UPDATE ON POWDERY MILDEW RESISTANCE SCREENING IN WATERMELON

Powdery mildew has been reported on Citrullus lanatus in Africa and Europe for the past nine years, and in the United States for the past 6 years. During this time, it has occurred in the main watermelon production areas in the U.S. and has been documented in nine states (South Carolina, Georgia, Florida, Oklahoma, Texas, Maryland, New York, Arizona, and California). This is of great concern to the watermelon industry since powdery mildew is difficult to control and can have a severe impact on yield and fruit quality due to loss of photosynthetic area and sunscald. Finding resistant C. lanatus germplasm is needed for the development of commercial varieties containing this resistance. This report summarized the status of an ongoing project to screen the entire USDA–ARS C. lanatus germplasm collection. Currently, the collection is being screened for race 1 and race 2 Podosphaera xanthii (syn. Sphaerotheca fuliginea auct. p.p.), the causal agent of powdery mildew in C. lanatus in the United States. Resistance genes appear to exist for both races and the genes conferring resistance to race 1 appear to be different than race 2 resistance genes. Allelism tests are currently in process to determine the number of resistance genes present.

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UPDATE ON POWDERY MILDEW RESISTANCE SCREENING IN WATERMELON

HortScience ◽

10.21273/hortsci.40.3.872c ◽

2005 ◽

Vol 40 (3) ◽

pp. 872c-872

Author(s):

Angela R. Davis ◽

Todd C. Wehner ◽

Amnon Levi ◽

Stephen R. King

Keyword(s):

United States ◽

South Carolina ◽

Powdery Mildew ◽

Resistance Genes ◽

Citrullus Lanatus ◽

Germplasm Collection ◽

The United States ◽

The Past ◽

Race 1 ◽

Race 2

Powdery mildew has been reported on Citrullus lanatus in Africa and Europe for the past 9 years, and in the United States for the past 6 years. During this time, it has occurred in the main watermelon production areas in the U.S. and has been documented in nine states (South Carolina, Georgia, Florida, Oklahoma, Texas, Maryland, New York, Arizona, and California). This is of great concern to the watermelon industry since powdery mildew is difficult to control and can have a severe impact on yield and fruit quality due to loss of photosynthetic area and sunscald. Finding resistant C. lanatus germplasm is needed for the development of commercial varieties containing this resistance. This report summarized the status of an ongoing project to screen the entire USDA–ARS C. lanatus germplasm collection. Currently, the collection is being screened for race 1 and race 2 Podosphaera xanthii (syn. Sphaerotheca fuliginea auct. p.p.), the causal agent of powdery mildew in C. lanatus in the United States. Resistance genes appear to exist for both races and the genes conferring resistance to race 1 appear to be different than race 2 resistance genes. Allelism tests are currently in process to determine the number of resistance genes present.

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First Report of Fusarium oxysporum f. sp. niveum Race 2 as Causal Agent of Fusarium Wilt of Watermelon in Indiana

Plant Disease ◽

10.1094/pd-89-0108a ◽

2005 ◽

Vol 89 (1) ◽

pp. 108-108 ◽

Cited By ~ 12

Author(s):

D. S. Egel ◽

R. Harikrishnan ◽

R. Martyn

Keyword(s):

