麦田抗性生物型荠菜对苯磺隆的抗性机制研究

为明确抗性生物型荠菜对苯磺隆的抗性机制,分别测定了苯磺隆对抗性和敏感生物型荠菜体内乙酰乳酸合成酶(ALS)、谷胱甘肽-S-转移酶(GSTs)、超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)的影响。结果表明:离体条件下,抗性生物型荠菜体内ALS对苯磺隆的敏感性明显降低,苯磺隆对荠菜抗性和敏感生物型ALS的抑制中浓度(I50)分别为0.722 8和0.052 1 μmol/L,抗性与敏感生物型I50的比值为13.87;活体条件下,施用苯磺隆后,抗性和敏感生物型荠菜ALS活性均受到一定程度的抑制,但抗性生物型ALS活性受到抑制后能逐渐恢复,而敏感生物型则不能恢复;经苯磺隆处理后,抗性生物型GSTs相对活力明显高于敏感生物型,而抗性和敏感生物型体内POD、SOD和CAT相对活力无明显差异。研究表明,抗性生物型荠菜体内ALS对苯磺隆敏感性降低是其抗药性产生的原因之一,而GSTs对苯磺隆代谢能力的差异也可能与荠菜对苯磺隆的抗性有关。     

Comparative spatial dispersal ofTomato yellow leaf curl virus vectored by B and Q biotypes ofBemisia tabaci in Tomato glasshouses

The spatial dispersal patterns ofTomato yellow leaf curl virus (TYLCV) disease vectored by the B and Q biotypes of the whiteflyBemisia tabaci in tomato glasshouses were compared. Tomato plants were arranged in glasshouses and TYLCV-infected plants were placed in the center of each plot. Adult whiteflies of each biotype were released onto TYLCV-infected plants and the insects were then freely dispersed in the glasshouses under high or moderate temperature conditions. The abundance and spatial distribution of dispersed whiteflies did not differ between the B and Q biotypes in tomato glasshouses. The disease incidence and dispersion of TYLCV as a result of short-distance movement of the whiteflies were also similar between the two biotypes, although on several investigation dates there was a tendency for the disease incidence caused by the B biotype to be slightly greater than that caused by the Q biotype. These results demonstrated that the aspects of spatial spread of TYLCV vectored by the B and Q biotypes ofB. tabaci in tomato glasshouses are similar. http://www.phytoparasitica.org posting Dec. 11, 2007.     

L-阿拉伯糖对B型和Q型烟粉虱毒性及取食行为的影响

为明确L-阿拉伯糖对B型和Q型烟粉虱毒性及其取食行为的影响,调查了饲喂含有L-阿拉伯糖人工饲料后烟粉虱的死亡率,利用刺吸电位技术(EPG)记录其取食行为,并观察了饲喂后其在人工饲料膜上的刺孔数量及直径。结果表明,B型和Q型烟粉虱的校正死亡率均随L-阿拉伯糖浓度及饲喂时间的增加而升高;在3种浓度下,B型烟粉虱校正死亡率均显著高于Q型烟粉虱;在5%、10%浓度下,Q型烟粉虱校正死亡率分别在第5天和第3天达100%,B型烟粉虱分别在第3天和第2天达到100%;5%L-阿拉伯糖对B型烟粉虱取食行为影响比Q型大;在5%浓度下,B型和Q型烟粉虱在膜上的刺孔数量总体少于对照组。研究表明,L-阿拉伯糖对烟粉虱具有杀虫活性,且对B型和Q型烟粉虱的毒性效果不同。     

PCR-RFLP identification ofBemisia tabaci biotypes in the Mediterranean Basin

At least 20 genetic biotypes, with varying degrees of biological characterization, are currently recognized within theBemisia tabaci (Hemiptera: Aleyrodidae) species complex. Their identification relies on a set of different molecular techniques. However, none of the available markers is completely adequate, due to technical difficulties or lack of reproducibility. We therefore developed a method for rapid biotyping ofB. tabaci populations. The five biotypes (B, Q, M, S and T) reported until now in the Mediterranean Basin have been tested by PCR amplification of the cytochrome oxidase I mitochondrial gene followed by restriction with the enzymeTru9I. The digestion patterns produced by this enzyme were able to identify the five biotypes clearly. Digestion with another enzyme,TaqI, discriminated only between biotypes B and Q. The newly developed method enables rapid biotyping and can be applied in studies aimed at assessing biotype distribution and competition at least in the Mediterranean area. http://www.phytoparasitica.org May 14, 2006.     

