Sensitivity of Venturia inaequalis to trifloxystrobin

The sensitivity of Venturia inaequalis to trifloxystrobin was monitored by both in vitro (spore germination) and in vivo tests (on apple seedlings). There was good correlation between the in vitro and in vivo results. Baseline sensitivity was established with 95 bulk isolates from Europe between 1995 and 1998 which showed a narrow sensitivity range-factor of up to 17 between the least and most sensitive isolates. Monitoring of populations originating from trifloxystrobin-treated and untreated orchards between 1995 and 1999 showed only sensitive isolates and no performance deficiencies were reported. Data also show that trifloxystrobin is not cross-resistant to anilinopyrimidines and triazoles, but is cross-resistant to kresoxim-methyl, another strobilurin which also inhibits the cytochrome bc1 enzyme complex at the Qo-site in the respiration chain of fungal mitochondria (QoI inhibitors). Under experimental conditions from a specific trial site in Switzerland, where trifloxystrobin has been tested since 1994, isolates containing conidia resistant to Qo inhibitors were detected in 1997 and 1999. However no obvious performance deficiencies were reported. Nevertheless these results demonstrate a risk for the development of practical resistance in V inaequalis to Qo inhibitors and therefore a need to apply resistance management principles strictly.     

Populations of Phytophthora infestans in Israel Underwent Three Major Genetic Changes During 1983 to 2000

ABSTRACT In this survey, 799 isolates of Phytophthora infestans collected from potato crops in Israel during 1983 to 2000 were analyzed for mating type and sensitivity to metalaxyl, and 324 were analyzed for race structure. The A(2) mating type, first recorded in 1983, fully dominated the pathogen population from 1983 until 1991 (9 years). It was thereafter replaced by the A(1) mating type, which dominated the population during 1993 to 2000. Metalaxyl-resistant isolates were first recorded in 1982. During 1983 to 1991, the majority of the isolates were resistant. Isolates with intermediate sensitivity (I) to this fungicide were first observed in 1993, when both A(1) and A(2) mating types occurred in the population. The proportion of I isolates gradually increased, reaching 39 to 41% in 1997 to 1998, and then declined to approximately 15% in 1999 to 2000. Pathogenicity to nine potato differential cultivars was determined for 80 potato isolates collected in 1983 to 1991, to 11 potato differentials in 173 isolates collected in 1993 to 1998, and in 71 potato isolates collected in 1999 to 2000. The first population was composed of 5 races with race 1,3,4,7,8,10 predominating (76%), the second population was composed of 19 races with race 1,3,4,7,8,10,11 predominating (63%), and the third population exhibited 42 (34 new) races with no single predominating race. RG-57 DNA fingerprinting and allozymes loci assays of 23 isolates revealed that isolates collected during 1984 to 1986 belonged to the PO-57 lineage, whereas those collected during 1997 to 1999 belonged to the RFO-39 lineage. Among isolates collected during 1993 to 1995, two unreported DNA fingerprinting patterns were found. Severe late blight epidemics occurred in tomato crops during 1998 to 2000. Of 35 tomato isolates, 28 were A(1) and only 7 were A(2). Of these tomato isolates, 94% were sensitive to metalaxyl. Almost every isolate had a different race structure on the 11 potato differentials. When inoculated onto three tomato differential cultivars, tomato isolates showed a virulence much more enhanced than potato isolates. The data suggest the Israeli population of P. infestans has passed through three major genetic changes during the past 18 years: in 1983, 1993, and 1999. The recent change included host specialization to tomato.     

Sensitivity of European Plasmopara viticola populations to cymoxanil

Between 1995 and 1997, 278 grape downy mildew (Plasmopara viticola) populations originating from European vineyards were characterised for their sensitivity to cymoxanil in a leaf-disc assay. The sensitivity profile revealed a wide distribution, with minimum inhibitory concentrations (MIC) ranging from 10 to more than 800 mg litre⁻¹. EC₅₀ values ranged from 1 to more than 800 mg litre⁻¹ with an average of 125 mg litre⁻¹. The sensitivity distribution was stable between 1995 and 1997. Surprisingly, populations from Portugal appeared significantly more sensitive than those from France or Italy, which could not be linked to differential cymoxanil usage in these countries. P viticola populations collected outside Europe and never exposed to cymoxanil appeared significantly more sensitive than exposed European populations, with an average EC₅₀ value of 10 mg litre⁻¹. The level of sensitivity of European P viticola populations was relatively unaffected by the number of cymoxanil applications made during a season or by the number of years of cymoxanil use. No link was found between the level of sensitivity in the leaf-disc assay and the level of performance of the cymoxanil mixtures used in the fields where the populations originated. Specific field trials conducted in Italy and Portugal have shown that the performance of cymoxanil-based mixtures remained good even on populations of the grape downy mildew fungus characterised as less sensitive in the leaf-disc assay. While there are no baseline sensitivity data for pre-commercialisation P viticola populations, the results of our study suggest that a shift in sensitivity (12.5-fold) may have occurred in some areas since introduction of cymoxanil on grapes nearly 20 years ago. Because cymoxanil is never used alone, it is difficult to determine whether or not practical resistance is occurring in European vineyards. © 1999 Society of Chemical Industry     

