The detection and distribution of organophosphorus and carbamate insecticide-resistant Myzus persicae (Sulz.) in Britain in 1976

Examination of the enzyme that determines the level of resistance to organophosphorus insecticides and carbamates in Myzus persicae (Sulz.) and bioassays were used to establish the frequency and resistance levels of resistant aphids on outdoor crops in Britain in 1976. The biochemical tests, staining esterase-4 after electrophoresis and total esterase determination, were more sensitive than bioassays. However the dip-test, a simple, rapid and inexpensive bioassay designed to detect resistance and its different levels gave satisfactory results which warrant its use where biochemical detection of resistance is not possible. Carboxylesterase activities of M. persicae collected in 1976 fell into three groups: low, moderate and high, and these were correlated with differences in tolerance to dimethoate, demeton-S-methyl and pirimicarb. Aphids with low esterase activity were susceptible(S). Those with the moderately active enzyme (R₁) had five- to seven-fold resistance to the two organophosphorus insecticides and were marginally resistant (about two-fold) to pirimicarb. The insects with the most active esterase (R₂) were strongly resistant to dimethoate (resistance factor, RF × 126) and moderately resistant to demeton-S-methyl (RF × 17) and pirimicarb (RF × 8). Some R₁, but no S aphids survived the recommended dose of demeton-S-methyl on field crops probably because they were under the lowest leaves and therefore protected from direct contact with the spray. Laboratory tests demonstrated that these R₁ aphids tolerated the residual deposit and systemic dose present in the leaves of the treated potato-plants. This enabled their numbers to recover in treated fields much faster than the susceptible insects which could do so by immigration only when the residual dose in the plant was no longer toxic. R₁ aphids were common throughout the country particularly in eastern England where susceptible aphids were rare, but in the Shardlow area of Derbyshire susceptible aphids were in the majority throughout the summer. R₂ aphids were found only in samples from the west of Scotland and northern England. The implications of the presence of aphids with different levels of resistance for aphid control are discussed.     

The symbiotes of Myzus persicae (Sulz.) in strains resistant and susceptible to demeton-S-methyl

The lengths of individual symbiotes and the numbers of these per unit area in ultrathin sections of the mycetomes did not differ significantly between strains of Myzus persicae (Sulz.) that were resistant or susceptible to demeton-S-methyl in Britain. This is contrary to observations made in Germany on the symbiotes of similar aphids resistant or susceptible to parathion.     

Elucidating resistance in cotton genotypes to whitefly, <Emphasis Type="Italic">Bemisia tabaci,</Emphasis> by population buildup studies

Plant resistance has become an important component of integrated pest management (IPM) for management of whitefly, Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), an important pest of cotton in India. The present studies were undertaken to standardize the plant stage and identify resistant cotton genotypes against whitefly. Nine plant stages of F846, a susceptible cotton genotype, were exposed to whitefly for 25 days under no-choice conditions. The population buildup (eggs, nymphs, pupae and adults) was recorded. The 12-, 14- and 16-leaf stages were suitable for plant resistance studies against whitefly, and the 14-leaf stage was taken for further studies. Ten cotton genotypes of Gossypium hirsutum and two of G. arboreum were covered with split cages in which five pairs of B. tabaci (F₁) were released. The population buildup was recorded to categorize genotypes as resistant, moderately resistant, moderately susceptible or susceptible. The experiment was repeated with F₂ and F₃ generation whiteflies. Based on overall average score of three experiments, LD694 was rated as resistant; LK861, Supriya, RS2013, CNH911 and PA183 as moderately resistant; IS-376/4/1/20/72, NHH44, TxMaroon2-78, Bt 6304 and RS2098 as moderately susceptible; and F846 as susceptible. LD694 was found to be resistant in three consecutive generations of whitefly.     

