Characterization of a dicarboximide-fungicide-resistant laboratory isolate ofMonilinia laxa

Monilinia laxa, the incitant of blossom blight in stone fruits in Israel, is sensitive to 5μg/ml of the dicarboximide fungicides vinclozolin and iprodione in the growth medium. When a large number of spores, from an isolate never exposed to these fungicides, was seeded on a medium containing 15 μg/ml iprodione, spontaneous resistant mutants appeared at 10^-5 frequency. These mutants showed cross resistance to the dicarboximide fungicides vinclozolin, procymidone, l-(3,5-dichloro-phenyl)-3-propen(2)-pyrrolidin-2,5-dion (Co 4462), l-(3,5-dichlorophenyl)-3-methoxymethyl-pyrrolidin-2,5-dion (Co 6054), and to dicloran. Growth rate on fungicide-free medium was similar to that of the parental sensitive strain but sporulation was much reduced. Growth rate on media supplemented with dicarboximide fungicides decreased gradually with increasing fungicide concentrations. The resistance has been stable for more than one year in the absence of fungicides. Artificial inoculation of cherry, apricot and plum fruits previously treated with 500 μg/ml vinclozolin, iprodione, procymidone or Co 6054, with a resistant strain, resulted in brown rot; similar treatments provided full protection of the fruits against the sensitive strain.     

Morphological and physiological characteristics of dicarboximide-sensitive and resistant isolates of Botrytis cinerea1

Various morphological and physiological characteristics, such as mycelial colour and appearance, mycelial growth rates, sporulation, pathogenicity on different hosts, activity of cell-wall degrading enzymes, competitive ability and osmotic sensitivity of five dicarboximide-resistant isolates of Botrytis cinerea were compared to those of their sensitive parent strains. There were only small reductions in mycelial growth rates of resistant strains as compared to the sensitive ones, whereas all of them showed greatly reduced rates of sporulation. With only one exception, the pathogenicity of the resistant isolates was reduced by varying extents compared with the sensitive parent strains. While the proteolytic activity of resistant strains tended to be higher, the activities of peclolytic enzymes were often lower than those of the sensitive isolates. In competition tests, resistant conidia often completely disappeared after a few passages on untreated plants. In only one of the resistant isolates tested so far was dicarboximide resistance related to a high osmotic sensitivity.     

Failure to detect highly resistant strains in dicarboximide resistant field populations of Botrytis cinerea1

Field isolates of Botrytis cinerea with moderate levels of resistance to dicarboximide fungicides (ED50 1.0–4.9 μg ml^?1) and to dicloran were obtained from glasshouses where vinclozolin and iprodione failed to control grey mould. From sensitive and moderatcly-resistant cultures, laboratory isolates were selected on dicarboximide-amended medium, which were highly resistant to these fungicides (ED50 125->3000 μg ml^?1). Conidia of all the resistant isolates germinated well on media amended with 100 μg ml^?1 of the dicarboximides vinclozolin, iprodione, procymidone and myclozolin and with 5 μg ml^?1 of metomeclan. However, the spores of the moderately resistant isolates did not germinate on 100 μg ml^?1 metomeclan while the spores of the highly resistant isolates germinated well. Using media with 100 μg ml^?1 of metomeclan to distinguish between the two phenotypes, no highly resistant strain was detected among 312 resistant samples from five cucumber glasshouses with a high frequency of moderately resistant strains. From air-borne inoculum of five glasshouses with 100% resistant populations, 1604 colonies were recovered on vinclozolin-amended (100 μg ml^?1) medium and none on metomeclan-amended (100 μg ml^?1) medium. It is concluded that strains of B. cinerea highly resistant to dicarboximides are absent from field populations.     