United States ◽

Fusarium Oxysporum ◽

Fusarium Wilt ◽

Citrullus Lanatus ◽

The United States ◽

Mineral Salts ◽

First Report ◽

Race 1 ◽

Race 2 ◽

Greenhouse Assay

Fusarium oxysporum f. sp. niveum race 1 is uniformly distributed throughout watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) growing regions, but F. oxysporum f. sp. niveum race 2 has a limited known distribution in the United States (Texas, Florida, Oklahoma, Maryland, and Delaware) (3,4). Since the spring of 2001, commercial watermelon fields in Knox and Gibson counties in southwestern Indiana have been observed with symptoms of one-sided wilt and vascular discoloration typical of Fusarium wilt. Race 2 of F. oxysporum f. sp. niveum was suspected as the casual agent since the diseased watermelon cultivars are considered resistant to races 0 and 1. Two isolates of F. oxysporum obtained from wilted watermelon plants in two different commercial fields and one isolate obtained from a wilted seedling in a transplant house were compared for pathogenicity in a greenhouse assay. Known isolates of F. oxysporum f. sp. niveum races 0, 1, and 2 were obtained from Don Hopkins (University of Florida, Apopka), Kate Everts (University of Maryland/University of Delaware, Salisbury, MD), and Ray Martyn (Purdue University, West Lafayette, IN), respectively, and were used for comparison. All isolates were grown in shake cultures in a mineral salts liquid medium. (1). After 72 hr, the predominately microconidal suspensions were filtered through cheesecloth and adjusted to 1 × 105 conidia/ml with the aid of a hemacytometer. A concentration of 1 × 105 condia/ml was shown previously to cause the desired disease reaction in the standard cultivars. Seedlings of the differential cvs, Black Diamond (universal susceptible), Charleston Gray (race 0 resistant), and Calhoun Gray (race 0 and 1 resistant) were grown in a 1:1, (v:v) sand/ vermiculite mixture to the first true-leaf stage after which the plants were uprooted and the roots carefully washed prior to root dip inoculation. Subsequent to inoculation, seedlings were planted in a sand/vermiculite/ peat mixture (4:1:1, [v:v:v]) with four seedlings to a 15-cm-diameter pot. The experimental design was a randomized complete block with five replications. Two isolates from the commercial field plants caused an average of 100% wilt on cv. Black Diamond, 95% wilt on cv. Charleston Gray, and 80% wilt on cv. Calhoun Gray, resulting in a designation of race 2. The isolate from a commercial transplant house resulted in 100, 60, and 15% wilt, respectively, on the three standard cultivars resulting in a race 1 designation. The presence of F. oxysporum f. sp. niveum race 2 in Indiana is significant because Indiana currently ranks fifth in the United States in watermelon production and there are no commercially available cultivars that possess resistance to race 2. To our knowledge, this is the first report of F. oxysporum f. sp. niveum race 2 in Indiana and the first report of race 2 from the Midwest region of the United States. Race 2, first described from the United States in 1985 (2), has now been confirmed in six states. References: (1) R. Esposito and A. Fletcher. Arch. Biochem. Biophys. 93:369, 1961. (2) R. Martyn, Plant Dis. 69:1007, 1985. (3) R. Martyn, Plant Dis. 71:233, 1987. (4) X. Zhou and K. Everts. Plant Dis. 87:692, 2003.

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Distribution and Characterization of Podosphaera macularis Virulent on Hop Cultivars Possessing R6-Based Resistance to Powdery Mildew

Plant Disease ◽

10.1094/pdis-12-15-1449-re ◽

2016 ◽

Vol 100 (6) ◽

pp. 1212-1221 ◽

Cited By ~ 12

Author(s):

Sierra N. Wolfenbarger ◽

Stephen T. Massie ◽

Cynthia Ocamb ◽

Emily B. Eck ◽

Gary G. Grove ◽

...

Keyword(s):

United States ◽

Powdery Mildew ◽

Mating Type ◽

Resistance Genes ◽

Severe Disease ◽

The United States ◽

Fitness Cost ◽

Eastern United States ◽

Host Genotype ◽

Podosphaera Macularis

Host resistance, both quantitative and qualitative, is the preferred long-term approach for disease management in many pathosystems, including powdery mildew of hop (Podosphaera macularis). In 2012, an epidemic of powdery mildew occurred in Washington and Idaho on previously resistant cultivars whose resistance was putatively based on the gene designated R6. In 2013, isolates capable of causing severe disease on cultivars with R6-based resistance were confirmed in Oregon and became widespread during 2014. Surveys of commercial hop yards during 2012 to 2014 documented that powdery mildew is now widespread on cultivars possessing R6 resistance in Washington and Oregon, and the incidence of disease is progressively increasing. Pathogenic fitness, race, and mating type of R6-virulent isolates were compared with isolates of P. macularis lacking R6 virulence. All isolates were positive for the mating type idiomorph MAT1-1 and were able to overcome resistance genes Rb, R3, and R5 but not R1 or R2. In addition, R6-virulent isolates were shown to infect differential cultivars reported to possess the R6 gene and also the R4 gene, although R4 has not yet been broadly deployed in the United States. R6-virulent isolates were not detected from the eastern United States during 2012 to 2015. In growth chamber studies, R6-virulent isolates of P. macularis had a significantly longer latent period and produced fewer lesions on plants with R6 as compared with plants lacking R6, indicating a fitness cost to the fungus. R6-virulent isolates also produced fewer conidia when compared with isolates lacking R6 virulence, independent of whether the isolates were grown on a plant with or without R6. Thus, it is possible that the fitness cost of R6 virulence occurs regardless of host genotype. In field studies, powdery mildew was suppressed by at least 50% on plants possessing R6 as compared with those without R6 when coinoculated with R6-virulent and avirulent isolates. R6 virulence in P. macularis appears to be race specific and, at this time, imposes a measurable fitness penalty on the fungus. Resistance genes R1 and R2 appear to remain effective against R6-virulent isolates of P. macularis in the U.S. Pacific Northwest.