The cross-resistance to pyrethrins and eight synthetic pyrethroids,of an organophosphorus-resistant strain of the rust-red flour beetle Tribolium castaneum (herbst)

Comparisons with standard susceptible insects showed that a strain of Tribolium castaneum, with a specific resistance to malathion and its carboxylic ester analogues, had no cross-resistance to topical applications of natural pyrethrins. Another strain of T. castaneum, showing resistance to many organophosphorus (OP) insecticides, was cross-resistant to pyrethrins ( × 34) and eight synthetic pyrethroids also applied topically; least cross-resistance occurred with resmethrin ( × 2.2), bioresmethrin ( × 3.3) and phenothrin ( × 4.0). Generally larger resistance factors were recorded with formulations synergised by piperonyl butoxide (PB). The greatest cross-resistance encountered was with unsynergised tetramethrin ( × 338). Apart from tetramethrin, factors of synergism did not exceed 5.7 with either the susceptible or multi-OP resistant strains. PB antagonised six of the nine pyrethroids against the multi-OP resistant strain. Antagonism also occurred with two of these six, permethrin (cis: trans ratio 1:3) and 5-prop-2-ynylfurfuryl ( 1RS)-cis,trans-chrysanthemate (‘Prothrin’), against the susceptible strain. Considering only formulations without the synergist, the most effective compounds against the susceptible strain, relative to pyrethrins, were bioresmethrin (2.7) and permethrin (2.4). Similarly with the multi-OP resistant strain the most effective compounds were bioresmethrin (28), resmethrin (14) and permethrin (6.6). Thus the LD₅₀ (the dose required to kill 50% of the test species) for bioresmethrin against the resistant strain (0.14 μg) only slightly exceeded the LD₅₀ for pyrethrins against the susceptible strain (0.12 μg).     

Field strains of Stemphylium vesicarium with a resistance to dicarboximide fungicides correlated with changes in a two-component histidine kinase

In Stemphylium vesicarium, four phenotypes were recognized according to their in vitro responses to dicarboximide fungicides: S (sensitive), S₊ (low resistant to iprodione and procymidone but moderately resistant to vinclozolin), R₁ (moderately resistant to iprodione and vinclozolin but highly resistant to procymidone), R₂ (highly resistant to all dicarboximides). Cross-resistance was observed between dicarboximides and aromatic hydrocarbon fungicides in all cases while cross-resistance to phenylpyrroles was only detected in R₂ phenotype. Moreover, no changes were noted in sensitivity to oxidative and osmotic stress inducers. An osmosensing histidine kinase gene, homologous to OS1 from Neurospora crassa, was sequenced from several field isolates of Stemphylium vesicarium. This gene is predicted to encode a 1,329 amino acid protein, comprising a conserved histidine-kinase domain in the C-terminal region and six tandem repeats of about 90 amino acids at the N-terminal end. In S₊ and R₁ phenotype isolates, a single amino acid substitution was observed in the first amino acid repeat; F267L and L290S respectively. For the R₂ isolates, the exchanges T765R or Q777R were located within the histidine-kinase domain.     

The activity of some pyrethroids against Periplaneta americana and Blattella germanica

The knockdown and contact killing actions of various pyrethroids were compared using Blattella germanica and Periplaneta americana. A wide range of knockdown activity was found; 5-benzyl-3-furylmethyl (1R)-cis-3-(dihydro-2-oxo-3-thienylidenemethyl)-2,2-dimethylcyclopropanecarboxylate (RU 15525) acted fastest, more rapidly than pyrethrins, against B. germanica as well as having a low LD₅₀ value. Topical application and direct spray tests showed that (S)-α-cyano-3-phenoxybenzyl (1R)-cir-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropanecarboxylate (NRDC 161) was more active as a killing agent, by an order of magnitude, than cismethrin, the next most active compound, and also had considerable knockdown activity. Piperonyl butoxide generally had little synergist effect. Female P. americana were over three times more tolerant than males to a range of insecticides applied topically. Residual knockdown action in the WHO resistance test was observed to provide baseline data. There was little overlap in speed of action between pyrethroids and other insecticides among the compounds tested.     