抗氟吡菌胺辣椒疫霉菌株的诱导及其生物学特性的研究

 采用菌丝生长速率法, 测定了采自泰安、平谷、杭州和昆明4个地区的42株辣椒疫霉病菌对氟吡菌胺的敏感性, 结果表明, 其EC₅₀值在0.618 ~0.927 μg·mL^-1之间, 平均EC₅₀ =(0.743±0.067 7) μg·mL^-1。 42个菌株对氟吡菌胺的敏感性分布呈单峰曲线, 未出现抗性的病原菌亚群体, 可将其单峰曲线作为辣椒疫霉对氟吡菌胺的敏感性基线。采用药剂驯化和紫外照射对辣椒疫霉敏感菌株TA进行诱变处理, 获得了2株辣椒疫霉抗氟吡菌胺菌株;利用菌落直径法测定抗氟吡菌胺菌株的遗传稳定性、菌丝生长速率及对其它杀菌剂的交互抗性;通过活体叶盘法测定抗氟吡菌胺菌株和敏感菌株的致病力及产孢子囊能力, 分析抗性和敏感菌株之间生物学特性差异。结果表明, 敏感菌株TA经过氟吡菌胺 48代连续汰选, 其抗性达58.0倍, 获得中抗菌株TA-R;紫外照射获得了抗性达260.6倍的高抗菌株TA-UV, 且其抗性均能稳定遗传;TA-R和TA-UV对甲霜灵、霜脲氰表现出正交互抗性, 对烯酰吗啉、百菌清、代森锰锌和丙森锌无交互抗性;抗氟吡菌胺菌株TA-R、TA-UV与敏感菌株在活体叶盘上的致病力、离体产孢能力均差异不显著(P＜0.05), 但其菌丝生长速率、菌丝干重均低于敏感菌株。     

Effect of Phenylpyrrole-resistance Mutations on Ecological Fitness of <Emphasis Type="Italic">Botrytis cinerea</Emphasis> and their Genetical Basis in <Emphasis Type="Italic">Ustilago maydis</Emphasis>

Mutants of Botrytis cinerea and Ustilago maydis highly resistant to fludioxonil were isolated at a high frequency, after nitrosoguanidine or UV mutagenesis, respectively, and selection on media containing fludioxonil. Tests on the response of mutant strains to high osmotic pressure resulted in the identification of two fludioxonil-resistant phenotypes (FLD_osm/s and FLD_osm/r), regarding the sensitivity to high osmolarity. Approximately 95% of fludioxonil-resistant mutants were found to be more sensitive to high osmotic pressure than the wild-type parent strains. Genetic analysis of phenylpyrrole-resistance in the phytopathogenic basidiomycete U. maydis, showed that fludioxonil-resistance was coded by three unlinked chromosomal loci (U/fld-1, U/fld-2 and U/fld-3), from which only the U/fld-1 mutation coded an osmotic sensitivity similar to that of the wild-types. Cross-resistance studies with fungicides from other chemical groups showed that the mutations for resistance to phenylpyrroles affect the sensitivity of mutant strains to the aromatic hydrocarbon and dicarboximide fungicides, but not to the benzimidazoles, anilinopyrimidines, phenylpyridinamines, hydroxyanilides or the sterol biosynthesis inhibiting fungicides. A study of fitness parameters in the wild-type and fludioxonil-resistant mutants of B. cinerea, showed that all osmotic sensitive (B/FLD_osm/s) isolates had significant reductions in the characteristics determining saprophytic fitness such as mycelial growth, sporulation, conidial germination and sclerotial production. Contrary to that, with the exception of mycelial growth, the fitness parameters were unaffected or only slightly affected in most of the osmotic resistant (B/FLD_osm/r) isolates. Tests on cucumber seedlings showed that the osmotic-sensitive strains were significantly less pathogenic compared with the wild-type and B/FLD_osm/r strains of B. cinerea. Preventative applications of the commercial products Saphire 50 WP (fludioxonil) and Rovral 50 WP (iprodione) were effective against lesion development on cotyledons by the wild-type and the mutant strains of B. cinerea that were resistant to the anilinopyrimidine cyprodinil (B/CPL-27) and to the hydroxyanilide fenhexamid (B/FNH-21), but ineffective, even at high concentrations, against disease caused by the fludioxonil-resistant isolates (B/FLD) and a mutant strain resistant to the dicarboximide iprodione (B/IPR-1). Experiments on the stability of the fludioxonil-resistant phenotype showed a reduction of resistance, mainly in osmotic-sensitive isolates, when the mutants were grown on inhibitor-free medium. A rapid recovery of the high resistance was observed after mutants were returned to the selection medium. Studies on the competitive ability of mutant isolates against the wild-type parent strain of B. cinerea, by applications of a mixed conidial population, showed that, in vitro, all mutants were less competitive than the wild-type strain. However, the competitive ability of osmotic-resistant mutants was higher than the osmotic-sensitive ones. Furthermore, competition tests, in planta, showed a significant reduction of the frequency of both phenylpyrrole-resistant phenotypes, with a respective increase in the population of the wild-type strain of the pathogen.     

