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

Benincasa hispida (Thunb.) Cogn. (syn. B. cerifera Savi, Cucurbita hispida Thunb.), called wax gourd or ash gourd, is a cucurbitaceous vine grown for medicinal purposes and commercial values of its large fruits in Southeast Asia (Al-Snafi 2013). During the summer and autumn of 2020, leaves of wax gourd were observed to be affected by powdery mildew with 100% disease incidence in an experimental plot of Jeonbuk National University (35°50′55″N, 127°07′48″E), Korea. Fungal colonies were initially circular to irregular, forming white patches on both sides of the leaves and young stems, finally covering entire leaves and causing premature senescence of the leaves and poor growth. A representative voucher specimen was deposited in the Korea University herbarium (KUS-F32171). At least 30 measurements were taken for each asexual diagnostic features. Conidiophores arising from superficial hyphae were straight, 100 to 210 μm long, and produced 3 to 7 immature conidia in chains with a crenate outline. Foot-cells were cylindrical, 46 to 74 ×10 to 12 μm, followed by 1 to 2 shorter cells. Conidia were ellipsoid-ovoid to barrel-shaped, 30 to 40 × 18 to 23 μm with a length/width ratio of 1.4 to 2.0 and contained conspicuous fibrosin bodies. Germ tubes were produced from a lateral position on conidia. Sexual stage was not observed during the growing season. The morphological characteristics of the fungus were compatible with those of Podosphaera xanthii (Castagne) U. Braun & Shishkoff (Braun and Cook 2012), a well-known cucurbitaceous powdery mildew. DNA was extracted from mycelium, and primer sets ITS1F/PM6 and PM3/TW14 were used for amplification of ITS1-5.8S-ITS2 regions and 5´-end of 28S rDNA gene, respectively (Takamatsu and Kano 2001). Sequences determined in this study were deposited to the GenBank under the accession numbers MW559231 and MW559420, respectively. The sequences for ITS regions and 28S rDNA gene showed 99.78% and 99.07% similarity respectively with those of P. xanthii (MH465242, MH465243, MT250855 for ITS, and MK357436, MT826247 for LSU). Pathogenicity was confirmed twice by pressing a diseased leaf onto young leaves of five wax gourd plants. Five non-inoculated plants were used as controls. Inoculated leaves developed symptoms after 5 days, whereas the control plants remained symptomless. The fungus present on the inoculated plants was identical morphologically to that originally observed on diseased plants. Sphaerotheca fuliginea (syn. P. xanthii) on B. hispida has been listed in Hungary, India, Japan, Singapore, and Taiwan so far (Farr and Rossman 2021). Recently, the identity of P. xanthii on B. hispida in Taiwan was confirmed with morphological examination and molecular analysis by Wu and Kirschner (2017). To our knowledge, this is the first report of powdery mildew caused by P. xanthii on B. hispida in Korea. Since wax gourd production is only recently started on a commercial scale in the southern part of Korea, powdery mildew infections pose a serious threat to the safe production of the fruits, especially in organic farming where chemical control options are limited.

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First Report of Powdery Mildew Caused by Podosphaera xanthii on Cucurbita argyrosperma in Mexico

Plant Disease ◽

10.1094/pdis-11-21-2458-pdn ◽

2021 ◽

Author(s):

José Francisco Díaz-Nájera ◽

Sergio Ayvar-Serna ◽

Antonio Mena-Bahena ◽

Guadalupe Arlene Mora-Romero ◽

Karla Yeriana Leyva-Madrigal ◽

...

