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 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.

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 Effect of nitrogen doses on disease severity and watermelon yield

2009 ◽  
Vol 27 (3) ◽  
pp. 330-334 ◽  
Author(s):  
Gil R dos Santos ◽  
Manoel D de Castro Neto ◽  
Hudson SM de Almeida ◽  
Leandro N Ramos ◽  
Renato A Sarmento ◽  
...  
Keyword(s):  
Disease Severity ◽  
Nitrogen Fertilization ◽  
Citrullus Lanatus ◽  
Fruit Yield ◽  
Control Treatment ◽  
Average Weight ◽  
Stem Blight ◽  
Gummy Stem Blight ◽  
Yield And Quality ◽  
Severity Levels

Nitrogen fertilization is an important step for watermelon (Citrullus lanatus) production due to its influence over yield, fruit quality, and disease severity. Currently, the gummy stem blight (Didymella bryoniae) and the downy mildew (Pseudoperonospora cubensis) can be taken as the most important watermelon diseases, since they impose severe impairment to the crop. Furthermore, studies focusing on plant responses to nitrogen fertilization regarding fruit yield and quality, and disease resistance are rare. Hence, the present study aimed at evaluating the effect of nitrogen doses on fruit yield and quality, and on disease prevalence in watermelon. Two experiments were carried out at the Universidade Federal de Tocantins, employing sprinkler irrigation, in an area previously used to grow watermelon. The experimental design was blocks at random, with five treatments (N doses, applied twice as side-dressing, in kg ha-1, as follows: T1= control treatment without N, T2= 20, T3= 40, T4= 80, and T5= 120), and four replications. Urea (45% N) was used as the N source. In the first assay, the highest fruit yield and average weight were observed when 40 kg ha-1 of N were applied. The highest severity of the gummy stem blight was observed when the highest nitrogen doses were applied (80 and 120 kg ha-1). In the second assay, the highest severity levels of the gummy stem blight, as well as of mildew, were observed again when N doses were the highest (80 and 120 kg ha-1). The lowest severity levels for both diseases were observed in the control treatment.

scholarly journals Inheritance of Resistance to Gummy Stem Blight in Watermelon

HortScience ◽  
2017 ◽  
Vol 52 (11) ◽  
pp. 1477-1482 ◽  
Author(s):  
Gabriele Gusmini ◽  
Luis A. Rivera-Burgos ◽  
Todd C. Wehner
Keyword(s):  
Citrullus Lanatus ◽  
Single Gene ◽  
Genetic System ◽  
The United States ◽  
Inheritance Of Resistance ◽  
Didymella Bryoniae ◽  
Stem Blight ◽  
Gummy Stem Blight ◽  
Mendelian Gene ◽  
Production Areas

Gummy stem blight (GSB), caused by three related species of Stagonosporopsis [Stagonosporopsis cucurbitacearum (syn. Didymella bryoniae), Stagonosporopsis citrulli, and Stagonosporopsis caricae], is a major disease of watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] in most production areas of the United States. We studied the inheritance of resistance to GSB using three PI accessions of watermelon. Four families of six progenies (Pr, Ps, F1, F2, BC1Pr, and BC1Ps) were developed from four crosses of resistant PI accessions by susceptible cultivars. Each family was tested in 2002 and 2003 in North Carolina under field and greenhouse conditions for resistance to GSB. Artificial inoculation was used to induce uniform and strong epidemics. The effect of the Mendelian gene for resistance, db, was tested. Partial failure of the data to fit the single-gene inheritance suggested that resistance to GSB of PI 482283 and PI 526233 may be under the control of a more complex genetic system.

scholarly journals First Report of Gummy Stem Blight, Caused by Didymella bryoniae, on Watermelon Transplants in California

Plant Disease ◽  
1997 ◽  
Vol 81 (11) ◽  
pp. 1331-1331 ◽  
Author(s):  
S. T. Koike
Keyword(s):  
Citrullus Lanatus ◽  
Potato Dextrose Agar ◽  
Fruiting Bodies ◽  
Didymella Bryoniae ◽  
Dark Cycle ◽  
Disease Symptoms ◽  
Stem Blight ◽  
Gummy Stem Blight ◽  
Cucumber Fruit ◽  
Phoma Cucurbitacearum