Effect of chlorothalonil on resistance of Botrytis cinerea to dicarboximides in cucumber glasshouses1

Failures to control grey mould by dicarboximides on winter-grown cucumbers in glasshouses in Israel were attributed to the development of resistance to these fungicides in populations of Botrytis cinerea. A survey of 18 glasshouses in the winter of 1983-84 revealed that resistance is widespread where dicarboximides have been used extensively. During the summer, resistant B. cinerea populations often shift back to sensitivity; however, following few dicarboximide sprays in the subsequent winter, resistant strains reappear, increase rapidly and become dominant in the pathogen population. In two out of three glasshouse experiments, combination of chlorothalonil and dicarboximides in spray programmes slowed down the increase of resistant strains, whereas in a third experiment such a programme had no effect. The usefulness of chlorothalonil in fungicide-alternation programme to suppress dicarboximide resistance is dicussed in relation to the fitness properties of established versus newly-appearing resistant mutants.     

Fungicide resistance in Czech populations of cucurbit powdery mildews

A total of 108 isolates of cucurbit powdery mildew (CPM) fungi, 78Golovinomyces cichoracearum (Gc) and 30Podosphaera xanthii (Px), originating from nine Czech regions and 22 districts of the Czech Republic were collected in the years 2001–2004. These isolates were screened for tolerance and/or resistance to the three frequently used fungicides (fenarimol, dinocap, benomyl). Fungicide sensitivity was determined by a modified leaf-disc bioassay with five concentrations. Fungicide efficacy differed significantly: fenarimol was the most effective and all isolates of both CPM were controlled by the recommended concentration (36μg a.i. ml⁻¹). Some isolates expressed resistance (profuse sporulation) or tolerance (limited sporulation) to lower concentrations (9.6 and 18μg a.i. ml⁻¹). Specific temporal variation in tolerance/resistance was observed, with some isolates ofGc from 2002 evincing tolerant or resistant reactions to these low fenarimol concentrations, but isolates with similar reactions were not detected during the years 2003–2004. Dinocap showed decreasing efficacy during all 3 years. A shift to more tolerant reactions in the CPM populations was detected forGc in 2001–2002, and forPx in 2001 and 2004. Benomyl was found to be ineffective, because the majority of screened isolates (88%Gc and 97%Px) belonged to the highly resistant strains, with resistant reaction on the recommended concentration (250μg a.i. ml⁻¹) and tolerance or resistance on higher concentrations (500 and 1000μg a.i. ml⁻¹). Sensitivity differed between the CPM species. Whereas practically allPx isolates (except one from 2003) were resistant, 12% ofGc isolates from the years 2001–2003 showed sensitive and/or tolerant reactions. In 2004, only benomyl-resistantGc strains were detected. Variation in tolerance/resistance was detected to all screened fungicides during the course of this study at some repeatedly sampled locations. http://www.phytoparasitica.org posting June 12, 2008.     

Field occurrence of vinclozolin resistance in Monilinia fructicola

Strains of Monilinia fructicola resistant to vinclozolin were isolated from fruit affected by brown rot from an orchard where the fungicide had been used over four seasons. Resistant isolates were pathogenic to peach fruit, and resistance of one isolate was confirmed following dipping of inoculated fruit in fungicide suspensions. In culture, one of four resistant isolates was identical in colony morphology and sporulation to sensitive isolates from different geographic areas. The other resistant isolates produced dark mycelium on PDA and were slower growing. Vinclozolin-resistant isolates were resistant in vitro to two other dicarboximide fungicides, iprodione and procymidone.     

