Occurrence of fenhexamid resistance in Botrytis cinerea from greenhouse strawberries in China

This study assessed the fenhexamid sensitivity of 143 Botrytis cinerea isolates collected from greenhouse strawberries in five regions of China between 2012 and 2013, and identified four isolates with moderate levels of resistance: two from the Xinjiang Uygur Autonomous Region and two from Hebei Province. The baseline fenhexamid sensitivity of B. cinerea exhibited a unimodal distribution with a mean EC₅₀ value of 0.20 ± 0.10 μg/ml (SD). The EC₅₀ values of the fenhexamid‐resistant isolates ranged from 0.05 to 0.40 μg/ml. Molecular analysis of the fenhexamid target gene erg27 revealed that the resistant isolates collected from Xinjiang (163‐6 and 163‐22) contained three mutations that led to amino acid changes (V365A, E368D and A378T) known to be associated with fenhexamid resistance, but that the isolates from Hebei lacked any mutations, indicating that an alternative mechanism could be responsible for their resistance. Most of the biological characteristics of the fenhexamid‐resistant isolates, such as mycelial growth, sclerotia production and pathogenicity, did not significantly differ from those of the sensitive ones (p ≤ .05), but it was noted that some of the resistant isolates exhibited reduced rates of sporulation and spore germination. In addition, the resistant isolates exhibited lower osmotic sensitivity than the sensitive ones. The study found no evidence of cross‐resistance with other fungicides, but that there was negative cross‐resistance with procymidone, iprodione, carbendazim and pyraclostrobin, which indicates that the inclusion of these fungicides within an integrated pest management (IPM) programme could help to minimize the risk of fenhexamid resistance developing in B. cinerea.     

Baseline sensitivity of Botrytis cinerea to fluazinam and cross‐resistance

Grey mould, caused by the fungus Botrytis cinerea Pers ex Fr., is a very destructive and important disease worldwide. Fluazinam is a phenylpyridinamine fungicide with broad‐spectrum activities. The baseline sensitivity of B. cinerea to fluazinam is yet to be established in Henan Province, China. In this study, a total of 117 field isolates of B. cinerea were collected from 49 commercial greenhouses in different locations of Henan Province, in 2016, and the sensitivities of these isolates to fluazinam were determined based on mycelial growth. The effective concentration for 50% (EC₅₀) values ranged from 0.0038 to 0.0441 μg/ml, and the mean EC₅₀ value was 0.0201 ± 0.0081 μg/ml for mycelial growth. The frequency distribution range presented a unimodal curve. To define the cross‐resistance relationships, the linear correlation coefficients of the EC₅₀ values between fluazinam and carbendazim, procymidone, pyrimethanil or boscalid were analysed. The results showed that no correlation was observed between fluazinam and the other tested fungicides. These results provide important information to growers for the prevention and control of grey mould.     

Detection and molecular characterization of carbendazim-resistant Colletotrichum truncatum Isolates causing anthracnose of soybean in Thailand

A loss of fungicide efficacy, particularly for carbendazim, was noted in soybean fields in Thailand and was considered to be due to the development of Colletotrichum truncatum resistance. The carbendazim sensitivity of C. truncatum populations isolated from various soybean fields in Thailand was thus evaluated with in vitro sensitivity assays and molecular characterization of mutations in the sequences of the ß₂-tubulin (TUB2) gene that confer carbendazim resistance in the pathogen. Among 52 isolates, 46 isolates were classified as highly resistant (HR) to carbendazim (EC₅₀ > 1,000 µg/ml). All HR isolates grew on PDA amended with carbendazim at 1,000 µg/ml. Six isolates were classified as carbendazim sensitive (S) (EC₅₀ < 1 µg/ml). Mycelial growth on PDA amended with 1 µg/ml carbendazim was inhibited by over 50% compared with growth on PDA alone. When a partial TUB2 gene from the isolates was amplified and analysed using predicted amino acid sequences, an alteration from glutamic acid to alanine at codon 198 (E198A) was found in 45 HR isolates for which the EC₅₀ was higher than 2000 µg/ml. This mutation resulted from a nucleotide substitution from adenine to cytosine (GA G → GC G). The other HR isolate, CtPhS_1, with EC₅₀ of 1,127 µg/ml, had an alteration at codon 200 (F200Y) (TT C → TA C).     

