scholarly journals Fungicide Rotation Programs for Managing Phytophthora Fruit Rot of Watermelon in Southeastern United States

2017 ◽  
Vol 18 (1) ◽  
pp. 28-34 ◽  
Author(s):  
Chandrasekar (Shaker) S. Kousik ◽  
Pingsheng Ji ◽  
Daniel S. Egel ◽  
Lina M. Quesada-Ocampo
Keyword(s):  
United States ◽  
South Carolina ◽  
Phytophthora Capsici ◽  
Southeastern United States ◽  
Heavy Rain ◽  
Integrated Approach ◽  
The United States ◽  
Fruit Rot ◽  
Management Options ◽  
Before And After

About 50% of the watermelons in the United States are produced in the southeastern states, where optimal conditions for development of Phytophthora fruit rot prevail. Phytophthora fruit rot significantly limits watermelon production by causing serious yield losses before and after fruit harvest. Efficacy of fungicide rotation programs and Melcast-scheduled sprays for managing Phytophthora fruit rot was determined by conducting experiments in Phytophthora capsici-infested fields at three locations in southeastern United States (North Carolina, South Carolina, and Georgia). The mini seedless cultivar Wonder and seeded cultivar Mickey Lee (pollenizer) were used. Five weekly applications of fungicides were made at all locations. Significant fruit rot (53 to 91%, mean 68%) was observed in the nontreated control plots in all three years (2013 to 2015) and across locations. All fungicide rotation programs significantly reduced Phytophthora fruit rot compared with nontreated controls. Overall, the rotation of Zampro alternated with Orondis was highly effective across three locations and two years. Rotations of Actigard followed by Ranman+Ridomil Gold, Presidio, V-10208, and Orondis, or rotation of Revus alternated with Presidio were similarly effective. Use of Melcast, a melon disease-forecasting tool, may occasionally enable savings of one spray application without significantly impacting control. Although many fungicides are available for use in rotations, under very heavy rain and pathogen pressure, the fungicides alone may not offer adequate protection; therefore, an integrated approach should be used with other management options including well-drained fields.

scholarly journals First Report of Insensitivity to Cyazofamid Among Isolates of Phytophthora capsici from the Southeastern United States

Plant Disease ◽  
2008 ◽  
Vol 92 (6) ◽  
pp. 979-979 ◽  
Author(s):  
C. S. Kousik ◽  
A. P. Keinath
Keyword(s):  
United States ◽  
South Carolina ◽  
Citrullus Lanatus ◽  
Phytophthora Capsici ◽  
Southeastern United States ◽  
Fruit Rot ◽  
Limiting Factor ◽  
Vegetable Production ◽  
Technical Grade ◽  
Lesion Diameter

