3-Acetyl deoxynivalenol production in a strain ofFusarium culmorum insensitive to the fungicide difenoconazole

The production of the mycotoxin, 3-acetyl deoxynivalenol (3-ADON), was investigated in a strain ofFusarium culmorum insensitive to the systemic fungicide, difenoconazole. On exposure to graded concentrations of the fungicide, the insensitive strain continued to synthesise 3-ADON when difenoconazole levels of 100 and 200μg/ ml media were used. In contrast, a control (sensitive) strain ceased production of 3-ADON at difenoconazole levels of 100 μg/ml. Differences between the two strains were also observed for 3-ADON production with time. Following incubation with fungicide at 0.1 μg/ ml, 3-ADON production occurred more rapidly in CS than in IS cultures. This is the first report of increased persistence and alteration of the pattern of production of a mycotoxin following the development of fungicide insensitivity in a fungal phytopathogen.     

The effect of seed treatment with benzimidazole-based fungicides on infection of the foliage of overwintered salad onions by Botrytis cinerea

Seed treatments of carbendazim (Bavistin 50% W.p.) and thiophanate-methyl (Mildothane 50% W.p.) applied to overwintered salad onions at 250 g a.i./kg seed protected the foliage of plants from infection by Botrytis cinerea during the seasons 1973–1976. Crop establishment and yield were also improved. Seed treatment with calomel was not effective. Chemical analysis of treated non-viable seeds, retrieved from the soil, indicated that 73% carbendazim and 46% thiophanate-methyl remained attached to the seeds after 9 months in the soil. Analyses of onion leaves revealed that each fungicide was represented by similar quantities of carbendazim, 5 μg/g fresh weight in October 1975 reducing to 1 μg/g fresh weight in May 1976. Bioassay tests showed that the fungicide was acropetally distributed and was present in all leaves early in the season (October) but was absent from some new leaves formed in the following spring. Carbendazim-insensitive isolates of B. cinerea occurred after three seasons' use of this chemical. Sensitive isolates failed to grow on agar containing 1 μg/ml benomyl but all insensitive isolates (31 total) grew normally at this concentration and some were capable of growth on agar containing 1000 μg/ml benomyl. The emergence of foliar isolates of the fungus insensitive to the benzimidazole-based compounds used in the treatment of seeds indicated that these fungicides did not provide a permanent solution to the disease problem.     

Resistance of Sclerotinia minor Isolates to Cyclic Imides in Lettuce Field Soils of Roussillon, France

Lettuce drop caused by Sclerotinia minor Jagger is the most common disease affecting lettuce crops during the fall and winter in Roussillon. Spraying of cyclic imide fungicides (iprodione, vinclozolin, and less commonly procymidone) generally provides satisfactory protection. However, since about 1985, the mean field efficacy of iprodione and vinclozolin has significantly decreased, whereas that of procymidone is currently not in question. The appearance of fungicide-resistant isolates of S.minor could explain the reduced efficacy of these fungicides. We thus looked for iprodione and procymidone-resistant isolates of S.minor in these problem fields. The investigations were earned on for over 3 years. Most of the isolates showed fungicide sensitivity (iprodione IC 50 = 0.17 mg 1⁻¹), about one quarter showed average resistance (iprodione IC 50 = 0.59 mg 1⁻¹) and a few were found to be highly resistant. Resistant isolates were also obtained in vitro when using high fungicide concentrations. Moreover, isolates resistant to iprodione were found to be resistant to procymidone. The most highly resistant isolates produced fewer and larger-sized sclerotia than the sensitive isolates, they were also more quickly inhibited by high osmotic pressures. Field variability was quite low: 73 of 74 isolates obtained from one field were found to be sensitive, with only one showing mild resistance. There did not seem to be any correlation between the observed decrease in the field efficacy of iprodione and the presence of resistant isolates.     