Phenotypic and genetic variation in Finnish potato-late blight populations, 1997–2000

This study was conducted on potato late blight samples collected for monitoring early attacks in Finland from 1997 to 2000. Most of the 1726 Phytophthora infestans isolates were collected soon after the onset of the epidemics. Most of the isolates were tested for mating type as well as metalaxyl and propamocarb hydrochloride (HCl) sensitivity, while virulence on potato R-gene differentials and mitochondrial DNA (mtDNA) haplotype were determined for a subset of the isolates. In half of the fields from which more than one isolate was tested, both mating types were detected, indicating strong potential for sexual reproduction. The mating types coexisted more often in organic fields or gardens than in conventional fields. The proportion of A1 mating type decreased from approximately 80% (1997 and 1998) to 22% by the year 2000. Simultaneously, the proportion of isolates resistant to metalaxyl decreased from approximately 40% to 16%. Resistance to metalaxyl was confined to the IIa mtDNA haplotype and clearly associated with the A1 mating type, as resistance was 10 times more common among A1 isolates than among A2 isolates. Resistance to metalaxyl therefore probably derives from common descent from an isolate with the IIa haplotype. Most of the regional variation in metalaxyl sensitivity was also linked to mating type, as both metalaxyl resistance and the A1 mating type were most common in the north and south-west of Finland. In contrast to metalaxyl, only three propamocarb-HCl-insensitive isolates were found, but propamocarb-HCl sensitivity decreased significantly during the study.     

2011年我国主要麦区小麦白粉病菌群体对三唑酮和苯锈啶的敏感性

 小麦白粉病(Wheat Powdery Mildew)是我国小麦生产上常发性病害之一^[1]。小麦白粉病的防治主要采用抗病品种和化学药剂,辅之以栽培措施的综合防治技术。由于目前生产上抗病品种相对缺乏,药剂防治成为我国小麦白粉病防治的主要措施之一^[2]。自20世纪80年代以来三唑类杀菌剂一直是我国防治小麦白粉病的主要药剂,由于长期、大范围、单一的使用导致小麦白粉病菌对三唑类杀菌剂的抗药性大大提高。监测结果表明,2009年我国小麦白粉病菌群体对三唑酮的平均抗性水平已经达到56.58倍,抗性频率达到99.09%,其中高抗菌株占49.09%^[3]。目前小麦白粉病菌对三唑酮的抗性形势十分严峻,寻找三唑类杀菌剂的替代药剂成为控制该病害的迫切需求。     

The Dynamics of Mefenoxam Insensitivity in a Recombining Population of Phytophthora capsici Characterized with Amplified Fragment Length Polymorphism Markers

ABSTRACT Recent findings from Michigan suggest that recombination may play a role in the survival and evolution of sensitivity to the fungicide mefenoxam in populations of Phytophthora capsici on cucurbit hosts. In 1998, 63 mefenoxam insensitive isolates were recovered from a squash field in which mefenoxam had been applied. Additional isolates were recovered from untreated squash fields planted at this location in 1999 (200 isolates) and the spring of 2000 (34 isolates). Isolates from 1998 and 1999 were characterized using fluorescent amplified fragment length polymorphism (AFLP) markers and all isolates were screened for compatibility type and mefenoxam sensitivity. In 1998 and 1999, 92 and 71% of the isolates, respectively, had unique multilocus AFLP genotypes with no identical isolates recovered between years. Seventy-two identical AFLP markers were clearly resolved in both the 1998 and 1999 sample sets, and fixation indices for the 37 polymorphic AFLP loci indicate little differentiation between years. There was no decrease in the frequency of resistant isolates during the 2 years without mefenoxam selection. We conclude that oospores play a key role in overwintering and that the frequency of mefenoxam insensitivity may not decrease in an agriculturally significant time period (2 years) once mefenoxam selection pressure is removed.     