Influence of spray schedules on fungicide resistant populations of Botrytis cinerea Pers. on grapevine

Treatments with dicarboximide fungicides provided only 20 to 40% control of grey mould on grape (cv. Moscato d'Asti) in vineyards where benzimidazole and dicarboximide resistant strains ofBotrytis cinerea Pers. constituted about 50% of the fungal population and a high disease pressure existed. The percentage of dicarboximide resistant strains increased after treatment. Fungicide combinations of a benzimidazole with diethofencarb, sprayed twice per season or once alternated with a dicarboximide, provided satisfactory control of grey mould and decreased the percetage of benzimidazole resistant strains. A combination of thiram and procymidone controlled grey mould, but increased dicarboximide resistance in the population.     

A High Multi-drug Resistance to Chemically Unrelated Oomycete Fungicides in Phytophthora infestans

Mutants of Phytophthora infestans with high resistance to the amidocarbamates iprovalicarb and benthiavalicarb and to the cyanoimidazole cyazofamid were isolated after UV-mutagenesis and selection on media containing one of the above fungicides. In vitro fungitoxicity tests showed that all resistant strains presented a highly reduced sensitivity to both cyazofamid and to the amidocarbamates. Cross-resistance studies with other oomycete fungicides from different chemical groups showed that the mutation(s) for resistance to iprovalicarb (IPV), benthiavalicarb (BVC) and cyazofamid (CZF) also greatly reduced the sensitivity of mutant strains to the phenylamide metalaxyl, acetamide cymoxanil, morpholine dimethomorph, benzamide zoxamide and to chlorothalonil. A lower reduction of sensitivity of mutant strains to the strobilurins azoxystrobin, kresoxim-methyl, pyraclostrobin and trifloxystrobin, azolones famoxadone and fenamidone and to antimycin A was observed. A resistance correlation was not apparent for the dithiocarbamate propineb and phenylpyridinamine fluazinam. Studies of fitness parameters in the wild-type and mutant strains of P. infestans showed that most resistant isolates had significantly reduced sporulation and sporangial germination, but not in the differentiation of sporangia into zoospores. Pathogenicity tests on tomato seedlings showed that most resistant isolates were significantly less pathogenic compared to the wild-type parent strain. However, experiments on the stability of the resistant phenotypes did not show a reduction in resistance when the mutants were grown for more than eleven generations on inhibitor-free medium. This is believed to be the first report of high level multi-drug resistance in fungal pathogens to chemically unrelated fungicides inhibiting different sites of cellular pathway.     

Studies on the Inherent Resistance Risk to Fenhexamid in Botrytis cinerea

After chemical mutagenesis with N-methyl-N-nitrosoguanidine (MNNG) two phenotypes that were highly or moderately resistant to fenhexamid, were isolated from a wild-type strain of Botrytis cinerea, at a mutation frequency of 0.9 × 10^–5. Resistance factors, based on EC⁵⁰ values, were 460–570 and 10–15, respectively. The mutation(s) for resistance to fenhexamid did not affect the sensitivity of mutant strains to the benzimidazole benomyl, the phenylpyridinamine fluazinam, the anilinopyrimidine cyprodinil, the guanidine iminoctadine or to the sterol-biosynthesis-inhibiting fungicides fenarimol, fenpropimorph and tridemorph. On the contrary, an increased sensitivity (EC⁵⁰ ratios of 0.2–0.6) of fenhexamid-resistant strains to the phenylpyrrole fludioxonil and the dicarboximide iprodione was observed. Study of fitness parameters of fenhexamid-resistant isolates of both phenotypic classes showed that these mutation(s) had no effect on mycelial growth and sensitivity to high osmolarity, but they did affect one or more of some other characteristics, such as sporulation, conidial germination and sclerotia production. In tests on cucumber seedlings under greenhouse conditions, all highly fenhexamid-resistant isolates tested presented decreased infection ability compared with the wild-type. Preventive applications of a commercial formulation of fenhexamid, Teldor 50 WP, were effective against lesion development on cotyledons by the wild-type, but ineffective, even in high concentrations, against disease caused by the fenhexamid-resistant isolates. The risk of resistance problems arising during commercial use of fenhexamid is discussed.     

