Outbreak of Cucurbit Powdery Mildew on Watermelon Fruit Caused by Podosphaera xanthii in Southwest Florida

Cucurbit powdery mildew caused by the obligate parasite Podosphaera xanthii occurs commonly on foliage, petioles, and stems of most cucurbit crops grown in the United States. (3). However, in the field, fruit infection on cucurbits including watermelon (Citrullus lanatus), is rarely, if ever, observed (2). Consequently, it was atypical when severe powdery mildew-like symptoms were observed on seedless and seeded watermelon fruit on several commercial farms in southwestern Florida during November and December 2010. Severe powdery mildew was also observed on ‘Tri-X 313’ and ‘Mickey Lee’ fruit grown at SWFREC, Immokalee, FL. Infected fruit developed poorly and were not marketable. Powdery mildew symptoms were mainly observed on young immature fruit, but not on mature older fruit. Abundant powdery mildew conidia occurred on fruit surface, but not on the leaves. Conidia were produced in chains and averaged 35 × 21 μm. Observation of conidia in 3% KOH indicated the presence of fibrosin bodies commonly found in the cucurbit powdery mildew genus Podosphaera (3). Orange-to-dark brown chasmothecia (formerly cleisthothecia) containing a single ascus were detected on the surface of some fruit samples. Conidial DNA was subjected to PCR using specific primers designed to amplify the internal transcribed spacer (ITS) region of Podosphaera (4). The resulting amplicons were sequenced and found to be 100% identical to the ITS sequences of P. xanthii in the NCBI database (D84387, EU367960, AY450961, AB040322, AB040315). Sequences from the watermelon fruit isolate were also identical to several P. fusca (synonym P. xanthii), P. phaseoli (GQ927253), and P. balsaminae (AB462803) sequences. On the basis of morphological characteristics and ITS sequence analysis, the pathogen infecting watermelon fruit can be considered as P. xanthii (1,3,4). The powdery mildew isolate from watermelon fruit was maintained on cotyledons of squash (Cucurbita pepo, ‘Early Prolific Straight Neck’). Cotyledons and leaves of five plants each of various cucurbits and beans were inoculated with 10 μl of a conidial suspension (105conidia/ml) in water (0.02% Tween 20). Two weeks after inoculation, abundant conidia were observed on cucumber (Cucumis sativus, ‘SMR-58’) and melon (Cucumis melo) powdery mildew race differentials ‘Iran H’ and ‘Vedrantais’. However, no growth was observed on melon differentials ‘PI 414723’, ‘Edisto 47’, ‘PMR 5’, ‘PMR 45’, ‘MR 1’, and ‘WMR 29’ (2,3). The powdery mildew isolate from watermelon fruit behaved as melon race 1 (3). Mycelium and conidia were also observed on fruit surface of watermelon ‘Sugar Baby’ and a susceptible U.S. plant introduction (PI 538888) 3 weeks after inoculation. However, the disease was not as severe as what was observed in the fields in fall 2010. The pathogen did not grow on plants of Impatiens balsamina or on select bean (Phaseolus vulgaris) cultivars (‘Red Kidney’, ‘Kentucky Blue’, and ‘Derby Bush’), but did grow and produce abundant conidia on ‘Pinto bush bean’. Powdery mildew on watermelon fruit in production fields can be considered as a potentially new and serious threat requiring further studies to develop management strategies. References: (1) U. Braun and S. Takamatsu. Schlechtendalia 4:1, 2000. (2) A. R. Davis et al. J. Am. Soc. Hortic. Sci. 132:790, 2007. (3) M. T. McGrath and C. E. Thomas. In: Compendium of Cucurbit Diseases. American Phytopathological Society, St. Paul, MN, 1996. (4) S. Takamatsu and Y. Kano. Mycoscience 42:135, 2001.

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First Report of Powdery Mildew Caused by Oidium neolycopersici on Tomato in China

Plant Disease ◽

10.1094/pdis-92-9-1370c ◽

2008 ◽

Vol 92 (9) ◽

pp. 1370-1370 ◽

Cited By ~ 3

Author(s):

C. W. Li ◽

D. L. Pei ◽

W. J. Wang ◽

Y. S. Ma ◽

L. Wang ◽

...