Baseline sensitivities to azoxystrobin and tebuconazole in Sclerotinia sclerotiorum isolates from sunflower in Iran related to sensitivities to carbendazim and iprodione

In this study, sensitivities of 156 Sclerotinia sclerotiorum isolates collected from sunflower fields of West Azarbaijan province, Iran, were assessed to carbendazim and iprodione, and the baseline sensitivities were established for azoxystrobin and tebuconazole. Resistance to carbendazim and iprodione was observed in 53.85% and 4.49% of the isolates, respectively. The 50% effective concentration (EC₅₀) values of azoxystrobin for the isolates ranged from 0.017 to 3.515 μg/ml with a mean of 0.330 μg/ml, and 8.97% of the strains showed low levels of resistance to the fungicide. However, in the presence of salicylhydroxamic acid, all isolates were sensitive to azoxystrobin and EC₅₀ values ranged from 0.015 to 0.263 μg/ml with a mean of 0.086 μg/ml. All isolates were found to be sensitive to tebuconazole, and EC₅₀ values ranged from 0.003 to 0.177 μg/ml with a mean of 0.036 μg/ml. Among the multiple-resistant isolates, the strains exhibiting resistance to both carbendazim and iprodione were detected in the highest frequency (4.49%). No correlation was observed between mycelial growth and aggressiveness with fungicide sensitivity of the isolates suggesting the absence of fitness cost associated with resistance to the studied fungicides. The results indicated that iprodione, azoxystrobin and tebuconazole could be effectively used in rotation or mixture in spray programmes to manage S. sclerotiorum in the region. The baselines established for azoxystrobin and tebuconazole would be useful in monitoring the fungal populations in the province to assess possible shifts in fungicide sensitivity of S. sclerotiorum isolates in the future.     

Molecular characterization of benzimidazole-resistant isolates of Cladosporium fulvum

The benzimidazole fungicide thiophanate-methyl is commonly applied to control leaf mould of tomato caused by Cladosporium fulvum in China. In this study, 32 isolates of C. fulvum were examined for their sensitivities to thiophanate-methyl, and two benzimidazole-resistant (BenR) phenotypes BenR1 and BenR2 were identified. The BenR1 isolates were resistant to thiophanate-methyl, but were more sensitive to the phenylcarbamate fungicide diethofencarb than the wild-type isolates. The BenR2 isolates resistant to thiophanate-methyl were insensitive to diethofencarb. All tested isolates were sensitive to the dicarboximide fungicide iprodione. The complete beta-tubulin gene was isolated from this fungus to study its potential role in benzimidazole resistance. Analysis of the DNA sequence of the beta-tubulin gene showed that the BenR1 isolates had a point mutation at codon 198, causing a substitution of glutamic acid to alanine. In the BenR2 isolates, a point mutation at codon 200 causing a substitution of phenylalanine to tyrosine was detected. Based on these point mutations, a multiplex allele-specific PCR method was developed successfully for the first time to detect two point mutations at the beta-tubulin gene simultaneously in single PCR amplifications.     

THE ADAPTATION OF FUNGI TO FUNGICIDES: ADAPTATION TO THIRAM, ZIRAM, FERBAM, NABAM AND ZINEB

The concentrations of thiram preventing germination of spores of Botrytis cinerea in drops of a 1% solution of sucrose, and on the surface of a sucrose-nitrate agar have been determined. Thiram had much less effect on germination in the agar medium, even when a purified agar was used. There was no growth on sucrose-nitrate agar if the concentration of thiram exceeded 31 p.p.m. Attempts to obtain strains able to grow at higher concentrations were unsuccessful.
Similar results were obtained with ziram, nabam and zineb.
Ferbam also was more effective in preventing spore germination in spore drops than on agar media; this effect was obtained with ordinary and with purified agar.
On a sucrose-nitrate agar generally there was no growth if the concentration of ferbam exceeded 125 p.p.m., but in one of forty-eight plates containing 250 p.p.m. ferbam, five slowly growing colonies were produced, and from these colonies arose mycelium which grew and sporulated rapidly on 500 p.p.m. ferbam agar. Agar disk inocula were transferred from these cultures to agar containing higher concentrations of ferbam and in this way, and by repeating the process, a strain was obtained which grew slowly but continuously, and sporulated on agar containing 5000 p.p.m. ferbam. However, the poor solubility of this fungicide made it difficult to assess quantitatively the degree of adaptation.
A proportion of the spores from this strain germinated in drops containing about twice the concentration of ferbam which prevented germination of parent spores.
The resistance of the mycelium of the resistant strain was not lost after repeated subculture on fungicide-free agar. The resistant strain was as susceptible as the parent strain to thiram, ziram, nabam and zineb.
Attempts to obtain strains of Venturia inaequalis resistant to thiram, ferbam, ziram and zineb were unsuccessful.     