Keyword(s):

Powdery Mildew ◽

Microscopic Examination ◽

Disease Incidence ◽

Phylogenetic Analyses ◽

Its Region ◽

Likelihood Method ◽

28S Rrna ◽

Podosphaera Xanthii ◽

Voucher Specimen ◽

First Report

Cucurbita argyrosperma, commonly named as winter or cushaw squash, is highly sought for its seeds, which have important uses in culinary arts. During the autumn 2021, powdery mildew-like signs and symptoms were observed on cushaw squash in several commercial fields located in Cocula, Guerrero, Mexico. Signs were initially appeared as whitish powdery patches on both sides of leaves and then covering entire leaves and causing premature senescence. The disease incidence was estimated to be 80% in about 1000 plants in two fields. The mycelium was amphigenous, persistent, white in color, and occurred in dense patches. A voucher specimen was deposited in the Herbarium of the Colegio Superior Agropecuario del Estado de Guerrero under the accession number CSAEG22. For the morphological characterization by light microscopy, fungal structures were mounted in a drop of lactic acid on a glass slide. Microscopic examination showed nipple-shaped hyphal appressoria. Conidiophores (n = 30) were straight, 100 to 190 × 10 to 12 μm and produced 2 to 6 conidia in chains. Foot-cells were cylindrical, 41 to 78 μm long, followed by 1 to 2 shorter cells. Conidia (n = 100) were ellipsoid-ovoid to barrel-shaped, 29.5 to 39.1 × 19.4 to 22.7 μm, and contained conspicuous fibrosin bodies. Germ tubes were produced from a lateral position on conidia. Chasmothecia were not observed during the growing season. The morphological characters were consistent with those of the anamorphic state of Podosphaera xanthii (Braun and Cook 2012). For further confirmation, total DNA was extracted from conidia and mycelia following the CTAB method (Doyle and Doyle 1990), and the internal transcribed spacer (ITS) region and part of the 28S gene were amplified by PCR, and sequenced. The ITS region of rDNA was amplified using the primers ITS5/ITS4 (White et al. 1990). For amplification of the 28S rRNA partial gene, a nested PCR was performed using the primer sets PM3 (Takamatsu and Kano 2001)/TW14 (Mori et al. 2000) and NL1/TW14 (Mori et al. 2000) for the first and second reactions, respectively. Phylogenetic analyses using the Maximum Likelihood method, including ITS and 28S sequences of isolates of Podosphaera spp. were performed and confirmed the results obtained in the morphological analysis. The isolate CSAEG22 grouped in a clade with isolates of Podosphaera xanthii. The ITS and 28S sequences were deposited in GenBank under accession numbers OL423329 and OL423343, respectively. Pathogenicity was confirmed by gently dusting conidia from infected leaves onto ten leaves of healthy C. argyrosperma plants. Five non-inoculated leaves served as controls. The plants were maintained in a greenhouse at 25 to 35 ºC, and relative humidity of 60 to 70%. All inoculated leaves developed similar signs to the original observation after 10 days, whereas control leaves remained symptomless. Microscopic examination of the fungus on inoculated leaves showed that it was morphologically identical to that originally observed on diseased plants, fulfilling Koch’s postulates. Podosphaera xanthii has been previously reported on C. maxima, C. moschata, and C. pepo in Mexico (Yañez-Morales et al. 2009; Farr and Rossman 2021). To our knowledge, this is the first report of P. xanthii causing powdery mildew on C. argyrosperma in Mexico. This pathogen is a serious threat to C. argyrosperma production in Mexico and disease management strategies should be developed.

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First Report of Powdery Mildew on Leucophyllum frutescens Caused by Podosphaera xanthii in Mexico

Plant Disease ◽

10.1094/pdis-06-20-1368-pdn ◽

2020 ◽

Author(s):

Hugo Beltrán-Peña ◽

Ruben Felix-Gastelum ◽

Moises Camacho-Tapia ◽

Kamila C. Correia ◽

Gabriel Herrera-Rodriguez ◽

...