The effect of timing of fungicide applications on control of frogeye leaf spot and grain yield of soybeans

Soybean cultivar Samsoy 1, and the breeding lines TGx 849-313D and TGx 996-26E, grown in a field with a heavy epidemic of frogeye leaf spot caused byCercospora sojina, were treated with double foliar applications of the fungicide benomyl. The treatments were made using four application schedules at six different growth stages, starting from V₃ (fully developed leaves, beginning with trifoliate nodes) to R₅ (beginning seed_, to determine the effect of the fungucide timing on frogeye leaf spot severity, soybean grain yield and grain quality. Generally, applications at R₁ (beginning bloom) and R₃ (beginning pod) significantly (P<-0.05) reduced disease severity in the 2 susceptible genotypes, Samsoy 1 and TGx 849-313D. Plot yields of these genotypes were also significantly greater than the untreated controls when the fungicide applications were made at R₁ and R₃. There was no significant difference in diseave severity or grain yield, between the untreated control and the different times of application, on the resistant genotype TGx 996-26E. Improved seed germination and lower levels of seed infection byC. sojina occurred for all fungicide timings in the susceptible genotypes. The results suggest that fungicide spraying initiated at R₁ and followed up at R₃ is most effective in frogeye leaf spot control and can also result in higher grain yields, than applications made earlier or later in the season. Control of frogeye leaf spot, however, is best achieved by growing resistant cultivars.     

Evaluation and QTL mapping of resistance to powdery mildew in lettuce

Lettuce (Lactuca sativa) is the major leafy vegetable that is susceptible to powdery mildew disease under greenhouse and field conditions. Quantitative trait loci (QTLs) for resistance to powdery mildew under greenhouse conditions were mapped in an interspecific population derived from a cross between susceptible L. sativa cultivar Salinas and the highly susceptible L. serriola accession UC96US23. Four significant QTLs were detected on linkage groups LG 1 (pm‐1.1), LG 2 (pm‐2.1 and pm‐2.2) and LG 7 (pm‐7.1), each explaining between 35 to 42% of the phenotypic variation. The four QTLs are not located in the documented hotspots of lettuce resistance genes. Alleles for the disease resistance at the four QTLs originated from both parents (two from each), demonstrating that even highly susceptible accessions may provide alleles for resistance to powdery mildew. These QTLs appeared to operate during limited periods of time. Results of the field trials with F_2:3 and F_3:4 families derived from a Soraya (moderately resistant) × Salinas cross demonstrated effective transfer of resistance to powdery mildew in this material. An integrated rating approach was used to estimate relative levels of resistance in 80 cultivars and accessions tested in a total of 23 field and greenhouse experiments. Generally, very low resistance was observed in crisphead‐type lettuces, while the highest relative resistance was recorded in leaf and butterhead types. Comparison of two disease assessment methods (percentage rating and the area under the disease progress steps, AUDPS) for detection of QTLs shows that the two approaches complement each other.     

Characterization of acephate resistance in the diamondback moth Plutella xylostella

Decreased acetylcholinesterase (AChE) sensitivity and metabolic detoxification mediated by glutathione S-transferases (GSTs) were examined for their involvement in resistance to acephate in the diamondback moth, Plutella xylostella. The resistant strain showed 47.5-fold higher acephate resistance than the susceptible strain had. However, the resistant strain was only 2.3-fold more resistant to prothiofos than the susceptible strain. The resistant strain included insects having the A298S and G324A mutations in AChE1, which are reportedly involved in prothiofos resistance in P. xylostella, showing reduced AChE sensitivity to inhibition by methamidophos, suggesting that decreased AChE1 sensitivity is one factor conferring acephate resistance. However, allele frequencies at both mutation sites in the resistant strain were low (only 26%). These results suggest that other factors such as GSTs are involved in acephate resistance. Expression of GST genes available in P. xylostella to date was examined using the resistant and susceptible strains, revealing no significant correlation between the expression and resistance levels.     