不同体色生物型烟蚜的取食特性分析

为探究不同体色生物型烟蚜Myzus persicae取食行为的差异,明确其在烟田的分布特征,利用刺探电位图谱(EPG)技术测定了红色型、绿色型和褐色型3种体色生物型烟蚜在烟草上的取食行为。结果表明:红色型烟蚜刺探取食之前对烟草寄主所花费的识别时间最短,为2.20 min,极显著短于褐色型烟蚜的10.09 min。绿色型烟蚜在刺探过程中pd波平均持续时间为7.45 s,显著长于红色型烟蚜的6.85 s,极显著长于褐色型烟蚜的3.95 s,但3种体色生物型烟蚜的pd波次数无显著差异。首次刺吸至第1次出现E2波所需时间,绿色型和褐色型烟蚜均约为红色型烟蚜的2倍。韧皮部取食阶段,3种体色生物型烟蚜分泌唾液(E1波)的时间无显著差异;红色型烟蚜被动吸食汁液(E2波)时间为112.28 min,显著长于绿色型烟蚜的70.02 min和褐色型烟蚜的75.15 min。褐色型烟蚜在木质部主动摄取汁液(G波)的时间最短为8.58 min,与另外2种体色生物型烟蚜差异显著。表明3种体色生物型烟蚜各自具有不同的取食策略,但总体而言红色型烟蚜对烟草的适应性最强。     

Biotype Q of<Emphasis Type="Italic">Bemisia tabaci</Emphasis> identified in Israel

The biotype status of samples of the whiteflyBemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) collected from several field and greenhouse sites in Israel during 1999–2000 was determined by polyacrylamide gel electrophoresis (PAGE) for general esterases, and by RAPD-PCR using primers of arbitrary sequence. Results of this survey provide the first published evidence for the occurrence of theB. tabaci Q biotype, alongside the more widely distributed B biotype. Based on the collected samples, it appears that both the B and Q biotypes are present in Israel, and that field populations consist of a mixture of the two biotypes. A possible link betweenB. tabaci biotypes and insecticide resistance is discussed. Contribution no. 508/02 from the Inst. of Plant Protection, ARO, The Volcani Center, Bet Dagan, Israel. http://www.phytoparasitica.org posting Dec. 5, 2002.     

Physiological and molecular basis for ALS inhibitor resistance in Bromus tectorum biotypes

Primisulfuron‐resistant (AR and MR) and ‐susceptible (AS and MS) Bromus tectorum biotypes were collected from a Poa pratensis field at Athena, Oregon, and in research plots at Madras, Oregon. Studies were conducted to characterize the resistance of the B. tectorum biotypes. Whole plant bioassay and acetolactate synthase (ALS) enzyme assay revealed that the AR biotype was highly resistant to the sulfonylurea (SU) herbicides, primisulfuron and sulfosulfuron and to a sulfonylaminocarbonyltriazolinone (SCT) herbicide, propoxycarbazone‐sodium. However, the AR biotype was not resistant to imazamox, an imidazolinone (IMI) herbicide. Results of the whole plant bioassay studies showed that the MR biotype was moderately resistant to all ALS inhibitors tested. However, there were no differences in ALS sensitivities between the MR and MS biotypes. The nucleotide and amino acid sequence analysis of the als gene demonstrated a single‐point mutation from C to T, conferring the exchange of the amino acid proline to serine at position 197 in the AR biotype. However, this mutation was not found in the MR biotype. Results of this research indicate that: the resistance of the AR biotype to SU and SCT herbicides is based on an altered target site due to a single‐point mutation; resistance in the MR biotype is not due to a target site mutation.     

