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

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 Powdery Mildew Caused By Golovinomyces monardae on Scarlet Beebalm (Monarda didyma) in China

Plant Disease ◽

10.1094/pdis-08-21-1803-pdn ◽

2021 ◽

Author(s):

Yuan Yuan Xu ◽

Jia Tong Zhang ◽

Man Xu ◽

Dong Mei Liu ◽

Jinping Ding ◽

...

Keyword(s):

Powdery Mildew ◽

Flowering Plant ◽

Width Ratio ◽

Morphological Comparison ◽

First Report ◽

Blastn Analysis ◽

Voucher Specimens ◽

Length Width ◽

Monarda Didyma ◽

A Chain

Scarlet Beebalm (Monarda didyma) is a perennial ornamental flowering plant in the mint family, Labiatae. Due to low-maintenance, and a long blooming period, it is commonly cultivated in gardens as an ornamental plant in China. In May 2021, a disease was observed on the leaves of a capitals beebalm plant in a Ten Mile Flower Sea in Xiayi county (116°13′8″E, 34°14′45″N), Henan province of China. Symptoms first appeared as nearly circular, small, white, powdery mildew-like spots on the leaves which gradually expand, covering the entire leaves. The lesions spread from the lower leaves to the upper canopy, and the stems were also covered by white mycelia. In severe cases, early defoliation occured. About 30% plants were affected. Representative voucher specimens (SQNUMd04, SQNUDn4) were deposited in the herbarium of Shangqiu Normal University (SQNU), Shangqiu, China. Conidiophores (n = 30) were cylindrical, 92.0 to 142.2 µm long and 10.8 to 14.2 µm wide, and produced 5 to 7 immature conidia in a chain. Foot-cells of conidiophores were mostly curved at the base. Conidia (n = 30) were hyaline, ellipsoid, 23.3 to 29.8 μm (avg. 26.6 μm) long, and 11.2 to 16.9 μm (avg. 14.5μm) width, a length/width ratio of 1.5 to 2.1, and germ tubes were produced at the perihilar position. No chasmothecia were observed. Based on morphological comparison using the description by Scholler et al. (2016) description the fungus was tentatively identified as Golovinomyces monardae (G.S. Nagy) M. Scholler, U. Braun & Anke Schmidt. For molecular identification, DNA was extracted from mycelia and conidia, which were collected by scraping symptomatic leaves.The ITS regions and LSU were amplified using primers ITS1/ITS4 (White et al. 1990) and NL1/NL4 (Horisawa et al. 2013). BLASTn analysis of the (MZ303741) and LSU (MZ305434) sequences showed 100% identity with those of G. monardae (AB307667, LC076800, LC076802, LC076808, and AB077691) reported on Monarda species (Matsuda et al. 2003; Takamatsu et al. 2013; Scholler et al. 2016). Pathogenicity tests were carried out by gently dusting conidia from infected leaves onto healthy leaves of five M. didyma plants and five non-inoculated plants used as controls. After 9 days, typical powdery mildew colonies started to appear on the inoculated leaves while control plants remained disease free. All plants were placed in a greenhouse without temperature and humidity control. Based on morphology, fungus was identified as the same as that used for inoculum, fulfilling Koch's postulates. Although G. monardae has been reported on various genera in the Labiatae and Verbenaceae (Farr and Rossman 2021), to our knowledge, this is the first report of G. monardae causing powdery mildew of Scarlet Beebalm(M. didyma) in China.

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First Report of Powdery Mildew Caused by Podosphaera xanthii on Calendula officinalis in Italy

Plant Disease ◽

10.1094/pdis-92-1-0174c ◽

2008 ◽

Vol 92 (1) ◽

pp. 174-174 ◽

Cited By ~ 1

Author(s):

A. Garibaldi ◽

G. Gilardi ◽

M. L. Gullino

Keyword(s):