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Identifying Races of Fusarium oxysporum f. sp. niveum in South Carolina Recovered From Watermelon Seedlings, Plants, and Field Soil

Plant Disease ◽

10.1094/pdis-11-19-2385-re ◽

2020 ◽

Vol 104 (9) ◽

pp. 2481-2488

Author(s):

Anthony P. Keinath ◽

Virginia B. DuBose ◽

Melanie M. Katawczik ◽

W. Patrick Wechter

Keyword(s):

South Carolina ◽

Fusarium Oxysporum ◽

Management Practices ◽

Integrated Management ◽

Citrullus Lanatus ◽

Field Soil ◽

Specific Primers ◽

Race 1 ◽

Race 2 ◽

Race Identification

Fusarium wilt of watermelon (Citrullus lanatus), caused by the soilborne fungus Fusarium oxysporum f. sp. niveum, is the most serious disease of watermelon in South Carolina and other southeastern U.S. states. Isolates of F. oxysporum collected from field-grown plants, greenhouse-grown seedlings, and field soil between 1999 and 2018 were inoculated onto three differential watermelon cultivars to identify races. Of 197 isolates obtained from plants, 12% were nonpathogenic, 2% were race 0, 23% were race 1, and 63% were race 2. One collection of isolates from greenhouse seedlings was exclusively race 1 and the other was exclusively race 2. Seventeen of 81 soil isolates were pathogenic: five were race 1 and 12 were race 2. Reactions of C. amarus PI 296341-FR, Carolina Strongback, and SP-6, cultigens with resistance to race 2, did not differ significantly among five highly virulent race 2 isolates and a standard race 2 isolate, indicating a lack of a race 3 phenotype. Forma specialis-specific primers matched phenotypic race identification for 74% of the isolates. Race-specific primers based on a secreted-in-xylem elicitor present in race 0 and 1 isolates matched phenotypic race identification for 66% of the isolates. Because a majority of the F. oxysporum f. sp. niveum isolates from South Carolina were race 2, integrated management practices should be used until commercial cultivars with resistance to race 2 are available.

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First Report of Race 2 of Colletotrichum trifolii Causing Anthracnose on Alfalfa (Medicago sativa) in Wisconsin

Plant Disease ◽

10.1094/pdis-08-13-0808-pdn ◽

2014 ◽

Vol 98 (6) ◽

pp. 843-843 ◽

Cited By ~ 2

Author(s):

D. A. Samac ◽

S. Allen ◽

D. Witte ◽

D. Miller ◽

J. Peterson

Keyword(s):

