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Bioactivities of eight fungicides (boscalid, difenoconazole, propiconazole, flusilazole, carbendazim, prochloraz, dimethachlon, mancozeb) to the pathogen of a tobacco leaf spot, Didymella segeticola, were determined using bioassay method at the mycelial growth stage. In vivo protective and curative effects of these fungicides against D. segeticolla on detached tabbaco leaves were also analyzed. The results showed that eight fungicides exhibited different inhibitory activities against mycelial growth of the pathogen, and also showed some protective and curative efficacies against the leaf spot. The most effecient one against mycelial growth of the pathogen was boscalid, with an EC50 value of (0.047 0 ± 0.012 0) mg/L; followed by difenoconazole [(0.079 0 ± 0.005 0) mg/L], prochloraz [(0.29 ± 0.08) mg/L], propiconazole [(0.69 ± 0.12) mg/L], dimethachlon [(1.08 ± 0.33) mg/L], carbendazim [(1.22 ± 0.29) mg/L], flusilazole [(1.38 ± 0.07) mg/L]; and most least effecient one was mancozeb with an EC50 value of (22.80 ± 10.51) mg/L. Flusilazole, difenoconazole, propiconazole, boscalid and dimethachlon all had better protective activity for the control of this disease with >82% efficacy at 25 mg/L dosage treatment than 100 mg/L mancozeb showed 70.51% efficacy. Both boscalid and flusilazole showed better curative activities, with efficacies of >80% at 25 mg/L dosage treatment, followed by prochloraz, difenoconazole, carbendazim and dimethachlon; mancozeb showed relatively poor activity with 63.31% efficacy at 100 mg/L dosage treatment. The results provide scientific basis and reference for the screening of fungicides to control tobacco leaf spot. [ABSTRACT FROM AUTHOR]

Effective and safe smoke generators were urgently needed to control gray mold of Chinese chives. In this study, the feasibility of processing nine commonly used fungicides into smoke generator was evaluated from five aspects: inhibition activity of active compounds, toxicity of smoke, smoke formation rate, safety, and field control. The inhibition activity of active compounds results showed that EC50 values of fluazinam, fludioxonil, and pyrisoxazole against mycelial growth were 0.13, 0.05, and 0.12 mg/L; EC50 values of pyrazolamide, fluopyram, and boscalid against conidial germination were 0.84, 0.68, and 1.16 mg/L. In a 0.108 m³ containment device, the toxicity of the smoke of fungicides at the same dose of 0.01 g was tested, the results showed that with the same dose of 0.01 g, the mycelial growth were completely inhibited by smoked fludioxonil, while the conidial germination was completely inhibited by smoked pyrazolamide, fluopyram, and boscalid, the inhibition rates of registered procymidone smoke generator against mycelial growth and conidial germination were 54.39% and 43.27%. The smoking rate of fludioxonil, boscalid, and fluopyram were 85.93%, 91.35%, and 82.86%, which conform to the criterion of active ingredient for fabricating smoke generators. Seven days after fungicide smokes treatment, there was no significant difference in plant height and stem diameter of Chinese chives compared with the untreated control. The results of the field trials in 2019 and 2020 showed that the curative efficacy of active ingredient of 120 g/hm² fludioxonil smoke generator to gray mold were 72.31% and 79.78%, and the curative efficacy of active ingredient of 375 g/hm² boscalid smoke generator to gray mold were 81.17% and 83.81%. Their curative efficacy was all higher than the procymidone smoke generator at the highest registered dose (the active ingredient of 450 g/hm² ), in the treatment of grey mold of Chinese chives (59.86% and 63.71%). At the above doses, the preventative efficacies of three smoke generators to control gray mold were all above 90%. The dissipation dynamics of curves of the fludioxonil and boscalid were both in line with the first-order kinetic equation. The both half-lives of fludioxonil and boscalid in Chinese chives plant were 3-4 d. It is recommended that fludioxonil and boscalid are processed into smoke generators and registered for the prevention and control of gray mold of Chinese chives. [ABSTRACT FROM AUTHOR]