Keyword(s):

Powdery Mildew ◽

Urban Areas ◽

Disease Incidence ◽

Phylogenetic Analyses ◽

Morphological Characteristics ◽

Podosphaera Xanthii ◽

Monitoring And Control ◽

Voucher Specimen ◽

First Report ◽

Initial Symptoms

Leucophyllum frutescens (Scrophulariaceae family), commonly known as Texas sage or cenizo, is an evergreen shrub native to southwestern United States and northern Mexico. This plant is commercially sold as a native, drought-tolerant ornamental. During the spring of 2019 and 2020, typical symptoms of powdery mildew were found on cenizo plants growing as ornamentals in urban areas in the municipality of Ahome, Sinaloa, Mexico. Disease incidence was 95% from a sampled population of 120 plants. Initial symptoms of powdery mildew developed as irregular white colonies on upper leaf surfaces which expanded as infections progressed. In severe infections, leaves became distorted, exhibiting premature defoliation. Microscopic examination showed nipple-shaped appressoria. Conidiophores (n= 30) were hyaline, cylindrical, erect, 89.4 to 134.2 μm long, and forming catenescent conidia. Foot-cells were cylindrical, 35.7 to 65.3 × 10.2 to 13.5 μm, followed by 1–3 shorter cells. Conidia (n= 100) were hyaline, ellipsoid to ovoid, 27.9 to 40.5 × 13.8 to 18.9 μm, containing distinct fibrosin bodies. Germ tubes were simple to forked and laterally produced from the middle of conidia. Chasmothecia were not found during the sampling period on the infected leaves. Based on morphological characteristics, the fungus was identified as Podosphaera xanthii (Braun and Cook 2012). A voucher specimen (accession no. FAVF219) was deposited in the Herbarium of the Faculty of Agronomy of El Fuerte Valley at the Autonomous University of Sinaloa (Juan Jose Rios, Sinaloa, Mexico). To further confirm the identification, total DNA was extracted, and the internal transcribed spacer (ITS) region was amplified by PCR using the primers ITS5/ITS4 (White et al. 1990) and sequenced. The resulting 503 bp sequence (GenBank accession no. MT624793) had 100% coverage and 100% identity to those of P. xanthii (MT568609–MT568611, MT472035, MT309699, MT250855, MT242593). A phylogenetic tree using the maximum parsimony (MP) and maximum likelihood (ML) methods and including published ITS sequences for Podosphaera species was obtained. Phylogenetic analyses revealed that ITS sequence from FAVF219 isolate was grouped into a clade with P. xanthii. Pathogenicity was demonstrated by gently dusting conidia from infected leaves onto 50 leaves of five healthy plants. Five non-inoculated plants served as controls. All plants were covered with polyethylene bags for 48 h to maintain high humidity and were maintained in a greenhouse at temperatures ranging from 20 to 35ºC. All inoculated plants developed similar symptoms to the original observations after 19 days, whereas no symptoms of powdery mildew were observed on control plants. The fungus present on the inoculated plants was morphologically identical to that originally observed on diseased plants, fulfilling Koch’s postulates. This fungus has been reported infecting members of the Cucurbitaceae in Mexico (Félix-Gastélum et al. 2017; Farr and Rossman 2020). However, to our knowledge, this is the first report of P. xanthii causing powdery mildew on a member of Scrophulariaceae, specifically L. frutescens in Mexico and worldwide. Further studies for monitoring and control strategies of powdery mildew on Texas sage are required.

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First Report of Powdery Mildew Caused by Podosphaera xanthii on Cuphea hyssopifolia (Lythraceae) in Mainland China

Plant Disease ◽

10.1094/pdis-03-21-0545-pdn ◽

2021 ◽

Author(s):

Irum Mukhtar ◽

Ruiting Li ◽

IBATSAM KHOKHAR ◽

Ruanni Chen ◽

Yunying Cheng ◽

...