High-throughput allelic discrimination of B and Q biotypes of the whitefly, Bemisia tabaci, using TaqMan allele-selective PCR

BACKGROUND: B and Q biotypes of the whitefly, Bemisia tabaci (Gennadius), are generally regarded as the most significant given their global distribution and strong resistance to insecticides. Since these biotypes can coexist and differ markedly in their insecticide resistance profiles, a rapid but reliable means of discriminating between them would be a valuable complement to resistance monitoring and management programmes. Recently, PCR‐based methods have been developed to determine the biotype status of B. tabaci populations. However, these require post‐amplification procedures, which increase time and labour. RESULTS: The authors have developed an allelic discrimination real‐time PCR assay using fluorescent dye‐labelled probes to distinguish the B and Q biotypes. The assay targets a single nucleotide polymorphism (SNP) in the mitochondrial cytochrome oxidase I (mtCOI) gene. To evaluate the assay, DNA was extracted from individual whiteflies of six known biotype strains, and all scored correctly as either a B or Q biotype. As further validation, 72 individuals from field samples collected in different parts of the world were also tested by the assay. No failed reactions were observed, with all 72 samples scoring clearly as either the B or Q biotype. CONCLUSION: The development of this rapid and high‐throughput assay has important potential for routine monitoring of B and Q biotypes on ornamental plants and for the screening of B. tabaci populations in countries where these biotypes are not yet established. Copyright © 2007 Society of Chemical Industry     

Biotype and insecticide resistance status of the whitefly Bemisia tabaci from China

BACKGROUND: Resistance to numerous insecticide classes in Bemisia tabaci Gennadius has impaired field control efficacy in south‐eastern China. The biotype and resistance status of B. tabaci collected from these areas was investigated. RESULTS: Two different biotypes of B. tabaci (B‐biotype and Q‐biotype) were detected in south‐eastern China, and the samples collected from geographical regions showed a prevalence of the Q‐biotype and the coexistence of B‐ and Q‐biotypes in some regions. Moderate to high levels of resistance to two neonicotinoids were established in both biotypes (28–1900‐fold to imidacloprid, 29–1200‐fold to thiamethoxam). Medium to high levels of resistance to alpha‐cypermethrin (22–610‐fold) were also detected in both biotypes. Four out of 12 populations had low to medium levels of resistance to fipronil (10–25‐fold). Four out of 12 populations showed low levels of resistance to spinosad (5.7–6.4‐fold). All populations tested were susceptible to abamectin. CONCLUSION: The Q‐biotype B. tabaci is supplanting the B‐biotype which used to be ubiquitous in China. Field populations of both B‐ and Q‐biotypes of B. tabaci have developed high levels of resistance to imidacloprid and thiamethoxam. Abamectin is the most effective insecticide against adult B. tabaci from all populations. Copyright © 2010 Society of Chemical Industry     

Molecular phylogenetic analysis reveals at least five genetic races of<Emphasis Type="Italic">Bemisia tabaci</Emphasis> in China

Phylogenetic analysis using ITS1 and CO1 nucleotide sequences has revealed six major races ofBemisia tabaci in the world, including three major indigenous races in the Asia-Pacific region,viz., B. tabaci (Asia),B. tabaci (Bali) andB. tabaci (Australia), but the status of a large collection of genotypes in this region remains unresolved. The ITS1 sequences of representative whitefly samples collected from around China were determined in this study. These sequences and other homologous sequences retrieved from GenBank were then used to conduct a phylogenetic analysis. The results demonstrated that the whiteflies collected in China were split genetically into four groups, where at least five genetic races were revealed,i.e., B biotype (SDLe, XJEp, XJAt, HNNt, BJIb, GDEp, XJGh, GDHrs, XJSm and SHEp), Bali group (ZJGh), M biotype (Hainan1), G biotype (GXCm) and Asian H/K group (FJIb, GDCv), although the Asian H/K group with low bootstrap score remains unresolved. Of all genetic races, the B biotype is the most extensively distributed. In the dendogram, the J biotype, L biotype and Q biotype cluster together and form a sister clade to the B biotype. The data indicate that extensive migration ofB. tabaci has taken place in Asian countries. The populations ZJGh, FJIb, GDCv, GXCm and Hainanl collected in China might have originated there, but the possibility that they were introduced from elsewhere cannot be excluded at this point. Using PyR from Israel as a reference Q biotype, the random amplified polymorphic DNA banding patterns of SDLe, XJEp, XJAt and HNNt were shown to be consistent with that of the Q biotype, which indicated that the four local whitefly populations identified as the B biotype based on ITS1 sequences were closely related to the Q biotype. http//www.phytoparasitica.org posting Sept. 12, 2006.     