The sensitivity of Monilinia fructicola to boscalid was determined by the mycelial growth rate method. Meanwhile, the study investigated the biological characteristics of isolates with different sensitivities, the correlation between the amino acid mutations of SDHB protein with resistance to boscalid, and the cross-resistance of M. fructicola between boscalid and other 3 tested succinate dehydrogenase inhibitors (SDHIs), Y12196, penflufen and fluopyram. The results showed that boscalid had a good inhibitory activity and therapeutic effect against M. fructicola. However, M. fructicola has developed a certain degree of resistance, and the resistant isolates have comparable fitness with the sensitive ones. The sequence analysis of SDHB gene showed that the amino acid point mutations of M. fructicola SDHB subunits were not significantly correlated with the resistance to boscalid. The crossresistance studies indicated that there was cross-resistance between boscalid and the other three SDHIs, Y12196, penflufen, and fluopyram. In order to retard the occurrence and exacerbation of resistance, the rational mixes or rotations of boscalid with other kinds of fungicides rather than SDHIs are recommended during the prevention and control of cherry brown rot disease. [ABSTRACT FROM AUTHOR]

A total of 112 isolates of Stagonosporppsis citrulli were collected from 5 locations in Zhejiang Province. The resistance to thiophanate-methyl（Ben） and boscalid（Bos） was detected by the method of differentiated doses. The results showed that the respective resistance frequencies were 100%and 28.6% to Ben and Bos, respectively. The high-level resistance（Ben HR） of thiophanate-methyl reached 100%, and the low-level resistance（Bos LR） and high-level resistance（Bos HR） of boscalid were18.8% and 9.8%, respectively. Further studies on the molecular mechanism of resistance showed that the Ben HR of S. citrulli was caused by the E198 A point mutation in β-tubulin, which was the mutation of198 th amino acid of from Glu（E） to Ala（A）. The mechanism of Bos HR was the point mutation in 277 th amino acid of Sdh B from His（H） to Tyr（Y）, but the mechanism of low-level resistance（Bos LR） still needs to be studied. To sum up, the resistance of S. citrulli population to benzimidazole fungicides in Zhejiang Province was very serious. Most isolates were sensitive to boscalid, but the high-level resistance has occurred in some regions. Therefore, attention should be paid to the scientific use of SDHIs and resistance monitoring should be strengthened. [ABSTRACT FROM AUTHOR]

The pathogenic fungus causing tobacco brown spot in Guizhou Province was isolated and identified from diseased samples collected during 2014 to 2015, which have never been treated with succinate dehydrogenase inhibitors(SDHIs), and their sensitivity baseline to boscalid was established by mycelial growth rate tests. The results suggested that there were significant differences in colony and conidium morphlogy, and pathogencicity among these isolates. However, all isolates were identified as Alternaria alternata. In addition, the EC50 values of boscalid inhibiting the growth of A. alternata population (n = 102) from tobacco fitted unimodal distribution and varied from 0.186 to 5.818 μg/mL with the mean value of (2.157 ± 1.112) μg/mL, which could be adopted as the baseline sensitivity of A. alternata on tobacco to boscalid and used for monitoring the sensitivity shift in future. Further study indicated that there was some nucleotide polymorphism in codons, such as 209, 277 and 224 in Sdh B of A. alternata. However, no relationship was observed between this nucleotide diversity and the sensitivity to boscalid in A. alternata causing tobacco brown spot. [ABSTRACT FROM AUTHOR]