Keyword(s):

Powdery Mildew ◽

Disease Incidence ◽

Large Subunit ◽

Mainland China ◽

Lsu Rdna ◽

Podosphaera Xanthii ◽

Powdery Mildew Fungus ◽

Potential Threat ◽

First Report ◽

Plant Pathol

Cuphea hyssopifolia (Mexican heather) is a popular evergreen perennial shrub used for ornamental and medicinal purposes. Due to its high ornamental value, it is often used as a ground cover in parks and gardens in China. During February and March 2019 & 2020, powdery mildew was observed on C. hyssopifolia in the districts of Minhou and Jinshan of Fuzhou, China. Disease incidence was 70% but of low severity with only a few older leaves showing yellowing and wilting. Sparse irregular patches of white superficial powdery mildew observed on both sides of mature and young leaves. The powdery mildew fungal appressoria that occurred on epigenous hyphae, were indistinct to nipple-shaped, hyaline, and smooth. Conidiophores were erect, smooth, 80 to 210 × 10 to 12 µm, and produced two to eight crenate-shaped conidia in chains. Foot-cells of conidiophores were straight, cylindric, and 30 to 65 × 10 to12 µm. Conidia were hyaline, smooth, ellipsoid-ovoid to barrel-shaped, 25 to 38 × 16 to 20 µm with distinct fibrosin bodies. Germ tubes were simple to forked and produced from the lateral position of the germinating conidia. No chasmothecia were observed on the surface of infected leaves. Based on the morphology of the imperfect state, the powdery mildew fungus was identified as Podosphaera xanthii (Castagne) U. Braun & N. Shishkoff (Braun and Cook 2012). To confirm fungal identification, total DNA was extracted (Mukhtar et al., 2018) directly from epiphytic mycelia on infected leaves collected from both districts. Internal transcribed spacer (ITS) regions and the partial large subunit (LSU) rDNA were amplified using primers ITS1/ITS4 and LSU1/LSU2 (Scholin et al. 1994, White et al. 1990), respectively. The sequences were deposited in GenBank (ITS: MW692364, MW692365; LSU: MW699924, MW699925). The ITS and LSU sequences were 99 to 100 % identical to those of P. xanthii in GenBank, (ITS: MT568609, MT472035, MT250855, and AB462800; LSU: AB936276, JX896687, AB936277, and AB936274). Koch’s postulates were completed by gently pressing diseased leaves onto leaves of five healthy potted C. hyssopifolia plants that were held in a greenhouse at 24 to 30°C without humidity control. Five non-inoculated plants served as controls. Inoculated plants developed symptoms after 6 to 10 days, whereas the controls remained symptomless. The morphology of the fungus on the inoculated leaves was identical to that observed on the originally diseased leaves. Previously, Podosphaera sp. has been reported on C. rosea in the United Kingdom (Beales & Cook 2008) and P. xanthii on C. hyssopifolia in Taiwan (Yeh et al. 2021). To our knowledge, this is the first report of powdery mildew caused by P. xanthii on C. hyssopifolia in mainland China. Our field observations suggest that the P. xanthii infections would be a potential threat to the health of C. hyssopifolia in China. References: Beales, P. A., and Cook, R. T. A. 2008. Plant Pathol. 57:778. Braun, U., Cook, R. T. A. 2012. The Taxonomic Manual of the Erysiphales (Powdery Mildews). CBS Biodiversity Series 11: CBS. Utrecht, The Netherlands. Mukhtar, I., et al. 2018. Sydowia.70:155. Scholin, C. A., et al. 1994. J. Phycol. 30:999. White, T. J., et al. 1990. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA. Yeh, Y. W., et al. 2021. Trop. Plant Pathol. 46:44.

