First Report of Powdery Mildew of Cashew Caused by Oidium anacardii in South Africa

The cashew plant (Anacardium occidentale L.) (family Anacardiaceae) is native to Brazil. It was introduced in East Africa by the Portuguese in the 16th century where it is now widely cultivated, especially in Tanzania, Kenya, and Mozambique. The processed kernels are the most important product derived from the plant, although in Brazil and India, juices, jam, and alcoholic and soft drinks are also made from the pear-shaped edible receptacle. The plant is currently being evaluated in South Africa for commercial production. During May 2002, at least 25% of 5-year-old cashew trees grown from seed in the northern KwaZulu-Natal Province of South Africa were infected with powdery mildew. Signs included extensive growth of white, superficial mycelium bearing upright conidiophores on young shoots with tender leaves, inflorescences, and young receptacles. In severely affected trees, approximately 35% of young shoots and 45% of young receptacles displayed signs of powdery mildew. Severely infected young leaves were brown and deformed in contrast to older leaves that were unaffected. Microscopic examination of diseased tissue revealed hyaline, cylindrical-to-slightly doliform, single-celled conidia (10 to 17.5 × 2.5 to 5 μm) borne in chains. The pathogen was subsequently identified as Oidium anacardii Noack on the basis of morphology (1). No other species of powdery mildew fungi have been reported on cashew. A pathogenicity test was conducted by gently pressing a heavily diseased leaf onto two healthy leaves of each of 10 cashew plants maintained in pots on open benches in the glasshouse at 22 to 25°C and mean relative humidity of 65%. Control treatments entailed pressing an asymptomatic leaf onto each of two healthy leaves per plant. The experiment was conducted three times. After 14 days, at least one powdery mildew colony had developed on 80% of inoculated leaves but were absent from all replications of the control treatment. The source of inoculum for this reported outbreak is unknown, although O. anacardii is known to occur in southern Mozambique less than 100 km from the infected site. Cashew powdery mildew was first officially reported in Tanzania in 1979 where significant crop losses, partially attributable to the pathogen, have been recorded since (3). No significant damage to production has been recorded in Brazil (2). To our knowledge, this is the first report of O. anacardii occurring on cashew in South Africa. References: (1) E. Castellani and F. Casulli. Rivista di Agricoltura Subtropicale e Tropicale 75:211, 1981. (2) F. C. O. Freire et al. Crop Prot. 21:489, 2002. (3) P. J. Martin et al. Crop Prot. 16:5, 1996.

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First Report of Powdery Mildew Caused by Golovinomyces biocellatus on Agastache rugosa in Korea

Plant Disease ◽

10.1094/pdis-03-14-0298-pdn ◽

2014 ◽

Vol 98 (9) ◽

pp. 1278-1278 ◽

Cited By ~ 1

Author(s):

S. E. Cho ◽

J. H. Park ◽

S. H. Hong ◽

I. Y. Choi ◽

H. D. Shin

Keyword(s):