Keyword(s):

Powdery Mildew ◽

Average Length ◽

Pathogenic Fungus ◽

Fruit Size ◽

Morphological Characteristics ◽

Conidial Suspension ◽

Oidium Neolycopersici ◽

First Report ◽

Its Sequence Analysis ◽

Tomato Powdery Mildew

Tomato powdery mildew can cause remarkable reduction in fruit size and quality (4). In March of 2008, powdery mildew appeared as circular, white colonies on leaves, petioles, and stems of tomato plants grown in greenhouses in Shangqiu, Henan Province, China. The pathogenic fungus had unbranched conidiophores with an average length of 58.4 μm and width of 5.1 μm. Conidia were hyaline, elliptical, and were borne singly. Average length and width of conidia were 30.6 and 15.1 μm, respectively. Germ tubes were straight and formed at the ends or very close to the ends of conidia. Chasmothecium was not found in the collected samples. Different tomato cultivars and species, including Lycopersicon esculentum Mill (cvs. Moneymaker, Micro-Tom, Zaofen, Fenguo, and Zhongza series), L. peruvianum cv. LA2172, and L. hirsutum cv. G1.1560, were inoculated with a conidial suspension with a concentration of 5 × 104 conidia/ml. Plants developed powdery mildew symptoms as early as 4 days after inoculation. Susceptible symptoms developed on all L. esculentum cultivars, while L. peruvianum LA2172 and L. hirsutum G1.1560 displayed complete resistance, which is similar to the results of Bai et al 2004 (1) and Lindhout and Pet 1990 (3). Morphological characteristics of the pathogen on susceptible genotypes were similar to those from naturally infected plants. On the basis of the characteristics of the asexual stage, the pathogen was identified as an isolate of Oidium neolycopersici L. Kiss, which was confirmed by internal transcribed spacer (ITS) sequence analysis. PCR amplification and sequencing of the ITS region were performed with primers ITS1 and ITS4. The nucleotide sequence was assigned GenBank Accession No. EU486992, which had a 100% homology with 10 ITS sequences of O. neolycopersici in GenBank (Accession Nos. EU047559 to 047568) (2). In Asia, the spread of this pathogen has been recently reported in Japan (2). To our knowledge, this is the first report of tomato powdery mildew in China. Voucher specimens are available at the Specimen Center in the Department of Life Science, Shangqiu Normal University. References: (1) Y. Bai et al. Mol. Plant-Microbe. Interact. 18:354, 2005. (2) T. Jankovics et al. Phytopathology 98:529, 2008. (3) P. Lindhout and G. Pet. Tomato Gen. Coop. Rep. 40:19, 1990. (4) J. M. Whipps et al. Plant Pathol. 47:36, 1998.

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First Report of the Cucurbit Powdery Mildew Fungus (Podosphaera xanthii) Resistant to Strobilurin Fungicides in the United States

Plant Disease ◽

10.1094/pdis.2003.87.8.1007a ◽

2003 ◽

Vol 87 (8) ◽

pp. 1007-1007 ◽

Cited By ~ 18

Author(s):

M. T. McGrath ◽

N. Shishkoff

Keyword(s):

