Boscalid Insensitivity Documented in Didymella bryoniae Isolated from Watermelon in Florida and North Carolina

2012 ◽  
Vol 13 (1) ◽  
pp. 42
Author(s):  
Katherine L. Stevenson ◽  
Anthony P. Keinath ◽  
Anna Thomas ◽  
David B. Langston ◽  
Pamela D. Roberts ◽  
...  
Keyword(s):  
North Carolina ◽  
South Carolina ◽  
High Frequency ◽  
In Vitro Assays ◽  
Didymella Bryoniae ◽  
Triazole Fungicides ◽  
Stem Blight ◽  
Gummy Stem Blight ◽  
Commercial Mixture

The fungicide Pristine, a commercial mixture of pyraclostrobin and boscalid, has been used widely on watermelon and other cucurbits to control gummy stem blight, caused by the fungus Didymella bryoniae. Since 2007, isolates of D. bryoniae insensitive to boscalid have been found in Georgia, Indiana, and South Carolina. Most isolates of D. bryoniae obtained in 2009 and 2010 from diseased watermelon leaves collected in several counties in Florida and North Carolina were found to be insensitive to boscalid using in vitro assays. Gummy stem blight would not be effectively managed with Pristine in any of the counties where samples were collected due to the high frequency of insensitivity to boscalid. Fortunately growers can instead use several triazole fungicides registered for use on cucurbits since 2009. Accepted for publication 30 March 2012. Published 18 May 2012.

scholarly journals Relationship Between Fungicide Sensitivity and Control of Gummy Stem Blight of Watermelon Under Field Conditions

Plant Disease ◽  
2012 ◽  
Vol 96 (12) ◽  
pp. 1780-1784 ◽  
Author(s):  
A. Thomas ◽  
D. B. Langston ◽  
H. F. Sanders ◽  
K. L. Stevenson
Keyword(s):  
Fungicide Resistance ◽  
Field Experiments ◽  
In Vitro Assays ◽  
Didymella Bryoniae ◽  
Fungicide Sensitivity ◽  
Thiophanate Methyl ◽  
Stem Blight ◽  
Gummy Stem Blight ◽  
And Control

Gummy stem blight (GSB), caused by the fungus Didymella bryoniae, is the most destructive disease of watermelon and is managed primarily with fungicides. D. bryoniae has developed resistance to many fungicides that were once very effective, including azoxystrobin, boscalid, and thiophanate-methyl. Field experiments were conducted in Tifton (TN) and Reidsville (RV), GA in 2009 and 2010 to establish a relationship between frequency of resistance to a fungicide based on in vitro assays and its efficacy in the management of GSB. Frequency of resistance to boscalid, thiophanate-methyl, and azoxystrobin was >0.80 in isolates collected from nontreated plots in both locations and years. All isolates collected after six applications of boscalid, thiophanate-methyl, or azoxystrobin were resistant to the respective fungicide. All isolates collected from treated and nontreated plots were sensitive to tebuconazole and difenoconazole. GSB severity was assessed on a weekly basis from 63 days after planting. GSB severity in plots treated with boscalid, thiophanate-methyl, or azoxystrobin was not significantly different from that in the nontreated plots (39%, TN-2009; 45%, TN-2010; and 16%, RV-2010). GSB severity in tebuconazole-treated plots (27%, TN-2009; 14%, TN-2010; and 4%, RV-2010) was significantly lower than all other treatments and the nontreated control. There was a consistent negative association between frequency of fungicide resistance and disease control in the field. Thus, knowledge of the frequency of fungicide resistance in the pathogen population will be helpful in selecting the most effective fungicides for the management of GSB in watermelon fields.

scholarly journals Baseline Sensitivity of Didymella bryoniae to Cyprodinil and Fludioxonil and Field Efficacy of these Fungicides Against Isolates Resistant to Pyraclostrobin and Boscalid

Plant Disease ◽  
2015 ◽  
Vol 99 (6) ◽  
pp. 815-822 ◽  
Author(s):  
Anthony P. Keinath
Keyword(s):  
South Carolina ◽  
Citrullus Lanatus ◽  
Control Treatment ◽  
Didymella Bryoniae ◽  
Water Control ◽  
Baseline Sensitivity ◽  
Qoi Fungicides ◽  
Stem Blight ◽  
Gummy Stem Blight ◽  
Development Of Resistance