Phytophthora capsici is rapidly becoming an important limiting factor in vegetable production in the southeastern United States, particularly on cucurbits as fruit rots. One of the strategies used to manage diseases caused by P. capsici is the regular application of fungicides. Recently the new fungicide cyazofamid (trade name Ranman, FRAC Group 21, FMC Corporation, EPA Reg. No. 71512-3-279) was registered for management of P. capsici on cucurbits. Cyazofamid has been reported to be very effective against P. capsici on peppers (1). In a recent evaluation, we observed that cyazofamid was not very effective on fruit rot of watermelon in a field artificially infested with P. capsici (3). Hence, we evaluated our collection of isolates for sensitivity to cyazofamid. We confirmed our isolates as P. capsici based on morphology of colonies and sporangia and amplification of internal transcribed spacer regions using specific PCR primers (4). Mycelial growth of 28 isolates from the southeastern United States including North (NC) and South Carolina (SC), Georgia (GA), and Florida (FL) was evaluated on Ranman amended (0, 25, 100, 310, 518, and 1,000 mg/liter of the active ingredient cyazofamid) V8 juice agar using similar techniques as described before (2). The EC50 (50% effective concentration) values ranged from 3.8 to 535 mg/liter. Thirteen isolates (8 GA, 3 SC, 1 NC, and 1 FL) had EC50 >100 mg/liter. Similar results were obtained when technical grade cyazofamid was used. The same 28 isolates were evaluated on media amended with technical grade cyazofamid (0, 1, 10, and 100 mg/liter) and 100 mg/liter of salicylhydroxaymic acid, which was added to inhibit the alternative oxidase enzyme. The EC50 values ranged from <1 to >100 mg/liter. Six isolates (5 GA and 1 NC) had EC50 >100 mg/liter. Three isolates, one sensitive and two insensitive, were used to inoculate cucumber (Cucumis sativus) fruits treated with commercial Ranman at 0, 10, 100, 300, and 1,000 mg/liter of cyazofamid plus the surfactant Silwett L-77 (0.52 ml/liter). Mycelial plugs (7-mm diameter) were placed on nonwounded fruits. Fruits were kept under high humidity at 25 ± 1°C in an incubator for 3 days. Two measurements of each lesion at right angles were averaged to get the lesion diameter. The EC50 value for lesion diameter on fruits varied from 13 mg/liter for the sensitive isolate to >233 mg/liter for the insensitive isolates. EC50 values for diameter of the lesion with sporulation ranged from 3 to 107 mg/liter. Relative lesion diameters of the insensitive isolates at 100 mg/liter treatment compared with nonsprayed check were 70 to 93%, and at 300 mg/liter, it was 38 to 80%. Similarly in another experiment, watermelon (Citrullus lanatus var. lanatus) fruits were sprayed with a recommended field rate of Ranman (284 mg of cyazofamid/liter) plus Silwett L-77 (0.52 ml/liter) till runoff and inoculated with four isolates. The relative lesion diameter for insensitive isolates on Ranman treated watermelon fruits were 76 to 100% of nonsprayed fruits. To our knowledge, these insensitive isolates were collected from fields that were never sprayed with Ranman. Because of the existence of cyazofamid insensitive P. capsici isolates, it should be rotated with fungicides from other chemical classes to prevent extensive selection of insensitive isolates. References: (1) K. L. Ivors et al. Plant Dis. Manage. Rep. 1:V088, 2007. (2) A. P. Keinath. Plant Dis. 91:743, 2007. (3) C. S. Kousik and R. Hassell. Plant Dis. Manage. Rep. 1:V010, 2007. (4) J. B. Ristaino et al. Appl. Environ. Microbiol. 64:948, 1998.

scholarly journals First Report of Resistance to Mefenoxam in Phytophthora cactorum in the United States and Elsewhere

Plant Disease ◽  
2004 ◽  
Vol 88 (5) ◽  
pp. 576-576 ◽  
Author(s):  
S. N. Jeffers ◽  
G. Schnabel ◽  
J. P. Smith
Keyword(s):  
United States ◽  
South Carolina ◽  
Tap Water ◽  
Southeastern United States ◽  
Crop Protection ◽  
The United States ◽  
Crown Rot ◽  
Phytophthora Cactorum ◽  
Mycelium Growth ◽  
First Report