Corynespora leaf spot caused by Corynespora cassiicola has become an important disease affecting cucumber. To provide the basis of biological research for exploring different resistance mechanisms of C. cassiicola to boscalid, the biological characteristics and environmental fitness of C. cassiicola with different types of resistance to boscalid were determined in this study. A total of 24 strains of C. cassiicola collected from different regions with different resistant types to boscalid were randomly selected. Seven types of resistant mutants cross-resistance to several different succinate dehydrogenase inhibitors (SDHIs) were analyzed and whether the mutants could inherite stably after cultivated nine generations on PDA plates without any fungicides selection pressure were determined. Meanwhile, the biological characteristics of resistant mutants under different carbon and nitrogen sources, temperature and other conditions were also determined to evaluate the fitness of resistant mutants under different environmental conditions. The results indicated that only SdhB-H278Y and SdhB-H278R mutants showed negative cross-resistance between boscalid and fluopyram, while drug resistance in all strains of the different mutation types could be inherited stably. Pathogenicity of different mutation types strains were discrepant, and the SdhD-D95E mutants had the strongest pathogenicity. The most favorable carbon source for the growth of all resistant mutants was maltose, and no discrepancy was showed in the effects of different nitrogen sources. The most optimal growth temperature range of each mutant strain was 25-30 ℃, while SdhD-D95E mutants grew faster than other mutants at temperatures greater than 30 ℃. In the study of heat resistance, the resistant mutants were not able to survive after treated at 65 ℃ for 45 min. At the same time, the mutant could grow normally under the condition of 60 ℃, while the sensitive strain could not. The mycelium growth rate of SdhDD95E mutants were faster than that of other mutant strains, while SdhB-H278Y mutants were slower than that of other mutant strains under treatment with various concentrations of NaCl. Glucose was important to the growth of SdhB-H278R mutants. The results showed that the biological characteristics and fitness of C. cassiicola with different boscalid-resistance were discrepant. The adaptability of SdhD-D95E mutants was improved, indicating that the mutant had stronger competitiveness in the field and was easy to form a dominant population. [ABSTRACT FROM AUTHOR]

To evaluate the safety of boscalid in watercress, the samples were pretreated using QuEChERS method and quantitatively analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The final residues in watercress were detected, and a comparative analysis of long-term intake risk using two different diets was conducted. The results showed that the average recoveries of boscalid in watercress was 89%-100%, with the relative standard deviation (RSD) of 5%-12%. Under the GAP conditions, the final residue was between 0.16-37.1 mg/kg. National estimates daily intake (NEDI) of boscalid was 1.215 1 mg/(kg bw). Therefore, risk quotient (RQ) was 48.2%, which indicated that potential health risk caused by boscalid was not significant. If the individual dietary intake of each agricultural product provided by WHO was considered, the daily intake of boscalid was 0.083 0 mg/(kg bw), which lead to the RQ of 3.3%. Using comparative analysis, it is recommended to use diet data provided by WHO for long-term dietary risk assessment. [ABSTRACT FROM AUTHOR]

The sensitivity of Rhizopus oryzae to six fungicides (mancozeb, carbendazim, pyrimethanil, azoxystrobin, boscalid, fluazinam) and the preservation conditions of this pathogen were determined using the conidia germination method. Efficacy of these fungicides against tobacco pole rot disease was also evaluated on the detached leaves. Results showed that all the six fungicides presented different inhibitory activities against both conidia germination and pole rot. For the conidia germination, the highest inhibitions were found in the cases with fluazinam and boscalid, with EC90 values of 0.67 mg/L and 1.53 mg/L, respectively. Lower inhibition rates were detected in the cases with mancozeb and azoxystrobin (15.16 and 17.66 mg/L). And the lowest inhibition rates were observed in the cases with pyrimethanil and carbendazim (71.87 and 81.96 mg/L). For the disease control efficacy, the highest inhibition rate was observed in the group treated by azoxystrobin at 50 mg/L with the efficacy of 85%. Lower inhibition rate was detected after the boscalid treatment, which showed 83% efficacy at 200 mg/L, while a poor inhibition rate (48%) was observed by fluazinam treatment at the concentration of 1 000 mg/L. And mancozeb, carbendazim, pyrimethanil all exhibited efficacy of < 20% at their respectively highest dosages of 4 000, 800 and 800 mg/L. The screening results of six different pathogen preservation conditions showed that conidia germination ratio of R. oryzae decreased variously by using different methods. The conidia germination ratio of the conidial suspension in 20% glycerol was 60% at 4 °C, and, for dry conidia samples, that was 36% at 4 °C. In terms of the conidial suspension stored at 4 °C and the conidial suspension stored at –20 °C, the germination ratios in 20% glycerol were both < 20%. With regard to the dry conidia samples stored at –20 °C, the conidia germination ratio was 11%, and, for the conidial suspension stored at –20 °C, that was 6%. Results of this study have provided reference and basis for both the chemical control of tobacco pole rot and the storage of R. oryzae. [ABSTRACT FROM AUTHOR]