Genetic and biological characteristics ofTyphula ishikariensis isolates from Norway

Isolates ofTyphula ishikariensis, a snow mold fungus, were collected from five localities in Norway. They were divided into three groups according to genetics, cultural morphology, etc. Group I grew normally at 10 °C. Its mating patterns with Japanese taxa were variable: compatible with both biotypes A and B; compatible with biotype A but incompatible with biotype B; and incompatible with both biotypes. Group I was prevalent in southern inland districts such as Buskerud, Oppland, and Hedmark. Group II had smaller sclerotia as compared to other groups, and its sclerotia were often covered with white mycelium in nature and in culture. Group II was compatible with biotype B only. Group III was characterized by irregular growth at 10 ° C and genetic incompatibility with biotypes A and B. Cultural morphology of group III resembled that of group I at 0 °C. Rind cell patterns of sclerotia did not separate these two groups or biotypes. Isolates of groups II and III were often obtained from coastal regions in Finmark. Mating reactions were variable: monokaryons were compatible with their respective dikaryons, and monokaryons of groups II and III occasionally mated with group I dikaryons. Dikaryons of groups II and III, however did dikaryotize monokaryons of other groups. Norwegian isolates ofT. ishikariensis were highly variable, and the orthodox nomenclature system seemed inapplicalbe at the infraspecific level.     

Resistance of Amaranthus hybridus to atrazine

Resistance of weeds to triazine herbicides has been recorded in many countries. The extent of the problem in South Africa is uncertain. In a pilot study, the atrazine resistance of Amaranthus hybridus L. (smooth pigweed) was investigated. Suspected resistant (R) and susceptible (S) biotypes were treated with commercially formulated atrazine. After post-and pre-emergence applications under tunnel conditions, it was found that the suspected R biotype plants were not affected at herbicide dosages of belween 1.25 and 25.0 kg a.i. ha^-1, i.e. up to 20 times gieater than the lowest recommended dosage. However, the S biotype plants were killed by the lowest dosage. In the fieid, mortalities in the R biolype were not observed after post-emergence applications of 1.25-10.00 kg a.i. ha^-1. In contrast, all S biotype plants were killed. In tunnel experiments, the R biotype was also found to be resistant to cyanazine and cyanazine+atrazine, while slight tolerance to linuron was observed. All these treatments resulted in 100% mortality of the S biotype. Although S biotype seeds oi A. hybridus were found to germinate slightly sooner under controlled conditions than R biotype seeds, preliminary results suggest that there are no major differences. Indications are that, although the growth of the S biotype may be greater than that of the R biotype, the competitive effect of the two biotypes on crop seedlings may well be similar.     

Mechanism of resistance to bensulfuron-methyl in Alisma plantago-aquatica biotypes from Portuguese rice paddy fields

