scholarly journals Fungicide resistance characterised across seven chemical classes in a Botrytis cinerea population isolated from Australian vineyards

2021 ◽  
Author(s):  
Lincoln A. Harper ◽  
Scott Paton ◽  
Barbara Hall ◽  
Suzanne McKay ◽  
Richard P. Oliver ◽  
...  
Keyword(s):  
Adverse Effect ◽  
Botrytis Cinerea ◽  
Fungicide Resistance ◽  
Chemical Control ◽  
Management Strategies ◽  
Resistance Management ◽  
Gray Mold ◽  
Chemical Groups ◽  
Important Disease ◽  
Selection Of

AbstractGray mold, caused by Botrytis cinerea, is an economically important disease of grapes in Australia and across grape growing regions worldwide. Control of this disease relies heavily on canopy management and the application of single site fungicides. Fungicide application can lead to the selection of fungicide resistant B. cinerea populations, which has an adverse effect on the chemical control of the disease. Characterising the distribution and severity of resistant B. cinerea populations is needed to inform resistance management strategies. In this study, 725 isolates were sampled from 75 Australian vineyards during 2013 – 2016 and were screened against seven fungicides with different MOAs. The resistance frequencies for azoxystrobin, boscalid, fenhexamid, fludioxonil, iprodione, pyrimethanil and tebuconazole were 5, 2.8, 2.1, 6.2, 11.6, 7.7 and 2.9% respectively. Nearly half of the resistant isolates (43.7%) were resistant to more than one of the fungicides tested. The frequency of vineyards with at least one isolate simultaneously resistant to 1, 2, 3, 4 or 5 fungicides was 19.5, 7.8, 6.5, 10.4 and 2.6%.Resistance was associated with previously published genotypes in CytB (G143A), SdhB (H272R/Y), Erg27 (F412S), Mrr1 (D354Y), Os1 (I365S, N373S + Q369P, I365S + D757N) and Pos5 (P319A, L412F). Expression analysis was used to characterise fludioxonil resistant isolates exhibiting overexpression (6.3 - 9.6-fold) of the ABC transporter encoded by AtrB (MDR1 phenotype). Novel genotypes were also described in Mrr1 (S611N, D616G) and Cyp51 (P357S). Resistance frequencies were lower when compared to most previously published surveys of both grape and non-grape B. cinerea resistance. Nonetheless, continued monitoring of critical chemical groups used in Australian vineyards is recommended.

scholarly journals First Report of Botrytis cinerea Causing Gray Mold Disease on Peach from Pakistan

2018 ◽  
Vol 7 (3) ◽  
pp. 131-131
Author(s):  
Raees Ahmed ◽  
Amjad S. Gondal ◽  
Muhammad Tariq Khan ◽  
Shazia Shahzaman ◽  
Sajjad Hyder
Keyword(s):  
Botrytis Cinerea ◽  
Mycelial Growth ◽  
Agar Medium ◽  
Management Strategies ◽  
Gray Mold ◽  
First Report ◽  
Average Production ◽  
Conducive Environment ◽  
Hyphal Tip ◽  
Important Disease

Gray mold caused by Botrytis cinerea is an important disease that attacks fruits, leaves and twigs of peach. Peach is grown on an area of 18,008 ha with an average production of 72,085 tons per year in Pakistan (FAO, 2017). During May 2017, brown spots on 33% of the peach fruits examined were observed in Swat district of KPK province of Pakistan. Infected fruits were incubated at 25±2 °C in a humid chamber resulted in greyish mycelial growth with light brown lesions. Hyphal growths on infected fruits were cultured on PDA media and purified by hyphal tip method. Morphologically whitish grey growth was observed on PDA and later on dark sclerotia were observed after 6-7 days of incubation. Hyphae were found septate with branched hyaline conidiophores having a bunch of ovoid conidia at their tips. Further confirmations were done by amplifying internal transcribed spacer regions (Andrew et al., 2009) and glyceraldehyde-3-phosphate dehydrogenase (G3PDH) region of the isolates (Li et al., 2012). Amplicons sequenced from Macrogen Korea were blasted and submitted in NCBI showed that ITS sequences (Accessions MH049690 and MH049691) were 99% identical with already reported (MG878388 and MG654661) sequences and the G3PDH gene sequences (Accessions MH560352 and MH560353) were 99 % identical with already reported (Accessions MG204876) sequences of B. cinerea. Pathogenicity was confirmed on healthy peach fruits disinfected with 50% ethanol, inoculated by placing a plug of about 1cm2 taken from the edge of actively growing B. cinerea isolate (BTS-16). Fruits were incubated at 25±2 °C in a humid chamber (Abata et al., 2016). A set of healthy fruits mock-inoculated with a plug of agar medium were used as control. Three days after inoculation, inoculated fruits showed sunken lesions with cottony greyish mycelial growth on their surface. Fungus isolated from these infections was re-confirmed as B. cinerea. Conducive environment for the disease progression in nearby areas can result into a huge loss in peach produce so there is a need to devise management strategies to cope with the pathogen. This is the first report of gray mold disease of peach caused by B. cinerea from Pakistan. 