Effects of time and concentration on mortality of phosphine-resistant Sitophilus oryzae (L) fumigated with phosphine

The effects of exposure period and phosphine concentration on mortality of susceptible and resistant Sitophilus oryzae (L) were investigated. Although S oryzae is one of the world's most serious pests of stored grain there are few data on the practical significance of phosphine resistance in this species. The strains investigated were an Australian susceptible strain, a homozygous resistant strain exhibiting a level of resistance common in Australia and an unselected field strain from China with a much stronger resistance. Fumigations were carried out at 25 degrees C on adults and mixed-age cultures. For adults of all three strains and mixed-age cultures of the susceptible and resistant Australian strains, the relationship between concentration and time could be described by equations of the form Cnt = k. In all cases n < 1, indicating that time was a more important variable than concentration. In all fumigations of adults the resistant strains were harder to kill than the susceptible strain. However, in fumigations of mixed-age cultures, which contained the tolerant pupal stage, the difference between susceptible and resistant strains was more pronounced at lower concentrations than higher concentrations. For example, at 0.02 mg litre-1 the estimated LT99.9 for mixed-age cultures of the Australian resistant strain (27 days) is 3.4 times that of the susceptible strain (8 days), but at 1 mg litre-1 there is no difference between the two strains (4 days). Limited data on the Chinese resistant strain supported this finding. Twenty-three days exposure at 0.02 mg litre-1 had no effect on mixed-age cultures of this strain, but there were no survivors after 5 days exposure to 1 mg litre-1.     

Biological properties of the novel fungicide cyazofamid against Phytophthora infestans on tomato and Pseudoperonospora cubensis on cucumber

Cyazofamid (ISO proposed common name), 4-chloro-2-cyano-N,N-dimethyl-5-p-tolylimidazole-1-sulfonamide is a novel fungicide exhibiting specific activity against diseases caused by Oomycetes. In tests, cyazofamid at 0.4-1.6 mg litre-1 exhibited excellent preventative activity against Phytophthora infestans on tomato and Pseudoperonospora cubensis on cucumber. Minimum inhibitory concentrations of cyazofamid against both diseases were over 63 times lower than those of mancozeb and at least 16 times lower than those of metalaxyl. Cyazofamid at 1.6-25 mg litre-1 exhibited not only preventative activity, but also stable residual activity and rainfastness. Cyazofamid at 6.3 mg litre-1 reduced zoosporangia formation of P infestans and P cubensis on host plants by 100 and 94% respectively. Cyazofamid also exhibited translaminar and curative activity. Cyazofamid has a new mode of action for fungicides and exhibits no cross-resistance with other currently registered and commonly used fungicides. These properties lead to a high level control by cyazofamid in field.     

Insecticidal properties of essential plant oils against the mosquito Culex pipiens molestus (Diptera: Culicidae)

The insecticidal activities of essential oil extracts from leaves and flowers of aromatic plants against fourth-instar larvae of the mosquito Culex pipiens molestus Forskal were determined. Extracts of Myrtus communis L were found to be the most toxic, followed by those of Origanum syriacum L, Mentha microcorphylla Koch, Pistacia lentiscus L and Lavandula stoechas L with LC50 values of 16, 36, 39, 70 and 89 mg litre-1, respectively. Over 20 major components were identified in extracts from each plant species. Eight pure components (1,8-cineole, menthone, linalool, terpineol, carvacrol, thymol, (1S)-(-)-alpha-pinene and (1R)-(+)-alpha-pinene) were tested against the larvae. Thymol, carvacrol, (1R)-(+)-alpha-pinene and (1S)-(-)-alpha-pinene were the most toxic (LC50 = 36-49 mg litre-1), while menthone, 1,8-cineole, linalool and terpineol (LC50 = 156-194 mg litre-1) were less toxic.     