United States ◽

Medicago Sativa ◽

The United States ◽

Crown Rot ◽

Growth Chamber ◽

Its Sequence ◽

Colletotrichum Trifolii ◽

Differential Cultivars ◽

Race 1 ◽

Race 2

Anthracnose of alfalfa (Medicago sativa), caused by Colletotrichum trifolii, is widespread in the United States. In addition to loss of forage due to death of stems, the pathogen causes crown rot, reducing stand life and winter survival (2), making it one of the most serious diseases of alfalfa. Three physiological races have been described (2). Race 1 is reported to be the dominant race that is present wherever alfalfa is grown, while race 2 was reported in a limited area in the Mid-Atlantic states, and race 4 was found in Ohio (1). Conspicuous, straw-colored dead stems with a “shepherd's crook” wilt and large, sunken, diamond-shaped lesions with a dark border were observed in experimental plots and breeding nurseries of experimental lines in Clinton and West Salem, WI, in August 2011 and in West Salem, WI, in mid-August 2012. Acervuli with black setae and orange spore masses were observed in lesions placed in moist chambers for 2 days at room temperature with ambient room lighting. Conidia were germinated on 1% water agar and then single hyphae were transferred to potato dextrose agar (PDA) plates. DNA was extracted from pure cultures of strains DA-1 (Clinton, WI) and FGI-3 (West Salem, WI), the rDNA ITS1-5.8S-ITS2 region was amplified with primers ITS1 (5′-TCCGTAGGTGAACCTGCGG-3′) and ITS4 (5′-TCCTCCGCTTATTGATATGC-3′), the products sequenced directly, and the sequences compared to the ITS region of known race 1 and race 2 strains of C. trifolii. The sequences from DA-1 and FGI-3 were identical to the ITS sequence of C. trifolii 2sp2 (race 1; KF444778) and C. trifolii SB-2 (race 2; KF444779), but distinct from the ITS sequence of C. destructivum (JQ005764) and C. dematium (JX567507), which can cause anthracnose on alfalfa (1). Conidia from DA-1 and FGI-3 were harvested from 7-day-old cultures grown on PDA plates, diluted to 2 × 106 conidia/ml, and sprayed to runoff on 10-day-old growth chamber grown plants of three differential cultivars: Saranac (susceptible to races 1 and 2), Arc (resistant to race 1, susceptible to race 2), and Saranac AR (resistant to races 1 and 2). Plants were maintained at 100% relative humidity for 48 h and then grown in a growth chamber at 24°C with a 16-h photoperiod. Symptoms were rated at 14 days after inoculation. In the three repetitions of the experiment using 75 plants of each cultivar in each experiment, less than 10% of the Saranac and Arc plants survived, while survival of Saranac AR was 31 to 44%. The approximate expected survival of differential cultivars inoculated with race 1 is 1% for Saranac, 65 to 70% for Arc, and 45% for Saranac AR (2). Aggressiveness of race 2 strains on Saranac AR is variable, ranging from 12 to 68% plant survival (3). The susceptibility of Arc when inoculated with DA-1 and FGI-3 is consistent with the reaction to race 2 strains, indicating that both strains are race 2. The isolation of race 2 strains in major alfalfa growing regions in Wisconsin indicates that this physiological race is currently more widespread than previously observed. Although most modern alfalfa cultivars have resistance to race 1, few cultivars with resistance to race 2 are available. The occurrence of C. trifolii race 2 in the Midwest United States should be considered in alfalfa breeding programs when developing multi-pest resistant alfalfa cultivars. References: (1) J. J. Ariss and L. H. Rhodes. Plant Dis. 91:1362, 2007. (2) N. R. O'Neill. Plant Dis. 80:450, 1996. (3) N. R. O'Neill et al. Phytopathology 79:750, 1989.

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A New Race of Colletotrichum trifolii Identified on Alfalfa in Ohio

Plant Disease ◽

10.1094/pdis-91-10-1362b ◽

2007 ◽

Vol 91 (10) ◽

pp. 1362-1362 ◽

Cited By ~ 2

Author(s):

J. J. Ariss ◽

L. H. Rhodes

Keyword(s):