Activity of Fluazinam against Strains of Botrytis cinerea Resistant to Benzimidazoles and/or Dicarboximides and to a Benzimidazole-phenylcarbamate Mixture

Fluazinam is a new active ingredient for the control of grey mould, belonging to the novel broad spectum phenylpyridinamine fungicides. The effect of fluazinam was studied on one wild type and four strains of Botrytis cinerea , which had been isolated from vegetable crops in Greece, and were resistant to benzimidazoles and/or dicarboximides and to the mixture of benzimidazoles (carbendazim) + phenylcarbamates (diethofencarb). In vitro fluazinam was found to be highly active against strains of B. cinerea which were sensitive or resistant to benzimidazoles or exhibited multiple resistance to benzimidazoles, dicarboximides and to the mixture carbendazim + diethofencarb [EC₅₀ and EC₉₅ values (concentration of active ingredient that suppresses mycelial growth to 50 and 95%, respectively, of that of the fungus on fungicide-free agar medium) calculated with probit analysis, ranged from 0.044 to 0.069 and 0.58 to 1.6 μg/ml, respectively]. No cross-resistance was observed between fluazinam and the market products benomyl, iprodione or carbendazim + diethofencarb. Preventive applications of fluazinam in vivo completely inhibited infections of cucumber seedlings by all the above-mentioned resistant strains of B. cinerea . Benomyl and iprodione did not effectively control the benzimidazole- and dicarboximide-resistant strains. The mixture of carbendazim + diethofencarb insufficiently controlled the strain of B. cinerea with moderate resistance to benzimidazoles. The results of this investigation indicate that it should be possible to use fluazinam as an alternative in resistance management programmes against grey mould.     

THE ADAPTATION OF FUNGI TO FUNGICIDES: ADAPTATION TO COPPER AND MERCURY SALTS

The susceptibility of Botrytis cinerea to copper sulphate in liquid media increased when the volume, and therefore the depth, of the medium in culture bottles exceeded certain values; when the volume was 40 ml. the maximum concentration allowing growth was 300 p.p.m.
By growing mycelium in media containing progressively higher concentrations of copper sulphate a strain was produced which grew at a concentration of 750 p.p.m.
In high concentrations of copper sulphate growth always started at the edge of the liquid, and inocula grew only if they were placed in this position.
In germination tests spores from the resistant strain were more resistant to copper sulphate than were spores of the parent strain.
The resistance of mycelium, and to a lesser extent of spores, was retained after growth of the resistant strain for six months in fungicide-free media.
Spore and mycelial inocula grew in much higher concentrations of copper sulphate when nutrient media were solidified with agar.
The strain resistant in liquid media was no more resistant than the parent strain on agar media.
The resistance of the fungus was not increased after growth for long periods on agar containing high concentrations of copper sulphate. The resistance of the strain resistant in liquid media was not lost after growth on agar media for 3 months.
Attempts to produce strains more resistant than the parent to mercuric chloride were unsuccessful.
The results obtained with phenyl-mercuric acetate were essentially similar to those obtained with copper sulphate, but relatively much more resistant strains were produced.     

In vitro Selection of Strains of Phytophthora cactorum Resistant to Metalaxyl

Isolates of Phytophthora cactorum resistant to the systemic fungicide metalaxyl were obtained by exposing them to sequentially increased concentrations of metalaxyl. A linear relationship was observed between the concentrations of metalaxyl and percentage inhibition of mycelial growth of P. cactorum. The stability of metalaxyl-resistant isolates 150R and 250R was confirmed after six serial transfers on corn meal agar without fungicide. The in vitro metalaxyl-resistant isolate (Ph10) was less aggressive on apple rootstocks compared with the Ph07 isolated from metalaxyl-treated trees and the Ph03 isolated from untreated trees. Metalaxyl-resistant and sensitive isolates remained sensitive to the chemically unrelated fungicide fosetyl-Al at high concentration (600 μg/ml), to mancozeb, and to a mixture of metalaxyl + mancozeb. Significant differences in resistance to metalaxyl existed among P. cactorum field isolates.     

Selection of strains of Epicoccum purpurascens for tolerance to fungicides and improved biocontrol of Sclerotinia sclerotiorum

A wild-type isolate of Epicoccum purpurascens was exposed to shortwave ultraviolet light. One of the resulting cultures (M-20-A) was grown on media amended with the fungicides iprodione or vinclozolin and fungicide-tolerant strains were obtained. Several comparisons were made between new strains and the wild type. Sporulation was improved compared with the wild type. Strains varied in their tolerance to iprodione and vinclozolin but were not tolerant to the fungicide benomyl. Strains R4000, 16-B, and 7-A inhibited Sclerotinia sclerotiorum in vitro more than either the wild type or M-20-A, and exhibited improved control of white mold of bean in the greenhouse compared with M-20-A. Key words: biological control, fungicide resistance, white mold, iprodione, vinclozolin.     