United States ◽

New York ◽

Powdery Mildew ◽

The United States ◽

Podosphaera Xanthii ◽

Commercial Use ◽

Strobilurin Fungicides ◽

Research Fields ◽

Cucurbit Powdery Mildew ◽

Dmi Resistance

Resistance to strobilurin fungicides was documented in isolates collected from three fungicide efficacy experiments conducted in research fields in Georgia (GA), North Carolina (NC), and New York (NY). In these fields in 2002, strobilurins (fungicide group 11, quinone outside inhibitors [QoI]) when used alone on a 7-day schedule (use pattern not labeled) did not effectively control cucurbit powdery mildew. Strobilurin efficacy declined dramatically after the second application in New York (3). Efficacy also was reduced in commercial fields in Kentucky and research fields in Arizona, California, Kentucky, Illinois, Michigan, and Virginia in 2002 where strobilurins were used predominantly or exclusively. Isolates were collected on 22 July and 8 and 17 October after the last of four, five, and five applications of strobilurin (trifloxystrobin formulated as Flint or azoxystrobin formulated as Quadris) in experiments conducted by J. D. Moore in Chula, GA, M. McGrath in Riverhead, NY, and G. J. Holmes in Clayton, NC, respectively. A leaf-disk bioassay was used to determine fungicide sensitivity (2). Strobilurin sensitivity was determined using trifloxystrobin at 0, 0.5, 5, 50, and 100 μg/ml. Four of nine NY isolates, 19 of 21 GA isolates, and 13 of 15 NC isolates were resistant to strobilurins (grew well on disks treated with trifloxystrobin at 100 μg/ml). The geometric mean of the azoxystrobin baseline was 0.258 μg/ml for Podosphaera xanthii isolates collected in 1998 and 1999 in North America (4). Poor control with strobilurins under field conditions was associated with reduced sensitivity in vitro. Strobilurin sensitivity appeared to be qualitative as reported elsewhere (1). Two sensitive and three resistant isolates responded similarly when tested in another laboratory using kresoxim-methyl and pyraclostrobin (H. Ypema, personal communication). These findings and experiences elsewhere with QoI-resistant P. xanthii indicate that cross-resistance probably extends among multiple QoI's (1). Strobilurins have been available for commercial use in the United States since 1998, when azoxystrobin received Section 18 registration in some states. Federal registration was granted in March 1999. Strobilurin resistance was detected after 2 years of commercial use elsewhere in the world (1). All isolates tested in the current study were from research fields where selection pressure for resistance could have been higher than in commercial fields where strobilurins are used with demethylation inhibitors (DMIs; fungicide group 3) and contact fungicides in alternation or tank mixtures to prevent or delay resistance development. Resistance in commercial fields will reduce the utility of strobilurins, including those not yet registered, and eliminate an important tool for managing DMI resistance. Strobilurins and DMIs are the only systemic fungicides registered for cucurbit powdery mildew in the United States. Managing DMI resistance may be challenged by multiresistant strains. Strobilurin-resistant isolates also exhibited reduced sensitivity to DMIs, tolerating triadimefon at 50 to 100 μg/ml (2). One suggestion to improve resistance management is to apply a contact fungicide with strobilurins as well as DMIs. References: (1) H. Ishii et al. Phytopathology 91:1166, 2001. (2) M. T. McGrath et al. Plant Dis. 80:697, 1996. (3) M. T. McGrath and N. Shishkoff. Fungic. Nematic. Tests. (In press). (4) G. Olaya et al. Phytopathology (Abstr.) 90 (suppl):S57, 2000.

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Transformation of the cucurbit powdery mildew pathogen Podosphaera xanthii by Agrobacterium tumefaciens

New Phytologist ◽

10.1111/nph.14297 ◽

2016 ◽

Vol 213 (4) ◽

pp. 1961-1973 ◽

Cited By ~ 18

Author(s):

Jesús Martínez‐Cruz ◽

Diego Romero ◽

Antonio Vicente ◽

Alejandro Pérez‐García

Keyword(s):

Agrobacterium Tumefaciens ◽

Powdery Mildew ◽

Podosphaera Xanthii ◽

Powdery Mildew Pathogen ◽

Cucurbit Powdery Mildew

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First Report of Powdery Mildew, Caused by Erysiphe cichoracearum, on Coneflowers

Plant Disease ◽

10.1094/pdis.1999.83.7.694b ◽

1999 ◽

Vol 83 (7) ◽

pp. 694-694 ◽

Cited By ~ 2

Author(s):

P. L. Sholberg ◽

J. H. Ginns ◽

T. S. C. Li

Keyword(s):