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First Report of Powdery Mildew Caused by Erysiphe buhrii on Gypsophila paniculata in Korea

Plant Disease ◽

10.1094/pdis-03-14-0237-pdn ◽

2014 ◽

Vol 98 (7) ◽

pp. 1013-1013 ◽

Cited By ~ 4

Author(s):

I. Y. Choi ◽

B. S. Kim ◽

S. E. Cho ◽

J. H. Park ◽

H. D. Shin

Keyword(s):

Powdery Mildew ◽

Host Range ◽

Disease Incidence ◽

Width Ratio ◽

Korean Isolate ◽

Pathogenicity Test ◽

Cut Flower ◽

Voucher Specimen ◽

First Report ◽

Gypsophila Paniculata

Gypsophila paniculata L. (baby's breath, family Caryophyllaceae), native to Central and Eastern Europe, is commonly cultivated as a commercial cut flower crop in greenhouses in Korea. Since 2011, baby's breath cv. Cassiopeia has been observed affected by a powdery mildew with nearly 100% disease incidence at the stage of harvesting in Iksan City. Powdery mildew colonies first appeared as thin white patches on stems and both sides of the leaves. As disease progressed, plants were covered with dense masses of spores, followed by senescence and reduction of quality of cut flowers. A voucher specimen was deposited in the Korea University Herbarium (Accession KUS-F27313). Appressoria were well-developed, multilobed or moderately lobed, and single or opposite in pairs. Conidiophores were straight, 95 to 150 × 7 to 10 μm, and composed of 3 to 4 cells. Foot-cells were cylindric or slightly sinuous at the base and 37 to 53 μm long. Singly produced conidia were cylindrical to oblong-elliptical, 35 to 56 × 12.5 to 18 μm with a length/width ratio of 2.1 to 3.6, devoid of fibrosin bodies, and with angular/rectangular wrinkling of outer walls. Germ tubes were in the perihilar position on conidia, and ended with lobed appressoria. No chasmothecia were found. These structures are typical of the Pseudoidium anamorph of the genus Erysiphe. Specific measurements and host range were consistent with those of E. buhrii U. Braun (2). To confirm identification, the complete internal transcribed spacer (ITS) region of rDNA of isolate KUS-F27313 was amplified with primers ITS1/ITS4, and sequenced directly. The resulting 725-bp sequence was deposited in GenBank (KJ530705). A GenBank BLAST search of the Korean isolate showed 99% similarity with E. buhrii on Acanthophyllum sp. (Caryophyllaceae) from Iran (AB128924). Pathogenicity was confirmed through inoculation by gently dusting conidia onto leaves of five healthy, potted baby's breath cv. Cassiopeia. Five non-inoculated plants served as controls. Inoculated plants were isolated from non-inoculated plants in separate rooms in a greenhouse at 25 ± 2°C. Inoculated plants developed signs and symptoms after 7 days, whereas the control plants remained symptomless. The fungus present on the inoculated plants was identical morphologically to that originally observed on diseased plants. Pathogenicity test was repeated twice. The powdery mildew disease caused by E. buhrii on baby's breath has been recorded in the former Soviet Union (Armenia, Kazakhstan, Ukraine), Romania, Turkey, Iran, Mongolia, and Argentina (1,3). Also, a fungus occurring on baby's breath was recorded as Oidium sp. from Japan (4). To our knowledge, this is the first report of powdery mildew caused by E. buhrii on baby's breath in Korea. Powdery mildew infections pose a serious threat to production of this cut flower crop. References: (1) K. Amano. Host Range and Geographical Distribution of the Powdery Mildew Fungi. Japan Scientific Societies Press, Tokyo, 1986. (2) U. Braun and R. T. A. Cook. Taxonomic Manual of the Erysiphales (Powdery Mildews), CBS Biodiversity Series No. 11. CBS, Utrecht, 2012. (3) D. F. Farr and A. Y. Rossman. Fungal Databases. Syst. Mycol. Microbiol. Lab., Online publication, ARS, USDA, Retrieved February 18, 2014. (4) M. Satou et al. Ann. Phytopathol. Soc. Jpn. 62:541, 1996.