Guttation droplets of <Emphasis Type="Italic">Penicillium nordicum</Emphasis> and <Emphasis Type="Italic">Penicillium verrucosum</Emphasis> contain high concentrations of the mycotoxins ochratoxin A and B

Eight of eleven ochratoxigenic isolates of Penicillium nordicum and Penicillium verrucosum produced guttation droplets when grown on Czapek yeast extract (CYA) agar for 10–14 days at 25°C. Parallel cultivation of one strain each of P. nordicum and P. verrucosum on malt extract agar demonstrated that higher volumes of exudate are produced on this agar. However, HPLC analyses revealed higher concentrations of ochratoxin A (OTA) and B (OTB) in droplets originating from cultures on CYA. For quantitative determination of the mycotoxin contents, triplicates of three isolates each of P. nordicum and P. verrucosum were grown as single spot cultures on CYA for up to 14 days at 25°C. Guttation droplets were carefully collected between day 11 and 14 with a microliter syringe from each culture. Extracts from exudates and corresponding mycelia as well as fungal free agar were analyzed by HPLC for the occurrence of ochratoxin A (OTA) and B (OTB). Mean concentrations ranging between 92.7–8667.0 ng OTA and 159.7–2943.3 ng OTB per ml were detected in the guttation fluids. Considerably lower toxin levels were found in corresponding samples of the underlying mycelia (9.0–819.3 ng OTA and 4.5–409.7 ng OTB/g) and fungal free agar (15.3–417.0 ng OTA and 12.7–151.3 ng OTB/g). This is the first report which shows that high amounts of mycotoxins could be excreted from toxigenic Penicillium isolates into guttation droplets.     

Microsatellite stability in the plant pathogen Botrytis cinerea after exposure to different selective pressures

The stability of microsatellite markers was investigated in the spore-producing fungus Botrytis cinerea exposed to four growth conditions. This knowledge is essential in order to differentiate mutations from genetic exchanges or recombination in population genetics studies. It is also important when using strains from collections that need to be regularly propagated on medium. Successive spore generations of four isolates of the fungus were realised in plates on different agar media: a nutrient-rich medium, a nutrient-poor medium, a medium supplemented with the antibiotic pyrrolnitrin and a medium supplemented with the fungicide iprodione. The stability of nine microsatellite markers was studied by comparing the molecular pattern obtained between the wild type parent strains and the final generations obtained. The results showed that, despite the phenotypic changes observed in some generations, no changes were observed in the allele size at nine microsatellite loci whatever the selective pressure endured by the fungus. This is the first study that reveals long-term stability of microsatellite markers of a spore-producing fungus exposed to different stresses.     

Relative sensitivities of environmental legionellae to selective isolation procedures

A survey of water samples to determine the efficacy of standard procedures for the isolation of environmental legionellae was conducted. Marked variations in intraspecies resistance to selective agents and treatments were observed, and in experiments with one of the isolates, the response was modified by culture conditions. Five selective procedures incorporating acid (pH 2.2) and heat (50 degrees C, 30 min) treatments, with and without plating on buffered charcoal-yeast extract agar supplemented with vancomycin (5 micrograms/ml), polymyxin B (60 U/ml), and cycloheximide (80 micrograms/ml), caused 5 to 99% decreases in viable counts of pure cultures in water suspensions. The differences in the responses of the cultures to the five treatments were statistically significant. Cells in retained samples of naturally contaminated water from which the original cultures had been isolated were significantly less sensitive than artificially grown isolates. The sensitivities of the laboratory-grown cells to the treatments were affected by the length of incubation on buffered charcoal-yeast extract agar. Whereas acid resistance increased after 24 h of incubation, resistance to the antibiotic mixture decreased.     

Relative sensitivities of environmental legionellae to selective isolation procedures.