Powdery Mildew ◽

Ornamental Plants ◽

Echinacea Purpurea ◽

The United States ◽

Plant Diseases ◽

Conidial Suspension ◽

Decay Fungi ◽

Erysiphe Cichoracearum ◽

Epidermal Surface ◽

Medicinal Properties

Purple coneflowers (Echinacea purpurea) are grown in North America and Europe for their medicinal properties and as ornamental plants. In September 1997 and again in 1998, a previously undescribed disease was noticed on fully grown coneflower plants in Summerland and Oliver, British Columbia. Mycelia were observed on stems, foliage, and flowers, and distinct dark red to black, round (approximately 5 mm in diameter) lesions were observed on the flower petals. The disease appeared similar to powdery mildews that have been reported on numerous genera of the Asteraceae. Samples of the diseased tissue were examined and the salient features of the fungus on two specimens were determined: cleistothecia infrequent, subglobose or flattened on the side next to the leaf surface, 121 to 209 μm in diameter; epidermal (surface) cells 20 μm in diameter; appendages hyphoid, 5 μm in diameter, up to 200 μm long; asci, 10 to 19 in each cleistothecium, broadly ellipsoid, 47 to 85 × 28 to 37 μm with a short stalk, about 8 to 13 μm long and 8 μm in diameter; ascospores, immature, two per ascus, ellipsoid to broadly ellipsoid, 17 to 25 × 11 to 13 μm, thin walled, hyaline, and smooth; conidia oblong with sides slightly convex and apices truncate, 27 to 40 × 14 to 20 μm, walls hyaline, thin, smooth. Based on the occurrence of asci that contained two ascospores and the hyphoid appendages on the cleistothecia we concluded that the fungus was Erysiphe cichoracearum DC. Damage due to this disease was minimal in 1997 and 1998 because it developed very late in the growing season and occurred sporadically within the plantings. In order to complete Koch's postulates, Echinacea purpurea plants grown in the greenhouse were inoculated with a conidial suspension (105 to 106 conidia per ml) from field-infected plants. Powdery mildew first appeared 3 months later, eventually infecting leaves and stems of 12 of 49 inoculated plants. It was distinctly white and in discrete patches on leaves, compared with coalescing dark brown areas on the stems. Microscopic examination of the conidia confirmed that they were E. cichoracearum. Although powdery mildew caused by E. cichoracearum has been widely reported on lettuce, safflower, and other cultivated and wild Compositae, we found no reference to it on Echinacea spp. in Canada (1,2), the U.S. (3), or elsewhere in the world (4). The specimens have been deposited in the National Mycological Herbarium of Canada (DAOM) with accession numbers 225933 and 225934 for Oliver and Summerland, B.C., respectively. References: (1) U. Braun. Beih. Nova Hedwigia 89:1, 1987. (2) I. L. Conners. 1967. An annotated index of plant diseases in Canada and fungi recorded on plants in Alaska, Canada, and Greenland. Canada Dept. of Agric. Pub. 1251. (3) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN. (4) J. Ginns. 1986. Compendium of plant disease and decay fungi in Canada, 1960-1980. Agriculture Canada Pub. 1813.

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First Report of Anthracnose of Onion Caused by Colletotrichum coccodes in Ohio

Plant Disease ◽

10.1094/pdis-01-14-0032-pdn ◽

2014 ◽

Vol 98 (9) ◽

pp. 1271-1271 ◽

Cited By ~ 2

Author(s):

F. Baysal-Gurel ◽

N. Subedi ◽

D. P. Mamiro ◽

S. A. Miller

Keyword(s):

Leaf Tissue ◽

Its Region ◽

The United States ◽

Tween 20 ◽

Colletotrichum Coccodes ◽

Academic Press ◽

Conidial Suspension ◽

First Report ◽

Allium Cepa L ◽

Total Dna

Dry bulb onion (Allium cepa L. cvs. Pulsar, Bradley, and Livingston) plants with symptoms of anthracnose were observed in three commercial fields totaling 76.5 ha in Huron Co., Ohio, in July 2013. Symptoms were oval leaf lesions and yellowing, curling, twisting, chlorosis, and death of leaves. Nearly half of the plants in a 32.8-ha field of the cv. Pulsar were symptomatic. Concentric rings of acervuli with salmon-colored conidial masses were observed in the lesions. Conidia were straight with tapered ends and 16 to 23 × 3 to 6 μm (2). Colletotrichum coccodes (Wallr.) S. Hughes was regularly isolated from infected plants (2). Culturing diseased leaf tissue on potato dextrose agar (PDA) amended with 30 ppm rifampicin and 100 ppm ampicillin at room temperature yielded white aerial mycelia and salmon-colored conidial masses in acervuli. Numerous spherical, black microsclerotia were produced on the surface of colonies after 10 to 14 days. To confirm pathogen identity, total DNA was extracted directly from a 7-day-old culture of isolate SAM30-13 grown on PDA, using the Wizard SV Genomic DNA Purification System (Promega, Madison, WI) following the manufacturer's instructions. The ribosomal DNA internal transcribed spacer (ITS) region was amplified by PCR using the primer pair ITS1 and ITS4 (2), and sequenced. The sequence, deposited in GenBank (KF894404), was 99% identical to that of a C. coccodes isolate from Michigan (JQ682644) (1). Ten onion seedlings cv. Ebenezer White at the two- to three-leaf stage of growth were spray-inoculated with a conidial suspension (1 × 105 conidia/ml containing 0.01% Tween 20, with 10 ml applied/plant). Plants were maintained in a greenhouse (21 to 23°C) until symptoms appeared. Control plants were sprayed with sterilized water containing 0.01% Tween 20, and maintained in the same environment. After 30 days, sunken, oval lesions each with a salmon-colored center developed on the inoculated plants, and microscopic examination revealed the same pathogen morphology as the original isolates. C. coccodes was re-isolated consistently from leaf lesions. All non-inoculated control plants remained disease-free, and C. coccodes was not re-isolated from leaves of control plants. C. coccodes was reported infecting onions in the United States for the first time in Michigan in 2012 (1). This is the first report of anthracnose of onion caused by C. coccodes in Ohio. Unusually wet, warm conditions in Ohio in 2013 likely contributed to the outbreak of this disease. Timely fungicide applications will be necessary to manage this disease in affected areas. References: (1) A. K. Lees and A. J. Hilton. Plant Pathol. 52:3. 2003. (2) L. M. Rodriguez-Salamanca et al. Plant Dis. 96:769. 2012. (3) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA, 1990.