A 10-year Survey of Populations of Leptosphaeria maculans in France Indicates a Rapid Adaptation Towards the Rlm1 Resistance Gene of Oilseed Rape

Leptosphaeria maculans, the cause of stem canker of oilseed rape (OSR), exhibits gene-for-gene interactions with its host plant. The race structure of L. maculans was assessed on the basis of the analysis of 1011 isolates collected in France between 1990 and 2000, with regards to three AVR genes, AvrLm1, AvrLm2 and AvrLm4. The effect of selection pressure, due to large-scale cropping of Rlm1 cultivars, on the evolution of races of the fungus was also evaluated. The results revealed a scarcity or complete absence of isolates harbouring AvrLm2, whereas isolates harbouring AvrLm4 were present at a variable level, that was as high as 17.2–31.2% depending on the sample year and location. When obtained from rlm1 cultivars, isolates harbouring AvrLm1 always represented more than 83% of the populations until the 1997–1998 growing season. As a consequence, the Rlm1 cultivars had been highly efficient at controlling the disease and were grown on an estimated 43.7% of the total French acreage in OSR in 1998–1999. However, the increased commercial success of Rlm1 cultivars was paralleled by a decrease in the proportion of isolates harbouring AvrLm1 in 1997–1998 and 1998–1999. This resulted in less than 13% of isolates harbouring AvrLm1 in populations being collected from rlm1 cultivars in 1999 and 2000, and contributed to the loss of efficiency of the Rlm1 resistance in the field. The present study is an illustration of one round of a `boom and bust' cycle that occurred for a pathosystem where it has never been reported before. These data and the high evolutionary potential of L. maculans are fully supportive of one pathogen species with a high risk of breaking down resistance genes in OSR and suggest that the development of integrated strategies aiming at maximising the durability of novel resistance is now a priority for this pathosystem.     

Larvicidal activity against Plutella xylostella of cordycepin from the fruiting body of Cordyceps militaris

The insecticidal activities of methanol extracts of Cordyceps militaris Link (Ascomycotina: Clavicipitaceae) cultured on fresh pupae of Bombyx mori L against 3rd-instar larvae of Plutella xylostella L were examined using direct contact application. The larvicidal activity was more pronounced in an extract of C militaris fruiting body than in an extract of the pupae separated from the culture. The biologically active constituent of the Cordyceps fruiting body was characterized as cordycepin (3'-deoxyadenosine) by spectroscopic analysis. Responses varied according to dose, exposure time and application method. In a leaf-dipping test, cordycepin at 500 mg litre-1 caused no mortality at 1 DAT (day after treatment) but 78 and 100% mortality at 2 and 4 DAT, respectively, whereas 34 and 88% mortality at 3 and 5 DAT, respectively was observed at 300 mg litre-1. Cordycepin caused body colour change from pale green to dark brown and eventually body lysis. These results suggested that the larvicidal action may be attributable to a direct effect rather than an inhibitory action on chitin synthesis. There was a significant difference in insecticidal activity of cordycepin between leaf dipping (500 mg litre-1) with 100% mortality and topical application (10 micrograms per larva) with 0% mortality, suggesting that cordycepin has stomach action. Cordycepin merits further study as a potential P xylostella control agent or as a lead compound.     

Repetitive Applications of the Biocontrol Agent Pseudomonas putida 06909-rif/nal and Effects on Populations of Phytophthora parasitica in Citrus Orchards

ABSTRACT Pseudomonas putida 06909-rif/nal was applied repetitively during the irrigation season in two citrus orchards over 3 years. In a mature (50-yearold) commercial citrus orchard covering 2.02 ha, weekly applications of Pseudomonas putida 06909-rif/nal with an in-field fermentor resulted in soil populations that fluctuated between 2.83 log CFU + 1 per g of soil and 4.35 log CFU + 1 per g of soil. Resulting rhizosphere populations of Phytophthora parasitica were significantly reduced in 1999 but not 1997 or 1998. In a newly planted citrus orchard, yearly applications of Pseudomonas putida 06909-rif/nal at the beginning of the irrigation season resulted in high soil populations of Pseudomonas putida 06909-rif/nal that declined rapidly and never reduced the rhizosphere populations of Phytophthora parasitica. When Pseudomonas putida 06909-rif/nal was applied weekly, soil populations increased throughout the 1997 and 1998 irrigation seasons, reaching a maximum in 1998 and remained high throughout the 1999 irrigation season. Rhizosphere populations of Phytophthora parasitica were significantly reduced in 1998. Yearly applications of the fungicide metalaxyl and the nematicide phenamiphos reduced rhizosphere populations of Phytophthora parasitica in 1997 but not in 1998 or 1999. Pseudomonas putida 06909-rif/nal was uniformly distributed throughout the soil profile to a depth of 75 cm in both yearly and weekly applications. When applied through low-volume minisprinklers, Pseudomonas putida 06909-rif/nal was found in aerosols up to 3 m away.     