Two Alisma plantago‐aquatica biotypes resistant to bensulfuron‐methyl were detected in rice paddy fields in Portugal’s Mondego (biotype T) and Tagus and Sorraia (biotype Q) River valleys. The fields had been treated with bensulfuron‐methyl‐based herbicide mixtures for 4–6 years. In order to characterize the resistant (R) biotypes, dose–response experiments, absorption and translocation assays, metabolism studies and acetolactate synthase (ALS) activity assays were performed. There were marked differences between R and susceptible (S) biotypes, with a resistance index (ED₅₀R/S) of 500 and 6.25 for biotypes Q and T respectively. Cross‐resistance to azimsulfuron, cinosulfuron and ethoxysulfuron, but not to metsulfuron‐methyl, imazethapyr, bentazone, propanil and MCPA was demonstrated. No differences in the absorption and translocation of ¹⁴C‐bensulfuron‐methyl were found between the biotypes studied. Maximum absorption attained 1.12, 2.02 and 2.56 nmol g⁻¹ dry weight after 96 h incubation with herbicide, for S, Q and T biotypes respectively. Most of the radioactivity taken up by the roots was translocated to shoots. Bensulfuron‐methyl metabolism in shoots was similar in all biotypes. The R biotypes displayed a higher level of ALS activity than the S biotype, both in the presence and absence of herbicide and the resistance indices (IC₅₀R/S) were 20 197 and 10 for biotypes Q and T respectively. These data confirm for the first time that resistance to bensulfuron‐methyl in A. plantago‐aquatica is target‐site‐based. In practice, to control target site R biotypes, it would be preferable to use mixtures of ALS inhibitors with herbicides with other modes of action.     

Spatial genetic structure and dispersal of the cacao pathogen Moniliophthora perniciosa in the Brazilian Amazon

Moniliophthora perniciosa is the causal agent of witches’ broom in Theobroma cacao (cacao). Three biotypes of M. perniciosa are recognized, differing in host specificity, with two causing symptoms on cacao or Solanaceae species (C‐ and S‐biotypes), and the third found growing endophytically on lianas (L‐biotype). The objectives of this study were to clarify the genetic relationship between the three biotypes, and to identify those regions in the Brazilian Amazon with the greatest genetic diversity for the C‐biotype. Phylogenetic reconstruction based on the rRNA ITS regions showed that the C‐ and S‐biotypes formed a well‐supported clade separated from the L‐biotype. Analysis of 131 isolates genotyped at 11 microsatellite loci found that S‐ and especially L‐biotypes showed a higher genetic diversity. A significant spatial genetic structure was detected for the C‐biotype populations in Amazonia for up to 137 km, suggesting ‘isolation by distance’ mode of dispersal. However, in regions containing extensive cacao plantings, C‐biotype populations were essentially ‘clonal’, as evidenced by high frequency of repeated multilocus genotypes. Among the Amazonian C‐biotype populations, Acre and West Amazon displayed the largest genotypic diversity and might be part of the centre of diversity of the fungus. The pathogen dispersal may have followed the direction of river flow downstream from Acre, Rondônia and West Amazon eastward to the rest of the Amazon valley, where cacao is not endemic. The Bahia population exhibited the lowest genotypic diversity, but high allele richness, suggesting multiple invasions, with origin assigned to Rondônia and West Amazon, possibly through isolates from the Lower Amazon population.     

Enhanced weed‐crop competition effects on growth and seed production of herbicide‐resistant and herbicide‐susceptible annual sowthistle (Sonchus oleraceus)

Enhanced crop competition could aid in the management of annual sowthistle (Sonchus oleraceus L.), a dominant weed of Australian cropping systems. A two‐year pot study was conducted to evaluate the effect of wheat (Triticum aestivum L.) planting densities (0, 82, and 164 wheat plants/m²) on growth and seed production of glyphosate‐resistant (GR) and glyphosate‐susceptible (GS) biotypes of annual sowthistle. Without competition, both biotypes produced a similar number of leaves and biomass, but the GS biotype produced 80% more seeds (46,050 per plant) than the GR biotype. In competition with 164 wheat plants/m², the number of leaves in the GR and GS biotypes was reduced by 62 and 61%, respectively, in comparison with the no‐competition treatment, and similarly, weed biomass was reduced by 78 and 77%, respectively. Compared to no‐competition treatment, the seed production of GR and GS biotypes was reduced by 33 and 69%, respectively, when grown with 82 wheat plants/m², but increasing wheat density from 82 to 164 plants/m² reduced the number of seeds only in the GS biotype (81%). Both biotypes produced greater than 6,000 seeds per plant when grown in competition with 164 plants/m², suggesting that increased crop density should be integrated with other weed management strategies for efficient control of annual sowthistle.     

Germination and seedling emergence of glyphosate‐resistant and susceptible biotypes of goosegrass (Eleusine indica[L.] Gaertn.)