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First Report of Podosphaera xanthii Causing Powdery Mildew on Zinnia elegans in Taiwan

Plant Disease ◽

10.1094/pdis-06-20-1263-pdn ◽

2020 ◽

Author(s):

Yi-Ting Xiao ◽

Yuan-Min Shen ◽

Chao-Jen Wang ◽

Tung-Ching Huang

Keyword(s):

Powdery Mildew ◽

Average Length ◽

Zinnia Elegans ◽

Flowering Plant ◽

Tween 20 ◽

Width Ratio ◽

Podosphaera Xanthii ◽

Bedding Plants ◽

Taichung City ◽

Voucher Specimens

Zinnia elegans L., known as common zinnia, is an annual flowering plant belonging to the Asteraceae family and native to North America. The plant has colorful flowers and is one of the popular ornamental bedding plants for gardening. In March 2020, powdery mildew symptoms were observed in a zinnia floral field with an incidence of >70% in Dacun Township, Changhua County, Taiwan. The symptoms were spotted on the stems, flower petals and leaves which appeared as irregular colonies and white patches on the surfaces. When disease progressed, most of the plant surfaces were covered by the white fungal colonies and became yellowish. Under microscopic examination, hyphal appressoria of the fungus were indistinct or slightly nipple-shaped. The conidiophores were unbranched, erect, straight, smooth to slightly rough, 75.0 to 200.0 × 10.0 to 15.0 µm (n=10), composed of a cylindrical, flexuous foot cell, 40.0 to 100.0 × 8.8 to 15.0 µm (n=10), and following 1 to 5 shorter cells. The conidia were ellipsoid to ovoid, 25.0 to 37.5 × 15.0 to 23.8 µm (n=60), with an average length-to-width ratio of 1.8 and contained fibrosin bodies. No chasmothecia were found. Three voucher specimens (TNM Nos. F0033680, F0033681, and F0033682) were deposited in the National Museum of Natural Science, Taichung City, Taiwan. To confirm the identification, the internal transcribed spacer (ITS) regions of the three specimens were amplified using primer pairs ITS1/PM6 and PM5/ITS4 (Shen et al. 2015) and sequenced from both ends. The resulting sequences were deposited in GenBank under Accession Nos. MT568609, MT568610, and MT568611. The sequences were identical to each other and shared a 100% identity with that of Podosphaera xanthii MUMH 338 on Z. elegans from Japan (Accession No. AB040355) (Ito and Takamatsu 2010) over a 475 bp alignment. Accordingly, the fungus was identified as P. xanthii (Castagne) U. Braun & Shishkoff (Braun and Cook 2012) based on its morphological and molecular characters. Pathogenicity was demonstrated through inoculation by gently pressing naturally infected leaves onto leaves of three healthy potted common zinnia that had been sprayed with 0.02% Tween 20. Additional three non-inoculated plants treated in the same way without inoculating the powdery mildew served as the controls. Powdery mildew colonies were observed on inoculated leaves after 10 days at room temperature, later the diseased leaves became yellowish and deteriorated. The morphological traits of the fungus on the inoculated leaves were similar to those of the first observed. In addition, the ITS sequence from a colony on the inoculated leaves was 100% identical to MT568609-MT568611, fulfilling the Koch’s postulates. All the controls remained symptomless. Z. elegans is known to be a host for different species of powdery mildew in the genus Erysiphe, Golovinomyces, and Podosphaera (Farr and Rossman 2020). In Taiwan, powdery mildew has been briefly reported on zinnia without detailed descriptions (Hsieh 1983). This study confirmed P. xanthii as a causal agent of powdery mildew in Taiwan and the awareness of the disease may benefit the floral industry. To our knowledge, this is the first confirmed report of P. xanthii on Z. elegans in Taiwan.