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.     

Occurrence and management of fungicide resistance in Botrytis cinerea on tomato from greenhouses in Hebei,China

Grey mould, caused by the fungal pathogen Botrytis cinerea, is one of the most devastating tomato diseases, and the control of this disease is mainly by the application of chemicals. In this study, 512 isolates of B. cinerea were collected from tomato grown in greenhouses at 10 locations in 10 cities of Hebei Province from 2011 to 2016 and tested for their sensitivities to carbendazim (Car), diethofencarb (Die), iprodione (Ipr) and pyrimethanil (Pyr). Of these tested isolates, 95.7%, 95.2%, 31.6% and 89.4% were resistant to Car, Die, Ipr and Pyr, respectively. There were nine fungicide‐resistant phenotypes in the tested isolates. Car^RPyr^RDie^RIPR^S and Car^RPyr^RDie^RIPR^R were the most common phenotypes, accounting for 59.6%, and 31.1% of the tested isolates, respectively. The field trials showed that the control efficacies (CE) of carbendazim + diethofencarb (WP, 25% + 25%), pyrimethanil (EC, 40%) and iprodione (WP, 50%) at the recommended doses were 22.75%–29.23%, 58.44%–64.19% and 61.02%–65.17%, respectively, significantly lower than those of boscalid (WG, 50%) and pyrisoxazole (EC, 25%). The resistance management trial conducted from 2015 to 2017 indicated that the CE of tomato grey mould in the experimental fields was higher than 90% and the sensitivity to carbendazim, diethofencarb and pyrimethanil of B. cinerea isolates from the experimental fields increased on a yearly basis. These results showed that the frequency of resistance to Car, Die, Ipr and Pyr was high, and these four fungicides could not effectively control tomato grey mould. Tomato grey mould could be controlled by using biopesticides and newly synthesized fungicides with different modes of action. Our findings would be useful in designing and implementing fungicide resistance management spray programmes for the control of tomato grey mould.     

Baseline sensitivity and efficacy of fluopyram against Botrytis cinerea from table grape in Italy

Succinate dehydrogenase inhibitor (SDHI) fungicides constitute a relatively recent fungicide class registered for the treatment of grey mould on grapevine in Italy. The sensitivity profile to a novel compound fluopyram was established for a set of 203 Botrytis cinerea isolates collected from Sicilian vineyards within 2009–2012 prior its introduction into market. In addition, its performances were compared in in vitro and in vivo assays with other registered SDHI fungicide boscalid, to evaluate their frequency distributions EC₅₀ values and cross‐resistance patterns. Results of the article showed that EC₅₀ values for fluopyram ranged from 0.05 to 1.98 µg mL^?1. Although EC₅₀ values of boscalid ranged from 0.01 to 89.52 µg mL^?1, no cross‐resistance relationship was observed between the two fungicides (r = 0.003; P = 0.964) within our B. cinerea population. On further confirming these data, boscalid failed in controlling grey mould infections when boscalid‐resistant isolates were inoculated on grape berries whereas fluopyram exhibited a good efficacy against the same isolates. This study represents the first report on the baseline sensitivity to fluopyram within B. cinerea population from Sicilian table grape vineyards in Italy, and it clearly shows the lack of cross‐resistance in vitro and in vivo between fluopyram and boscalid for the field pathogen isolates. These results provided useful information for managing of fungicide resistance suggesting that fluopyram could be a valid alternative to boscalid for the control of grey mould of table grape.     