Phytophthora cactorum causes crown rot of strawberry (Fragaria × ananassa) (2), a disease that has been particularly severe during the last 5 years in the southeastern United States. In the fall of 2001, strawberry plants (cv. Camarosa) in a field in Lexington County, South Carolina exhibited typical crown rot symptoms (2) 1 to 2 weeks after transplanting, even though plants had been drenched with mefenoxam (Ridomil Gold; Syngenta Crop Protection, Greensboro, NC) immediately after transplanting. Initially, we observed leaves that had marginal necrosis, were smaller than normal, and were discolored. Soon after, diseased plants appeared stunted and unthrifty compared with other plants in the field, and some of these plants eventually wilted and died. Severely affected plants had necrotic roots and decayed crowns. Ten symptomatic plants were collected for isolation. In the laboratory, root and crown tissues were rinsed in running tap water and blotted dry, small pieces of necrotic tissue were placed aseptically on PAR-V8 selective medium (1), and isolation plates were placed at 20°C in the dark for up to 7 days. P. cactorum was recovered from six plants. Isolates produced characteristic asexual and sexual structures directly on the isolation plates (i.e., papillate sporangia on sympodial sporangiophores and oospores with paragynous antheridia) (2). A single hypha of an isolate from each plant was transferred to fresh PAR-V8, and pure cultures were stored on cornmeal agar in glass vials at 15°C in the dark. All six isolates from the Lexington County field and nine other isolates of P. cactorum from strawberry (three from South Carolina, three from North Carolina, and three from Florida) were tested for sensitivity to mefenoxam on fungicide-amended medium. Mefenoxam was added to 10% clarified V8 juice agar (cV8A) after autoclaving so the concentration in the medium was 100 ppm. Agar plugs from active colonies were transferred to mefenoxam-amended and nonamended cV8A (three replicates per treatment), plates were placed at 25°C in the dark for 3 days, and linear mycelium growth was measured. All six isolates from Lexington County were highly resistant to mefenoxam with mycelium growth relatively unrestricted on mefenoxam-amended medium (73 to 89% of that on nonamended medium). In comparison, the other nine isolates were sensitive to mefenoxam with mycelium growth severely restricted by 100 ppm of mefenoxam (0 to 7% of that on nonamended medium). To our knowledge, this is the first report of mefenoxam resistance in P. cactorum on strawberry or any other crop in the United States and elsewhere. Because mefenoxam is the primary fungicide used to manage Phytophthora crown rot in the southeastern United States, resistance may limit use of this fungicide in strawberry production. References: (1) A. J. Ferguson and S. N. Jeffers. Plant Dis. 83:1129, 1999. (2) E. Seemüller. Crown rot. Pages 50–51 in: Compendium of Strawberry Diseases, 2nd ed. J. L. Maas, ed. The American Phytopathological Society, St. Paul, MN, 1998.

Copper tolerance in Xanthomonas arboricola pv. pruni in South Carolina peach orchards

Plant Disease ◽  
2021 ◽  
Author(s):  
Brodie Cox ◽  
Hehe Wang ◽  
Guido Schnabel
Keyword(s):  
United States ◽  
South Carolina ◽  
Management Practices ◽  
Southeastern United States ◽  
The United States ◽  
Copper Tolerance ◽  
Bacterial Spot ◽  
Organic Farm ◽  
Xanthomonas Arboricola ◽  
Tolerance To Copper

Bacterial spot of peach, caused by Xanthomonas arboricola pv. pruni (Xap), causes yield loss every year in southeastern United States peach orchards. Management is mainly driven by season-long applications of copper-based products, site location, and choice of cultivar. Although tolerance to copper has not been reported in Xap in the United States, adaptation of populations due to frequent use is a concern. We collected Xap from shoot cankers, leaves, and fruit of cv. O'Henry over two years from three conventional farms and one organic farm in South Carolina, one orchard per farm. The four farms had been using copper extensively for years to control bacterial spot. Xap was isolated from four canker types (bud canker, tip canker, non-concentric canker, and concentric canker) in early spring (‘bud break’), as well as from leaf and fruit tissues later in the season at phenological stages ‘pit hardening’ and ‘final swell’. Xap was most frequently isolated from cankers of the organic farm (24% of the cankers) and most isolates (45%) came from bud cankers. Xap isolates were assessed for sensitivity to copper using minimal glucose yeast agar and nutrient agar amended with 38 µg/ml or 51 µg/ml of Cu2+. Two phenotypes of copper-tolerance in Xap were discovered: low copper tolerance (LCT: growth up to 38 µg/ml Cu2+) and high copper tolerance (HCT: growth up to 51 µg/ml Cu2+). A total of 26 (23 LCT and 3 HCT) out of 165 isolates in 2018 and 32 (20 LCT and 12 HCT) out of 133 isolates in 2019 were tolerant to copper. Peach leaves on potted trees were sprayed with copper rates typically applied at ‘delayed dormancy’ (high rate; 2,397 µg/ml Cu2+), at ‘shuck split’ (medium rate; 599 µg/ml Cu2+), and during ‘summer cover sprays’ (low rate; 120 µg/ml Cu2+) and subsequently inoculated with sensitive, LCT and HCT strains. Results indicated that the low and medium rates of copper reduced bacterial spot incidence caused by the sensitive strain but not by the LCT and HCT strains. This study confirms existence of Xap tolerance to copper in commercial peach orchards in the southeastern United States and suggests its contribution to bacterial spot development under current management practices.