番茄灰霉病菌对咯菌腈的抗性诱变及抗药突变体的生物学特性

为评估番茄灰霉病菌Botrytis cinerea对咯菌腈的抗性风险,就室内经紫外照射获得抗药突变体的方法及抗性突变体的生物学性状进行了研究。结果表明:番茄灰霉病菌分生孢子的紫外照射亚致死时间为90~120 s;经亚致死时间紫外照射后,4个亲本菌株中有2个菌株共产生了6个抗咯菌腈的突变体,其EC50值是亲本菌株的310倍以上,抗性突变频率为3.13×10-7;经紫外照射诱变获得的所有抗性突变体在菌丝生长速率、产孢量、产菌核能力及其在番茄果实上的致病性方面均比其亲本菌株明显降低。相关分析显示,所得抗咯菌腈突变体对氟啶胺、啶菌唑、啶酰菌胺和嘧霉胺无交互抗性。表明番茄灰霉病菌对咯菌腈的抗药性风险较低。     

Pseudocercospora griseola,the causal agent of common bean angular leaf spot: Strain characterization and sensitivity to fungicides

Angular leaf spot (ALS), an important disease of common bean (Phaseolus vulgaris), is caused by the fungus Pseudocercospora griseola. This pathogen has a wide genetic variability and, therefore, poses a challenge to integrated disease management. The use of resistant cultivars is difficult; hence, the application of fungicides has been a common practice in common bean cultivation. P. griseola strains were morphophysiologically characterized and their sensitivity to common fungicides used to control ALS was studied. The strains were evaluated for sporulation capacity and a representative sample of 34 strains was bioassayed to determine their sensitivity to commercial concentrations of five fungicides, namely pyraclostrobin, mancozeb, pyraclostrobin + metconazole, chlorothalonil and tebuconazole. Another sample of 29 strains was studied for conidial germination and dimensions. Sporulation capacity ranged from 0.88 to 27.67 × 10⁴ conidia/ml and germination percentage ranged from 39% to 72%. The large differences among strains suggest a wide genetic variability among the strains. A wide variability in aggressiveness of P. griseola was observed, which has consequences for breeding programmes aimed at resistance. The behaviour of pathogen strains differed in every fungicide evaluated, even in a population that has not been under selection pressure in the field. These results confirm the need for further studies and may guide future research with this pathogen.     

Sensitivity of <Emphasis Type="Italic">Botrytis cinerea</Emphasis> to propamidine: in vitro determination of baseline sensitivity and the risk of resistance

The baseline sensitivity of Botrytis cinerea to propamidine and assessment of the risk of propamidine resistance in vitro are presented in this article. The baseline sensitivities of 41 wild-type strains were distributed as a unimodal curve with EC₅₀ values of mycelial growth ranging from 0.182 to 1.460 μg ml⁻¹, with a mean of 0.79 ± 0.27 μg ml⁻¹. A total of 10 resistant mutants, obtained from one parental strain, were induced by UV irradiation and selected for resistance to propamidine with an average frequency of 1.98 × 10⁻⁹ and 0.025 respectively. These mutants were divided into three classes of resistant phenotypes with low (LR), moderate (MR) and high (HR) levels of resistance, determined by the EC₅₀ values of 5.0–15.0 μg ml⁻¹, 15.1–75.0 μg ml⁻¹ and more than 75.0 μg ml⁻¹ respectively. Neither positive cross-resistance nor negative cross-resistance was detected between propamidine and the fungicides, benzimidazole carbendazim, anilino-pyrimidine pyrimethanil, dicarboximide iprodione or procymidone. All 10 propamidine-resistant mutants showed reduced mycelial growth in vitro, sporulation, spore germination and pathogenicity when compared with the parental strain. These studies demonstrated that propamidine possesses a low risk of resistance developing. However, as B. cinerea is a high-risk pathogen, appropriate precautions against resistance development should be taken.     

