraviolet (UV) irradiation, culturing on zinc thiazole‐amended nutrient agar (NA) plates, and culturing on zinc thiazole‐treated rice plants. These zinc thiazole‐resistant mutants had resistance factors (RF = EC50 value of a mutant / EC50 value of the wildtype parent of this mutant) of 12·4 to 186·1 with a mean RF value of 44·1. Mutants obtained via UV irradiation, culturing on NA plates and culturing on rice plants had mean RF values of 51·8, 24·5 and 14·4, respectively. All mutants showed decreases in resistance to zinc thiazole after 20 successive transfers on bactericide‐free media or 10 successive inoculation–reisolations on bactericide‐free rice plants. No significant difference was found in bacterial growth and sensitivity to bismerthiazol between zinc thiazole‐resistant mutants and their parents. However, a significant decrease was observed in the pathogenicity of zinc thiazole‐resistant mutants compared with their parents, especially for mutants obtained via UV irradiation.  相似文献   

19.
Summary. A linear increase from 933 to 15,943 ppmw of copper occurred in hydrilla (Hydrilla verticillata Casp.) 4 days after treatment with copper sulphate pentahydrate (CUSO4. 5H2O, CSP) at 0·5–4·0 ppmw of copper. Neither increase in calcium levels to 0·8 MM in the ambient solution nor aeration affected the amount of copper in excised hydrilla tissue during a 24-h treatment period with CSP at 1·0 ppmw of copper. Part of the accumulated copper appeared to be bound in hydrilla. A higher accumulation of copper occurred after treatment with an organic copper complex (cutrine) than with either CSP or copper chloride (CuCI2.2H2O, at 1·0 ppmw of copper. This high accumulation with cutrine appeared to be related principally to the amount of copper remaining in the treatment solution.  相似文献   

20.
Pristine® (pyraclostrobin + boscalid) is a fungicide registered for the control of alternaria late blight in pistachio. A total of 95 isolates of Alternaria alternata collected from orchards with and without a prior history of Pristine® sprays were tested for their sensitivity towards pyraclostrobin, boscalid and Pristine® in conidial germination assays. The EC50 values for 35 isolates from orchards without Pristine® sprays ranged from 0·09 to 3·14 µg mL?1 and < 0·01 to 2·04 µg mL?1 for boscalid and Pristine®, respectively. For pyraclostrobin, 27 isolates had EC50 < 0·01 µg mL?1 and six had low resistance (mean EC50 value = 4·71 µg mL?1). Only one isolate was resistant to all three fungicides tested, with EC50 > 100 µg mL?1. Among 59 isolates from the orchard with a history of Pristine® sprays, 56 were resistant to pyraclostrobin; only two were sensitive (EC50 < 0·01 µg mL?1) and one was weakly resistant (EC50 = 10 µg mL?1). For the majority of these isolates EC50 values ranged from 0·06 to 4·22 µg mL?1 for boscalid and from 0·22 to 7·74 µg mL?1 for Pristine®. However, seven isolates resistant to pyraclostrobin were also highly resistant to boscalid and Pristine® and remained pathogenic on pistachio treated with Pristine®. Whereas strobilurin resistance is a common occurrence in Alternaria of pistachio, this is the first report of resistance to boscalid in field isolates of phytopathogenic fungi. No cross resistance between pyraclostrobin and boscalid was detected, suggesting that Pristine® resistance appears as a case of multiple resistance.  相似文献   

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