Effects of environmental factors on the germination and seedling emergence of glyphosate‐resistant (R) and ‐susceptible (S) biotypes of Eleusine indica (L.) Gaertn. were examined under laboratory and greenhouse conditions. The R biotype exhibited a higher germination percentage compared with the S biotype at constant temperatures of 20 and 35°C under dark conditions, and alternating temperatures of 30/25°C, and 35/25°C during a 12 h photo period. For both biotypes, germination was optimal at alternating temperatures of 30/20°C and 35/20°C. However, there was no significant difference (P > 0.05) in the germination between the R and S biotypes at these temperature regimes. The germination of both biotypes was inhibited by osmotic stress imposed by a water potential of ?0.80 MPa. When the moisture stress was released and the seeds were subsequently transferred to distilled water, the germination was enhanced to approximately 90% and 16% for the R and S biotype seeds, respectively. Higher emergence rates were obtained in shallow seed depths (0 or 2 cm) compared to deep depths. Emergence percentage of the R biotype was higher than that of the S biotype at 0 cm and 2 cm depths. The maximum emergence percentage of the R biotype was higher than that of S biotype when seeds were sown on the surface of either loamy or clay loam soil taken from three different sites.     

Glyphosate resistance in common ragweed ( A mbrosia artemisiifolia L.) from Mississippi,USA

Glyphosate is one of the most commonly used broad‐spectrum herbicides over the last 40 years. Due to the widespread adoption of glyphosate‐resistant (GR) crop technology, especially corn, cotton and soybean, several weed species have evolved resistance to this herbicide. Research was conducted to confirm and characterize the magnitude and mechanism of glyphosate resistance in two GR common ragweed ( A mbrosia artemisiifolia L.) biotypes from Mississippi, USA. A glyphosate‐susceptible (GS) biotype was included for comparison. The effective glyphosate dose to reduce the growth of the treated plants by 50% for the GR1, GR2 and GS biotypes was 0.58, 0.46 and 0.11 kg ae ha^?1, respectively, indicating that the level of resistance was five and fourfold that of the GS biotype for GR1 and GR2, respectively. Studies using ¹⁴ C‐glyphosate have not indicated any difference in its absorption between the biotypes, but the GR1 and GR2 biotypes translocated more ¹⁴ C‐glyphosate, compared to the GS biotype. This difference in translocation within resistant biotypes is unique. There was no amino acid substitution at codon 106 that was detected by the 5‐enolpyruvylshikimate‐3‐phosphate synthase gene sequence analysis of the resistant and susceptible biotypes. Therefore, the mechanism of resistance to glyphosate in common ragweed biotypes from Mississippi is not related to a target site mutation or reduced absorption and/or translocation of glyphosate.     

Effects of isoproturon on photosynthesis in susceptible and resistant biotypes of Phalaris minor and wheat

Wheat (cv. WH-147) and five biotypes of Phalaris minor Retz. (KR-1, H-4, K-2, H-2 and J-1) were treated with isoproturon in controlled environmental conditions to assess their level of resistance. Resistance of P. minor to isoproturon was found in the order of KR-1 > H-4 > K-2 > H-2 = J-1. Compared with the susceptible (S) biotype (H-2), the resistant (R) biotypes (KR-1. H-4 and K-2) of P. minor required 13.0, 4.5 and 2.7 times higher doses of isoproturon for a 50% reduction in growth (GR₅₀) and 2.4 times that of the S biotype (H-2) by wheat. The corresponding figures for KR-1, H-4, K-2 biotypes and wheat were 18, 4.1, 2.4 and 4.6 times based on dry weight reduction. The effect of isoproturon on photosynthesis was studied in vitro using five biotypes of P. minor and in viro with wheat. KR-1 (R) and H-2 (S) biotypes of P. minor. Under in vitro treatment conditions isoproturon inhibited the photosynthesis of all five P. minor biotypes, whereas in vivo the recovery was greater in the R biotype than in the wheat and the S biotype. Effects on chlorophyll fluorescence were also measured in wheat and the KR-1 (R) and H-2 (S) biotypes of P. minor. A 4-h treatment of excised leaves incubaled in isoproluron solution (0.025 and 0.05 mm concentration) resulted in a decreased fluorescence coefficient (F_v F_m ratio in which F_v= variable fluorescence (F_m - F^o): F_m= the maximum fluorescence and F_o= initial fiuorescence) in wheat (Triticum aestivum L.) and both biotypes of P. Minor. The recovery was, however, greater in the R biotype than in wheat and it was completely recovered within 24 h. No recovery was recorded in the case of the S biotype of P. minor and a greater recovery time was required for wheat than the R biotype. The higher dose required for growth inhibition in the R biotype and rapid recovery of oxygen evolution and fluorescence coeflicient under in viro conditions together with the absence of selectivity in vitro suggests that the target site was unaffected. It can be conjectured that resistance to isoproturon is most probably because of enhanced metabolism or sequestration of isoproturon, resulting in decreased target site delivery.     