Powdery Mildew ◽

Severe Disease ◽

Morphological Characteristics ◽

Control Measures ◽

Control Treatment ◽

Width Ratio ◽

Korean Isolate ◽

Pathogenicity Test ◽

Agastache Rugosa ◽

First Report

Agastache rugosa (Fisch. & C.A. Mey.) Kuntze, known as Korean mint, is an aromatic plant in the Lamiaceae. It is widely distributed in East Asian countries and is used as a Chinese traditional medicine. In Korea, fresh leaves are commonly added to fish soups and stews (3). In November 2008, several dozen Korean mints plants growing outdoors in Gimhae City, Korea, were found to be severely infected with a powdery mildew. The same symptoms had been observed in Korean mint plots in Busan and Miryang cities from 2008 to 2013. Symptoms first appeared as thin white colonies, which subsequently developed into abundant hyphal growth on stems and both sides of the leaves. Severe disease pressure caused withering and senescence of the leaves. Voucher specimens (n = 5) were deposited in the Korea University Herbarium (KUS). Appressoria on the mycelium were nipple-shaped or nearly absent. Conidiophores were 105 to 188 × 10 to 13 μm and produced 2 to 4 immature conidia in chains with a sinuate outline, followed by 2 to 3 cells. Foot-cells of the conidiophores were straight, cylindrical, slightly constricted at the base, and 37 to 58 μm long. Conidia were hyaline, ellipsoid to barrel-shaped, measured 25 to 40 × 15 to 23 μm (length/width ratio = 1.4 to 2.1), lacked distinct fibrosin bodies, and showed reticulate wrinkling of the outer walls. Primary conidia were obconically rounded at the apex and subtruncate at the base. Germ tubes were produced at the perihilar position of conidia. No chasmothecia were observed. The structures described above were typical of the Oidium subgenus Reticuloidium anamorph of the genus Golovinomyces. The measurements and morphological characteristics were compatible with those of G. biocellatus (Ehrenb.) V.P. Heluta (1). To confirm the identification, molecular analysis of the sequence of the internal transcribed spacer (ITS) region of ribosomal DNA (rDNA) of isolate KUS-F27200 was conducted. The complete ITS rDNA sequence was amplified using primers ITS5 and P3 (4). The resulting 514-bp sequence was deposited in GenBank (Accession No. KJ585415). A GenBank BLAST search of the Korean isolate sequence showed >99% similarity with the ITS sequence of many G. biocellatus isolates on plants in the Lamiaceae (e.g., Accession Nos. AB307669, AB769437, and JQ340358). Pathogenicity was confirmed by gently pressing diseased leaf onto leaves of five healthy, potted Korean mint plants. Five non-inoculated plants served as a control treatment. Inoculated plants developed symptoms after 7 days, whereas the control plants remained symptomless. The fungus present on inoculated plants was identical morphologically to that observed on the original diseased plants. The pathogenicity test was repeated with identical results. A powdery mildew on A. rugosa caused by G. biocellatus was reported from Romania (2). To our knowledge, this is the first report of powdery mildew caused by G. biocellatus on A. rugosa in Korea. The plant is mostly grown using organic farming methods with limited chemical control options. Therefore, alternative control measures should be considered. 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, USDA ARS, retrieved 17 February 2014. (3) T. H. Kim et al. J. Sci. Food Agric. 81:569, 2001. (4) S. Takamatsu et al. Mycol. Res. 113:117, 2009.

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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 of Kenaf Caused by Leveillula taurica in South Africa

Plant Disease ◽

10.1094/pdis.2001.85.8.923c ◽

2001 ◽

Vol 85 (8) ◽

pp. 923-923

Author(s):

W. J. Swart ◽

J. Terblanche

Keyword(s):