scholarly journals First Report of Colletotrichum scovillei Causing Anthracnose Fruit Rot on Pepper in South Carolina, United States

Plant Disease ◽  
2020 ◽  
Author(s):  
Sean M Toporek ◽  
Anthony P. Keinath
Keyword(s):  
United States ◽  
South Carolina ◽  
Average Length ◽  
The United States ◽  
Fruit Rot ◽  
Lesion Length ◽  
Pathogenicity Test ◽  
Conidial Suspension ◽  
Accession Number ◽  
First Report

Anthracnose fruit rot caused by various Colletotrichum spp. is a serious disease for pepper (Capsicum annuum) growers, resulting in extensive fruit loss (Harp et al. 2008). Samples of five pepper fruits were obtained from two commercial farms in Lexington and Pickens counties, South Carolina, in August and September 2019, respectively. All fruits had two or more soft, sunken lesions covered with salmon-colored spore masses. Pieces of diseased tissue cut from the margins of lesions were surface disinfested in 0.6% sodium hypochlorite, rinsed in sterile deionized water, blotted dry, and placed on one-quarter-strength potato dextrose agar (PDA/4) amended with 100 mg chloramphenicol, 100 mg streptomycin sulfate, and 60.5 mg mefenoxam (0.25 ml Ridomil Gold EC) per liter. Two isolates of Colletotrichum sp. per fruit were preserved on dried filter paper and stored at 10º C. One additional isolate of Colletotrichum sp. had been collected from a jalapeño pepper fruit on a farm in Charleston County, South Carolina, in 1997. Colony morphology of three isolates, one per county, on Spezieller Nährstoffarmer Agar (SNA) was pale grey with a faint orange tint. All isolates readily produced conidia on SNA with an average length of 16.4 μm (std. dev. = 1.8 μm) and a width of 2.2 μm (std. dev. = 0.2 μm). Conidia were hyaline, smooth, straight, aseptate, cylindrical to fusiform with one or both ends slightly acute or round, matching the description of C. scovillei (Damm et al. 2012). The glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and beta-tubulin (TUB2) genes from three isolates were amplified and sequenced with the primer pairs GDF1/GDR1 and T1/Bt2b, respectively. Species within the C. acutatum clade can be readily distinguished with GAPDH or TUB2 (Cannon et al. 2012). The GAPDH and TUB2 sequences for all three isolates were 100% similar to each other and strain CBS 126529 (GAPDH accession number JQ948597; TUB2 accession number JQ949918) of C. scovillei (Damm et al. 2012). GAPDH and TUB2 sequences for each isolate were deposited in GenBank under the accessions MT826948–MT826950 and MT826951-MT826953, respectively. A pathogenicity test was conducted on jalapeño pepper fruits by placing a 10-ul droplet of a 5 x 105 conidial suspension of each isolate onto a wound made with a sterile toothpick. Control peppers were mock inoculated with 10 ul sterile distilled water. A humid chamber was prepared by placing moist paper towels on the bottom of a sealed crisper box. Inoculated peppers were placed on upside-down 60 ml plastic condiment cups. Three replicate boxes each containing all four treatments were prepared. The experiment was repeated once. After 7 days in the humid chamber at 26ºC, disease did not develop on control fruits, whereas soft, sunken lesions covered with salmon-colored spores developed on inoculated fruits. Lesions were measured and C. scovillei was re-isolated onto amended PDA/4 as previously described. Lesion length averaged 15.6 mm (std dev. = 4.1 mm) by 11.5 mm (std dev. = 2.0 mm). Colletotrichum sp. resembling the original isolate were recovered from all inoculated fruit, but not from non-inoculated fruit. C. scovillei has been reported in Brazil in South America and in China, Indonesia, Japan, Malaysia, South Korea, Taiwan, and Thailand in Asia (Farr and Rossman 2020). This is the first report of C. scovillei as the casual organism of anthracnose fruit rot on pepper in South Carolina and the United States.

scholarly journals Development of Pre- and Postharvest Phytophthora Fruit Rot on Watermelons Treated with Fungicides in the Field