scholarly journals Characterization of Botrytis cinerea From Commercial Cut Flower Roses

Plant Disease ◽  
2019 ◽  
Vol 103 (7) ◽  
pp. 1577-1583 ◽  
Author(s):  
M. Muñoz ◽  
J. E. Faust ◽  
G. Schnabel
Keyword(s):  
Botrytis Cinerea ◽  
Fungicide Resistance ◽  
Management Practices ◽  
Cultural Practices ◽  
Disease Incidence ◽  
Resistance Management ◽  
Gray Mold ◽  
Economic Losses ◽  
Cut Flower ◽  
Aspergillus Brasiliensis

Botrytis cinerea Pers. infects cut flower roses (Rosa × hybrida L.) during greenhouse production and gray mold symptoms are often expressed in the postharvest environment, resulting in significant economic losses. Disease management is based on cultural practices and preventative chemical treatments; however, gray mold outbreaks continue to occur. Rose tissues from six commercial shipments from two greenhouses in Colombia were evaluated to determine the Botrytis species composition as well as identify other pathogens present, gray mold incidence and severity, and fungicide resistance profiles. Botrytis isolates (49 total) were grouped into six morphological phenotypes, and all were identified to be B. cinerea sensu stricto. Disease incidence was higher in the petals than in the stem, stamen, ovary, sepal, or leaf tissues. Other fungi were isolated infrequently and included Alternaria alternata, Cladosporium cladosporioides, Epicoccum nigrum, Penicillium citrinum, Aspergillus brasiliensis, and Diplodia sp. Fungicide resistance profiles were determined using previously established discriminatory doses. Isolates resistant to thiophanate-methyl, iprodione, boscalid, and cyprodinil were found frequently in all shipments and in both greenhouses. The frequency of resistance to penthiopyrad, fenhexamid, fluopyram, isofetamid, and fludioxonil varied between shipments and greenhouses. No resistance to pydiflumetofen was observed at the discriminatory doses tested. Isolates with resistance to multiple chemical classes were commonly found. These results indicate that fungicide resistance management practices may improve preharvest and postharvest gray mold control of cut flower roses.

scholarly journals Fungicide Resistance Profiling in Botrytis cinerea Populations from Blueberry in California and Washington and Their Impact on Control of Gray Mold

Plant Disease ◽  
2016 ◽  
Vol 100 (10) ◽  
pp. 2087-2093 ◽  
Author(s):  
S. Saito ◽  
T. J. Michailides ◽  
C. L. Xiao
Keyword(s):  
Botrytis Cinerea ◽  
Fungicide Resistance ◽  
Resistance Management ◽  
Central Valley ◽  
Gray Mold ◽  
Postharvest Disease ◽  
Quinone Outside Inhibitor ◽  
Development Of Resistance ◽  
Western Washington ◽  
Moderately Resistant

Gray mold caused by Botrytis cinerea is a major postharvest disease of blueberry grown in the Central Valley of California and western Washington State. Sensitivities to boscalid, cyprodinil, fenhexamid, fludioxonil, and pyraclostrobin, representing five different fungicide classes, were examined for 249 (California) and 106 (Washington) B. cinerea isolates recovered from decayed blueberry fruit or flowers. In California and Washington, 7 and 17 fungicide-resistant phenotypes, respectively, were detected: 66 and 49% of the isolates were resistant to boscalid, 20 and 29% were moderately resistant to cyprodinil, 29 and 29% were resistant to fenhexamid, and 66 and 55% were resistant to pyraclostrobin. All isolates from California were sensitive to fludioxonil, whereas 70% of the isolates from Washington showed reduced sensitivity to fludioxonil. In California, 26 and 30% of the isolates were resistant to two and three classes of fungicides, respectively. In Washington, 31, 14, 16, and 9% of the isolates were resistant to two, three, four, and five classes of fungicides, respectively. Inherent risk of the development of resistance to quinone outside inhibitor (QoI) fungicides was assessed by detecting the presence of the Bcbi-143/144 intron in gene cytb. The intron was detected in 11.8 and 40% of the isolates in California and Washington, respectively, suggesting that the risk of QoI resistance is higher in California than in Washington. On detached blueberry fruit inoculated with 11 isolates exhibiting different fungicide-resistant phenotypes, most fungicides failed to control gray mold on fruit inoculated with the respective resistant phenotypes but the mixture of cyprodinil and fludioxonil was effective against all fungicide-resistant phenotypes tested. Our findings would be useful in designing and implementing fungicide resistance management spray programs for control of gray mold in blueberry.