Molecular basis of diverse responses to acetolactate synthase-inhibiting herbicides in sulfonylurea-resistant biotypes of Schoenoplectus juncoides

Sulfonylurea-resistant biotypes of Schoenoplectus juncoides were collected from Nakafurano, Shiwa, Matsuyama, and Yurihonjyo in Japan. All of the four biotypes showed resistance to bensulfuron-methyl and thifensulfuron-methyl in whole-plant experiments. The growth of the Nakafurano, Shiwa, and Matsuyama biotypes was inhibited by imazaquin-ammonium and bispyribac-sodium, whereas the Yurihonjyo biotype grew normally after treatment with these herbicides. The herbicide concentration required to inhibit the acetolactate synthase (ALS) enzyme by 50% (I₅₀), obtained using in vivo ALS assays, indicated that the four biotypes were > 10-fold more resistant to thifensulfuron-methyl than a susceptible biotype. The Nakafurano, Shiwa, and Matsuyama biotypes exhibited no or little resistance to imazaquin-ammonium, whereas the Yurihonjyo biotype exhibited 6700-fold resistance to the herbicide. The Nakafurano and Shiwa biotypes exhibited no resistance to bispyribac-sodium, but the Matsuyama biotype exhibited 21-fold resistance and the Yurihonjyo biotype exhibited 260-fold resistance to the herbicide. Two S. juncoides ALS genes (ALS1 and ALS2) were isolated and each was found to contain one intron and to encode an ALS protein of 645 amino acids. Sequencing of the ALS genes revealed an amino acid substitution at Pro₁₉₇ in either encoded protein (ALS1 or ALS2) in the biotypes from Nakafurano (Pro₁₉₇ → Ser₁₉₇), Shiwa (Pro₁₉₇ → His₁₉₇), and Matsuyama (Pro₁₉₇ → Leu₁₉₇). The ALS2 of the biotype from Yurihonjyo was found to contain a Trp₅₇₄ → Leu₅₇₄ substitution. The relationships between the responses to ALS-inhibiting herbicides and the amino acid substitutions, which are consistent with previous reports in other plants, indicate that the substitutions at Pro₁₉₇ and Trp₅₇₄ are the basis of the resistance to sulfonylureas in these S. juncoides biotypes.     

Spread of proso millet (Panicum miliaceum L.) in Ontario, Canada. I. Rate of spread and crop susceptibility

The infestations of two biotypes of Panicum miliaceum L. were monitored over a 5-year period (1981–1985) as they occurred in two townships in southwestern Ontario, Canada. On average, 16·5% of the cultivated fields in Hullett township were infested with the black-seeded biotype while 12·9% of the fields in North Norwich township were infested with the golden-seeded biotype. Neither population showed clear signs of increasing. The two biotypes were similar in their ability to persist as adult infestations. The black-seeded biotype showed a greater potential for colonizing uninfested fields. The crops grown in this region showed different susceptibilities to infestation by P. miliaceum. Corn (maize) fields were susceptible while most grain fields were resistant to infestation. White beans were susceptible to infestation by the black-seeded biotype. Wheat and oat crops were more resistant to infestation by the golden-seeded biotype than to those of the black-seeded biotype.