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First Report of Powdery Mildew caused by Podosphaera xanthii on Euphorbia tithymaloides in Malaysia

Plant Disease ◽

10.1094/pdis-08-20-1700-pdn ◽

2020 ◽

Author(s):

Siti Izera Ismail ◽

Aziera Roslen

Keyword(s):

Powdery Mildew ◽

Sequence Data ◽

Morphological Characteristics ◽

Pathogenicity Test ◽

Podosphaera Xanthii ◽

Sequence Alignments ◽

Voucher Specimen ◽

First Report ◽

Initial Symptoms ◽

Young Leaves

Euphorbia tithymaloides L. (zig-zag plant) is a succulent, perennial shrub belonging to the Euphorbiaceae family and is widely cultivated in Malaysia for ornamental purposes and commercial values. In June 2019, typical symptoms of powdery mildew were observed on over 50% of the leaves of E. tithymaloides in a garden at Universiti Putra Malaysia, Serdang city of Selangor province, Malaysia. Initial symptoms included circular to irregular white powdery fungal colonies on both leaf surfaces and later covered the entire leaf surface. Severely infected leaves became necrotic, distorted and senesced. A voucher specimen Ma (PM001-Ma) was deposited in the Mycology laboratory, Faculty of Agriculture, UPM. Microscopic observation showed hyphae hyaline, branched, thin-walled, smooth, 3 to 6 µm wide with nipple-shaped appressoria. Conidiophores were straight, measured 30 to 90 μm long × 8 to 12 μm wide and composed of a cylindrical foot cell, 50 to 75 μm long. Conidia formed in chains were hyaline, ellipsoid to oval with fibrosin bodies, measured 25 to 36 × 16 to 20.1 μm in size and chasmothecia were not observed on the infected leaves. Genomic DNA was directly isolated from mycelia and conidia of isolate Ma using DNeasy Plant Mini Kit (Qiagen, USA). The universal primer pair ITS4/ITS5 of rDNA (White et al. 1990) was used for amplification and the resulting 569-bp sequence was deposited in GenBank (Accession no. MT704550). A BLAST nucleotide search revealed 100% similarity with that of Podosphaera xanthii on Momordica charantia wild from Taiwan (Accession no. KM505135) (Kirschner and Liu 2015). Both the morphological characteristics of the anamorph and ITS sequence data support the identification of this powdery mildew on E. tithymaloides as Podosphaera xanthii (Castagne) U. Braun & Shishkoff (Braun and Cook 2012). A pathogenicity test was conducted by gently pressing the infected leaves onto young leaves of five healthy potted plants. Five noninoculated plants were used as controls. The inoculated plants were maintained in a greenhouse at 25 ± 2°C and the test was repeated. Seven days after inoculation, white powdery symptoms were observed similar to those on the naturally infected leaves, while control plants remained asymptomatic. The fungus on the inoculated leaves was morphologically and molecularly identical to the fungus on the original specimens. Sequence alignments were made using MAFFT v.7.0 (Katoh et al. 2019) and a maximum likelihood phylogram was generated by MEGA v.7.0 (Kumar et al. 2016). Isolate Ma grouped in a strongly supported clade (100% bootstrap value) with the related species of P. xanthii available in GenBank based on the ITS region. Powdery mildew caused by P. xanthii has been reported as a damaging disease that can infect a broad range of plants worldwide (Farr and Rossman 2020). It also has been recently reported on Sonchus asper in China (Shi et al. 2020). According to our knowledge, this is the first report of powdery mildew caused by P. xanthii on E. tithymaloides worldwide. The occurrence of powdery mildew on E. tithymaloides could pose a serious threat to the health of this plant, resulting in death and premature senescence of young leaves.