Stereochemical and chiral aspects in the synthesis of 3-(2,2- dihalovinyl)-2,2-dimethylcyclopropanecarboxylic acids

The synthesis of (1RS)-cis,trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylic acid by dehydrohalogenation of 4,6,6,6-tetrahalohexanoates has been modified to produce stereo-selectively the cis-isomer. A new stereospecific synthesis of cis-3-(2,2-dihalovinyl)-2,2-dimethylcyclopropanecarboxylic acids using a bicyclic lactone and its extension to the preparation of the optically active (1R)-cis acid are described.     

八种除草剂对小麦田三种抗精噁唑禾草灵杂草的生物活性

为筛选能有效防除抗精噁唑禾草灵杂草的除草剂,采用温室盆栽法测定菵草(敏感S_w、抗性R_w)、日本看麦娘(敏感S_r、抗性R_r)、耿氏硬草(敏感S_y、抗性R_y)对精噁唑禾草灵的抗性水平,并研究了8种除草剂对这3种抗性杂草的生物活性。结果显示,3种杂草抗性种群对精噁唑禾草灵的抗性指数均大于33.7,已达高抗水平。3种杂草抗性种群均对同类乙酰辅酶A羧化酶类抑制剂唑啉草酯和炔草酯产生了11.6~56.5倍不等的高水平抗性。对部分乙酰乳酸合成酶类抑制剂产生了2.0~4.8倍的低水平抗性,氟唑磺隆对3种杂草抗性种群防效较差,GR_(90)为67.31~114.39g(a.i.)/hm~2;啶磺草胺仅对Rr种群防效较好,GR_(90)为4.67 g(a.i.)/hm~2;甲基二磺隆对3种杂草抗性种群防效均较好,但对Rr种群存在抗性风险,已出现2.0倍低水平抗性;磺酰磺隆对Ry和Rr种群防效较好;丙苯磺隆对Rr种群防效好。细胞分裂抑制剂氟噻草胺对3种杂草抗性种群防效均最好,在田间推荐剂量120 g(a.i.)/hm~2下可达90%以上的防效。     

Comparative analysis of early H2O2 accumulation in compatible and incompatible wheat–powdery mildew interactions

Comparative analysis was carried out for hydrogen peroxide (H₂O₂) accumulation in response to powdery mildew (Blumeria graminis[Erysiphe graminis] f.sp. tritici) primary germ tube (PGT) and appressorial germ tube (AGT) contact, and in papilla (cell wall apposition) and hypersensitive responses (HR) in wheat (Triticum aestivum). Using primary leaves of three susceptible wheat lines (Bainong 3217; Beijing 837; Jingshuang 16) and five resistant lines [Mardler (Pm2 + Pm6); Ulka/8 × Cc (Pm2); Mardler/7 × Bainong 3217 (Pm2); Pm16; Pm16/7 × Beijing 837 (Pm16)], early H₂O₂ accumulation between 10 and 48 h after inoculation was studied. Strong H₂O₂ accumulation was found in effective papillae and associated cytosolic vesicles in both susceptible and resistant wheat lines, suggesting the important role of H₂O₂ in effective papillae formed as a general plant defence against powdery mildew. High frequency of effective papilla formation was observed in all five resistant lines. Among resistant lines, hypersensitive cell death was detected earlier in Mardler and Ulka/8 × Cc than in Pm16 and Pm16/7 × Beijing 837. In all cases this was associated with H₂O₂ accumulation in attacked epidermal cells. Interestingly, penetration resistance but not HR appeared to be mediated by the Pm2 gene in the Mardler/7 × Bainong 3217 line, suggesting that Pm2 may govern an HR-independent defence pathway in this genetic background. As effective papillae and HR did not occur in the same cells, papilla deposition may be independent of the HR response, despite the fact that both defence mechanisms were associated with high H₂O₂ accumulation. In wheat powdery mildew-incompatible interactions, HR acts as a second line of defence to contain infection when the papilla defence fails.     