To prevent yield reductions from gummy stem blight, fungicides often must be applied to watermelon (Citrullus lanatus) and muskmelon (Cucumis melo). Didymella bryoniae, the ascomycete fungus that causes gummy stem blight, is resistant to thiophanate-methyl, quinone-outside inhibitors (QoI), boscalid, and penthiopyrad. In place of these fungicides, premixtures of cyprodinil and fludioxonil (Switch 62.5WG) or cyprodinil and difenoconazole (Inspire Super 2.82SC) are used. The objectives of this study were to examine baseline isolates of D. bryoniae for sensitivity to cyprodinil and fludioxonil and to determine the efficacy of cyprodinil-fludioxonil and cyprodinil-difenoconazole against isolates resistant to QoI fungicides and boscalid. Colony diameters of 146 isolates of D. bryoniae collected in South Carolina and other U.S. states prior to 2008 were measured on glucose minimal medium amended with cyprodinil or fludioxonil. Mean effective concentration values that reduced relative colony diameter by 50% were 0.052 and 0.099 mg/liter cyprodinil and fludioxonil, respectively. In autumn 2008, 2009, and 2011, field-grown watermelon inoculated with isolates resistant to QoI fungicides and boscalid was treated with boscalid-pyraclostrobin alternated with chlorothalonil, cyprodinil-fludioxonil alternated with chlorothalonil, cyprodinil-difenoconazole alternated with chlorothalonil, tebuconazole alternated with chlorothalonil, chlorothalonil, or water. In 2008 and 2011, both cyprodinil treatments reduced disease severity compared with the water control treatment and chlorothalonil alone. In 2008 and 2009, cyprodinil-fludioxonil reduced severity compared with boscalid-pyraclostrobin and, in 2008, cyprodinil-difenoconazole and tebuconazole also did. Use of cyprodinil-fludioxonil should control gummy stem blight effectively and may delay development of resistance to cyprodinil and fludioxonil in D. bryoniae. However, because Botrytis cinerea became resistant to both cyprodinil and fludioxonil after multiple applications of cyprodinil-fludioxonil per season, prudent fungicide rotations should be followed when using cyprodinil-containing fungicides against D. bryoniae.

scholarly journals Screening the Cucumber Germplasm Collection for Resistance to Gummy Stem Blight in North Carolina Field Tests

HortScience ◽  
2000 ◽  
Vol 35 (6) ◽  
pp. 1132-1140 ◽  
Author(s):  
Todd C. Wehner ◽  
Nischit V. Shetty
Keyword(s):  
North Carolina ◽  
Germplasm Collection ◽  
Field Tests ◽  
Plant Introduction ◽  
Lesion Size ◽  
Didymella Bryoniae ◽  
Breeding Lines ◽  
Stem Blight ◽  
Gummy Stem Blight ◽  
And Control

Gummy stem blight (Didymella blight), caused by Didymella bryoniae (Auersw.) Rehm and its anamorph Phoma cucurbitacearum (Fr.:Fr.) Sacc., is the second most important disease of cucumber (Cucumis sativus L.) in North Carolina after root knot nematodes Meloidogyne sp. Both Didymella blight and Phoma blight, caused by Phoma exigua Desm., have similar symptoms and control practices, and are generally referred to as gummy stem blight. In order to determine whether resistance existed to North Carolina isolates of D. bryoniae, 851 cultigens [cultivars, breeding lines, and plant introduction (PI) lines] were evaluated in the field. Plants were inoculated with one selected isolate (highly pathogenic in preliminary greenhouse tests) at the vine tip-over stage. They were rated for foliage lesion size and number on a 0 to 9 visual scale (0 = no disease, 9 = plant killed) and average ratings for 10 plants per plot were analyzed. The ratings ranged from 2.0 (highly resistant) to 8.5 (highly susceptible) with a mean of 6.2. The most resistant breeding lines and PI accessions were PI 200815, PI 390243, `LJ 90430', PI 279469, and PI 432855. The most resistant cultivars were `Homegreen #2', `Little John', `Transamerica', and `Poinsett 76'. The most susceptible cultigens in the study were PI 288238, PI 357843, PI 357865, and PI 167134. Two popular cultivars in North Carolina, `Calypso' and `Dasher II', were moderately resistant.

scholarly journals First Report of Benomyl Resistance in Didymella bryoniae in Delaware and Maryland