South Africa ◽

Powdery Mildew ◽

Seed Quality ◽

Leaf Surface ◽

Hibiscus Cannabinus ◽

First Report ◽

Leveillula Taurica ◽

Abaxial Leaf Surface ◽

Extensive Growth ◽

Northwest Province

Kenaf (Hibiscus cannabinus L.) is a fast-growing, bamboo-like annual plant belonging to the Malvaceae. The stem, which ranges from 1.5 to 4 m, presents a source of high-quality cellulose fibers. The plant is being investigated in South Africa with a view to commercial production. In April 2001, at least 50% of 4- to 5-month-old kenaf plants grown from seed in trials near Rustenburg, Northwest Province, South Africa, were observed as having powdery mildew. Signs included extensive growth of white, superficial mycelium and emergent conidiophores on the abaxial leaf surface, followed by partial defoliation. On older leaves, the abaxial leaf surface was completely covered by powdery mildew, and chlorotic and necrotic patches were clearly visible on the adaxial surface. Symptoms were observed on all five planted cultivars (Everglades 41, Cuba 108, El Salvador, SF459, and Tainung 2), and no difference in disease severity was noted among cultivars. Leveillula taurica (Lév.) Arnaud (anamorph Oidiopsis taurica [Lév.] Salmon) was subsequently identified by the presence of endophytic mycelia, often branched conidiophores, and dimorphic conidia borne singly or in short chains (1). In 100 measurements of each type, pyriform conidia averaged 69 ± 5 × 18 ± 2 μm and cylindrical conidia averaged 62 ± 6 × 16 ± 2 μm. The teleomorph was not observed. The source of L. taurica for this reported outbreak is unknown, and powdery mildew was not observed in a field of mature cotton (Gossypium hirsutum L.) growing within 10 m of the kenaf plot. L. taurica was reported on kenaf in Texas in 1992 (2) and in Italy in 1995 (3). The pathogen can cause significant losses in seed yield and reduce seed quality in susceptible kenaf cultivars. Although L. taurica has been reported from Hibiscus sabdariffa in Egypt (4), to our knowledge this is the first report of the pathogen occurring on kenaf in Africa. References: (1) H. J. Boesewinkel. Bot Rev. 46:167, 1980. (2) C. G. Cook and J. L. Riggs. Plant Dis. 79:968, 1995. (3) S. Frisullo et al. Inf. Fitopatol. 45:37–41, 1995. (4) M. Khairy, et al. Phytopathol. Medit. 10:269–271, 1971.

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First Report of Powdery Mildew Caused by Oidium Subgenus Pseudoidium on Mandevilla splendens in Italy

Plant Disease ◽

10.1094/pdis.2004.88.6.682a ◽

2004 ◽

Vol 88 (6) ◽

pp. 682-682

Author(s):

A. Garibaldi ◽

A. Minuto ◽

M. L. Gullino

Keyword(s):

Powdery Mildew ◽

Lower Surface ◽

Northern Italy ◽

Pathogenicity Test ◽

American Phytopathological Society ◽

First Report ◽

Tropical Plant ◽

Comprehensive Treatise ◽

Young Leaves ◽

The University

Mandevilla splendens (Hook.) Woodson is a tropical plant belonging to the Apocynaceae family and grown in Italy as an ornamental. It is generally potted and used to create small barriers on terraces and gardens. During February 2003, severe outbreaks of a previously unknown powdery mildew were observed in a commercial glasshouse located at Albenga (northern Italy) where 30% of the plants were affected by the disease. Infected young leaves were covered on both sides with white mycelia. Mycelia were more evident on the lower surface of older leaves. As the disease progressed, infected leaves turned reddish and eventually became yellow and died. Powdery mildew infections sometimes cause leaves to distort and have reduced growth. Conidia were hyaline, ellipsoid or cylindrical, sometimes appeared to adhere in chains, measured 9 to 15 × 14 to 28 μm (average 12 × 21 μm), and did not show fibrosin bodies. Foot cell was cylindric and appressorium lobed. Cleistothecia were not observed. The pathogen was identified as Oidium sp. subgenus Pseudoidium (1,2,3). Pathogenicity was confirmed by gently pressing diseased leaves onto young leaves of healthy, 1-year-old M. splendens plants grown in 3.5 liter pots. Three plants were inoculated, while three noninoculated plants served as controls. After inoculation, plants were maintained in a growth chamber at 18°C (12-h light, relative humidity >75%). After 60 days, powdery mildew symptoms were observed on inoculated plants. Noninoculated plants remained healthy. The pathogenicity test was carried out twice. To our knowledge, this is the first report of powdery mildew on M. splendens in Italy, as well as in the world. Specimens of this disease are available at the DIVAPRA Collection at the University of Torino. References: (1) R. Belanger et al., eds. The powdery mildew A comprehensive treatise. The American Phytopathological Society, St Paul, MN, 2002. (2) U. Braun. Nova Hedwigia, 89:700, 1987. (3) R. T. A. Cook et al. Mycol. Res. 101:975, 1997.