Shift of sensitivity to boscalid in Botrytis cinerea collected from plastic tunnels growing fruits and vegetables in Zhejiang Province was monitored by the mycelial growth rate assay based on our previously reported sensitivity baseline, (1.07 ± 0.11) mg/L for the wild sensitive isolates collected from 2004 to 2006. The results showed that resistance to boscalid in B. cinerea was developed rapidly. The mean EC50 was (5.23 ± 7.79) and (24.30 ± 49.33) mg/L, respectively for isolates collected during 2012 to 2013 and during 2017 to 2018. The total resistance frequency during 2012 to 2013 was 15.3% and all resistant isolates were low-level resistant (LR). For the isolates collected from 2017 to 2018, the total resistance frequency was increased to 53.2%, including 7.5% MR isolates and 1.3% HR isolates. There was no significant difference in mycelial growth, sporulation, sclerotial production, and pathogenicity between boscalid resistant and sensitive isolates. No point mutation was detected in SDH A and SDH D. However, a single point mutation, H272R, P225, or N230I, was found in SDH B of all boscalid-resistant B. cinerea. Among them, 88.5% of resistant isolates were H272R. And no obvious association was found between boscalid-resistance and mutations (G85A + I93V + M158V + V168I) in SDH C. [ABSTRACT FROM AUTHOR]

In order to clarify the sensitivity and resistance risk of Rhizoctonia solani to thifluzamide in Shandong Province, 102 isolates of R. solani in 6 areas in Shandong, including Tai’an, Linyi, Weifang, Laiwu, Rizhao and Qingdao, were investigated using the mycelial growth rate method. The EC50 values of thifluzamide against different isolates of the pathogen ranged from 0.010 to 0.194 μg/mL, with an average EC50 value of (0.086 ± 0.004) μg/mL, which showed a single-peak curve distribution. Five drug-resistant isolates were obtained by UV induction and one resistant mutant was obtained by drug domestication. Their resistance levels ranged from 6.46 to 20.08. The mutation frequencies were 0.87% and 0.52%, respectively. Five drug-resistant isolates obtained by UV induction could not be stably inherited. While one mutant QD2-Y4 obtained by acclimation of the drug could be stably inherited. Studies on the biological traits of antagonistic mutants showed that the mycelial growth rate of TA3-X2 isolate was higher than that of the parent isolates, and no other obvious difference was detected. The dry weight of mycelium and the dry weight of sclerotia of the five resistant isolates and one resistant mutant were all lower than the parent isolates. The pathogenicity of TA3-X2, WF6-A2 and QD2-Y4 was lower than that of the parent isolates. However, the pathogenicity of TA17-X6, LY8-3 and QD14-Y7 was not significantly different from that of the parental isolates. There was no cross-resistance between thifluzamide and some other fungicides, including tebuconazole, propiconazole, fludioxonil, validamycin, difenoconazole and carbendazim. However, the cross-resistance among thifluzamide, boscalid and penflufen was observed. Overall, R. solani is sensitive to thiafuramide in 6 areas of Shandong Province. It is speculated that thiafidamide can be used as an ideal candidate for controlling banded leaf sheath blight in corn. [ABSTRACT FROM AUTHOR]

In order to evaluate the sensitivity and the resistant mechanism of Botrytis cinerea Pers. (the causal agent of gray mold disease) from strawberry to boscalid, the sensitivity of 195 isolates in 6 districts in Shanghai were tested with petri plate. And the succinate dehydrogenase subunits genes of 20 isolates with different sensitivity were sequenced. The results showed that the lowest EC50 value of mycelial growth inhibition was 0.15 μg/mL, and the highest value was over 110 μg/mL. The lowest EC50 value of conidial germination was 0.19 μg/mL, while the highest value was over 50 μg/mL. In Shanghai, the resistance frequency was 29.74% (resistance factor >10), and the frequency of high resistance was 20.51% (resistance factor >100). Resistance mechanism analysis indicated that the resistance to boscalid could be attributed to point mutations at codon 272 or 225, which would lead to the substitution of histidine to arginine (H272R), or proline to phenylalanine (P225F) in SdhB subunit of succinate dehydrogenase. And the H272R substitution was more common. This study showed the high resistance level and frequency to boscalid of B. cinerea from strawberry in Shanghai, and revealed that the H272R substitution in SdhB could be the main cause of the resistance. [ABSTRACT FROM AUTHOR]