Powdery Mildew ◽

Its Region ◽

Pathogenicity Test ◽

Podosphaera Xanthii ◽

Calendula Officinalis ◽

First Report ◽

Potted Plants ◽

Blastn Analysis ◽

Voucher Specimens ◽

Pot Marigold

Calendula officinalis L. (Asteraceae) (pot marigold or English marigold) is an ornamental species grown in gardens and as potted plants for the production of cut flower. It was also used in ancient Greek, Roman, Arabic, and Indian cultures as a medicinal herb as well as a dye for fabrics, foods, and cosmetics. During the summer of 2007, severe outbreaks of a previously unknown powdery mildew were observed on plants in several gardens near Biella (northern Italy). Both surfaces of leaves of infected plants were covered with dense, white mycelia and conidia. As the disease progressed, infected leaves turned yellow and died. Mycelia and conidia also were observed on stems and flower calyxes. Conidia were hyaline, ellipsoid, born in short chains (four to six conidia per chain), and measured 27.0 to 32.1 (31.4) × 12.9 to 18.4 (18.2) μm. Conidiophores measured 49 to 77.3 (67.2) × 8 to 13.3 (10.8) μm and showed a foot cell measuring 44 to 59 (51.9) × 9.3 to 12.6 (11.3) μm followed by one shorter cell measuring 15.6 to 18.9 (17.6) × 10.4 to 13.6 (12.2) μm. Fibrosin bodies were present. Chasmothecia were spherical, amber colored, with a diameter of 89 to 100 (94.5) μm. Each chasmothecium contained one ascus with eight ascospores. On the basis of its morphology, the causal agent was determined to be a Podosphaera sp. (2). The internal transcribed spacer (ITS) region of rDNA was amplified using the primers ITS4/ITS6 and sequenced. BLASTn analysis (1) of the 588 bp showed a 100% homology with the sequence of Podosphaera xanthii (2). The nucleotide sequence has been assigned GenBank Accession No. EU100973. Pathogenicity was confirmed through inoculations by gently pressing diseased leaves onto leaves of healthy C. officinalis plants. Five plants were inoculated. Five noninoculated plants served as control. Plants were maintained in a greenhouse at temperatures ranging from 20 to 26°C. Eleven days after inoculation, typical symptoms of powdery mildew developed on inoculated plants. Noninoculated plants did not show symptoms. The pathogenicity test was carried out twice. To our knowledge, this is the first report of powdery mildew on C. officinalis in Italy. C. officinalis was previously described as a host to Sphaerotheca fuliginea (synonym S. fusca) in Great Britain (4) as well as in Romania (3). Voucher specimens are available at the AGROINNOVA Collection, University of Torino. References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) U. Braun and S. Takamatsu. Schlechtendalia 4:1, 2000. (3) E. Eliade. Rev. Appl. Mycol. 39:710, 1960. (4) F. J. Moore. Rev. Appl. Mycol. 32:380, 1953.

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First Report of Powdery Mildew Caused by Golovinomyces cichoracearum on English Daisy (Bellis perennis) in Italy

Plant Disease ◽

10.1094/pdis-92-3-0484a ◽

2008 ◽

Vol 92 (3) ◽

pp. 484-484 ◽

Cited By ~ 1

Author(s):

A. Garibaldi ◽

A. Minuto ◽

M. L. Gullino

Keyword(s):

Powdery Mildew ◽

Its Region ◽

Northern Italy ◽

Flowering Plant ◽

Pathogenicity Test ◽

First Report ◽

Golovinomyces Cichoracearum ◽

Blastn Analysis ◽

Commercial Farms ◽

Voucher Specimens

Bellis perennis (English daisy) is a flowering plant belonging to the Asteraceae and is increasingly grown as a potted plant in Liguria (northern Italy). In February 2007, severe outbreaks of a previously unknown powdery mildew were observed on plants in commercial farms at Albenga (northern Italy). Both surfaces of leaves of affected plants were covered with white mycelia and conidia. As the disease progressed, infected leaves turned yellow. Mycelia and conidia also were observed on stems and flower calyxes. Conidia were hyaline, ellipsoid, borne in chains (as many as three conidia per chain), and measured 27.7 × 16.9 (15.0 to 45.0 × 10.0 to 30.0) μm. Conidiophores measured 114.0 × 12.0 (109.0 to 117.0 × 11.0 to 13.0) μm and showed a foot cell measuring 78.0 × 11.0 (72.0 to 80.0 × 11.0 to 12.0) μm followed by two shorter cells. Fibrosin bodies were absent. Chasmothecia were not observed in the collected samples. The internal transcribed spacer (ITS) region of rDNA was amplified using primers ITS4/ITS6 and sequenced. BLASTn analysis (1) of the 415 bp obtained showed an E-value of 7e–155 with Golovinomyces cichoracearum (3). The nucleotide sequence has been assigned the GenBank Accession No. AB077627.1 Pathogenicity was confirmed through inoculations by gently pressing diseased leaves onto leaves of healthy B. perennis plants. Twenty plants were inoculated. Fifteen noninoculated plants served as a control. Plants were maintained in a greenhouse at temperatures ranging from 10 to 30°C. Seven days after inoculation, typical symptoms of powdery mildew developed on inoculated plants. The fungus observed on inoculated plants was morphologically identical to that originally observed. Noninoculated plants did not show symptoms. The pathogenicity test was carried out twice. To our knowledge, this is the first report of powdery mildew on B. perennis in Italy. The disease was already reported in other European countries (2). Voucher specimens are available at the AGROINNOVA Collection, University of Torino. References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) U. Braun The Powdery Mildews (Erysiphales) of Europe. Gustav Fischer Verlag, Jena, Germany, 1995. (3) U. Braun and S. Takamatsu. Schlechtendalia 4:1, 2000.