In vitro sensitivity of Verticillium fungicola to selected fungicides

Twenty isolates of Verticillium fungicola var. fungicola collected from diseased fruit-bodies of Agaricus bisporus from prochloraz-treated crops, were exposed to a range of concentrations of six chemicals (benomyl, chlorothalonil, formaldehyde, iprodione, prochloraz-Mn-complex and prochloraz + carbendazim) in vitro. EC₅₀ values were determined for each fungus-fungicide combination. All isolates were more sensitive to prochloraz-Mn-complex (EC₅₀ values less than 5 mg 1^–1) than to the remainder fungicides, and only seven isolates were moderately sensitive (EC₅₀ values between 5 and 50 mg 1^–1) to prochloraz + carbendazim. All isolates were moderately sensitive to formaldehyde, whereas the majority of isolates were very resistant to the other three fungicides (benomyl, chlorothalonil and iprodione).     

Activity of fungicide mixtures against Botrytis cinerea isolates resistant to benzimidazoles,strobilurins and dicarboximides

Botrytis cinerea, the causal agent of grey mould in a broad range of crops, is considered a high‐risk plant pathogen for fungicide resistance development. The use of fungicide mixtures, particularly combinations with synergistic activity, can be a useful tactic to counteract resistance build‐up in pathogen populations. The present study aimed to investigate the effects of different ratios of two‐way mixtures of carbendazim, iprodione, kresoxim‐methyl, tebuconazole and penconazole on four B. cinerea isolates that were sensitive or resistant to benzimidazoles, dicarboximides and strobilurins. The isolates that were resistant to benzimidazoles and strobilurins had E198A and G143A mutations in β‐tubulin and cytochrome b genes, respectively. The mixtures had different effects on each of the isolates in vitro but, in 13 combinations, the synergistic effect was observed against all or three isolates. In greenhouse experiments, 11 fungicide combinations used in decreased (EC₇₅) concentrations showed the maximum control efficiency. The two follow‐up greenhouse experiments using six selected combinations revealed they were highly effective against additional isolates with various fungicide resistance profiles. The identified mixtures‐ratios have potential for use in grey mould management programs in the greenhouse.     

Sensitivity to Fludioxonil of Botrytis cinerea Isolates from Tomato in Henan Province of China and Characterizations of Fludioxonil‐resistant Mutants

Grey mould, caused by Botrytis cinerea Pers ex Fr., is one of the most common diseases of tomato worldwide. Fludioxonil belongs to the phenylpyrrole fungicides, which have high activity against B. cinerea. The sensitivity of fludioxonil was evaluated on the basis of the level of inhibition of mycelium growth in 274 B. cinerea isolates collected from different locations (untreated with this fungicide) in Henan Province, China. The EC₅₀ values for fludioxonil ranged from 0.0033 to 0.0415 mg/l, and the average EC₅₀ values were 0.0156 ± 0.0078 mg/l. Three fludioxonil‐resistant mutants were obtained by subculturing fludioxonil‐sensitive wild‐type isolates on continuously increasing fludioxonil concentrations. For the cross‐resistance assay, fludioxonil revealed positive cross‐resistance with procymidone but did not reveal cross‐resistance with pyrimethanil, boscalid and trifloxystrobin. Mycelial growth, conidial production, hyphal dry weight and pathogenicity were diminished significantly between the fludioxonil‐resistant mutants and their sensitive wild‐type parental isolates. This study shows for the first time that fludioxonil‐resistant isolates of B. cinerea are still not present in Henan Province because this fungicide is an attractive and effective fungicide for chemical control. Recommendations can be made to growers to use fludioxonil to control grey mould and to consider the potential moderate resistance risk of using this fungicide.     

Sensitivity to boscalid in field isolates of Sclerotinia sclerotiorum from rapeseed in Henan Province,China

Sclerotinia stem rot caused by Sclerotinia sclerotiorum is an important disease of oilseed rape in Henan province of China. Boscalid belongs to succinate dehydrogenase inhibitor (SDHI) fungicides, many of which have strong antifungal activity against S. sclerotiorum. In 2015, a total of 175 isolates of S. sclerotiorum were collected from diseased oilseed rape plants in seven different regions of Henan Province. The EC₅₀ values of 175 isolates of S. sclerotiorum to boscalid ranged from 0.0073 to 0.3880 μg ml^?1, and the mean EC₅₀ value was 0.15 ± 0.09 μg ml^?1. The frequency distribution was unimodal. There was no cross‐resistance between boscalid and carbendazim, procymidone, iprodione, dimethachlone, fludioxonil or fluazinam. Field experiments showed that control efficacies of treatments with boscalid (50% WG) at 225, 300 and 375 g ai ha^?1 were 71%, 81% and 90%, respectively. In contrast, the control efficacy of carbendazim (50% WP) at 1,500 g ai ha^?1 was only 52%.     