In order to evaluate the safety of 38% pyraclostrobin·boscalid suspension concentrate (SC) (mass fraction of active ingredient: 12.8% of pyraclostrobin, 25.2% boscalid) in agricultural products and environment, the residues and dissipation dynamics of the agent were investigated in field experiments in Beijing and Shandong for two years (2015 and 2016). The residues of pyraclostrobin and boscalid simultaneously in strawberry and soil were determined by a new high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) analysis method. The samples were extracted by acetonitrile, purified by N-propyl ethylenediamine (PSA), measured by multiple reaction monitoring (MRM) using electrospray ionization and quantified via matrix matching external standard curve. At spiked levels of 0.015, 1.5 and 3.0 mg/kg, the average recoveries of pyraclostrobin in strawberry and soil samples were 97%-107% and 94%-106%, respectively, and RSDs were 1.8%-3.9% and 2.2%-4.1%, respectively. The limit of quantitation (LOQ) of pyraclostrobin in strawberry samples was 0.015 mg/kg. At spiked levels of 0.03, 3.0 and 6.0 mg/kg, the average recoveries of boscalid in strawberry and soil samples were 90%-101% and 92%-97%, respectively, and RSDs were 4.6%-13% and 2.9%-14%, respectively. The LOQ of boscalid in strawberry samples was 0.03 mg/kg. In the decline study, the dissipation equations of pyraclostrobin and boscalid in strawberry and soil samples fit the first-order kinetics equation, and the half-lives for the dissipation of these pesticides were 4.8-6.0 d and 5.1-11 d, respectively, in strawberry, while 3.4-10.0 d and 3.4-6.0 d, respectively, in soil. Following the recommended dosage of 38% pyraclostrobin o boscalid SC in strawberry (active ingredient: 228 and 342 g/hm2), the samples were applied for less than 4 times and collected 3, 5 and 7 d after the last application. The maximum final residue of pyraclostrobin in the strawberry was 0.13 mg/kg, which was below the maximum residual limit (MRL) (0.5 mg/kg) of EU. And that of boscalid was 0.78 mg/kg, which was lower than the MRL (3.0 mg/kg) of China. The safety interval of 38% pyraclostrobin. boscalid SC for strawberry is 3 days. The test results provide data support for the safe use of pesticides in strawberries and the food safety of agricultural products. [ABSTRACT FROM AUTHOR]

The resistance risk of Didymella bryoniae against boscalid was valuated and the resistance mechanism was investigated. By using fungicide adaptation in door, the boscalid-resistant mutants XF21-3 and YC60-1 were obtained, and their biological characteristics were investigated. The partial Sdh B gene sequences of resistant mutants were sequenced to study the molecular mechanism of resistance of D. bryoniae to boscalid. Results showed that the EC50 values of two resistant mutants, XF21-3 and YC60-1, were 108 and 124 μg/mL, with corresponding resistance ratio of 1 007 and 1 347, respectively. The mycelial growth rate and sporulation of two resistant mutants were better than that of their corresponding parents. There is no significant difference in pathogenicity between resistant mutants and their parents. However, resistant mutants showed reduced sensitivity to the high osmotic pressure compared to parental strains. Besides, the resistant mutants had cross-resistance with thifluzamid and had no cross-resistance with carboxin, diethofencrab, tebuconazole, and kresoxoimmethyl. The comparison of Sdh B gene sequencing showed that resistant mutants harbored the point mutation at position 277 in Sdh B subunit with amino acid changing from histidine to tyrosine. The findings indicated that it is easy for D. bryoniae to produce boscalid-resistance under higher selection pressure, and the in vitro fitness for resistant mutants was higher than that of sensitive strains. The results also showed that boscalid was a medium resistance risk fungicide, because the boscalid-resistant mutants showed cross-resistance between boscalid and thifluzamid. Finally, the point mutation at codon 277 (His→Tyr, CAC→TAC) in Sdh B may confer resistance of D. bryoniae to boscalid. [ABSTRACT FROM AUTHOR]