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First Report of Resistance to Boscalid in Podosphaera xanthii, Cucurbit Powdery Mildew, in South Carolina

Plant Health Progress ◽

10.1094/php-03-18-0009-br ◽

2018 ◽

Vol 19 (3) ◽

pp. 220-221 ◽

Cited By ~ 2

Author(s):

Anthony P. Keinath ◽

Gabriel Rennberger ◽

Chandrasekar S. Kousik

Keyword(s):

South Carolina ◽

Powdery Mildew ◽

Fungicide Resistance ◽

Southern United States ◽

Podosphaera Xanthii ◽

Powdery Mildew Fungus ◽

Action Committee ◽

Summer Squash ◽

Laboratory Bioassays ◽

Cucurbit Powdery Mildew

Resistance to boscalid, one of the older succinate-dehydrogenase inhibitors (SHDI) in Fungicide Resistance Action Committee (FRAC) code 7, was detected in Podosphaera xanthii, the cucurbit powdery mildew fungus, in South Carolina in July 2017. Resistance to the field rate (682 ppm) of boscalid was confirmed in greenhouse experiments and laboratory bioassays conducted on summer squash plants and cotyledons, respectively, that had been treated with a range of boscalid concentrations. This report is the first documentation of resistance to boscalid in P. xanthii in the southern United States.

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Monitoring Methyl Benzimidazole Carbamate-Resistant Isolates of the Cucurbit Powdery Mildew Pathogen, Podosphaera xanthii, Using Loop-Mediated Isothermal Amplification

Plant Disease ◽

10.1094/pdis-12-18-2256-re ◽

2019 ◽

Vol 103 (7) ◽

pp. 1515-1524 ◽

Cited By ~ 5

Author(s):

Alejandra Vielba-Fernández ◽

Antonio de Vicente ◽

Alejandro Pérez-García ◽

Dolores Fernández-Ortuño

Keyword(s):

Amino Acid ◽

Powdery Mildew ◽

Amino Acid Change ◽

Color Change ◽

Isothermal Amplification ◽

Podosphaera Xanthii ◽

Lamp Product ◽

Loop Mediated Isothermal Amplification ◽

Cucurbit Powdery Mildew ◽

Β Tubulin

Powdery mildew, caused by the fungus Podosphaera xanthii, is one of the most economically important diseases affecting cucurbit crops in Spain. Currently, chemical control offers the most efficient management of the disease; however, P. xanthii isolates resistant to multiple classes of site-specific fungicides have been reported in the Spanish cucurbit powdery mildew population. In previous studies, resistance to the fungicides known as methyl benzimidazole carbamates (MBCs) was found to be caused by the amino acid substitution E198A on β-tubulin. To detect MBC-resistant isolates in a faster, more efficient, and more specific way than the traditional methods used to date, a loop-mediated isothermal amplification (LAMP) system was developed. In this study, three sets of LAMP primers were designed. One set was designed for the detection of the wild-type allele and two sets were designed for the E198A amino acid change. Positive results were only obtained with both mutant sets; however, LAMP reaction conditions were only optimized with primer set 2, which was selected for optimal detection of the E198A amino acid change in P. xanthii-resistant isolates, along with the optimal temperature and duration parameters of 65°C for 75 min, respectively. The hydroxynaphthol blue (HNB) metal indicator was used for quick visualization of results through the color change from violet to sky blue when the amplification was positive. HNB was added before the amplification to avoid opening the lids, thus decreasing the probability of contamination. To confirm that the amplified product corresponded to the β-tubulin gene, the LAMP product was digested with the enzyme LweI and sequenced. Our results show that the LAMP technique is a specific and reproducible method that could be used for monitoring MBC resistance of P. xanthii directly in the field.