The mixture of kresoxim‐methyl and boscalid,an excellent alternative controlling grey mould caused by Botrytis cinerea

Grey mould, caused by the fungus Botrytis cinerea, is one of the most destructive diseases in greenhouses for which serious fungicide resistance has developed. Between 2003 and 2005, 213 isolates of B. cinerea from two geographical regions were characterised for baseline sensitivity to kresoxim‐methyl. In the absence of salicylhydroxamic acid (SHAM), the mean 50% effective concentration (EC₅₀) values were 6.67 ± 0.61 (mean ± SD) and 0.37 ± 0.10 mg L^?1 during growth and germination, respectively. In the presence of 100 mg L^?1 SHAM, baseline sensitivities were distributed as unimodal curves with mean EC₅₀ values of 2.38 ± 0.21 and 0.28 ± 0.09 mg L^?1 for inhibiting growth and inhibiting germination, respectively. The mixture of kresoxim‐methyl and boscalid showed good control efficacy against strawberry grey mould disease. After the mixture was extensively used on strawberry for 2 years, 50 isolates were collected and determined for their sensitivity to kresoxim‐methyl and boscalid, respectively. The mean EC₅₀ of germination inhibition by boscalid was 0.39 ± 0.08 mg L^?1. The mean EC₅₀ of germination inhibition by kresoxim‐methyl was 0.26 ± 0.07 mg L^?1 in the presence of 100 mg L^?1 SHAM. Sensitivities of B. cinerea to both kresoxim‐methyl and boscalid did not show any significant decrease. These results suggest that their mixture is a satisfactory alternative candidate for management of grey mould disease in greenhouses.     

Carbendazim resistance and dimethachlone sensitivity of field isolates of Sclerotinia sclerotiorum from oilseed rape in Henan Province,China

Sclerotinia stem rot caused by Sclerotinia sclerotiorum is one of the most important diseases in oilseed rape‐growing areas of China. To determine the frequency of resistance of field isolates of S. sclerotiorum to carbendazim and dimethachlone, a total of 556 isolates from 10 different regions of Henan Province were obtained between 2015 and 2016. The frequency of isolates with a high‐resistance phenotype and a moderate‐resistance phenotype to carbendazim was 69.2% and 10.8%, respectively. However, S. sclerotiorum isolates resistant to dimethachlone were not detected. The baseline sensitivity of S. sclerotiorum to dimethachlone was distributed as a unimodal curve with a mean EC₅₀ value of 0.39 ± 0.09 μg ml^?1 for the inhibition of mycelial growth. Four dimethachlone‐resistant mutants were obtained from 20 wild‐type isolates induced by exposure to increasing concentrations of the fungicide in vitro. The mutants showed high levels of resistance to dimethachlone, with resistance factors that ranged from 179 to 323. Positive cross‐resistance occurred between dimethachlone and procymidone, iprodione, and fludioxonil; however, no cross‐resistance was observed for carbendazim and boscalid. The fitness of the dimethachlone‐resistant mutants was significantly lower than that of the wild‐type isolates, as measured by mycelial growth, hyphal dry weight, sclerotium number and dry weight, and pathogenicity. Additionally, based on osmotic tests, the inhibition of mycelial growth caused by NaCl applied at different concentrations was significantly higher for the dimethachlone‐resistant mutants than for their wild‐type parents.     

Molecular Characterization and Antifungal Susceptibility Testing of Sequentially Obtained Clinical <Emphasis Type="Italic">Cryptococcus deneoformans</Emphasis> and <Emphasis Type="Italic">Cryptococcus neoformans</Emphasis> Isolates from Ljubljana,Slovenia

Aim

To retrospectively investigate the epidemiology of cryptococcosis in Ljubljana, Slovenia.