In 1997, greenhouse-produced transplants of watermelon (Citrullus lanatus) developed water-soaked lesions on leaf petioles and main stems. As disease progressed, petioles and stems became necrotic and shriveled, and exuded a sticky, translucent tan liquid. Symptoms spread to leaves, which wilted and collapsed. Affected transplants eventually died. Although fruiting bodies were not observed on diseased plants, a fungal agent was consistently isolated from symptomatic tissues. When incubated under lights (12 h light/12 h dark cycle), isolates on potato dextrose agar produced numerous pycnidia with hyaline, cylindrical, one-septate conidia with mean dimensions of 5.6 × 2.8 μm. Under the same incubation conditions, isolates on V8 juice agar produced sparse ostiolate pseudothecia with bitunicate asci and hyaline, oval, one-septate ascospores with mean dimensions of 12.0 × 4.0 μm. Based on these characters, the isolates were identified as Didymella bryoniae (anamorph Phoma cucurbitacearum) (1,2). Pathogenicity was tested by producing conidial inocula of representative isolates and inoculating wounded cotyledons, true leaves, and petioles of watermelon (cv. Sangria), and wounded true leaves and petioles of cucumber (Cucumis sativus cv. Premier Hybrid) (3). Sterile, distilled water was applied to corresponding wounded tissues of control plants. All plants were kept in a humid chamber for 4 days. After 6 (watermelon) to 10 (cucumber) days, inoculated plants exhibited water-soaked lesions followed by necrosis, petiole and leaf wilting, and shriveling of tissues. Pycnidia were observed on cucumber plants after 18 days. The pathogen was reisolated from all inoculated plants and identified as D. bryoniae. Control plants developed no disease symptoms. In addition, agar plugs colonized with the watermelon isolates were placed onto cucumber fruit that were wounded slightly with a sterile scalpel. Fruit were incubated at 22 to 24°C in humid chambers and after 2 days sunken, circular lesions developed. The same pathogen was reisolated from the margins of fruit lesions. Wounded control fruit received sterile agar plugs and did not develop any symptoms. This is the first documentation of gummy stem blight on watermelon transplants in California. References: (1) W. F. Chiu and J. C. Walker. J. Agric. Res. 78:81, 1949. (2) A. P. Keinath et al. Phytopathology 85:364, 1995. (3) A. J. Wyszogrodzka et al. Euphytica 35:603, 1986.

scholarly journals Genetic Characterization of Didymella bryoniae Isolates Infecting Watermelon and Other Cucurbits in Florida and Georgia

Plant Disease ◽  
2015 ◽  
Vol 99 (11) ◽  
pp. 1488-1499 ◽  
Author(s):  
Binoy Babu ◽  
Yonas W. Kefialew ◽  
Ping-Fang Li ◽  
Xing-Ping Yang ◽  
Sheeja George ◽  
...  
Keyword(s):  
Citrullus Lanatus ◽  
Random Amplified Polymorphic Dna ◽  
Rflp Analysis ◽  
Genetic Profile ◽  
Its Sequence ◽  
Didymella Bryoniae ◽  
Stem Blight ◽  
Gummy Stem Blight ◽  
Its Sequence Analysis ◽  
Pcr Rflp

Gummy stem blight caused by Didymella bryoniae (anamorph Phoma cucurbitacearum) is a major fungal disease of watermelon (Citrullus lanatus) and other cucurbits. Thirty-five isolates of Didymella and Phoma spp. associated with symptoms of gummy stem blight on watermelon, Canary melon (Cucumis melo), muskmelon (C. melo), and winter squash (Cucurbita maxima) from Florida and Georgia were characterized based on morphology on agar media, pathogenicity on ‘Melody’ watermelon, the internal transcribed spacer (ITS) sequence of ribosomal DNA (rDNA), random amplified polymorphic DNA (RAPD) analysis, and polymerase chain reaction (PCR) restriction fragment length polymorphism (RFLP) analysis. All of the isolates were pathogenic on watermelon but differed in virulence. RAPD and ITS sequence analysis indicated genetic variability among the isolates but PCR-RFLP analysis did not show any variability. ITS sequence phylogenetic analysis identified two isolates, DB-05 and DB-33, which had a greater identity to that of D. bryoniae isolates from China (98 to 100% sequence homology) than other isolates from Florida and Georgia (95 to 98%). These two isolates possessed a single nucleotide substitution of A to G at position 131 of the ITS1 region. The study characterized the genetic profile of a collection of D. bryoniae isolates from Florida and Georgia in relation to isolates from other U.S. states and countries.

scholarly journals Differential Susceptibility of Nine Cucurbit Species to the Foliar Blight and Crown Canker Phases of Gummy Stem Blight