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

Plant Disease ◽

10.1094/pdis-06-11-0521 ◽

2011 ◽

Vol 95 (12) ◽

pp. 1586-1586 ◽

Cited By ~ 11

Author(s):

C. S. Kousik ◽

R. S. Donahoo ◽

C. G. Webster ◽

W. W. Turechek ◽

S. T. Adkins ◽

...

Keyword(s):

Powdery Mildew ◽

Morphological Characteristics ◽

The United States ◽

Tween 20 ◽

Conidial Suspension ◽

Podosphaera Xanthii ◽

Its Sequence Analysis ◽

Fruit Samples ◽

Cucurbit Powdery Mildew ◽

Fruit Surface

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 Golovinomyces cichoracearum on Zinnia elegans in Turkey

Plant Disease ◽

10.1094/pdis-06-11-0519 ◽

2011 ◽

Vol 95 (10) ◽

pp. 1317-1317 ◽

Cited By ~ 1

Author(s):

S. Soylu ◽

S. E. Cho ◽

H. D. Shin

Keyword(s):

Powdery Mildew ◽

Molecular Analysis ◽

Sequence Similarity ◽

Morphological Characteristics ◽

Signs And Symptoms ◽

Current Data ◽

Zinnia Elegans ◽

Width Ratio ◽

Rdna Sequences ◽

Powdery Mildews

Powdery mildews are one of the most common diseases of plants growing in many nurseries, city parks, and home gardens in Turkey. Common zinnia (Zinnia elegans Jacq.) is widely cultivated in Turkey for ornamental purposes. In September 2010, zinnia plants grown in Hatay, Turkey were found to be heavily infected with a powdery mildew. Pathogen mycelia and sporulation were observed as circular to irregular, white patches on both sides of the leaves and on stems and flower petals. As the disease progressed, infected leaves turned yellow and died. Hyphae were straight to wavy and 4 to 7 μm wide. Conidiophores arose from the upper part of the hyphae, measured 120 to 190 × 10 to 13 μm, were simple, and produced two to six immature conidia in chains with a sinuate edge, followed by two to three straight cells. Conidia were hyaline, ellipsoid to barrel-shaped, measured 25 to 42 × 14 to 22 μm (length/width ratio = 1.3 to 2.5), lacked distinct fibrosin bodies, and produced germ tubes on the perihilar position, with reticulate wrinkling of the outer walls. No chasmothecia were observed. The structures described above were typical of the Oidium subgenus Reticuloidium, anamorph of the genus Golovinomyces, and the fungus measurements were compatible with those of G. cichoracearum (DC.) V.P. Heluta described previously (1,3). To confirm the tentative identification based on morphological characteristics, molecular analysis of internal transcribed spacer (ITS) rDNA sequences from a representative material (MKU-ZK311077, duplicate KUS-F25655) was conducted. The complete ITS regions of rDNA were amplified using primers ITS5 and P3 as described by S. Takamatsu (4) and sequenced. The resulting sequence of 508 bp from MKU-ZK311077 was deposited in GenBank (Accession No. JN051414). A GenBank BLAST search using the current data revealed an exact match for several sequences of G. cichoracearum, including Australian and Korean powdery mildews on zinnia plants, with a 100% sequence similarity. Pathogenicity was confirmed through inoculation by gently pressing diseased leaves onto leaves of three healthy, potted zinnia plants. Three noninoculated plants served as controls. Plants were maintained in a greenhouse at 25°C. Inoculated plants developed signs and symptoms after 10 days, whereas the control plants remained healthy. The fungus present on the inoculated plants was morphologically identical to that originally observed on diseased plants. The powdery mildew infections of Z. elegans associated with G. cichoracearum are nearly circumglobal, including Europe, North America, South America, Africa, Oceania, and Western Asian localities like India, Nepal, Jordan, and Israel (1,2). The current work confirmed the occurrence of G. cichoracearum infecting Z. elegans in Turkey using detailed morphological and molecular analysis. References: (1) U. Braun. Beih. Nova Hedw. 89:1, 1987. (2) D. F. Farr and A. Y. Rossman. Fungal Databases. Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved from http://nt.ars-grin.gov/fungaldatabases/ , May 24, 2011. (3) M. J. Park et al. Plant Pathol. J. 27:85, 2011. (4) S. Takamatsu et al. Mycol. Res. 113:117, 2009.