Methodology

Forty-six sequentially obtained isolates from 19 patients were subjected to amplified fragment length polymorphism (AFLP) genotyping, microsatellite typing, mating- and serotype PCRs and antifungal susceptibility testing.

Results

Majority of the isolates were Cryptococcus deneoformans (n = 29/46; 63%) followed by Cryptococcus neoformans (n = 16/46; 34.8%) and their interspecies hybrid (n = 1/46; 2.2%). Mating-type α was predominant, two mating-type a C. deneoformans isolates and one mating-type a/α isolate were observed. Several mixed infections were found by microsatellite typing; one patient had a persisting C. deneoformans infection for > 2.5 years. For C. deneoformans, the in vitro antifungal MIC₉₀ and susceptibility ranges were for amphotericin B 0.25 µg/ml (0.031–0.25 µg/ml), 5-fluorocytosine 0.25 µg/ml (0.063–4 µg/ml), fluconazole 8 µg/ml (0.5–16 µg/ml), voriconazole 0.063 µg/ml (0.008–0.125 µg/ml), posaconazole 0.063 µg/ml (0.008–0.063 µg/ml) and itraconazole 0.063 µg/ml (0.031–0.125 µg/ml). For C. neoformans, these values were for amphotericin B 0.25 µg/ml (0.063–0.5 µg/ml), 5-fluorocytosine 1 µg/ml (0.063–1 µg/ml), fluconazole 16 µg/ml (0.5–64 µg/ml), voriconazole 0.125 µg/ml (0.008–0.25 µg/ml), posaconazole 0.063 µg/ml (0.008–0.063 µg/ml) and itraconazole 0.063 µg/ml (0.031–0.125 µg/ml).

Conclusions

Majority of the cases were caused by C. deneoformans; mating-type α was predominant. Several mixed infections were identified by AFLP genotyping and microsatellite typing. Despite antifungal therapy, a cryptococcal isolate could persist for years. Voriconazole, itraconazole and posaconazole were the most potent antifungal drugs.

     

Fungicide Resistance Phenotypes of Botrytis cinerea Isolates from Commercial Vineyards in South West Germany

Fungicide resistance frequencies of Botrytis cinerea populations in the German Wine Road region were determined for 4 years. Strains showing specific resistance against carbendazim, iprodione or fenhexamid were found to occur wide‐spread, but at low frequencies. In contrast, cyprodinil resistance increased from 5.4% in 2006 to 21.9% in 2008 and 16% in 2009, and strains resistant to boscalid increased from 2% in 2006 to 26.7% in 2009. Strains with multidrug resistance (MDR) phenotypes were found at high frequencies. One of the three MDR phenotypes, MDR1, with reduced sensitivity to cyprodinil and fludioxonil, was dominating, representing 19% to 35% of the total population. Strains with a combination of cyprodinil resistance and MDR1 were found to be strongly increasing in 2008 and 2009.     

In Vitro Antifungal Susceptibility of Malassezia pachydermatis Strains Isolated from Dogs with Chronic and Acute Otitis Externa

Malassezia pachydermatis is a yeast that is frequently involved as a secondary/perpetuating factor in canine otitis externa. Topical therapies with different antifungal agents, mainly azole compounds, are generally successful in controlling the yeast overgrowth, but treatment failure and rapid recurrences are common. This study compared the in vitro antifungal susceptibility of M. pachydermatis isolates obtained from chronic and acute cases of otitis externa. The aim was to assess the possible onset of resistance mechanisms in isolates involved in long-lasting episodes with poor response to treatment. We evaluated the in vitro susceptibility to miconazole (MCZ) and clotrimazole (CTZ) of 42 isolates of M. pachydermatis obtained from dogs with chronic (group A, n = 25) and acute otitis (group B, n = 17), using a modified CLSI M27-A3 microdilution method. All isolates were inhibited by the antifungal agents employed, but Malassezia isolates from group A were significantly associated with higher minimum inhibitory concentration (MIC) values for both agents (Median MIC values: MCZ group A 2 µg/ml, group B 1 µg/ml; CTZ group A 8 µg/ml, group B 4 µg/ml). These findings prove that these isolates had a reduced in vitro susceptibility to the antifungal agents tested. However, it is unlikely that this could have any influence on the outcome of a topical treatment. Indeed, marketed products include concentrations of the tested agents that largely exceed even the highest MICs found in this study (in most cases at least 1,000 × the MIC, or greater). In conclusion, this study suggests that isolates of M. pachydermatis involved in chronic cases of canine external otitis and exposed to repeated antifungal treatments are unlikely to develop mechanisms of resistance of clinical relevance.     