Plant Disease ◽  
1999 ◽  
Vol 83 (3) ◽  
pp. 304-304 ◽  
Author(s):  
K. L. Everts
Keyword(s):  
New York ◽  
South Carolina ◽  
Citrullus Lanatus ◽  
New York State ◽  
Didymella Bryoniae ◽  
Potato Dextrose Agar Medium ◽  
First Report ◽  
Stem Blight ◽  
Colony Diameter ◽  
Gummy Stem Blight

Gummy stem blight, caused by Didymella bryoniae (Auersw.) Rehm, is the most severe foliar disease of watermelon, Citrullus lanatus (Thunb.) Matsum. & Nakai, in eastern Maryland and southern Delaware. The fungicide benomyl is used in combination with chlorothalonil to manage gummy stem blight. Under conducive environmental conditions, yield losses are high even when fields are sprayed weekly. Resistance of D. bryoniae to benomyl has been reported in New York State and South Carolina (1). Gummy stem blight-infected leaves and stems were collected from nine and three fields in Wicomico County, MD, and Sussex County, DE, respectively, in 1996. Infected tissue was also collected from two Wicomico County fields in 1997. One single-spore subculture was obtained to represent each field. Agar plugs were taken from actively growing subcultures and inverted on a 25% (quarter strength) potato dextrose agar medium amended with 0 and 33.1 mg of benomyl per liter, the concentration of benomyl that reduced relative colony diameter of four resistant isolates in New York and South Carolina by 50% (1). Two replicate plates were used per experiment and each experiment was repeated once. After 6 days of growth at 21°C in the dark, the colony diameter was measured. Isolates were classified as sensitive if they were unable to grow, moderately sensitive if colony diameter was reduced 40 to 60%, and resistant if colony diameter was reduced less than 10% on the benomyl-amended media, compared with unamended media. Isolates that had previously been tested were used as sensitive (W03) and moderately sensitive (NY1) standards (1). In 1996, two isolates were sensitive, four isolates were moderately sensitive, and six isolates were resistant to benomyl. One isolate from 1997 was resistant and the other was moderately sensitive. This is the first report of resistance to benomyl within the D. bryoniae population in eastern Maryland and southern Delaware. Reference: (1) A. P. Keinath and T. A. Zitter. Plant Dis. 82:479, 1998.

scholarly journals Field Tests for Cucumber Resistance to Gummy Stem Blight in North Carolina

HortScience ◽  
1993 ◽  
Vol 28 (4) ◽  
pp. 327-329 ◽  
Author(s):  
Todd C. Wehner ◽  
Paul C. St. Amand
Keyword(s):  
North Carolina ◽  
Field Tests ◽  
Plant Introduction ◽  
Lesion Size ◽  
Didymella Bryoniae ◽  
Severe Problem ◽  
Breeding Lines ◽  
Stem Blight ◽  
Gummy Stem Blight ◽  
M 12

Gummy stem blight [Didymella bryoniae (Auersw.) Rehm] is the second most important pathogen of field-grown cucumbers (Cucumis sativus L.) in North Carolina and a severe problem for greenhouse-grown cucumbers worldwide. To determine whether resistance exists under North Carolina field conditions, 83 cultigens [cultivars, breeding lines, and plant introduction (PI) accessions] were evaluated in the field for 4 years for their resistance to a mixture of D. bryoniae isolates. Plants were inoculated at the vine tip-over stage and rated for foliar lesion size and number. Cultigens identified as resistant in Wisconsin and The Netherlands were not resistant in North Carolina. When averaged over years and locations, the most resistant C. sativus cultigens were PI 164433, `Slice', PI 390264, M 17, and M 12. Several accessions of related Cucumis species were highly resistant: PI 299568 (C. myriocarpus Naud.), PI 282450 (C. zeyheri Sond.), PI 299572 (C. myriocarpus), and PI 233646 (C. anguria L.). The most susceptible cultivars were `Colet', `Meresto', `Supergreen', `Dura', `Pioneer', `Marketmore 76', `Pickmore', and `Addis'. `Calypso' and `Dasher II', popular cultivars in North Carolina, were moderately susceptible.

scholarly journals Didymella bryoniae Isolates from Watermelon Seedlings in Florida Transplant Houses and Their Sensitivity to Boscalid