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Evaluation of Disease Resistance among 57 Varieties of Zinnia elegans

HortScience ◽

10.21273/hortsci.33.3.467a ◽

1998 ◽

Vol 33 (3) ◽

pp. 467a-467

Author(s):

Linda Gombert ◽

Susan Hamilton ◽

Mark Windham

Keyword(s):

Disease Resistance ◽

Powdery Mildew ◽

Xanthomonas Campestris ◽

Disease Susceptibility ◽

Growing Season ◽

Zinnia Elegans ◽

Field Conditions ◽

Uniform Field ◽

Bedding Plants ◽

Susceptibility And Resistance

Fifty-seven of the most widely grown, commercially popular varieties of Zinnia elegans were evaluated for disease susceptibility under uniform field conditions. Plants were started from seed and transplanted into cell-packs to be grown on as bedding plants. They were later transplanted into the field and observed for development and progression of the diseases alternaria blight (Alternaria zinniae), powdery mildew (Erisyphe cichoracearum), and bacterial leaf and flower spot (Xanthomonas campestris pv. zinniae). Evaluations were performed throughout the growing season in order to rate each variety on its susceptibility to disease based upon severity of infection as well as portion of plant affected. Results will be presented on disease susceptibility and resistance of the 57 varieties evaluated.

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First Confirmed Report of Powdery Mildew Caused by Podosphaera xanthii on Farfugium japonicum in Korea

Plant Disease ◽

10.1094/pdis-11-12-1069-pdn ◽

2013 ◽

Vol 97 (5) ◽

pp. 691-691 ◽

Cited By ~ 1

Author(s):

S. E. Cho ◽

M. J. Park ◽

C. H. Shin ◽

H. D. Shin

Keyword(s):