scholarly journals Independent Emergence of Resistance to Seven Chemical Classes of Fungicides in Botrytis cinerea

2015 ◽  
Vol 105 (4) ◽  
pp. 424-432 ◽  
Author(s):  
Dolores Fernández-Ortuño ◽  
Anja Grabke ◽  
Xingpeng Li ◽  
Guido Schnabel
Keyword(s):  
United States ◽  
Botrytis Cinerea ◽  
Target Genes ◽  
Management Strategies ◽  
Resistance Management ◽  
Monitoring Program ◽  
Gene Mutations ◽  
The United States ◽  
Gray Mold ◽  
Development Of Resistance

Gray mold, caused by the fungal pathogen Botrytis cinerea, is one of the most destructive diseases of small fruit crops and control is largely dependent on the application of fungicides. As part of a region-wide resistance-monitoring program that investigated 1,890 B. cinerea isolates from 189 fields in 10 states of the United States, we identified seven isolates (0.4%) from five locations in four different states with unprecedented resistance to all seven Fungicide Resistance Action Committee (FRAC) codes with single-site modes of action including FRAC 1, 2, 7, 9, 11, 12, and 17 registered in the United States for gray mold control. Resistance to thiophanate-methyl, iprodione, boscalid, pyraclostrobin, and fenhexamid was based on target gene mutations that conferred E198A and F200Y in β-tubulin, I365N/S in Bos1, H272R/Y in SdhB, G143A in Cytb, and T63I and F412S in Erg27. Isolates were grouped into MDR1 and MDR1h phenotypes based on sensitivity to fludioxonil and variations in transcription factor mrr1. MDR1h isolates had a previously described 3-bp deletion at position 497 in mrr1. Expression of ABC transporter atrB was increased in MDR1 isolates but highest in MDR1h isolates. None of the isolates with seven single resistances (SR) had identical nucleotide variations in target genes, indicating that they emerged independently. Multifungicide resistance phenotypes did not exhibit significant fitness penalties for the parameters used in this study, but MDR1h isolates produced more sclerotia at low temperatures and exhibited increased sensitivity to salt stress. In this study we show that current resistance management strategies have not been able to prevent the geographically independent development of resistance to all seven site-specific fungicides currently registered for gray mold control in the United States and document the presence of MDR1h in North America.

scholarly journals Within-Season Shift in Fungicide Resistance Profiles of Botrytis cinerea in California Strawberry Fields

Plant Disease ◽  
2019 ◽  
Vol 103 (1) ◽  
pp. 59-64 ◽  
Author(s):  
Scott D. Cosseboom ◽  
Kelly L. Ivors ◽  
Guido Schnabel ◽  
Patricia K. Bryson ◽  
Gerald J. Holmes
Keyword(s):  
Botrytis Cinerea ◽  
Fungicide Resistance ◽  
Mycelial Growth ◽  
Target Genes ◽  
Resistance Management ◽  
Gray Mold ◽  
Field Resistance ◽  
Early Season ◽  
Late Season ◽  
Growth Assay