Contribution of Pathogens to Peach Fruit Rot in Northern Greece and their Sensitivity to Iprodione, Carbendazim, Thiophanate-methyl and Tebuconazole Fungicides

This study identified the main pathogens causing fruit rots of mature peaches in northern Greece, the major peach producing area of Greece. The brown rot pathogen Monilinia laxa was responsible for approximately 70% and 78% of rotted peaches in 2005 and 2006 respectively. Serious damage (up to 5%) was also caused with the fungus Phomopsis amygdali. Other pathogens isolated from rotted peaches at a low percentage were Alternaria alternata, Aspergillus niger, Aspergillus flavus, Botrytis cinerea, Sclerotinia sclerotiorum, Fusarium spp., Colletotrichum gloeosporioides, Rhizopus stolonifer and Gilbertella persicaria. Most fungal isolates originated from the rotted peaches were tested for their sensitivity to the fungicides iprodione, carbendazim, thiophanate methyl and tebuconazole at label recommended concentrations. All fungicides inhibited the growth of M. laxa, A. niger, A. flavus, S. sclerotiorum, P. amygdali and B. cinerea on poisoned agar. Apart from iprodione, all other fungicides inhibited the mycelium growth of the pathogen Fusarium sp. The mycelium growth of Fusarium sp. was significantly less with iprodione than control. Only iprodione and tebuconazole were effective against A. alternata and R. stolonifer. Tebuconazole inhibited the mycelium growth of R. stolonifer, while iprodione reduced significantly in comparison to control. The mycelium growth of the fungus C. gloeosporioides was inhibited by tebuconazole and reduced significantly by the fungicides thiophanate methyl, carbendazim and iprodione. Among all the fungi tested, only M. laxa and B. cinerea isolates were found resistant to benzimidazoles [the EC50 (50% effective concentration) value was 100–200 mg/l and 200–300 mg/l for the largest number of thiophanate methyl‐ and carbendazim‐resistant M. laxa isolates respectively, while the biggest number of B. cinerea thiophanate methyl‐ and carbendazim‐resistant isolates showed EC50 value 200–300 mg/l and 300–400 mg/l, respectively]. However, these strains were sensitive to tebuconazole and iprodione. Therefore, these fungicides can be used as an alternative method to control benzimidazole‐resistant Monilinia and Botrytis isolates.     

Design,synthesis and fungicidal activity of novel 2-substituted aminocycloalkylsulfonamides

A series of novel 2-substituted aminocycloalkylsulfonamides were designed and synthesized by highly selective N-alkylation reaction, whose structures were characterized by ¹H NMR, ¹³C NMR and HRMS. Among them, the configuration of compounds III12 and III20 were confirmed by X-ray single crystal diffraction. Bioassays demonstrated that the title compounds had considerable effects on different strains of Botrytis cinerea and Pyricularia grisea. Comparing with positive control procymidone (EC₅₀ = 10.31 mg/L), compounds III28, III29, III30 and III31 showed excellent fungicidal activity against a strain of B. cinerea (CY-09), with EC₅₀ values of 3.17, 3.04, 2.54 and 1.99 mg/L respectively. Their in vivo fungicidal activities were also better than the positive controls cyprodinil, procymidone, boscalid and carbendazim in pot experiments. Moreover, the fungicidal activity of III28 (EC₅₀ = 4.62 mg/L) against P. grisea was also better than that of the positive control isoprothiolane (EC₅₀ = 6.11 mg/L). Compound III28 would be great promise as a hit compound for further study based on the structure-activity relationship.     