Occurrence of Globodera pallida in Hungary

Golden potato cyst nematode, Globodera rostochiensis , has been known to occur in Hungarian potato fields for more than 20 years. The Hungarian NPPO has been carrying out a country-wide Globodera monitoring programme since 1995 and has inspected 16 000 samples. Until 2000, all records were of G. rostochiensis . However, in 2001, three localities in Pest county were found to be infested with Globodera pallida . This was the first official record of G. pallida in Hungary. The two species have been found together in five fields. Unmixed populations of G. pallida have not been found. Identification was based on morphometric data, as well as on biochemical methods (ELISA technique).     

Biological Control of Soft Rot of Chinese Cabbage Using Single and Mixed Treatments of Bacteriocin-producing Avirulent Mutants of Erwinia carotovora subsp. carotovora

Two pathogenic strains of E. carotovora subsp. carotovora 2T-2 and TT-4 with high bacteriocin activity but low sensitivity to the bacteriocins of other strains were treated with ethyl methane sulphonate (EMS). Two avirulent mutants A-f-39 and B-e-19 developed from 2T-2 and TT-4, respectively, by this treatment had the same bacteriocin activity as their respective parents and inhibited the in vitro growth of pathogenic strains of this species. The disease control of these two mutant strains were compared in the field in 1995 and 1997 to the control by CGE234M403 (M403) (a commercialized biocontrol agent), a mixture of A-f-39 and M403, and an agrochemical (basic dithianon-copper chloride). The protection obtained with A-f-39 was comparable to M403 and was better than that with the chemical. The mixture of A-f-39 and M403 consistently gave the best results in all the field trials. Received 17 September 1999/ Accepted in revised form 22 February 2000     

乌鲁木齐市土地利用效益的耦合关系分析

根据系统科学理论与方法,选取1995-2007年统计资料,建立该市土地利用效益的指标体系和耦合模型,分析乌鲁木齐市土地利用社会经济效益与生态环境效益之间的协调程度.结果表明:1)1995～2007年乌鲁木齐市土地利用社会经济效益几乎呈指数形式增长;而生态环境效益总休上升,但起伏波动比较大;2)1998年以前,耦合度呈下...     

Investigating the in situ degradation of atrazine in groundwater

This study focused on whether or not atrazine could be degraded by indigenous groundwater bacteria as part of an in situ remediation approach. Groundwater was taken from an unconfined middle upper chalk site where concentrations of atrazine and nitrate were typically in the ranges 0.02-0.2 microg litre-1 and 11.6-25.1 mg NO3-N litre-1 respectively. Sacrificial batch studies were performed using this groundwater spiked with atrazine at a concentration of 10 microg litre-1 in conjunction with a minimal mineral salts liquid (Glu-MMSL) medium which contained glucose as the sole carbon source. Treatments comprised either the Glu-MMSL groundwater cultured bacteria or Pseudomonas sp. strain ADP. Results from sacrificial batches indicated the occurrence of bacterial growth and denitrification as monitored by optical density (absorbance at 600 nm) and NO3-N content. Analysis of atrazine content by solid phase extraction coupled with high-performance liquid chromatography showed no degradation of atrazine over a period of 103 days in either treatment. These results indicated that no acclimatised bacterial community featuring positive degraders to the herbicide atrazine had become established within this chalk aquifer in response to the trace levels encountered.     

Sensitivity of Uncinula necator to quinoxyfen: evaluation of isolates selected using a discriminatory dose screen

Quinoxyfen is a protectant fungicide that provides excellent control of many powdery mildew diseases. Prior to the launch of quinoxyfen in vines in 1998, a leaf disc sporulation assay was developed to assess the sensitivity of Uncinula necator (Schw) Burr to quinoxyfen. The distribution of EC(50) values from 56 monoconidial U. necator isolates collected from six countries between 1993 and 1996 was found to range from less than 0.03 to 2.6 mg litre(-1). Although this range of EC(50) values was quite broad, the inability to establish a minimum inhibitory concentration (MIC) for the majority of these isolates, including some of the most sensitive isolates, was unexpected and suggested that the leaf disc sporulation assay may not reflect the true activity of quinoxyfen in the field. In 2002, following the detection of isolates resistant to quinoxyfen in Blumeria graminis Speer f. sp. tritici Marchal, a discriminatory dose screen was developed to test large populations of U. necator for rare individuals with significantly decreased sensitivity to quinoxyfen. The individual isolates selected by this method were tested with the leaf disc sporulation assay. Although a significant proportion were found to have EC(50) values within the original distribution, a number of isolates with apparent reduced sensitivity to quinoxyfen were also detected. However, further examination of a subset of these isolates in a more quantitative germination/germ tube elongation inhibition assay suggested that the magnitude of the reduction in sensitivity for some of these isolates was much less than predicted by the sporulation assay. Thus, for an exclusively protectant fungicide such as quinoxyfen, a leaf disc sporulation assay may overestimate the frequency of isolates with significantly reduced sensitivity and the threat of decreased performance due to resistance.     