A survey of water samples to determine the efficacy of standard procedures for the isolation of environmental legionellae was conducted. Marked variations in intraspecies resistance to selective agents and treatments were observed, and in experiments with one of the isolates, the response was modified by culture conditions. Five selective procedures incorporating acid (pH 2.2) and heat (50 degrees C, 30 min) treatments, with and without plating on buffered charcoal-yeast extract agar supplemented with vancomycin (5 micrograms/ml), polymyxin B (60 U/ml), and cycloheximide (80 micrograms/ml), caused 5 to 99% decreases in viable counts of pure cultures in water suspensions. The differences in the responses of the cultures to the five treatments were statistically significant. Cells in retained samples of naturally contaminated water from which the original cultures had been isolated were significantly less sensitive than artificially grown isolates. The sensitivities of the laboratory-grown cells to the treatments were affected by the length of incubation on buffered charcoal-yeast extract agar. Whereas acid resistance increased after 24 h of incubation, resistance to the antibiotic mixture decreased.     

Oxidative Protective Mechanisms and Resistance to the Dicarboximide Fungicide, Iprodione, in Alternaria alternata

The free radical scavengers α-tocopherol and butylated hydroxytoluene, but not ascorbate, diminished the growth-inhibiting effects of the dicarboximide fungicide, iprodione in Alternaria alternata. Growth of A. alternata in the presence of iprodione increased the activities of superoxide dismutase and glutathione reductase while catalase was unaffected. Four iprodione sensitive and four iprodione resistant isolates of A. alternata were compared for activity of free radical enzymes. The isolates of A. alternata resistant to iprodione had more catalase activity than those which were sensitive, but did not differ in superoxide dismutase of glutathione reductase, activities. 3-Amino-1.24.-triazole, a specific inhibitor of catalas, reduced the ability of DAR 69775, a dicarboximide resistant isolate of A. alternata. to grow in the presence of iprodione. In A. alternata dicarboximide resistance appeats to be at least partially mediated by enhanced activitiesof, catalase.     

番茄早疫病菌Hog1 MAPK同源基因AsHog1的表达特性及其与抗药性的关联性

根据几种丝状真菌Hog1 MAPK(丝裂原活化蛋白激酶)的保守氨基酸序列设计简并引物,从番茄早疫病菌Alternaria solani中扩增出MAPK同源基因的部分片段,命名为AsHog1。用Real-timeRT-PCR技术比较了AsHog1在异菌脲敏感菌株和抗性菌株中的表达特性。结果表明,敏感菌株QX21经0.8mol/L NaCl和2mg/L异菌脲处理后,AsHog1相对表达量持续升高,在12h达到最大值,分别为对照的4.12倍和25.23倍,16h略有降低;而室内诱导抗性突变体和田间抗性菌株经相同处理后的AsHog1表达量变化不大,且明显低于敏感菌株。由此推测,番茄早疫病菌AsHog1基因表达特征与其对异菌脲抗药性相关。研究结果为深入研究病原菌对异菌脲抗药性的分子机理、建立抗药性分子监测技术、延缓和防止抗药性的产生及发展奠定了一定的理论基础。     

Leaf Disc Inoculation, a Fast and Precise Test for the Screening of Metalaxyl Tolerance in Sunflower Downy Mildew

A new method, based on leaf disc inoculation, was developed for the screening of metalaxyl tolerance in field isolates of Plasmopara halstedii . High-pressure liquid chromatography (HPLC) was used to determine the fungicide concentration in the inoculation medium and in the incubated leaf tissue over the test period. These measurements revealed that the fungicide concentration inside the leaf tissue within 24 h had adjusted to the concentration in the outer medium and remained constant for the time of cultivation over a period of more than 11 days. In contrast to whole seedling tests with application of the fungicide via seed dressing, the leaf disc method allows precise quantification of the effective fungicide concentration at the site of infection and is less space and time consuming. Metalaxyl tolerance of P. halstedii isolates was gradually determined according to the sporulation of the pathogen on sunflower leaf discs in the presence of increasing fungicide concentrations. Isolates collected in South Germany showed no tolerance and sporulation was prohibited when tests were carried out at 0.02  μ g (a.i.)/ml of metalaxyl or more. In contrast, a tolerant French isolate developed sporangia on leaf discs incubated in a metalaxyl solution of 100  μ g (a.i.)/ml.     