Sensitivity of Botrytis cinerea to seven fungicide chemical classes was determined for 888 isolates collected in 2016 from 47 California strawberry fields. Isolates were collected early season (minimum fungicide exposure) and late season (maximum fungicide exposure) from the same planting block in each field. Resistance was determined using a mycelial growth assay, and variable frequencies of resistance were observed to each fungicide at both sampling times (early season %, late season %): boscalid (12, 35), cyprodinil (12, 46), fenhexamid (53, 91), fludioxonil (1, 4), fluopyram (2, 7), iprodione (25, 8), isofetamid (0, 1), penthiopyrad (8, 25), pyraclostrobin (77, 98), and thiophanate-methyl (81, 96). Analysis of number of chemical class resistances (CCRs) revealed an increasing shift in CCR from the early to late season. Phenotypes of 40 isolates that were resistant or sensitive to different chemical classes were associated with presence or absence of mutations in target genes. Fungicide-resistance phenotypes determined in the mycelial growth assay closely matched (93.8%) the genotype observed. Previously described resistance-conferring mutations were found for each gene. A survey of fungicide use from 32 of the sampled fields revealed an average of 15 applications of gray mold–labeled fungicides per season at an average interval of 12 days. The most frequently applied fungicides (average number of applications during the 2016 season) were captan (7.3), pyraclostrobin (2.5), cyprodinil (2.3), fludioxonil (2.3), boscalid (1.8), and fenhexamid (1.4). Multifungicide resistance is widespread in California. Resistance management tactics that reduce selection pressure by limiting fungicide use, rotating among Fungicide Resistance Action Committee codes, and mixing/rotating site-specific fungicides with multisite fungicides need to be improved and implemented.

scholarly journals Occurrence of Fungicide Resistance in Botrytis cinerea from Greenhouse Tomato in Hubei Province, China

Plant Disease ◽  
2016 ◽  
Vol 100 (12) ◽  
pp. 2414-2421 ◽  
Author(s):  
F. Fan ◽  
N. Li ◽  
G. Q. Li ◽  
C. X. Luo
Keyword(s):  
Botrytis Cinerea ◽  
Fungicide Resistance ◽  
Management Strategies ◽  
Gray Mold ◽  
Hubei Province ◽  
Early Summer ◽  
Greenhouse Tomato ◽  
Tubulin Genes ◽  
Significant Difference ◽  
Stability Of Resistance

During the early summer of 2012 and 2013, samples of gray mold were collected from greenhouse tomato at eight locations in Hubei Province, and 221 isolates of Botrytis cinerea were obtained and evaluated for the sensitivity to fungicides carbendazim, diethofencarb, boscalid, fludioxonil, and cyprodinil. Results showed that isolates with resistance to carbendazim and cyprodinil were widespread, whereas isolates with resistance to carbendazim and diethofencarb were found at only two locations. No isolates with resistance to boscalid or fludioxonil were detected. Altogether, four resistant phenotypes were determined (i.e., CarRDieSCypS, CarRDieRCypS, CarRDieSCypR, and CarRDieRCypR). Among them, CarRDieSCypS and CarRDieSCypR were widely distributed, and there was a dominant resistant phenotype at each location. Interestingly, isolates resistant only to cyprodinil were not obtained because the resistance to cyprodinil was always associated with the resistance to carbendazim, demonstrating that a phenotype of multiple fungicide resistance of B. cinerea was more likely to have evolved from previously resistant subpopulations. Stability of resistance to carbendazim, diethofencarb, and cyprodinil was assessed, and the resistance was stable. Fitness tests showed that, as a group, the carbendazim-resistant isolates were not significantly different from sensitive isolates. However, the mycelial growth and virulence of the carbendazim, diethofencarb, and cyprodinil triple-resistant group were significantly lower than the sensitive group, indicating that the triple-resistant isolates suffered from the disability of colonizing the hosts. It should be noted that there was no significant difference for other fitness components (e.g., sporulation or osmotic sensitivity to NaCl), suggesting that the triple-resistant isolates were still competitive in these traits. To investigate the mechanisms of resistance to carbendazim and diethofencarb, partial β-tubulin genes of 10 carbendazim-resistant isolates and 5 isolates resistant to carbendazim and diethofencarb were sequenced, and all 10 carbendazim-resistant isolates harbored the mutation E198V or E198A. For the 5 isolates resistant to carbendazim and diethofencarb, all of them possessed the mutation E198K, and no other mutations were detected. The location-specific resistance profiles found in this study are crucial in designing proper gray mold management strategies in these areas.

scholarly journals Phenotypic Characterization of Multifungicide Resistance in Botrytis cinerea Isolates from Strawberry Fields in Florida

Plant Disease ◽  
2013 ◽  
Vol 97 (3) ◽  
pp. 393-401 ◽  
Author(s):  
A. Amiri ◽  
S. M. Heath ◽  
N. A. Peres
Keyword(s):  
Botrytis Cinerea ◽  
Management Strategies ◽  
Gray Mold ◽  
Phenotypic Characterization ◽  
Quinone Outside Inhibitor ◽  
Show Evidence ◽  
The One ◽  
Chemical Groups ◽  
Succinate Dehydrogenase Inhibitor