2014 ◽  
Vol 15 (3) ◽  
pp. 145-150 ◽  
Author(s):  
Chandrasekar S. Kousik ◽  
Jennifer L. Ikerd ◽  
Howard F. Harrison
Keyword(s):  
United States ◽  
Management Strategy ◽  
Phytophthora Capsici ◽  
Southeastern United States ◽  
Fruit Rot ◽  
Copper Hydroxide ◽  
The Past ◽  
Potassium Phosphite ◽  
Infested Field ◽  
Serious Disease

Fruit rot, caused by Phytophthora capsici, is a serious disease in most watermelon producing regions in the southeastern United States and has caused devastating losses over the past few years. Experiments were conducted from 2010 to 2013 in a P. capsici-infested field to identify fungicides effective for managing pre- and postharvest development of Phytophthora fruit rot. Weekly treatments of OXTP (Oxathiapiprolin), V-10208 (ethaboxam), Zampro (ametoctradin+dimethomorph), Forum (dimethomorph), Prophyt (potassium phosphite) + Kocide 2000 (copper hydroxide), Revus (mandipropamid) rotated with Prophyt + Kocide, and rotations of Revus with Presidio (fluopicolide) and Actigard with Revus significantly reduced preharvest fruit rot in the field compared to nontreated control. Symptomless fruit harvested four days after the last spray was inoculated with P. capsici and maintained in a humid chamber to evaluate postharvest fruit rot development. OXTP, Zampro, Forum, V-10208, Presidio rotated with Revus, and Actigard rotated with Revus applied in the field provided extended postharvest protection compared to nontreated control. Many of these fungicides belonging to different FRAC group should be used in rotations to manage Phytophthora fruit rot of watermelon and should be part of an overall management strategy that also includes use of well drained fields and proper irrigation practices. Accepted 25 August 2014. 29 September 2014.

scholarly journals Sensitivity of Isolates of Phytophthora capsici from the Eastern United States to Fluopicolide

Plant Disease ◽  
2011 ◽  
Vol 95 (11) ◽  
pp. 1414-1419 ◽  
Author(s):  
Anthony P. Keinath ◽  
Chandrasekar S. Kousik
Keyword(s):  
United States ◽  
North Carolina ◽  
South Carolina ◽  
Mycelial Growth ◽  
Phytophthora Capsici ◽  
The United States ◽  
Eastern United States ◽  
Baseline Sensitivity ◽  
First Report ◽  
Zoospore Production

Fluopicolide, a pyridinylmethyl-benzamide fungicide, was registered in the United States in 2008 to control diseases caused by Oomycete pathogens, such as Phytophthora capsici, on cucurbit and solanaceous vegetables. The main objective of this study was to determine baseline sensitivity to fluopicolide in isolates of P. capsici from the southeastern and midwestern United States. A total of 69 isolates from Florida (14 isolates), Georgia (14 isolates), Michigan (24 isolates), North Carolina (3 isolates), and South Carolina (17 isolates) that had not been previously exposed to fluopicolide were grown on fungicide-amended medium to determine sensitivity of mycelia, sporangia, and zoospores to the fungicide. All isolates of P. capsici tested (range of 54 to 69 isolates per assay) were sensitive to fluopicolide in all four assays. The median EC50 fluopicolide concentration was 0.22, 2.08, 0.048, and 0.10 mg/liter in the mycelial growth, zoospore germination, sporangia production, and zoospore production assays, respectively. For mycelial growth and zoospore germination, isolates from Michigan had a higher mean EC50 value than isolates from the four southeastern states. This is the first report of variation in baseline sensitivity to a fungicide by P. capsici isolates from different regions of the United States. In the sporangia production and zoospore production assays, isolates from different states did not differ in sensitivity. Single rates of fluopicolide were tested with additional isolates to validate discriminatory rates for monitoring sensitivity. A concentration of 0.3 or 1.0 mg/liter is recommended for mycelial growth, and 0.1 mg/liter is recommended for sporangia and zoospore production.

scholarly journals Emergence of Groundnut ringspot virus and Tomato chlorotic spot virus in Vegetables in Florida and the Southeastern United States