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First Report of Powdery Mildew Podoshaera tridactyla on Prunus hypoleuca in China

Plant Disease ◽

10.1094/pdis-09-14-0914-pdn ◽

2015 ◽

Vol 99 (2) ◽

pp. 289-289 ◽

Cited By ~ 1

Author(s):

L.-C. Bai ◽

Z.-M. Cao ◽

P.-Q. Li ◽

C. Liang

Keyword(s):

Powdery Mildew ◽

Present Report ◽

Phylogenetic Analyses ◽

Its Region ◽

28S Rdna ◽

Width Ratio ◽

Native Plant ◽

Bootstrap Analysis ◽

Voucher Specimen ◽

First Report

Prunus hypoleuca (≡ Maddenia hypoleuca), a native plant in China, grows in the Qinling Mountains that lie at the intersection of several forest regions in north, central, and southwest China. In October 2013, P. hypoleuca suffering from heavy powdery mildew infections was found with approximately 75% of the plants affected. The powdery mildew at first appeared as circular to irregular white patches, which subsequently showed abundant hyphal growth on both sides of leaves, leading to the withering of the leaves. A voucher specimen was maintained in the Mycological Herbarium of Northwest A & F University (Accession No. HMNWAFU-CF 2013166). Hyphal appressoria were nipple-shaped or nearly absent. Conidiophores were cylindrical, measured 83 to 110 × 10 to 12.5 μm, and produced two to five immature conidia in chains with a crenate outline. Foot-cells of conidiophores were straight, cylindrical, and 28 to 62 × 7 to 10 μm. Conidia were hyaline, ellipsoid to ovate, and measured 20 to 32 × 14 to 21 μm (length/width ratio 1.4:1.8). Chasmothecia were scattered or gregarious, depressed globose, and 65 to 112 μm in diameter. Appendages, arising from the upper half of the chasmothecia, usually had two to four dichotomous branches, and were one to three and a half times as long as the chasmothecial diameter. A single ascus in a chasmothecium was subglobose or broadly ellipsoid-ovoid, measured 66 to 86 × 47 to 76 μm and contained six to eight ascospores. The ascospores were ellipsoid-ovoid and 15 to 27 × 12 to 18 μm. The fungus was identified as Podosphaera tridactyla based on its anamorph and teleomorph characteristics (1,2). To confirm the identification, 28S rDNA and the ITS region were amplified. The ITS5/P3 and then PM5/ITS4 primers were used to amplify the ITS region by nested PCR. The primers LSU1/LSU2 were used to amplify the 28S rDNA, and the cloned fragments were sequenced. The 28S rDNA and ITS region sequences were deposited in GenBank (Accession Nos. KJ879240 and KM213121). A GenBank BLAST search of two sequences revealed 99% identity with P. tridactyla infecting Prunus salicina Lindl. in Korea (3). Based on ITS and a 28S rDNA phylogenetic tree, the two sequences retrieved from the Chinese specimen clustered within a strongly supported clade (bootstrap value = 100%) with P. tridactyla (JQ517296 and AB022393, respectively). Cladistic trees were constructed using the neighbor-joining method with the Kimura two-parameter substitution model in MEGA 5.0. Branch robustness was assessed via bootstrap analysis with 1,000 replicates. Phylogenetic analysis data were in agreement with morphological characters (3). To our knowledge, this is the first report of powdery mildew caused by P. tridactyla on P. hypoleuca. While Koch's postulates have not been carried out because of the biotrophic nature of the pathogen, the present report serves as a novel resource in order to improve the understanding of the etiology and epidemiology of the powdery mildew (P. tridactyla) on P. hypoleuca. The occurrence of P. tridactyla, a common powdery mildew on Prunus s. lat., supports recently published results of phylogenetic analyses of the Prunus complex, indicating that Maddenia must be reduced to synonymy with Prunus (4). References: (1) U. Braun. Beih. Nova Hedwigia 89:1, 1987. (2) U. Braun and R. T. A. Cook. Taxonomic Manual of the Erysiphales (Powdery Mildews), CBS Biodiversity Series No. 11. CBS, Utrecht, Netherlands, 2012. (3) S. C. Lee et al. Res. Plant Dis. 18:49, 2012. (4) J. Wen and W. T. Shi. PhytoKeys 17(2):39, 2012.