A biochemical mechanism of resistance to pirimicarb in two glasshouse clones of Aphis gossypii

The susceptibility of three clones of Aphis gossypii Glover to 15 insecticides was established by bioassay. A high level of resistance towards pirimicarb was confirmed for a clone from Holland (Dutch R) and a clone from Japan (Jap R), while the susceptible clone (S) was killed by very low doses of the insecticide. However, only limited cross-resistance was shown towards other carbamates and organophosphates, and no marked resistance to the pyrethroids tested. The acetylcholinesterase (AChE) of both resistant clones hydrolysed acetyl-choline faster than that of susceptible aphids, with greatest enzyme activity shown by the Dutch R clone. Inter-clone differences in these rates were consistent with differences in catalytic centre activities. Inhibition (I₅₀) of AChE by pirimicarb was approximately 900-fold higher for the resistant clones than for the S clone. First-order kinetics revealed that resistance to pirimicarb in Dutch R and Jap R involved a modified AChE which had a reduced (approximately 350-fold) affinity (K_d) for pirimicarb. The marked change in AChE affinity for pirimicarb was not repeated with the other carbamates tested, ethiofencarb and aldicarb. It was considered that the resistant aphids would not require mechanisms in addition to insensitive AChE in order to show the high level of resistance to pirimicarb shown in the bioassay.     

上海地区菜缢管蚜对有机磷的抗药性及其生化检测

呼伦贝尔盟农田杂草计49科、198属、348种,其中包括6个亚种、29个变种和1个变型。杂草发生特点:种类多、多年生杂草多、恶性杂草多、群落结构特殊、危害严重。主要优势群落:茅香和光稃茅香群落、匍匐冰草群落、野燕麦群落与裂边鼬瓣花群落。防治措施与策略:适当压缩小麦,扩大油菜种植面积,在休闲地应用草甘膦防治多年生杂草,用2甲4氯取代2,4-D丁酯防治小麦田杂草,发展应用磺酰脲类除草剂与禾草灵混用,以兼治野燕麦与宽叶杂草。     

辛氰和乐氰混剂对甘蓝桃蚜抗性演化的影响

用辛硫磷与氰戊菊酯,乐果与氰戊菊酯的最佳配比及其相应单剂对甘蓝桃蚜进行抗性选育,汰洗２０代时桃蚜对两种混剂的抗性,分别为４．２０和２．６８倍,比相应单剂的抗性发展速度慢,尤其比氰戊菊酯单剂（２８９倍）更慢,表明上述两种混剂都可延缓桃蚜的抗性发展。用酶抑制剂进行增效应用测定结果表明：Ｋ１和ＴＰＰ对辛硫磷和乐果都有增效作用,尤以Ｋ１的增效作用更显著,其增效比分中辊为１０５３和３８,说明桃蚜对辛硫磷和乐     

小麦白粉病反应型和产孢量的关系

利用小麦的6个品种及小麦白粉菌的3个小种研究了小麦苗期白粉病反应型与产孢量之间的关系。分别用累积单斑产孢量(LBSY)、累积单位面积产孢量(LASY)与反应型组建了反应型-产孢量关系模型:Y_1=exp(1.7178×lnX 0.0256X-2.484)(LBSY法);Y_2=exp(1.5168×lnX 0.052X-2.309)(LASY法)(X为反应型,Y为产孢系数)。通过LBSY方法获得反应型0,1,2,3~-,3,3~ ,4~-,4所对应的产孢系数分别为0,0.09,0.29,0.49,0.60,0.71,0.96,1。     

Inheritance of resistance in <Emphasis Type="Italic">Solanum nigrum</Emphasis> to <Emphasis Type="Italic">Phytophthora infestans</Emphasis>