2015 ◽  
Vol 105 (3) ◽  
pp. 388-398 ◽  
Author(s):  
Craig G. Webster ◽  
Galen Frantz ◽  
Stuart R. Reitz ◽  
Joseph E. Funderburk ◽  
H. Charles Mellinger ◽  
...  
Keyword(s):  
United States ◽  
New York ◽  
South Carolina ◽  
Southeastern United States ◽  
The United States ◽  
South Florida ◽  
Ringspot Virus ◽  
Spot Virus ◽  
Genomic Rnas ◽  
Chlorotic Spot

Groundnut ringspot virus (GRSV) and Tomato chlorotic spot virus (TCSV) are two emerging tospoviruses in Florida. In a survey of the southeastern United States, GRSV and TCSV were frequently detected in solanaceous crops and weeds with tospovirus-like symptoms in south Florida, and occurred sympatrically with Tomato spotted wilt virus (TSWV) in tomato and pepper in south Florida. TSWV was the only tospovirus detected in other survey locations, with the exceptions of GRSV from tomato (Solanum lycopersicum) in South Carolina and New York, both of which are first reports. Impatiens (Impatiens walleriana) and lettuce (Lactuca sativa) were the only non-solanaceous GRSV and/or TCSV hosts identified in experimental host range studies. Little genetic diversity was observed in GRSV and TCSV sequences, likely due to the recent introductions of both viruses. All GRSV isolates characterized were reassortants with the TCSV M RNA. In laboratory transmission studies, Frankliniella schultzei was a more efficient vector of GRSV than F. occidentalis. TCSV was acquired more efficiently than GRSV by F. occidentalis but upon acquisition, transmission frequencies were similar. Further spread of GRSV and TCSV in the United States is possible and detection of mixed infections highlights the opportunity for additional reassortment of tospovirus genomic RNAs.

scholarly journals Development of Phytophthora Fruit Rot Caused by Phytophthora capsici on Resistant and Susceptible Watermelon Fruit of Different Ages

Plant Disease ◽  
2018 ◽  
Vol 102 (2) ◽  
pp. 370-374 ◽  
Author(s):  
Chandrasekar S. Kousik ◽  
Jennifer L. Ikerd ◽  
William W. Turechek
Keyword(s):  
South Carolina ◽  
Phytophthora Capsici ◽  
The United States ◽  
Fruit Rot ◽  
Breeding Programs ◽  
Lesion Diameter ◽  
Agar Plug ◽  
Resistant Lines ◽  
Different Ages ◽  
Serious Disease

Watermelon is an important crop grown in 44 states in the United States. Phytophthora fruit rot caused by Phytophthora capsici is a serious disease in the southeastern U.S.A., where over 50% of the watermelons are produced. The disease has resulted in severe losses to watermelon growers, especially in Georgia, South Carolina, and North Carolina during the past few years. Several fruit rot-resistant watermelon germplasm lines have been developed for use in breeding programs. To evaluate the development of Phytophthora fruit rot on fruit of different ages, plants of fruit rot-resistant and susceptible lines were planted at weekly intervals for five consecutive weeks in experiments conducted over three years (2011 to 2013). Flowers were routinely inspected and hand pollinated to ensure having fruit of different ages. In each year, different aged fruit were harvested on the same day and inoculated with a 5-mm agar plug from an actively growing colony of P. capsici. Inoculated fruit were maintained in a room set to conditions conducive for disease development (>95% relative humidity, 26 ± 2°C). After 5 days, lesion diameter and intensity of sporulation was recorded for each fruit. Lesion diameter and sporulation intensity were significantly greater on fruit of susceptible lines compared with resistant lines. Fruit age did not have an effect on either measurement on susceptible (Sugar Baby) or resistant lines (PI 560020 and PI 595203). Our results showed that resistance to Phytophthora fruit rot in watermelon was not correlated with fruit age.