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First Report of Powdery Mildew Caused by Erysiphe diffusa, Oidium neolycopersici, and Podosphaera xanthii on Papaya in Taiwan

Plant Disease ◽

10.1094/pdis-05-11-0362 ◽

2011 ◽

Vol 95 (9) ◽

pp. 1188-1188 ◽

Cited By ~ 6

Author(s):

J.-G. Tsay ◽

R.-S. Chen ◽

H.-L. Wang ◽

W.-L. Wang ◽

B.-C. Weng

Keyword(s):

Powdery Mildew ◽

Morphological Characteristics ◽

Its Region ◽

Podosphaera Xanthii ◽

Oidium Neolycopersici ◽

First Report ◽

Plastic Bags ◽

The World ◽

Golovinomyces Cichoracearum ◽

Powdery Mildew Fungi

Powdery mildew can be found in most papaya (Carica papaya L.) fields during the winter and spring seasons in Taiwan. It usually causes severe yellowing of the leaf lamina and petiole and serious defoliation. Three types of powdery mildew fungi were isolated from papaya leaves in Chiayi City (23.28°N, 120.28°E) at the beginning of 2008. Conidia of the first one were single, globose, hyaline, and 24 to 36 × 14 to 18 μm (average 30.2 × 15.6 μm) without fibrosin bodies and with straight or occasionally flexuous conidiophores at the base. The second one had short pseudo-chains of two to four conidia which were ellipsoidal to ovoid, hyaline, and 24 to 40 × 12 to 16 μm (average 29.7 × 13.4 μm) without fibrosin bodies. The third type had chains of ellipsoidal conidia that were hyaline, 24 to 28 × 12 to 16 μm (average 26.3 × 14.4 μm) and contained fibrosin bodies. To confirm the identity of the three fungi, the internal transcribed spacer (ITS) region of rDNA was amplified using the primer pairs G1 (5′-TCC GTA GGT GAA CCT GCG GAA GGA T-3′)/Ed2 (5′-CGC GTA GAG CCC ACG TCG GA-3′), G1 (5′-TCC GTA GGT GAA CCT GCG GAA GGA T-3′)/On2 (5′-TGT GAT CCA TGT GAC TGG AA-3′), and S1 (5′-GGA TCA TTA CTG AGC GCG AGG CCC CG-3′)/S2 (5′-CGC CGC CCT GGC GCG AGA TAC A-3′). The alignment of obtained sequences (GenBank Accession Nos. GU358452, 507 bp; GU358451, 580 bp; and GU358450, 455 bp) showed a sequence identity of 100, 99, and 99% with the ITS sequences of Erysiphe diffusa, Oidium neolycopersici, and Podosphaera xanthii (GenBank Accession Nos. FJ378880, EU909694, and GQ927254), respectively. On the basis of morphological characteristics and ITS sequence similarities, these fungi were identified as E. diffusa (Cooke & Peck) U. Braun & S. Takam., O. neolycopersici L. Kiss, and P. xanthii (Castagne) U. Braun & S. Takam., respectively (1,3). Single colonies on papaya leaves infected with powdery mildew were identified in the laboratory and maintained on papaya leaves as inoculum. Pathogenicity was confirmed through inoculations by gently pressing a single colony of each fungus onto leaves of healthy papaya seedlings (cv. Horng-Fe). Five seedlings were inoculated for each fungus and then covered with plastic bags for 2 days. Five noninoculated seedlings served as control. After inoculation, treated plants were maintained separately from the control in different rooms of a greenhouse at 25°C under natural daylight conditions. Seven days after inoculation, typical symptoms of powdery mildew were observed on inoculated plants, but not on noninoculated plants. The same species from diseased lesions following artificial inoculation with each fungus were identified with light microscopy. Papaya was previously described as a host to O. caricae Noack in many tropical and subtropical areas of the world including Taiwan (2). However E. cruciferarum, Golovinomyces cichoracearum, Oidiopsis sicula, O. caricae, O. caricae-papayae, O. caricicola, O. indicum, O. papayae, Ovulariopsis papayae, P. caricae-papayae, P. macularis, P. xanthii, and Streptopodium caricae were reported to infect papaya (4). To our knowledge, this is the first report of papaya powdery mildew caused by E. diffusa and O. neolycopersici in the world and the first report of the three fungi found on papaya in Taiwan. References: (1) U. Braun and S. Takamatsu. Schlechtendalia 4:1, 2000. (2) H. S. Chien and H. L. Wang. J. Agric. Res. China 33:320, 1984. (3) L. Kiss et al. Mycol. Res. 105:684, 2001. (4) J. R. Liberato et al. Mycol. Res. 108:1185, 2004.