Solanum nigrum, black nightshade, is a wild non-tuber bearing hexaploid species with a high level of resistance to Phytophthora infestans (Colon et al. 1993), the causal agent of potato late blight, the most devastating disease in potato production. However, the genetic mode of resistance in S. nigrum is still poorly understood. In the present study, two S. nigrum accessions, 984750019 (N19) and #13, resistant (R) and susceptible (S), respectively, to three different isolates of P. infestans, were sexually crossed. The various kinds of progeny including F1, F2, F3, and backcross populations (BC₁; F1 × S), as well as two populations produced by self-pollinating the R parent and S parent, were each screened for susceptibility to P. infestans isolate MP 324 using detached leaf assays. Fifty seedling plant individuals of the F1 progeny were each resistant to this specific isolate, similarly to the seedling plants resulting from self-pollination of the resistant R parent. Thirty seedling plants obtained from self-pollination of the S parent were susceptible. Among a total of 180 F2 plants, the segregation ratio between resistant and susceptible plants was approximately 3: 1. Among the 66 seedling plants of the BC₁ progeny originating from crossing an F1 plant with the susceptible S parent, there were 26 susceptible and 40 resistant plants to P. infestans. The segregation patterns obtained indicated monogenic dominant inheritance of resistance to P. infestans isolate MP 324 in S. nigrum acc. 984750019. This gene, conferring resistance to P. infestans, may be useful for the transformation of potato cultivars susceptible to late blight.     

Comparison of screening methods to evaluate the response of St. Augustine grass to Magnaporthe oryzae

The objective of this study was to develop a reliable and high throughput screening method to evaluate the response of St. Augustine grass (Stenotaphrum secundatum) genotypes to the grey leaf spot (GLS) caused by Magnaporthe oryzae infection. Whole plant, detached stolon and detached leaf assays under growth chamber conditions were compared to field conditions on eight commercial and nine advanced breeding lines of St. Augustine grass. Disease was assessed using two variables, lesion size (LS) and overall plant disease severity (SEV). LS and SEV were highly correlated for field and growth chamber screening methods using the whole plant assay (LS r² = 0·79; SEV r² = 0·83; P ≤ 0·001), the detached stolon assay (LS r² = 0·75; SEV r² = 0·72; P ≤ 0·001), and the detached leaf assay (LS r² = 0·46; SEV r² = 0·60; P ≤ 0·001). Genotypic variation for resistance in 17 St. Augustine grass genotypes was identified using all screening methods for LS (P < 0·05) and SEV (P < 0·05). The rank‐sum method was used to classify St. Augustine grass genotypes into highly resistant (HR), resistant (R), moderately resistant (MR), moderately susceptible (MS), susceptible (S) and highly susceptible (HS) classes based on the rank‐sum values of LS and SEV. Two introduced African polyploids used as parents, and two F₁ interploid progeny obtained using an in vitro embryo rescue technique, were classified as highly resistant (HR), or resistant (R), across all screening methods.     

Tagging and mapping a second resistance gene for <Emphasis Type="Italic">Fusarium</Emphasis> wilt race 0 in chickpea

A second gene conferring resistance to the chickpea wilt pathogen, Fusarium oxysporum f. sp ciceris race 0, has been mapped to linkage group 2 (LG2) of the chickpea genetic map. Resistance to race 0 is controlled by two genes which segregate independently; one present in accession JG62 (Foc0 ₁ /foc0 ₁ ) and mapping to LG5 and the second present in accession CA2139 (Foc0 ₂ /foc0 ₂ ) but remaining unmapped. Both genes separately confer complete resistance to race 0 of the wilt pathogen. Using a Recombinant Inbred Line (RIL) population that segregated for both genes (CA2139 × JG62) and the genotypic information provided by two markers flanking Foc0 ₁ /foc0 ₁ ten resistant lines containing the resistant allele Foc0 ₂ /foc0 ₂ were selected. Genotypic analysis using these ten resistant lines paired with ten susceptible RILs, selected in the same population, revealed that sequence tagged microsatellite sites (STMS) markers sited on LG2 were strongly associated with Foc0 ₂ /foc0 ₂ . Linkage analysis, using data from two mapping populations (CA2139/JG62 and CA2156/JG62), located Foc0 ₂ /foc0 ₂ in a region where genes for resistance to wilt races 1, 2, 3, 4 and 5 have previously been reported and which is highly saturated with tightly-linked STMS markers that could be used in marker-assisted selection (MAS).