Baseline sensitivity and control efficacy of fluazinam against Sclerotinia sclerotiorum in Henan Province,China

Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, is a devastating disease in Henan Province, of the main rapeseed production areas in China. Fluazinam belongs to the broad‐spectrum phenylpyridinamine fungicides, which have high activity in inhibiting the mycelial growth of S. sclerotiorum. In this study, 191 field isolates were obtained from different oilseed rape fields in Henan Province, before being exposed to fluazinam in 2015. The baseline sensitivity of S. sclerotiorum to fluazinam was established. The effective concentration for 50% inhibition of mycelial growth (EC₅₀) ranged from 0.0019 to 0.0337 μg/ml, and the mean EC₅₀ value was 0.0084 ± 0.0055 μg/ml. The range of the frequency distribution was narrow. The results of a cross‐resistance assay revealed no cross‐resistance between fluazinam and carbendazim, dimethachlone, boscalid or fludioxonil. Field efficacy tests showed that the control efficacies of fluazinam (50% WG) applied at 150, 225 and 300 g ai ha^?1 were 67%, 73% and 88%, respectively. In contrast, the control efficacies of boscalid (50% WG) and carbendazim (50% WP) applied at 225 and 1,500 g ai ha^?1 were 71% and 52%, respectively.     

Effect of azoxystrobin and kresoxim‐methyl on rice blast and rice grain yield in China

Sensitivity to azoxystrobin and kresoxim‐methyl of 80 single‐spore isolates of Magnaporthe oryzae was determined. The EC₅₀ values for azoxystrobin and kresoxim‐methyl in inhibiting mycelial growth of the 80 M. oryzae isolates were 0.006–0.056 and 0.024–0.287 µg mL^?1, respectively. The EC₅₀ values for azoxystrobin and kresoxim‐methyl in inhibiting conidial germination of the M. oryzae populations were 0.004–0.051 and 0.012–0.105 µg mL^?1, respectively. There was significant difference in sensitivity to azoxystrobin or kresoxim‐methyl between the tested isolates representing differential sensitivity to carbendazim (MBC) and kitazin P (IBP); however, there was no correlation between this difference in sensitivity to azoxystrobin or kresoxim‐methyl and sensitivity to MBC or IBP, indicating that there was no cross‐resistance between azoxystrobin or kresoxim‐methyl and MBC or IBP. In the protective and curative experiments, kresoxim‐methyl exhibited higher protective and curative activity than azoxystrobin when applied at 150 and 250 µg mL^?1 accordingly, while azoxystrobin exhibited stronger inhibitory activity against M. oryzae isolates than that of kresoxim‐methyl in the in vitro test. The results of field experiments also suggested that both azoxystrobin and kresoxim‐methyl at 187.5 g.a.i. ha^?1 gave over 73% control efficacy in both sites, exhibiting excellent activity against rice blast. Taken together, azoxystrobin and kresoxim‐methyl could be a good substitute for MBC or IBP for controlling rice blast in China, but should be carefully used as they were both at‐risk.     

In vitro antifungal activity of antifungalmycin 702, a new polyene macrolide antibiotic, against the rice blast fungus Magnaporthe grisea

Antifungalmycin 702, a novel polyene macrolide antibiotic produced by Streptomyces padanus JAU4234, strongly inhibited mycelial growth of the rice blast fungus, Magnaporthe grisea, with EC₅₀ of 37 μg/ml and EC₉₀ of 136 μg/ml. Significant reduction in the number of conidia was observed at above 20 μg/ml. Conidia germination and appressorium formation were also suppressed and were not viable with >40 μg/ml. When treated with antifungalmycin 702, hyphae morphology became irregular. Based on microscopic examination, antifungalmycin 702 may exert its antifungal activity by changing the structure of cell membranes and the cytoskeleton and interacting with the organelles. Antifungalmycin 702 thus has potential as a new fungicide in the treatment of rice blast disease.