2015 ◽  
Vol 16 (1) ◽  
pp. 31-33 ◽  
Author(s):  
Katherine E. Hendricks ◽  
Pamela D. Roberts
Keyword(s):  
South Carolina ◽  
Molecular Mechanism ◽  
Previous History ◽  
Didymella Bryoniae ◽  
Stem Blight ◽  
Gummy Stem Blight ◽  
History Of ◽  
North And South

The purpose of this study was to examine why gummy stem blight was not being controlled in watermelon fields without a previous history of boscalid use and whether boscalid resistance could have originated from the transplants. The study evaluated Didymella bryoniae isolates collected from three Florida transplant houses for resistance to boscalid and compared the molecular mechanism of this resistance to that in the literature on isolates from North and South Carolina and Georgia. Accepted by publication 16 February 2015. Published 25 February 2015.

Factors Promoting Pycnidia Production of Didymella bryoniae, the Causal of Gummy Stem Blight in Cucurbits

2017 ◽  
Vol 45 (1) ◽  
pp. 173-187
Author(s):  
Abdel-Fattah El-Wakil ◽  
Amal Khalil ◽  
Ibrahim El -Abbasi
Keyword(s):  
Didymella Bryoniae ◽  
Stem Blight ◽  
Gummy Stem Blight

scholarly journals Resistance to Gummy Stem Blight in Muskmelon

HortScience ◽  
1993 ◽  
Vol 28 (9) ◽  
pp. 930-931 ◽  
Author(s):  
D.J. McGrath ◽  
L. Vawdrey ◽  
I.O. Walker
Keyword(s):  
Cucumis Melo ◽  
Didymella Bryoniae ◽  
Disease Reaction ◽  
Stem Blight ◽  
Gummy Stem Blight ◽  
Alternative Sources

Resistance to gummy stem blight [Didymella bryoniae (Auersw.) Rehm] was evaluated in two accessions of Cucumis melo L., PI 266935 and PI 266934. Based on disease reaction scores and dry weights, PI 266934 possessed much greater resistance than PI 266935. The quality of resistance of PI 266934 was unaffected by the ranges of seedling ages and inoculum concentrations used. No melon cultivar, to our knowledge, is highly resistant to gummy stem blight in the field, and alternative sources of superior resistance are potentially useful for breeding.

scholarly journals Evaluation of Resistance to Gummy Stem Blight (Didymella bryoniae) Disease in ipt (Isopentenyl Transferase) Transformed Watermelon Plants

HortScience ◽  
2004 ◽  
Vol 39 (4) ◽  
pp. 820E-821
Author(s):  
Fahrettin Goktepe ◽  
Harrison Hughes*
Keyword(s):  
Transgenic Plants ◽  
Infected Leaf ◽  
Wild Type ◽  
Didymella Bryoniae ◽  
Isopentenyl Transferase ◽  
Disease Symptoms ◽  
Stem Blight ◽  
Transformed Plants ◽  
Gummy Stem Blight ◽  
Run Off

Watermelon plants are susceptible to Gummy stem blight disease that considerably reduces yields worldwide. In order to develop non-specific resistance, watermelon cv. Crimson Sweet was transformed with copper inducible isopentenyl transferase (ipt), the rate-limiting step in cytokinin biosynthesis, gene via Agrobacterium tumafaciences (LBA4404). Transformed (ipt) and nontransformed plants were grown at approximately 28-30 °C day, 20-22 °C night and 16 hours daylight under greenhouse conditions. Once the plants initiated new growth both transgenic plants and wild type plants were sprayed with one of three different concentrations (0, 10 & 50 μm) of CuSO4. Plants were sprayed twice to run-off in a twenty-four hour time period before inoculation with the pathogen. Cultures of the pathogen Didymela bryonia (W353) were grown for about 3 weeks and an inoculum containing 105 conidia per mL was sprayed with the prepared suspension until initial run-off in a humidified chamber. The disease symptoms were evaluated after one week with resistance demonstrated in all treated transgenic plants. All nonsprayed transgenic and wild type plants showed similar disease symptoms. Infected leaf samples were surface sterilized and re-cultured on V8 medium. The characteristics of the recovered pathogen confirmed that it was identical to the stock culture of W353. The same experiment has been conducted on seedlings from transgenic (T1 generations) and non-transformed plants. The non-transformed seedlings showed the first disease symptoms on their cotyledons and lower leaves. Disease resistance was observed in seedlings of the treated transformed plants as compared to nontransformed ones.

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