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First Report of Powdery Mildew Caused by Leveillula clavata on Poinsettia (Euphorbia pulcherrima) in Italy

Plant Disease ◽

10.1094/pd-90-0827c ◽

2006 ◽

Vol 90 (6) ◽

pp. 827-827 ◽

Cited By ~ 6

Author(s):

A. Garibaldi ◽

A. Minuto ◽

M. L. Gullino

Keyword(s):

Powdery Mildew ◽

Morphological Characteristics ◽

Plant Diseases ◽

Flowering Plant ◽

Pathogenicity Test ◽

Euphorbia Pulcherrima ◽

Conidial Suspension ◽

Mesophyll Cells ◽

First Report ◽

Young Leaves

Euphorbia pulcherrima (poinsettia) is a winter-flowering plant grown primarily for Christmas sales. During the fall of 2005, severe outbreaks of a previously unknown powdery mildew were observed on cv. Gala in a commercial greenhouse located in Albenga (northern Italy). The abaxial surfaces of green leaves were irregularly covered with white mycelia and conidia, while the adaxial surfaces only showed slight chlorotic round lesions. As the disease progressed, mycelium turned from rose to reddish. Symptoms and signs were never observed on red bracts. Conidia were clavate (55 to 95 × 20 to 40 μm, average 70 × 23 μm) and borne singly on conidiophores that emerged through stomata. On the basis of host, morphological characteristics, and microscopic observations of the intercellular colonization of mesophyll cells, the pathogen was identified as a species of Oidiopsis. Although chasmothecia were not observed, the causal agent based on the literature is believed to be Leveillula clavata Nour (2). Pathogenicity was confirmed by inoculating young leaves of three 4-month-old E. pulcherrima plants, cv. Gala, with a conidial suspension (3 × 105 conidia/ml). Three noninoculated plants sprayed with deionized water served as control. After inoculation, plants were maintained in a growth chamber at 18°C with relative humidity ranging from 56 to 100%. After 20 days, powdery mildew symptoms were observed on leaves of inoculated plants. Noninoculated plants remained healthy. The pathogenicity test was carried out twice. To our knowledge, this is the first report of L. clavata on poinsettia in Italy and probably in Europe. It presently is restricted to a few commercial farms. L. clavata previously has been observed on poinsettia in Kenya (1,2). Voucher specimens are available at the AGROINNOVA Collection, University of Torino. References: (1) M. L. Daughtrey et al. Powdery Mildew Diseases. Pages 39–42 in: Compendium of Flowering Potted Plant Diseases. The American Phytopathological Society, St. Paul, MN, 1995. (2) M. A. Nour. Trans. Brit. Mycol. Soc. 40:477, 1957.

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First Report of Lasiodiplodia crassispora as a Pathogen of Grapevine Trunks in South Africa

Plant Disease ◽

10.1094/pdis-94-8-1063a ◽

2010 ◽

Vol 94 (8) ◽

pp. 1063-1063 ◽

Cited By ~ 10

Author(s):

J. M. van Niekerk ◽

W. Bester ◽

F. Halleen ◽

P. W. Crous ◽

P. H. Fourie

Keyword(s):