Detection of Thiophanate-methyl-resistant Strains in Diplocarpon mail, Causal Fungus of Apple Blotch

Isolates of Diplocarpon mali, causal fungus of apple blotch, collected from four prefectures in Japan in 1997–1998 were tested for sensitivity to thiophanate-methyl. Results from mycelial growth tests showed that MIC values of the fungicide were 0.19 μg/ml against all isolates from Akita, Nagano and Saga prefectures but 100 or 200 μg/ml against all isolates from the Tokusa area in Yamaguchi prefecture. Detached apple leaves sprayed with the fungicide developed severe symptoms when inoculated with the isolate from Tokusa, but developed no symptoms with the isolate from Nagano. These results are the first confirmation of thiophanate-methyl-resistant strains in D. mali. Received 1 September 1999/ Accepted in revised form 15 October 1999     

Effects of Angular Leaf Spot and Rust on Yield Loss of Phaseolus vulgaris

ABSTRACT Three field experiments were conducted in 1997, 1998, and 1999 to investigate the effects of angular leaf spot and rust, separately or combined, on host growth and yield of individual bean plants (Phaseolus vulgaris). In each experiment, three treatments were established by inoculating cv. Carioca with Phaeoisariopsis griseola, Uromyces appendiculatus, or with both pathogens. An additional control treatment was not inoculated, but was sprayed with a fungicide. In the 1997 and 1999 experiments, angular leaf spot reached higher disease levels than rust, whereas in 1998, rust was more severe than angular leaf spot. Host growth, expressed as healthy leaf area duration (HAD), and yield were the highest in 1997 and lowest in 1998. In each experiment, the treatments did not differ significantly to the area under leaf area progress curve, HAD, and healthy leaf area absorption (HAA). All inoculated treatments had significantly more severe disease and less yield than the control treatment. Based on the analysis of 60 plants in each experiment, yield was not related to the areas under disease progress curve for either or both diseases. In 1997 and 1999, yield was related to HAD (R(2) = 0.57 and 0.43) and HAA(R(2) = 0.60 and 0.55). Based on the combined analysis of all 36 plots, angular leaf spot reduced the leaf area because of defoliation, whereas rust did not affect the leaf area. Rust reduced yield more than four times that of angular leaf spot, although the decrease in photosynthesis to angular leaf spot was twice that of rust.     

Serological Methods for Detection of Polymyxa graminis, an Obligate Root Parasite and Vector of Plant Viruses

A purification procedure was developed to separate Polymyxa graminisresting spores from sorghum root materials. The spores were used as im-munogen to produce a polyclonal antiserum. In a direct antigen coating enzyme-linked immunosorbent assay (DAC ELISA), the antiserum could detect one sporosorus per well of the ELISA plate. In spiked root samples, the procedure detected one sporosorus per mg of dried sorghum roots. The majority of isolates of P. graminis from Europe, North America, and India reacted strongly with the antiserum. Interestingly, P. graminis isolates from the state of Rajasthan (northern India), from Pakistan, and an isolate from Senegal (West Africa) reacted weakly with the antiserum. The cross-reactivity of the serum with P. betae isolates from Belgium and Turkey was about 40% of that observed for the homologous isolate. There was no reaction with common fungi infecting roots or with the obligate parasite Olpidium brassicae. However, two isolates of Spongospora sub-terranea gave an absorbance similar to that observed with the homologous antigen. The DAC ELISA procedure was successfully used to detect various stages in the life cycle of P. graminis and to detect infection that occurred under natural and controlled environments. A simple procedure to conjugate antibodies to fluorescein 5-isothiocyanate (FITC) is described. Resting spores could be detected in root sections by using FITC-labeled antibodies. The potential for application of the two serological techniques for studying the epidemiology of peanut clump disease and for the characterization of Polymyxa isolates from various geographical origins is discussed.