Variable resistance factors of fungicides acting as sterol demethylation inhibitors

The ED₅₀ values and resistance factors of 20 fungicides that all act as inhibitors of the C-14 demethylation of 24-methylenedihydrolanosterol were determined for one wild-type and four resistant strains of Ustilago avenae. All fungicides were cross-resistant to each other; however, the resistance factors varied considerably, ranging from 50 (triadimenol) to 2·2 (miconazole). A tentative structural requirement for low resistant factors was the presence of two phenyl rings separated from each other by at least three atoms. Labeling of lipids with [¹⁴C]acetate in the absence and presence of the inhibitors and subsequent sterol analysis revealed that the variable resistance factors were not related to the presence of a second target site. In spite of reported second modes of action of fenarimol, tebuconazole or miconazole, accumulation of C-14 sterol precursors in both sensitive and resistant isolates was necessary to accomplish growth inhibition.     

Mefenoxam sensitivity and fitness analysis of Phytophthora nicotianae isolates from nurseries in Virginia, USA

Mefenoxam is one of the most commonly used fungicides for managing diseases caused by Phytophthora spp. on ornamentals. The objectives of this study were to determine whether Phytophthora nicotianae, a destructive pathogen of numerous herbaceous annual and perennial plant species in nurseries, has developed resistance to mefenoxam, and to evaluate the fitness of mefenoxam‐resistant isolates. Ninety‐five isolates of P. nicotianae were screened for sensitivity to mefenoxam on 20% clarified V8 agar at 100 a.i. µg mL^?1. Twenty‐five isolates were highly resistant to this compound with EC₅₀ values ranging from 235·2 to 466·3 µg mL^?1 and four were intermediately resistant with EC₅₀ values ranging from 1·6 to 2·9 µg mL^?1. Sixty‐six isolates were sensitive with EC₅₀ values less than 0·04 µg mL^?1. Nine resistant and seven sensitive isolates were tested for mefenoxam sensitivity on Pelargonium × hortorum cv. White Orbit. Mefenoxam provided good protection of pelargonium seedlings from colonization by sensitive isolates, but not by any resistant isolates. Four resistant and four sensitive isolates were compared for fitness components and their relative competitive ability on Lupinus Russell Hybrids in the absence of mefenoxam. Resistant isolates outcompeted sensitive ones within 3 to 6 sporulation cycles on lupin seedlings, regardless of their initial proportions in mixed zoospore inoculum. Resistant isolates exhibited greater infection rate and higher sporulation ability than sensitive ones when they were applied separately onto lupins. These results suggest that fungicide resistance may pose a serious challenge to the continued effectiveness of mefenoxam as a control option for nursery growers.     

Distribution and fitness of isolates of Botrytis cinerea with multiple fungicide resistance in Spanish greenhouses

Forty-nine greenhouses of vegetable crops were surveyed in southeast Spain at the beginning of the disease season in December 1992 to estimate frequencies of resistance to benzimidazoles, dicarboximides and N -phenylcarbamates (NPC) in B. cinerea . Out of 261 isolates collected, 28% were sensitive to both benzimidazoles and dicarboximides, 15% were benzimidazole-resistant and dicarboximide-sensitive, 8% were benzimidazole-sensitive and dicarboximide-resistant and 46% were benzimidazole- and dicarboximide-resistant. Resistance to benzimidazole, dicarboximide and N -phenylcarbamate was determined by measuring the ability of each isolate to grow in the presence of carbendazim, procymidone and diethofencarb fungicides respectively. Carbendazim- or procymidone- resistant isolates were found in all surveyed greenhouses. Three isolates were found with resistance to carbendazim, procymidone and diethofencarb collected in two adjacent greenhouses that were sprayed with the carbendazim and diethofencarb mixture. All other isolates were sensitive to the mixture because they were either sensitive to carbendazim and resistant to diethofencarb or vice versa. Fitness of 31 isolates of B. cinerea was determined in vivo by measuring their sporulation and lesion growth rate on leaf disks. No fitness costs were associated with resistance to iprodione (dicarboximide) and benomyl (benzimidazole). Isolates with EC₅₀ values higher than 101 mg/L for benomyl and 1.6 mg/L for iprodione were considered to be field resistant (they caused visible lesions on cucumber leaf disks treated with each fungicide).     