South Africa ◽

Control Treatment ◽

Fluorescent Light ◽

Vitis Vinifera L ◽

Ammonium Compound ◽

Pathogenicity Test ◽

Santalum Album ◽

First Report ◽

Agar Plug ◽

Northern Cape

In 2003 and 2004, a survey of grapevine (Vitis vinifera L.) trunk pathogens was conducted in 30 vineyards in the Western and Northern Cape and Limpopo provinces of South Africa. In each vineyard, 20 visually healthy plants were sampled randomly by removing the distal part of one cordon arm. Isolations were made onto potato dextrose agar (PDA) from the internal wood decay symptoms observed in the cordon samples. Seven Botryosphaeriaceae spp. were identified, including Lasiodiplodia crassispora (1). Other Botryosphaeriaceae spp. are known grapevine trunk pathogens (2). Species identity was confirmed by DNA sequence data of the partial translation factor 1-α gene (1) and sequences deposited in GenBank (GU233658 and GU233659). The L. crassispora isolates (CBS 125626 and 125627) were associated with brown internal necrosis, a known symptom of grapevine Botryosphaeriaceae spp. infection (3), in the cordon arms of Ruby Cabernet grapevines occurring in two vineyards in the Northern Cape Province. L. crassispora was described from cankered wood of Santalum album in Western Australia and endophytically from Eucalyptus urophylla in Venezuela (1). Its grapevine pathogen status was determined using both isolates in a repeated pathogenicity test that included three isolates each of Botryosphaeria dothidea and Neofusicoccum australe as positive controls (2), Trichoderma harzianum as a nonpathogen treatment, and an uncolonized agar plug as a negative control. The Botryosphaeriaceae spp. and T. harzianum were plated on PDA and incubated at 25°C for 7 days. Lignified, 6-month-old shoots of grapevine cv. Chardonnay were excised from grapevines with internodes 4 to 6 used for inoculations. Before wounding, shoots were disinfected by submersion for 1 min in a 1 ml/liter solution of a quaternary ammonium compound (Sporekill; ICA International Chemicals (Pty) Ltd, Stellenbosch, South Africa). Twelve shoots were used for each isolate or control treatment. Wounds were made 2 mm deep on the fifth internode of the shoots with a 5-mm flame-sterilized cork borer (2,3). Wounds were inoculated with a pathogen colonized agar plug (5 mm in diameter) or an uncolonized agar plug and then covered with Parafilm (2,3). Inoculated shoots were incubated in the dark in moist chambers for 14 days at 25°C. After incubation, the bark of the shoots was peeled from the area around the wound and the lengths of any resultant lesions were measured under sterile conditions. The inoculum effect was assessed by analysis of variance and Student's t-test. Results showed that significantly (P < 0.0001) longer lesions were caused by L. crassispora (13.36 mm) compared with N. australe (9.27 mm) and B. dothidea (5.28 mm) and also significantly longer than lesions caused by the nonpathogen and negative controls (3.23 and 2.90 mm, respectively). To determine if lesions were caused by inoculated fungi, isolations were made from the tissue at the edges of the lesions by aseptically removing five 0.5 × 1 mm pieces of wood and placing them on PDA dishes amended with 0.04 g/liter of streptomycin sulfate. Dishes were incubated under normal fluorescent light at 25°C for 14 days before identifying isolated fungi based on morphological and cultural characteristics (1). To our knowledge, this is the first report of L. crassispora as a grapevine pathogen. References: (1) T. I. Burgess et al. Mycologia 98:423, 2006. (2) J. M. van Niekerk et al. Mycologia 96:781, 2004. (4) J. M. van Niekerk et al. Phytopathol. Mediterr. 45:S43, 2006.

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First Report of Powdery Mildew Caused by Podosphaera leucotricha on Photinia × fraserii in Italy

Plant Disease ◽

10.1094/pd-89-1362d ◽

2005 ◽

Vol 89 (12) ◽

pp. 1362-1362

Author(s):

A. Garibaldi ◽

G. Gilardi ◽

M. L. Gullino

Keyword(s):