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First Report of Powdery Mildew Caused by Erysiphe elevata on Catalpa bignonioides in Korea

Plant Disease ◽

10.1094/pdis-12-13-1240-pdn ◽

2014 ◽

Vol 98 (6) ◽

pp. 856-856 ◽

Cited By ~ 1

Author(s):

S. E. Cho ◽

S. K. Lee ◽

S. H. Lee ◽

C. K. Lee ◽

H. D. Shin

Keyword(s):

Powdery Mildew ◽

Disease Incidence ◽

Its Region ◽

Width Ratio ◽

Poor Growth ◽

First Report ◽

Public Garden ◽

Voucher Specimens ◽

Severe Infections ◽

Length Width

Catalpa bignonioides Walter, known as southern catalpa or Indian bean tree, is native to the southeastern United States and are planted as shade trees throughout the world. In August 2009, typical powdery mildew symptoms on several leaves of the plants below 5% disease incidence were observed in a public garden of Hongcheon County of Korea. In 2011 to 2013, hundreds of southern catalpa trees were found heavily damaged by a powdery mildew with 90 to 100% disease incidence in a park of Incheon City of Korea, about 140 km apart from Hongcheon County. Symptoms appeared as circular to irregular white patches, which subsequently showed abundant mycelial growth on both sides of leaves and herbaceous stems. Severe infections caused poor growth and premature loss of leaves, resulting in reduced aesthetic value. Voucher specimens (n = 6) were deposited in the Korea University Herbarium (KUS). Appressoria on the mycelium were well-developed, lobed, and solitary or in opposite pairs. Conidiophores composed of 3 to 4 cells were 70 to 100 × 7.5 to 10 μm, and produced conidia singly. Foot-cells of conidiophores were flexuous or nearly straight, and 20 to 40 μm long. Conidia were oblong to oblong-elliptical, measured 30 to 42 × 13 to 20 μm (n = 30) with a length/width ratio of 1.6 to 2.5, devoid of distinct fibrosin bodies, and showed angular/rectangular wrinkling of outer walls. Primary conidia were apically rounded, basally subtruncate, and generally smaller than the secondary conidia. Germ tubes were produced on the end of conidia. Chasmothecia were not observed. These structures are typical of the Pseudoidium anamorph of the genus Erysiphe. The specific measurements and characteristics were compatible with those of E. elevata (Burrill) U. Braun & S. Takam. (1,2). To confirm the identification, the complete internal transcribed spacer (ITS) region of rDNA from KUS-F27676 was amplified with primers ITS5 and P3 (4) and sequenced directly. The resulting 675-bp sequence was deposited in GenBank (Accession No. KF840721). A GenBank BLAST search of the ITS sequence showed >99% similarity with isolates of E. elevata on C. bignonioides (Accession Nos. AY587012 to AY587014). Pathogenicity was confirmed through inoculation by gently dusting conidia onto leaves of five healthy southern catalpa seedlings. Five non-inoculated plants served as controls. Inoculated and non-inoculated plants were maintained in a greenhouse at 24 to 28°C in isolation. Inoculated plants developed symptoms after 6 days, whereas the control plants remained symptomless. The fungus present on the inoculated plants was identical morphologically to that originally observed on diseased plants. E.elevata is a North American powdery mildew on Catalpa species which was recently introduced into Europe (1,2,3). To our knowledge, this is the first report of powdery mildew caused by E. elevata on C. bignonioides in Asia as well as in Korea. The disease would be a serious threat to the widespread ornamental plantings of C. bignonioides in Korea. References: (1) N. Ale-Agha et al. Mycol. Prog. 3:291, 2004. (2) U. Braun and R. T. A. Cook. Taxonomic Manual of the Erysiphales (Powdery Mildews), CBS Biodiversity Series No.11. CBS, Utrecht, 2012. (3) D. F. Farr and A. Y. Rossman. Fungal Databases, Syst. Mycol. Microbiol. Lab., Online publication. ARS, USDA. Retrieved November 4, 2013. (4) S. Takamatsu et al. Mycol. Res. 113:117, 2009.

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