Selection and characterization of Phytophthora parasitica mutants with ultraviolet-induced resistance to dimethomorph or metalaxyl

Mutants of Phytophthora parasitica Dast. more or less resistant to dimethomorph or metalaxyl were obtained by treating mycelium with ultraviolet radiation. Some metalaxyl-resistant mutants exhibited levels of resistance (i.e. the ratio between the EC₅₀ values for the mutant and the wild-type strain) greater than 100, but those observed in the dimethomorph-resistant mutants never exceeded 25. Most mutants retained their resistance after sub-culturing on unamended agar medium. Single zoospore clones derived from a metalaxyl-resistant and a dimethomorph-resistant mutant, selected as amongst the most resistant, had levels of resistance similar to those of the parental strains. The metalaxyl-resistant mutants were also resistant to the related phenylamide fungicides, furalaxyl and benalaxyl, but remained sensitive to dimethomorph. The dimethomorph-resistant mutants were not resistant to phenylamide fungicides. The pathogenicity of some metalaxyl- or dimethomorph-resistant mutants on tobacco leaves was similar to that of the wild-type strains.     

水稻恶苗病菌田间抗咪鲜胺菌株的适合度及其交互抗性

恶苗病是水稻生产上较为严重的种传真菌病害,咪唑类广谱内吸性杀菌剂咪鲜胺是目前防治该病害的主要药剂。以对咪鲜胺抗性及敏感的田间水稻恶苗病菌为试材,研究了其适合度及对几种常用杀菌剂的交互抗性。结果显示:抗性菌株的抗药性可稳定遗传,其温度敏感性与敏感菌株无明显差异,部分抗性菌株在菌丝生长速率、产孢量、孢子萌发率和致病力方面显著高于田间敏感菌株;咪鲜胺与三唑类及2-氰基丙烯酸酯类杀菌剂之间均无交互抗性。研究表明,对咪鲜胺产生抗性的水稻恶苗病菌具有较强的适合度,在田间自然条件下有可能形成优势群体,因此需合理轮换使用不同作用机制的杀菌剂,以延缓其抗药性的发展。     

Stability and fitness of pyraclostrobin- and boscalid-resistant phenotypes in field isolates of Botrytis cinerea from apple

Phenotype stability, fitness, and competitive ability of pyraclostrobin- and boscalid-resistant isolates of Botrytis cinerea from apple were investigated. Stability of resistance was determined after consecutive transfers on potato dextrose agar (PDA) or being cycled on apple fruit. In vitro fitness components mycelial growth, osmotic sensitivity, conidial germination, and sporulation were evaluated on agar media. Pathogenicity, virulence and sporulation on apple fruit were evaluated at both 20 and 0°C. Competition between fungicide-resistant and -sensitive isolates on apple fruit also was evaluated. Resistance to the two fungicides was retained at levels similar to that of the initial generation after 20 and 10 transfers on PDA and five and three disease cycles on apple fruit at 20 and 0°C, respectively. Great variability in individual fitness components tested was observed among isolates within the same phenotype groups either sensitive or resistant to the fungicides but, when compared as phenotype groups, there were no significant differences in the mean values of these fitness components between resistant and sensitive phenotypes except that the phenotype resistant only to boscalid produced fewer conidia in vitro than sensitive isolates. Resistant isolates were as pathogenic and virulent on apple fruit as sensitive isolates. There was no significant correlation between the values of individual fitness components tested and the level of resistance to pyraclostrobin or boscalid, except that virulence at 20°C positively correlated with the level of resistance to the two fungicides. The final frequency of pyraclostrobin-resistant individuals in the populations was significantly decreased compared with the initial generation and no boscalid-resistant individuals were detected after four disease cycles on apple fruit inoculated with a pair mixture of a dual-sensitive isolate and one isolate each of the three phenotypes resistant to pyraclostrobin, boscalid, or both. The results suggest that resistance of B. cinerea to pyraclostrobin and boscalid was stable in the absence of the fungicides and that resistance to the two fungicides did not significantly impair individual fitness components tested. However, both pyraclostrobin- and boscalid-resistant isolates exhibited competitive disadvantage over the dual-sensitive isolate on apple fruit.