A series of novel 2-chloro-nicotinamides (3a-3h, 5a-5n) were designed and synthesized based on the lead compound boscalid. The structures were characterized by 1H NMR, 13C NMR and HRMS. The preliminary results showed that most of the compounds possessed some fungicidal activity to seven phytopathogenic fungi at 50 μg/mL. Notably, compound 3h showed similar fungicidal activity and the broadest spectrum as boscalid. It exhibited the inhibition rate of 94.1% and 95.6% to the Colletotrichum orbiculare and Botrytis cinerea, respectively and the EC50 value against Rhizoctonia solani, C. orbiculare and Phytophthora infestans was 4.56, 14.35 and 58.86 μg/mL, respectively. [ABSTRACT FROM AUTHOR]

Field experiments were conducted to study the residues and dissipation dynamics of boscalid in Chinese strawberry and soil in Shandong and Beijing for two years. The dispersive solid phase extraction combined with gas chromatography-mass spectrometry (GC-MS) method was established to determine the boscalid residue in strawberry and soil rapidly. The impact of different variety of agricultural products and environmental conditions on digestion rate were studied. The recoveries of boscalid in strawberry were 91%-121% with RSDs between 5.8% and 9.9% with spiking at 0.05, 0.3 and 3 mg/kg. The limit of quantitation (LOQ) of this method in strawberry samples was 0.05 mg/kg. The recoveries of boscalid in soil were 91%-100% with RSDs between 5.4% and 6.5% with spiking at 0.1, 0.3 and 3 mg/kg. The LOQ of this method in soil samples was 0.1 mg/kg, which could meet the requirement of max residue limits (MRLs) of boscalid. In decline study, the dissipation equations of boscalid in strawberry fit the pseudo-first-order reaction dynamic equations or the first-order reaction dynamic equations, and the half-lives of dissipation of boscalid were estimated to be 6.2 d and 11.8 d in strawberry. Boscalid was detected in soil samples from Shandong and Beijing, however, its dissipation dynamic equations did not fit the first-order reaction dynamic equation. The recommended dosage of 50% boscalid WG for control of grey mold in strawberry was 337.5 g/hm2, the drug may delivered no more than 3 times, each time should over 3 d interval. The maximum final residue of boscalid strawberry and soil were 1.97 mg/kg and 0.38 mg/kg, respectively. [ABSTRACT FROM AUTHOR]

In order to clarify the synergistic action of the mixtures of boscalid and pyrametostrobin against Botrytis cinerea, the inhibitory activity of the mixtures at different mixing ratios to isolate DZ3 was determined by mycelial growth rate method, and the synergistic radio was calculated according to the Wadley formula. The inhibitory activity of the best mixture to the other five isolates of B. cinerea was determined by inoculating fungicide-sprayed cucumber cotyledons with conidial suspension, and the control efficacy against tomato grey mould was determined in the field. The synergistic mechanism of the best synergistic combination was studied by detecting the content of dissolved oxygen, conductivity of the conidial suspension of isolate DZ3, and the content of malondialdehyde in the hyphae of isolate DZ3. The results showed that the mixtures of boscalid and pyrametostrobin (9 :1, 7 :1, 5 :1, 3 :1, 1 :1, 1 :3, 1 :5, 1 :7 and 1 :9,m/m) exhibited synergistic activity against the mycelial growth of isolate DZ3, and the 1 :3 mixture exhibited the most significant synergistic effects, with synergistic ratio up to 4.76. The 1 :3 mixture also showed synergistic inhibition to the other five isolates of B.cinerea. The control efficacy of the mixture (1 :3, m/m) against tomato gray mould in the field was 78.05%-93.96% at 200-300 g a.i./hm2, and the inhibitory activity of the mixture (1 :3, m/m) on the respiration of isolate DZ3 was similar to that of boscalid, but the impact on membrane permeability and mycelium membrane lipid peroxidation was more significant than that of individual boscalid and pyrametostrobin. The results of present study suggested that the mixture of boscalid and pyrametostrobin (1 :3, m/m) could be used in controling of tomato gray mould. [ABSTRACT FROM AUTHOR]