恶疫霉有性杂交后代的竞争能力研究*

５株杂交个体（携带对甲霜灵和地茂散的抗性标记）的游动孢子分别与其野生型亲本ＡＰ １４和ＰＫ９（对甲霜灵和地茂散均敏感）按１：１、１：９和１：４９比例混合涂布在１０％Ｖ６培养基平板上或接种在苹果片上生长４～５ｄ,并诱导产生孢子囊和释放游动孢子,经单孢分离建立单孢无性系,在含甲霜灵或地茂散的培养基上检测杂交个体的单孢后代所占的百分率。结果是,在Ｖ６培养基平板上混合生长的３０个组合中,仅３个组合杂交个体的单孢后代在其单孢无性系群体中所占的比例显著低于野生型亲本,其余组合均符合其各自的期望值;在苹果片上混合接种的３０个组合,杂交个体与野生型亲本的单孢后代所占比例均符合其各自的期望值。进一步测定２个杂交个体（ＡＰＫ－９和ＡＰＫ－２４）分别与其野生型亲本以１：１的比例混合后在Ｖ６培养基平板上和苹果片上连续３个产孢循环过程中两者比例的变化,结果是,在杂交个体与野生型亲本ＡＰ１４的组合中,杂交个体的后代所占的百分率由第一个产孢循环的４９．１％～５４．２％至第三个产孢循环下降为１．８％～６．２％：而在与另一野生型亲本ＰＫ９的组合中,杂交个体的后代所占的百分率从第一个产孢循环的４４．４％～５４．２％至第３个产孢循环上升为７２．１     

Mutational tolerance to carbendazim in Botrytis cinerea

No spontaneous mutation for tolerance to the fungicide carbendazim was detected in C. 10⁸ conidia from each of eight carbendazim-sensitive field isolates of Botrytis cinerea. Conidia of B. cinerea were highly insensitive to u.v.-irradiation, although after severe irradiation treatments mutant strains showing the same levels of tolerance as two groups of carbendazim-tolerant field isolates were selected at frequencies of between 10^-9 and 10^-6 of survivors. Mutants with low levels of tolerance (ED₅₀ > 10 μg ml^-1 carbendazim; ‘partially-tolerant’) were selected from irradiated conidia obtained from sensitive field isolates and a further series of mutants capable of growth on 10 000 μg ml^-1 carbendazim (‘fully-tolerant’) were selected from irradiated conidia from either partially-tolerant mutants or from partially-tolerant field isolates. Both mutation steps were confirmed in similar experiments in which tolerance to an unrelated fungicide, 2, 6-dichloro-4-nitroaniline (DCNA), was incorporated as a genetic marker in the parent strains.     

Mycotoxin production in a carbendazim-resistant strain of fusarium sporotrichioides

Mycelial yield and production of three trichothecenes, namely T-2 toxin, diacetoxyscirpenol (DAS) and neosolaniol (NEO) were compared in control (CS) and carbendazim-resistant strains (RS) ofFusarium sporotrichioides. Each strain was exposed to graded concentrations of carbendazim (0, 1, 2, and 4 μg/ml media) for 2, 5 and 7 days under shake-culture conditions at an incubation temperature of 25°C. Mycelial yield was significantly (P<0.001) affected by strain, carbendazim concentration and incubation time. The strain differences in mycelial mass at 2 days (P<0.05) became more pronounced at 5 and 7 days of incubation (P<0.001). However, mycelial growth differences between the two strains were greatest following exposure to carbendazim, with the effects becoming more divergent with time. Combined results for the three incubation times showed dose related effects in carbendazim inhibition of T-2 toxin production by CS isolates. In contrast, RS cultures exposed to the 2 μg/ml addition of carbendazim significantly increased T-2 toxin production (P<0.05 or better). At 1 and 4 μg/ml additions, T-2 toxin inhibition occurred but the effect was less marked than in the CS series. RS yielded more DAS than CS at 5 days (P<0.05) and at 7 days (P<0.01) of incubation. The major component of this strain difference arose from the effects of the 2 μg/ml addition of carbendazim (P<0.01). NEO production was also higher in RS than in CS, with the difference becoming progressively more pronounced from day 5 (P<0.05) to day 7 (P<0.01) of incubation. However, these differences reflected enhanced NEO output with carbendazim addition of 4 μg/ml (P<0.05) in day 5 extracts and of both 2 μg/ml (P<0.01) and 4 μg/ml additions (P<0.05) in day 7 samples. Moreover, the ratio of NEO to T-2 toxin production was affected by an interaction involving incubation time, strain and carbendazim dose (P<0.05 or better). On day 5, this ratio was greater in CS exposed to 2 μg/ml, but at 4 μg/ml, the ratio was higher in RS. It is concluded that carbendazim resistance induced genuine differences in the synthesis of T-2 toxin and NEO. It is suggested that the strain difference may reside in the conversion of NEO to T-2 toxin which may be sensitive to fungicide concentration. This would imply that carbendazim resistance induces changes in the terminal rather than initial phases of trichothecene biosynthesis.