Chemical control has always been essential for the management of gray mold, caused by Botrytis cinerea, to ensure sustainable strawberry production. However, lack of knowledge about actual resistance development may have disastrous consequences and lead to severe epidemics such as the one that affected several strawberry fields in 2012 in Florida. In this study, we tested 392 isolates collected from Florida strawberry fields between 2010 and 2012 for their sensitivity to boscalid (Bosc), a succinate dehydrogenase inhibitor (SdhI); pyraclostrobin, a quinone outside inhibitor (QoI); boscalid + pyraclostrobin (Pristine); fenhexamid, a hydroxyanilide (Hyd); pyrimethanil and cyprodinil, anilinopyrimidines; fludioxonil, a phenylpyrrole; and fludioxonil + cyprodinil (Switch). The respective resistance frequencies for boscalid, pyraclostrobin, Pristine, fenhexamid, cyprodinil, and pyrimethanil were 85.4, 86.5, 86.0, 44.4, 52.7, and 59.5%. Overall, 17.8 and 19.8% of isolates showed reduced sensitivity to fludioxonil and Switch, respectively. All fungicides sprayed preventively on detached strawberry fruit failed to control isolates with high levels of resistance to each fungicide except for fludioxonil and Switch. Four phenotypes with multifungicide resistance (MFR) were detected in B. cinerea populations from Florida. Isolates resistant to one fungicide (FR1), two (MFR2), three (MFR3), and four (MFR4) fungicides from different chemical groups represented 5.9, 28.6, 41.8, and 23.7% of the total resistant population, respectively. The MFR3 isolates were predominant and contained two subpopulations, the Bosc-QoI-APR isolates (56.5%) and the Bosc-QoI-HydR isolates (40.6%). In addition to reporting on very highly resistant populations to boscalid and QoI fungicides, we show evidence for a widespread multifungicide resistance to B. cinerea that warrants immediate implementation of novel management strategies to impede the development of more resistant populations.

scholarly journals Mixtures as a Fungicide Resistance Management Tactic

2014 ◽  
Vol 104 (12) ◽  
pp. 1264-1273 ◽  
Author(s):  
Frank van den Bosch ◽  
Neil Paveley ◽  
Femke van den Berg ◽  
Peter Hobbelen ◽  
Richard Oliver
Keyword(s):  
At Risk ◽  
Disease Control ◽  
Fungicide Resistance ◽  
Management Strategies ◽  
Resistance Management ◽  
Relative Effect ◽  
Resistance Evolution ◽  
Modes Of Action ◽  
Selection For ◽  
Effective Life

We have reviewed the experimental and modeling evidence on the use of mixtures of fungicides of differing modes of action as a resistance management tactic. The evidence supports the following conclusions. 1. Adding a mixing partner to a fungicide that is at-risk of resistance (without lowering the dose of the at-risk fungicide) reduces the rate of selection for fungicide resistance. This holds for the use of mixing partner fungicides that have either multi-site or single-site modes of action. The resulting predicted increase in the effective life of the at-risk fungicide can be large enough to be of practical relevance. The more effective the mixing partner (due to inherent activity and/or dose), the larger the reduction in selection and the larger the increase in effective life of the at-risk fungicide. 2. Adding a mixing partner while lowering the dose of the at-risk fungicide reduces the selection for fungicide resistance, without compromising effective disease control. The very few studies existing suggest that the reduction in selection is more sensitive to lowering the dose of the at-risk fungicide than to increasing the dose of the mixing partner. 3. Although there are very few studies, the existing evidence suggests that mixing two at-risk fungicides is also a useful resistance management tactic. The aspects that have received too little attention to draw generic conclusions about the effectiveness of fungicide mixtures as resistance management strategies are as follows: (i) the relative effect of the dose of the two mixing partners on selection for fungicide resistance, (ii) the effect of mixing on the effective life of a fungicide (the time from introduction of the fungicide mode of action to the time point where the fungicide can no longer maintain effective disease control), (iii) polygenically determined resistance, (iv) mixtures of two at-risk fungicides, (v) the emergence phase of resistance evolution and the effects of mixtures during this phase, and (vi) monocyclic diseases and nonfoliar diseases. The lack of studies on these aspects of mixture use of fungicides should be a warning against overinterpreting the findings in this review.

scholarly journals Point Mutations in the β-Tubulin of Phytophthora sojae Confer Resistance to Ethaboxam