United States ◽

North American ◽

The United States ◽

Morphological Characters ◽

First Report ◽

Anthracnose Resistance ◽

Colletotrichum Trifolii ◽

Race 1 ◽

Race 2 ◽

Race 4

Anthracnose of alfalfa (Medicago sativa L.), caused by the fungus Colletotrichum trifolii Bain & Essary, was identified as a potential problem of alfalfa in the United States in the late 1960s. Races 1 and 2 are known in the United States, and recently, race 4 was described in Australia (1). An additional race, race 3, had previously been reported in the United States, but isolates of this proposed race were not preserved and its status as a distinct race of C. trifolii is unclear. In June 2003, an isolate of C. trifolii was collected in Columbus, OH from a 4-year-old alfalfa stand of cv. 520. The isolate was obtained from typical anthracnose stem lesions. Stem sections with lesions were scraped with a sterile inoculation loop, and conidia were directly streaked onto acidified potato dextrose agar. Individual colonies were transferred to half-strength oatmeal agar. Morphological characters (conidia, acervuli, and setae) of this isolate, designated OH-WA-520, were consistent with those of other C. trifolii isolates and clearly distinguishable from C. destructivum or other Colletotrichum spp. that occur on alfalfa. The alfalfa differential cultivars Arc (resistant to race 1 and susceptible to race 2 of C. trifolii), Saranac AR (resistant to race 1 and race 2), and Saranac (susceptible to both races) were inoculated with conidia of isolate OH-WA-520 per the North American Alfalfa Improvement Conference standard protocol for determining anthracnose resistance (2). Isolate OH-WA-520 was avirulent on Arc but virulent on Saranac AR and Saranac. In each of three repetitions of the protocol, more than 65% of Arc plants survived, while less than 18% of Saranac and Saranac AR plants survived. These results indicate a physiological race inconsistent in reaction with C. trifolii race 1 or race 2, but similar in reaction to race 4 isolates previously described only from Australia (1). To our knowledge, this is the first report of a C. trifolii isolate virulent on Saranac AR but avirulent on Arc. This is also the first report of C. trifolii race 4 in the United States. References: (1) J. M. Mackie et al. Aust. J. Agric. Res. 54:829, 2003. (2) N. R. O'Neill. Anthracnose resistance. Page D-1 in: Standard Tests to Characterize Alfalfa Cultivars. Online publication. North American Alfalfa Improvement Conference, Beltsville, MD, 1991.

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Flowering Patterns of Pollenizer and Triploid Watermelon Cultivars

HortScience ◽

10.21273/hortsci.49.6.714 ◽

2014 ◽

Vol 49 (6) ◽

pp. 714-721 ◽

Cited By ~ 2

Author(s):

Cecilia E. McGregor ◽

Vickie Waters

Keyword(s):

United States ◽

Fruit Set ◽

Citrullus Lanatus ◽

Staminate Flower ◽

The United States ◽

Specific Production ◽

The Past ◽

Seedless Watermelon ◽

Triploid Watermelon ◽

Fundamental Requirement

The past 10 years has seen a steep increase in production of seedless watermelon (Citrullus lanatus) in the United States. Seedless fruit is produced on triploid plants that require pollination from diploid pollenizers for fruit set. Synchronization of the staminate flowers on the pollenizers with the appearance of pistillate flowers on the triploids is a fundamental requirement for this production system. Previous research suggested that pistillate flowers reach peak production early in the season, but data are only available for a small number of triploid cultivars. We compared the flowering patterns of 29 triploid cultivars and 20 pollenizers, including 10 harvested pollenizers, during the first 6 weeks after transplanting over 2 years. The average number of days from transplanting (DAT) to the first staminate flower was between 5.3 days and 19.1 days in 2012 and 9.7 days and 24.4 days in 2013 for the pollenizers and between 18.7 days and 27.6 days and 22.1 days and 32.7 days for the pistillate triploid flowers in the 2 years, respectively. K-means clustering of the weekly percentage of plants with staminate and pistillate flowers for the different cultivars shows that different triploid and pollenizer cultivars have different flowering patterns and that some combinations have better synchronized flowering than others. Growers should take particular care when choosing pollenizers for early-flowering triploid cultivars. Harvested pollenizers are better suited to late-flowering triploids and growers should choose triploid and pollenizer cultivar combinations with flowering patterns that best satisfy their specific production goals.

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Powdery Mildew Resistant Rootstocks that Impart Tolerance to Grafted Susceptible Watermelon Scion Seedlings

Plant Disease ◽

10.1094/pdis-09-17-1384-re ◽

2018 ◽

Vol 102 (7) ◽

pp. 1290-1298 ◽

Cited By ~ 7

Author(s):

Chandrasekar S. Kousik ◽

Mihir Mandal ◽

Richard Hassell

Keyword(s):