Powdery Mildew ◽

Signs And Symptoms ◽

Its Region ◽

Lateral Position ◽

Width Ratio ◽

Podosphaera Xanthii ◽

Potted Plants ◽

Ampelomyces Quisqualis ◽

Young Leaves ◽

Farfugium Japonicum

Farfugium japonicum (L.) Kitam., known as Japanese silver leaf, is native to Japan, Korea, and Taiwan. It is grown as an ornamental plant for garden plantings and containers not only in East Asia but more recently also in Europe and North America. Since 2003, powdery mildew infections of F. japonicum ‘Gigantea’ have been consistently found in the southern part of Korea, including the districts of Jeju, Seogwipo, Busan, Wando, and Ulleungdo. Specimens have been deposited in the Korea University Herbarium (KUS). Signs of powdery mildew first appeared as circular to irregular white patches on both sides of the leaves. The infections were usually severe on young leaves and caused malformation and browning. Appressoria on the mycelium were nipple-shaped or nearly absent. Conidiophores, measuring 160 to 280 × 10 to 12.5 μm, were simple and produced 2 to 12 immature conidia in chains, followed by 2 to 3 cells. Foot-cells in conidiophores were relatively short, 50 to 95 μm long, and constricted at the base. Conidia were hyaline, ellipsoid to ovate, 32 to 48 × 17.5 to 25 μm (length/width ratio = 1.4 to 2.3), had distinct fibrosin bodies, and produced germ tubes on the lateral position. No chasmothecia were observed. The morphology and dimentions of reproductive structures were compatible with those of Podosphaera xanthii (Castagne) U. Braun & Shishkoff (1). To confirm the identity of the causal fungus, the complete ITS region of rDNA from isolate KUS-F26469 was amplified with primers ITS5 and P3 (4) and directly sequenced. The resulting sequence of 475 bp was deposited in GenBank (Accession No. KC155426). A GenBank BLAST search of this sequence revealed 100% identity (475/475 bp) with those of many P. fusca isolates on plants in the Aster family plants including Calendula officinalis, Euryops pectinatus, Syneilesis palmata, and F. japonicum from Japan (e.g., AB040346). The P. fusca isolates listed above are now placed in P. xanthii (1). Pathogenicity was confirmed through inoculation by gently pressing diseased leaves onto leaves of three healthy potted plants of the same cultivar. Three non-inoculated plants served as controls. Plants were maintained in a greenhouse at 25 ± 2°C. Inoculated plants developed typical signs and symptoms of powdery mildew after 8 days, whereas the control plants remained symptomless. The fungus present on the inoculated leaves was morphologically identical to that originally observed on diseased plants. Powdery mildew infections of F. japonicum caused by P. fusca (syn. P. fuliginea) have been reported previously in both Japan and Korea (2). In Korea, it was listed simply as a host fungus of Ampelomyces quisqualis, which is hyperparasitic to powdery midlews, without any data on its identity (3). To our knowledge, this is the first confirmed report of powdery mildew caused by P. xanthii on F. japonicum in Korea. References: (1) U. Braun and R. T. A. Cook. Taxonomic Manual of the Erysiphales (Powdery Mildews), CBS Biodiversity Series No.11. CBS, Utrecht, 2012. (2) D. F. Farr and A. Y. Rossman. Fungal Databases. Syst. Mycol. Microbiol. Lab., Online publication, ARS, USDA, Retrieved November 14, 2012. (3) M. J. Park et al. Fungal Biol. 114:235, 2010. (4) S. Takamatsu et al. Mycol. Res. 113:117, 2009.

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First Report of Podosphaera xanthii Race 1W Causing Powdery Mildew of Watermelon in California

Plant Disease ◽

10.1094/pdis-05-13-0552-pdn ◽

2014 ◽

Vol 98 (1) ◽

pp. 158-158 ◽

Cited By ~ 7

Author(s):

J. Mercier ◽

M. J. Muscara ◽

A. R. Davis

Keyword(s):

Powdery Mildew ◽

Citrullus Lanatus ◽

Field Isolate ◽

Central Valley ◽

Spore Suspension ◽

Growth Chamber ◽

Tween 20 ◽

Podosphaera Xanthii ◽

Breeding Lines ◽

Field Plots

In September and October 2012, powdery mildew was detected on watermelon (Citrullus lanatus var. lanatus) plants of various breeding lines growing in field plots in Davis, California. Plants had partially necrotic leaves, yellowing to brown in color, with white surface mycelium and faint sporulation. No teleomorph was observed. Infected leaves were collected for examination and a spore suspension of the field isolate was made in water with 0.01% Tween 20 to spray inoculate watermelon seedlings of cultivar Dixie Lee with two true leaves. Plants were incubated in a growth chamber (22 to 26°C, 12-h photoperiod) for approximately 10 days, until sporulation was apparent. Microscopic observation of conidial chains showed that they had clearly crenate edges indicative of Podosphaera xanthii (4). To confirm the identity of the pathogen, we used Podosphaera-specific primers PFITS-F (5′-CCAACTCGTGCTGAGTGT-3′) and PF5.8-R (5′-TGTTGGTTTCTTTTCCTCCG-3′) to amplify and sequence the internal transcribed spacer regions of the nuclear rDNA. The 326-bp sequence had 98% homology to the GenBank sequence (accessions JQ340082.1 and AB774158.1) for P. xanthii. Infected ‘Dixie Lee’ leaves were used to make a spore suspension (approximately 5 × 104 conidia/ml) as described above to inoculate watermelon, melon, and squash seedlings (2 to 3 plants per cultivar) in a greenhouse. It caused severe symptoms on all watermelon plants cv. Charleston 76, P8, and Sugar Baby in the form of a powdery mildew with surface mycelium and chains of conidia, with leaves becoming gradually more necrotic and eventually dying, with the appearance of a melting down. Non-inoculated plants did not develop symptoms. The isolate also infected all squash plants ‘Zucchini Elite’ and melon powdery mildew differentials Iran H and ‘Védrantais.’ On these plants, the pathogen produced a powdery mildew (white surface mycelium with sporulation) but did not cause extensive necrosis. All other melon powdery mildew differentials (‘PMR5,’ ‘PMR45,’ WMR29, MR1, PI 124112, and PI 313970) did not develop any powdery mildew. A follow-up test in a growth chamber (22 to 26°C, 12-h photoperiod) with the same set of species and cultivars gave the same results. Based on these results, we conclude that this isolate belongs to race 1W (1,2). The presence of race 1W could have implications in disease management for this crop in the Central Valley of California as most cultivars are not resistant to it and the disease has been shown to cause severe damage in other states (1,3). References: (1) A. R. Davis et al. J. Am. Soc. Hort. Sci. 132:790, 2007. (2) J. D. McCreight. Amer. Soc. Hort. Sci. 131:59, 2006. (3) A. Y. Tetteh et al. Crop Sci. 50:933, 2010. (4) T. A. Zitter. Page 28 in: Compendium of Cucurbit Diseases, The American Phytopathological Society, St. Paul, MN, 1996.