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First Report of Powdery Mildew Caused by Blumeria graminis f. sp. bromi on Bromus catharticus in China

Plant Disease ◽

10.1094/pdis-09-20-1983-pdn ◽

2020 ◽

Author(s):

Mo Zhu ◽

Jie Ji ◽

Xiao Duan ◽

Wenqi Shi ◽

YongFang Li

Keyword(s):

Powdery Mildew ◽

Sequence Data ◽

Morphological Characteristics ◽

Signs And Symptoms ◽

The United States ◽

Blumeria Graminis ◽

Henan Province ◽

Width Ratio ◽

Causal Organism ◽

First Report

Bromus catharticus, rescuegrass, is a brome grass that has been cultivated for herbage production, and been widely naturalized in many provinces of China, including Henan province. During April and May 2020, powdery mildew was found on leaves of Br. catharticus on the campus of Henan Normal University, Xinxiang city (35.3°N; 113.9°E), Henan Province, China. Abundant white or grayish irregular or coalesced circular powdery colonies were scattered on the adaxial surface of leaves and 70% of the leaf areas were affected. Some of the infected leaves either were chlorotic or senescent. About 60% of the observed plants showed powdery mildew symptoms. Conidiophores (n = 25) were 32 to 45 μm × 7 to 15 μm and composed of foot cells and conidia (mostly 6 conidia) in chains. Conidia (n = 50) were 25 to 35 μm × 10 to 15 μm, on average 30 × 13 μm, with a length/width ratio of 2.3. Chasmothecia were not found. Based on these morphologic characteristics, the pathogen was initially identified as Blumeria graminis f. sp. bromi (Braun and Cook 2012; Troch et al. 2014). B. graminis mycelia and conidia were collected, and total genomic DNA was extracted (Zhu et al. 2019). The rDNA internal transcribed spacer (ITS) region was amplified with primer pairs ITS1/ITS4. The amplicon was cloned and sequenced. The sequence (574 bp) was deposited into GenBank under Accession No. MT892940. BLASTn analysis revealed that MT892940 was 100% identical to B. graminis f. sp. bromi on Br. catharticus (AB000935, 550 of 550 nucleotides) (Takamatsu et al. 1998). Phylogenetic analysis of MT892940 and ITS of other B. graminis ff. spp. clearly indicated least two phylogenetically distinct clades of B. graminis f. sp. bromi and that MT892940 clustered with the Takamatsu vouchers. Leaf surfaces of five healthy plants were fixed at the base of a settling tower and then inoculated by blowing conidia from diseased leaves using pressurized air. Five non-inoculated plants served as controls. The inoculated and non-inoculated plants were maintained separately in two growth chambers (humidity, 60%; light/dark, 16 h/8 h; temperature, 18℃). Thirteen- to fifteen-days after inoculation, B. graminis signs and symptoms were visible on inoculated leaves, whereas control plants remained asymptomatic. The pathogenicity assays were repeated twice with the same results. The observed signs and symptoms were morphologically identical to those of the originally infected leaves. Accordingly, the causal organism of the powdery mildew was confirmed as B. graminis f. sp. bromi by morphological characteristics and ITS sequence data. B. graminis has been reported on Br. catharticus in the United States (Klingeman et al. 2018), Japan (Inuma et al. 2007) and Argentina (Delhey et al. 2003). To our best knowledge, this is the first report of B. graminis on Br. catharticus in China. Since hybridization of B. graminis ff. spp. is a mechanism of adaptation to new hosts, Br. catharticus may serve as a primary inoculum reservoir of B. graminis to infect other species (Menardo et al. 2016). This report provides fundamental information for the powdery mildew that can be used to develop control management of the disease in Br. catharticus herbage production.

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