United States ◽

Powdery Mildew ◽

Disease Severity ◽

Citrullus Lanatus ◽

The United States ◽

Bottle Gourd ◽

Economic Losses ◽

Podosphaera Xanthii ◽

Lagenaria Siceraria ◽

True Leaf

Powdery mildew (PM) is a major foliar disease causing serious economic losses of cucurbit crops grown in the United States. The pathogen Podosphaera xanthii, which causes PM, is known to infect seedlings, stems, foliage, petioles, and fruit of cucurbit crops. In recent years, grafting watermelon on resistant rootstocks for managing soilborne diseases has been gaining popularity in the U.S.A. However, grafting for managing foliar diseases has not yet received adequate attention. Three greenhouse experiments were conducted during the summer months of 2012, 2013, and 2014 to determine if PM-resistant rootstocks could impart resistance to a susceptible watermelon scion. Susceptible watermelon scion ‘Mickey Lee’ seedlings were grafted onto 25 watermelon (Citrullus lanatus, C. amarus, C. mucosospermus) and four bottle gourd (Lagenaria siceraria) rootstocks. Grafted plants were inoculated with a 2 × 104 conidia ml−1 suspension of P. xanthii conidia and disease severity was rated 14 days after inoculation. Mickey Lee grafted on six PM-resistant watermelon rootstocks had significantly (P ≤ 0.05) lower PM severity on cotyledons, 2nd true leaf, and upper leaves (rating for 3rd to 7th or 8th true leaf) compared with Mickey Lee grafted on susceptible watermelon USVL677-PMS or bottle gourd USVL848-PMS rootstocks. However, some of the resistant watermelon rootstocks did not impart significant resistance to the scion. The resistant bottle gourd rootstocks USVL482-PMR and USVL351-PMR provided significantly greater levels of resistance, compared with many of the resistant watermelon rootstocks. Grafting watermelon on resistant rootstocks may help mitigate the effects of PM on susceptible scion seedlings.

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Expedition for Cucurbit Germplasm Exchange with China

HortScience ◽

10.21273/hortsci.30.4.890f ◽

1995 ◽

Vol 30 (4) ◽

pp. 890F-890

Author(s):

Todd C. Wehner ◽

James D. McCreight ◽

Bill B. Rhodes ◽

Xingping Zhang

Keyword(s):

United States ◽

Cucumis Melo ◽

Citrullus Lanatus ◽

Germplasm Collection ◽

The United States ◽

Cooperative Research ◽

Germplasm Exchange ◽

Republic Of China ◽

The Future ◽

Luffa Aegyptiaca

Cucumber (Cucumis sativus L.), melon (Cucumis melo L.), watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai], and luffa (Luffa aegyptiaca Mill) accessions were exchanged between scientists of the United States and the People's Republic of China. Exchanges were made during a July 1994 visit of cucurbit research institutions in Shanghai, ZhengZhou, Yangling, Urumqi, Turpan, ChiangJi City, Tianjin, and Beijing. The trip was coordinated by the Office of International Cooperation and Development, USDA. Chinese scientists received elite American accessions with useful traits, and the American scientists received classic accessions that will be preserved for use in the future by interested researchers. Accessions to be included in the USDA germplasm collection were 50 cucumbers, 30 melons, 51 watermelons, and 15 luffas. As a result of the visit, cucurbit scientists in the two countries learned about the programs of their counterparts, and are planning cooperative research for the future.

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International Research and Variation in Views of Ethnicity

Perspectives on Global Issues in Communication Sciences and Related Disorders ◽

10.1044/gics2.2.66 ◽

2012 ◽

Vol 2 (2) ◽

pp. 66-72

Author(s):

Ella Inglebret ◽

Amy Skinder-Meredith ◽

Shana Bailey ◽

Carla Jones ◽

Ashley France

Keyword(s):

United States ◽

Classification System ◽

International Research ◽

The United States ◽

Research Articles ◽

Journal Articles ◽

Research Participants ◽

The Past ◽

International Scale ◽

Publication Patterns

The authors in this article first identify the extent to which research articles published in three American Speech-Language-Hearing Association (ASHA) journals included participants, age birth to 18 years, from international backgrounds (i.e., residence outside of the United States), and go on to describe associated publication patterns over the past 12 years. These patterns then provide a context for examining variation in the conceptualization of ethnicity on an international scale. Further, the authors examine terminology and categories used by 11 countries where research participants resided. Each country uses a unique classification system. Thus, it can be expected that descriptions of the ethnic characteristics of international participants involved in research published in ASHA journal articles will widely vary.

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