2019 ◽  
Vol 109 (12) ◽  
pp. 2096-2106 ◽  
Author(s):  
Qin Peng ◽  
Zhiwen Wang ◽  
Yuan Fang ◽  
Weizhen Wang ◽  
Xingkai Cheng ◽  
...  
Keyword(s):  
Fungicide Resistance ◽  
Germination Rate ◽  
Management Strategies ◽  
Resistance Management ◽  
Point Mutations ◽  
Phytophthora Sojae ◽  
Cross Resistance ◽  
Baseline Sensitivity ◽  
Resistant Mutants ◽  
Β Tubulin

Ethaboxam is a β-tubulin inhibitor registered for the control of oomycete pathogens. The current study was established to determine the ethaboxam sensitivity of the plant pathogen Phytophthora sojae and investigate the potential for the emergence of fungicide resistance. The effective concentration for 50% inhibition (EC50) of 112 Phytophthora sojae isolates exhibited a unimodal distribution with a mean EC50 for ethaboxam of 0.033 µg/ml. Establishing this baseline sensitivity provided critical data for monitoring changes in ethaboxam-sensitivity in field populations. The potential for fungicide resistance was investigated using adaptation on ethaboxam-amended V8 agar, which resulted in the isolation of 20 resistant mutants. An assessment of the biological characteristics of the mutants including mycelial growth, sporulation, germination rate and pathogenicity indicated that the resistance risk in Phytophthora sojae was low to medium with no cross-resistance between ethaboxam and cymoxanil, metalaxyl, flumorph, and oxathiapiprolin being detected. However, positive cross-resistance was found between ethaboxam and zoxamide for Q8L and I258V but negative cross-resistance for C165Y. Further investigation revealed that the ethaboxam-resistant mutants had point mutations at amino acids Q8L, C165Y, or I258V of their β-tubulin protein sequences. CRISPR/Cas9-mediated transformation experiments confirmed that the Q8L, C165Y, or I258V mutations could confer ethaboxam resistance in Phytophthora sojae and that the C165Y mutation induces high levels of resistance. Taken together, the results of the study provide essential data for monitoring the emergence of resistance and resistance management strategies for ethaboxam, as well as for improving the design of novel β-tubulin inhibitors for future development.

scholarly journals Characterization of Botrytis cinerea Isolates from Strawberry with Reduced Sensitivity to Polyoxin D Zinc Salt

Plant Disease ◽  
2016 ◽  
Vol 100 (10) ◽  
pp. 2057-2061 ◽  
Author(s):  
Madeline E. Dowling ◽  
Meng-Jun Hu ◽  
Linus T. Schmitz ◽  
Jennifer R. Wilson ◽  
Guido Schnabel
Keyword(s):  
United States ◽  
South Carolina ◽  
Botrytis Cinerea ◽  
Tomato Fruit ◽  
Resistance Management ◽  
The United States ◽  
Gray Mold ◽  
Zinc Salt ◽  
Malt Extract ◽  
Action Committee

Polyoxin D is a Fungicide Resistance Action Committee (FRAC) code 19 fungicide that was recently registered for gray mold control of strawberry in the United States. In this study, we determined the sensitivity to polyoxin D zinc salt (hereafter, polyoxin D) of Botrytis cinerea isolates from 41 commercial strawberry farms in South Carolina, North Carolina, Maryland, Virginia, and Ohio and investigated the fitness of sensitive (S) and reduced sensitive (RS) isolates. Relative mycelial growth ranged between 0 and over 100% on malt extract agar amended with a discriminatory dose of polyoxin D at 5 μg/ml. Isolates that grew more than 70% at that dose were designated RS and were found in three of the five states. The 50% effective dose (EC50) values of three S and three RS isolates ranged from 0.59 to 2.27 and 4.6 to 5.8 μg/ml, respectively. The three RS isolates grew faster on detached tomato fruit treated with Ph-D WDG at recommended label dosage than S isolates (P < 0.008). In all, 25 randomly selected RS isolates exhibited reduced sporulation ability (P < 0.0001) and growth rate (P < 0.0001) but increased production of sclerotia (P < 0.0386) compared with 25 S isolates. Of 10 isolates tested per phenotype, the number of RS isolates producing sporulating lesions on apple, tomato, and strawberry was significantly lower compared with S isolates (P < 0.0001 for each fruit type). The results of this study indicate that resistance management is necessary for fungicides containing polyoxin D. To our knowledge, this is the first study demonstrating reduced sensitivity to FRAC 19 fungicides in B. cinerea isolates from the United States.

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