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First Report of Powdery Mildew Caused by Podosphaera xanthii on Papaya in Korea

Plant Disease ◽

10.1094/pdis-06-13-0581-pdn ◽

2013 ◽

Vol 97 (11) ◽

pp. 1514-1514 ◽

Cited By ~ 2

Author(s):

J. H. Joa ◽

B. N. Chung ◽

K. S. Han ◽

S. E. Cho ◽

H. D. Shin

Keyword(s):

Powdery Mildew ◽

Agricultural Research ◽

Morphological Characteristics ◽

Its Region ◽

Width Ratio ◽

Korean Isolate ◽

Podosphaera Xanthii ◽

First Report ◽

Powdery Mildews ◽

Basal Septum

In March 2013, papaya (Carica papaya L. cv. Sunrise) plants growing in polyethylene-film-covered greenhouses in Agricultural Research Center for Climate Change located in Jeju City, Korea, were observed severely affected by a powdery mildew. Symptoms appeared as circular to irregular white patches on both sides of the leaves. As the disease progressed, the plants were covered with dense masses of the spores, eventually causing senescence and withering of leaves. Voucher specimens were deposited in the Korea University Herbarium (KUS). Hyphae were flexuous to straight, branched, septate, and 5 to 8 μm wide. Conidiophores were 110 to 250 × 10 to 12.5 μm and produced 2 to 5 immature conidia in chains with a crenate outline followed by 2 to 3 cells. Foot-cells of conidiophores were straight, cylindric, slightly constricted at the basal septum, and 55 to 110 μm long. Conidia were hyaline, ellipsoid-ovoid, measured 22 to 38 × 18 to 21 μm with a length/width ratio of 1.2 to 1.8, and had distinct fibrosin bodies. Chasmothecia were scattered or partly clustered, dark brown, spherical, 80 to 100 μm in diameter, and each contained a single ascus. Appendages were mycelioid, 1- to 5-septate, brown at the base and becoming paler. Asci were sessile, 72 to 87 × 52 to 68 μm, had a terminal oculus of 17 to 23 μm wide, and contained 8 ascospores, each 17 to 23 × 12.5 to 15 μm. The morphological characteristics and measurements were consistent with those of Podosphaera xanthii (Castagne) U. Braun & Shishkoff (1). To confirm the identification, the complete internal transcribed spacer (ITS) region of rDNA of KUS-F27269 was amplified with the primers ITS5/P3 and sequenced (3). The resulting 443 bp sequence was deposited in GenBank (Accession No. KF111806). The Korean isolate showed >99% similarity with those of many P. xanthii isolates including an isolate on papaya from Taiwan (GU358450). Pathogenicity was confirmed through inoculation tests by gently pressing a diseased leaf onto young leaves of three asymptomatic, potted seedlings (cv. Sunrise). Three non-inoculated seedlings were used as control. Inoculated plants were isolated from non-inoculated plants in separate rooms in a greenhouse at 26 to 30°C. Inoculated leaves developed symptoms after 7 days, whereas the control plants remained symptomless. The fungus present on the inoculated leaves was identical morphologically to that observed on the original diseased leaves, fulfilling Koch's postulates. Powdery mildews of papaya caused by Podosphaera species including P. caricae-papayae have been reported in North America, South America, Hawaii, Africa, Ukraine, Australia, New Zealand, the Cook Islands, India, Thailand, Taiwan, and Japan (2,4). P. caricae-papayae is currently reduced to synonymy with P. xanthii (1). To our knowledge, this is the first report of powdery mildew caused by P. xanthii on papaya in Korea. Though papaya is a minor crop in Korea, producing about 300 M/T annually in greenhouses, powdery mildew disease is a threat to safe production of the fruits. References: (1) U. Braun and R. T. A. Cook. Taxonomic Manual of the Erysiphales (Powdery Mildews), CBS Biodiversity Series No. 11, CBS, Utrecht, 2012. (2) D. F. Farr and A. Y. Rossman. Fungal Databases. Syst. Mycol. Microbiol. Lab., Online publication, ARS, USDA, retrieved April 9, 2013. (3) S. Takamatsu et al. Mycol. Res. 113:117, 2009. (4) J. G. Tsay et al. Plant Dis. 95:1188, 2011.