Broad Resistance to Post-Harvest Fruit Rot in USVL Watermelon Germplasm Lines to isolates of Phytophthora capsici from across USA

Plant Disease ◽  
2021 ◽  
Author(s):  
Chandrasekar S Kousik ◽  
Jennifer Lauren Ikerd ◽  
William Wechter ◽  
Sandra Branham ◽  
William W Turechek
Keyword(s):  
South Carolina ◽  
United States Of America ◽  
Phytophthora Capsici ◽  
The United States ◽  
Fruit Rot ◽  
Vegetable Crop ◽  
Mature Fruit ◽  
Breeding Programs ◽  
The Past ◽  
Resistant Lines

Watermelon is an important cucurbit vegetable crop grown in most states in the United States of America (USA). Phytophthora fruit rot of watermelon caused by Phytophthora capsici has been a major factor, limiting production for the past 15 years in the southeastern USA. USDA-ARS released five Phytophthora fruit rot-resistant germplasm lines for use in breeding programs. These lines were developed by phenotyping using a local isolate of P. capsici from South Carolina. The present study was undertaken to determine if these resistant lines had broad resistance to diverse P. capsici isolates collected from different states and crops. Five resistant germplasm lines (USVL020-PFR, USVL203-PFR, USVL782-PFR, USVL489-PFR and USVL531-MDR) and two susceptible cultivars Sugar Baby and Mickey Lee used as checks were grown in a field in 2014 and 2015 to produce fruit for evaluation. Mature fruit were harvested and placed in a walk-in growth chamber and inoculated with 20 different P. capsici isolates. The chamber was maintained at 26±2°C and high relative humidity (>95%) using a humidifier. All five resistant germplasm lines were significantly more resistant than the two susceptible checks to all 20 P. capsici isolates. Among the five resistant germplasm lines, USVL020-PFR, USVL782-PFR and USVL531-MDR had broad resistance. Some P. capsici isolates induced minor lesions and rot on USVL489-PFR compared to the other resistant lines. Variation in virulence and genetic diversity among the 20 P. capsici isolates was also observed. The five watermelon germplasm lines will be useful for developing commercial watermelon cultivars with broad resistance to P. capsici.

scholarly journals Diversity Among Ralstonia solanacearum Strains Isolated from the Southeastern United States

2012 ◽  
Vol 102 (10) ◽  
pp. 924-936 ◽  
Author(s):  
Jason C. Hong ◽  
David J. Norman ◽  
David L. Reed ◽  
M. Timur Momol ◽  
Jeffrey B. Jones
Keyword(s):  
United States ◽  
South Carolina ◽  
Ralstonia Solanacearum ◽  
Phylogenetic Analyses ◽  
Southeastern United States ◽  
The United States ◽  
Hypersensitive Reaction ◽  
Systemic Movement ◽  
Solanacearum Strain ◽  
Unique Banding Pattern

This is the first comprehensive study of a collection of Ralstonia solanacearum strains from the southeastern United States to be characterized based on biovar, pathogenicity, hypersensitive reaction on tobacco, and phylogenetic analyses of the egl sequence. Rigorous phylogenetic analysis of the commonly used egl gene produced robust phylogenies that differed significantly from a neighbor-joining tree differed from and previously published phylogenies for R. solanacearum strains. These robust trees placed phylotype IV within the phylotype I clade, which may suggest that phylogenies based solely on egl may be misleading. As a result of phylogenetic analyses in this study, we determined that U.S. strains from Georgia, North Carolina, South Carolina, and older Florida strains isolated from solanaceous crops all belong to phylotype II sequevar 7. However, many strains recently isolated in Florida from tomato and other crops were more diverse than the southeastern United States population. These unique Florida strains grouped with strains mostly originating from the Caribbean and Central America. One of the exotic strains, which in a previous study was determined to be established in northern Florida, was characterized more extensively. Upon using Musa-specific multiplex polymerase chain reaction, this strain produced a unique banding pattern, which has not previously been reported. Inoculation of this strain into Musa spp. did not result in wilt symptoms; however, the plants were stunted and root masses were significantly reduced. Furthermore, following root inoculation, the bacterium, unlike a typical Florida race 1 biovar 1 strain, was recovered from the roots and stems, indicating systemic movement. This is the first report of an R. solanacearum strain isolated in the United States that is deleterious to the growth of Musa plants.

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