Plant Disease ◽  
2014 ◽  
Vol 98 (2) ◽  
pp. 247-254 ◽  
Author(s):  
Anthony P. Keinath
Keyword(s):  
Cucumis Melo ◽  
Citrullus Lanatus ◽  
Differential Susceptibility ◽  
Cucurbita Moschata ◽  
Didymella Bryoniae ◽  
Stem Blight ◽  
Gummy Stem Blight ◽  
Foliar Blight ◽  
Diseased Leaf Area ◽  
Stem Cankers

Eighteen cucurbit cultivars representing five genera, nine species, and 17 horticultural types were inoculated with Didymella bryoniae in field plots in Charleston, SC, in autumn 2008, autumn 2009, and spring 2011 to determine susceptibility to gummy stem blight. In each year, gummy stem blight cankers occurred more frequently on crowns or main stems of ‘Athena’ muskmelon (Cucumis melo) and ‘Green Striped Cushaw’ squash (Cucurbita argyrosperma) than on all other cultivars except ‘Rocio’ honeydew (Cucumis melo) in 2009, and bottle gourd (Lagenaria siceraria) and Ojakkyo citron (Citrullus lanatus var. citroides) in 2011. Cucurbita moschata was highly resistant to stem cankers. Severity of gummy stem blight on foliage was moderate to severe in autumn 2009, mild to severe in autumn 2008, and very mild in spring 2011 (due to unusually dry weather). Watermelon (Citrullus lanatus var. lanatus) and melon were the most susceptible to foliar blight in 2008 and 2009. In all 3 years, ‘Cheese’ and ‘Bugle’ squash (both Cucurbita moschata), and ‘Judgment III’ and ‘Lioness’ summer squash (C. pepo) were among the cultivars with the least diseased leaf area. C. moschata, C. pepo, C. maxima, and Luffa cylindrica (smooth loofah) were significantly less susceptible to foliar blight than Cucumis melo and three Citrullus lanatus cultivars in 2008 and 2009. This study also is the first documentation of susceptibility of Cucurbita argyrosperma to gummy stem blight.

scholarly journals Susceptibility of Cucurbit Rootstocks to Didymella bryoniae and Control of Gummy Stem Blight on Grafted Watermelon Seedlings with Fungicides

Plant Disease ◽  
2013 ◽  
Vol 97 (8) ◽  
pp. 1018-1024 ◽  
Author(s):  
Anthony P. Keinath
Keyword(s):  
Bottle Gourd ◽  
Cucurbita Moschata ◽  
Didymella Bryoniae ◽  
Water Control ◽  
Graft Union ◽  
Greenhouse Production ◽  
Stem Blight ◽  
Gummy Stem Blight ◽  
Seedless Watermelon ◽  
And Control

Seedlings of watermelon are susceptible to Didymella bryoniae, the cucurbit pathogen that causes gummy stem blight, particularly when they are grown in the greenhouse for use as transplants. Seedlings of bottle gourd (Lagenaria siceraria) and interspecific hybrid squash (Cucurbita moschata × C. maxima) that are used as rootstocks for grafting watermelon are susceptible to gummy stem blight when wounded. Nonwounded rootstock seedlings of both genera were as susceptible to gummy stem blight as seedless watermelon. Because grafted plants must be misted or held at high relative humidity for 1 week so the graft union will heal, fungicides may be necessary to manage gummy stem blight under these disease-conducive environmental conditions. Nine fungicides were applied as foliar treatments at labeled rates per 467 liters/ha water to nongrafted seedlings of watermelon and five rootstock cultivars. Fluopyram + tebuconazole injured all five bottle gourd and hybrid squash cultivars and stunted watermelon and hybrid squash seedlings. Cyprodinil + difenoconazole injured all five rootstock cultivars and watermelon. Tebuconazole stunted bottle gourd and watermelon seedlings. Four of the five fungicides that were not phytotoxic reduced incidence and severity of gummy stem blight on seedless watermelon grafted onto bottle gourd Emphasis and hybrid squash Strong Tosa. Difenoconazole and cyprodinil were more effective than mancozeb or cyprodinil + fludioxonil, which were more effective than thiophanate-methyl, which was not significantly different from the water control (P = 0.01). Nongrafted watermelon seedlings and watermelon seedlings grafted onto watermelon as the rootstock were as susceptible to gummy stem blight as watermelon seedlings grafted onto cucurbits. Although difenoconazole and cyprodinil are not registered currently on cucurbits, transplant growers can apply mancozeb or cyprodinil + fludioxonil to manage gummy stem blight on watermelon and rootstock seedlings during greenhouse production.

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.

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