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First Report of Golovinomyces cichoracearum Causing Powdery Mildew on Zinnia elegans in China

Plant Disease ◽

10.1094/pdis-11-20-2333-pdn ◽

2020 ◽

Author(s):

Mo Zhu ◽

Jie Ji ◽

Xiao Duan ◽

YongFang Li

Keyword(s):

Powdery Mildew ◽

Morphological Characteristics ◽

Signs And Symptoms ◽

Its Region ◽

Zinnia Elegans ◽

Width Ratio ◽

Post Inoculation ◽

First Report ◽

Golovinomyces Cichoracearum ◽

Length Width

Zinnia elegans, common zinnia, is an annual plant with highly ornamental values. It is widely planted in many nurseries, city parks, universities and home gardens in China. From August to October 2020, powdery mildew-like signs and symptoms were observed on leaves of Z. elegans growing on the campus of Henan Normal University, Henan Province, China. White powdery colonies in circular- or irregularly shaped-lesions were abundant on both surfaces of leaves and covered up to 95 % of the leaf area. Any infected leaves were chlorotic, deformed or senescence. More than 70 % of the monitored Z. elegans plants showed these signs and symptoms. Conidiophores (n = 20) were 100 to 200 × 9 to 13 μm and composed of foot cells, followed by straight cells and conidia. Mycelial appressoria were single and nipple-shaped. The oval-shaped conidia (n = 30) were 22 to 36 × 12 to 18 μm, with a length/width ratio of 1.4 to 2.7, and produced germ tubes from the polar ends of the spore. No chasmothecia were found. Based on these morphological characteristics, the pathogen was initially identified morphologically as Golovinomyces cichoracearum (Braun and Cook 2012). Structures of the pathogen were scraped from infected leaves and total genomic DNA was isolated using the method previously described by Zhu et al. (2019). The internal transcribed spacer (ITS) region of rDNA was amplified by PCR using the primers ITS1/ITS4 (White et al. 1990) and the amplicon was sequenced by Invitrogen (Shanghai, China). The sequence for the fungus was deposited into GenBank under Accession No. MW029904 and was 99.83 % identical (595/596 bp) to G. cichoracearum on Symphyotrichum novi-belgii (HM769725)(Mørk et al. 2011). To perform pathogenicity analysis, leaf surfaces of five healthy plants were fixed in a settling tower and then inoculated by blowing fungal conidia from mildew-infested leaves using pressurized air. Five non-inoculated plants served as a control. The inoculated and non-inoculated plants were separately maintained in two growth chambers (humidity, 60 %; light/dark, 16 h/8 h; temperature, 18 ℃). Eleven- to twelve-days post-inoculation, powdery mildew signs were conspicuous on inoculated plants, while control plants remained healthy. Similar results were obtained by conducting two repeated pathogenicity assays. Thus, based on the morphological characteristics and molecular analysis, the pathogen was identified and confirmed as G. cichoracearum. This pathogen has been reported on Z. elegans in India, Israel, Jordan, Korea, Nepal, Sri Lanka, Switzerland, and Turkey (Farr and Rossman 2020). To our best knowledge, this is the first report of G. cichoracearum on Z. elegans in China. The sudden outbreak of powdery mildew caused by G. cichoracearum on Z. elegans may adversely impact the plant health and ornamental value in China. Therefore, the confirmation of G. cichoracearum infecting Z. elegans expands the understanding of this pathogen and provides the fundamental knowledge for future powdery mildew control.

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