Powdery Mildew ◽

Morphological Characteristics ◽

The United States ◽

Pathogenicity Test ◽

Podosphaera Leucotricha ◽

Public Park ◽

First Report ◽

Golden Delicious ◽

Young Leaves ◽

Voucher Specimens

Photinia × fraserii, belonging to the family Rosaceae, is an evergreen shrub used in parks and gardens. During the spring of 2004, severe outbreaks of a previously unknown powdery mildew were observed in a public park at Torino (northern Italy) on established plantings of this species. The adaxial and abaxial surfaces of leaves were covered with white mycelium and conidia. Stems also had signs of powdery mildew and were chlorotic. As the disease progressed, infected leaves turned yellow and abscised. Conidia formed in chains and were hyaline, ellipsoid, and measured 16.8 to 33.6 × 12.0 to 24.0 μm (average 25.6 × 15.6 μm). On the basis of host, morphological characteristics, and the presence of fibrosin bodies, the pathogen was identified as Podosphaera leucotricha (Ellis & Everth.) E.S. Salmon (2). Pathogenicity was confirmed by inoculating young leaves of 2-year-old Photinia × fraserii plants with a spore suspension (3 × 105 spores per ml). Also, three 3-year-old cv. Golden Delicious potted apple plants were inoculated. Three noninoculated Photinia × fraserii and three noninoculated apple plants sprayed with deionized water served as a control. After inoculation, plants were maintained in a growth chamber at 25°C. After 17 days, powdery mildew symptoms were observed on inoculated plants of Photinia × fraserii and cv. Golden Delicious. Noninoculated plants remained healthy. The pathogenicity test was carried out twice. The pathogenicity on apple supported the identification of the pathogen as P. leucotricha. To our knowledge, this is the first report of powdery mildew on Photinia × fraserii in Italy. P. leucotricha was previously described on Photinia serrulata in Italy (1) and the United States (3). Voucher specimens are available at the AGROINNOVA Collection, University of Torino. References: (1) E. Baldacci. Rev. Appl. Mycol. 16:358, 1937. (2) R. T. A. Cook et al. Mycol. Res. 101:975, 1997. (3) J. A. Milbraith. Rev. Appl. Mycol. 17:751, 1938.

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First Report of Powdery Mildew Caused by Erysiphe cruciferarum on Chinese Cabbage in China

Plant Disease ◽

10.1094/pdis-06-13-0648-pdn ◽

2014 ◽

Vol 98 (3) ◽

pp. 421-421 ◽

Cited By ~ 4

Author(s):

H. H. Zhao ◽

H. H. Xing ◽

C. Liang ◽

X. Y. Yang ◽

S. E. Cho ◽

...

Keyword(s):

Powdery Mildew ◽

Chinese Cabbage ◽

Control Treatment ◽

Width Ratio ◽

Pathogenicity Test ◽

Potential Threat ◽

Voucher Specimen ◽

First Report ◽

Powdery Mildews ◽

Erysiphe Cruciferarum

Chinese cabbage, Brassica rapa ssp. pekinensis (syn. Brassica pekinensis (Lour.) Rupr.), in the Brassicaceae, is an important vegetable grown on about 3 million ha in China. Since 2012, a powdery mildew has been found infecting Chinese cabbage plants (cv. Qingyanchunbai No. 1) after bolting for seed production from autumn through spring 2013 in a greenhouse in Qingdao, China. Symptoms first appeared as circular to irregular white patches on both sides of the leaves, and on stems and pods, often thinly covering the whole surface. A voucher specimen was deposited in the herbarium of Qingdao Agricultural University (Accession No. HMQAU12216). Hyphae were thin-walled, smooth, hyaline, and 4 to 6 μm wide. Appressoria on the mycelia were well developed, lobed, solitary, or in pairs. Conidiophores were erect, cylindrical, 45 to 110 μm long, and comprised 3 to 4 cells. Foot-cells of conidiophores were straight, cylindrical, 16 to 28 μm long, and 7.6 to 10 μm wide. Singly-produced conidia were oblong to cylindrical or somewhat ellipsoid-doliiform, 32 to 56 × 12 to 18 μm, with a length/width ratio of 1.8 to 3.8, with angular/rectangular wrinkling of the outer wall surface, and lacked distinct fibrosin bodies. Germ tubes were produced in the perihilar position of conidia. No chasmothecia were found. These structures are typical of the powdery mildew Pseudoidium anamorph of Erysiphe (2). The specific measurements and characteristics (especially short foot-cells of conidiophores) were consistent with previous records of Erysiphe cruciferarum Opiz ex L. Junell (2,3). To confirm the identification, the complete internal transcribed spacer (ITS) region of rDNA of isolate HMQAU12216 was amplified (4) and sequenced directly. The resulting 649-bp sequence was deposited in GenBank (Accession No. KC878683). A GenBank BLAST search of ITS sequences showed an exact match with those of E. cruciferarum on B. oleracea var. acephala (GU721075) and Oidium sp. on B. pekinensis (AB522714). A pathogenicity test was conducted by gently pressing a symptomatic leaf loaded with conidia onto a leaf of each five, healthy, potted, 40-day-old plants (cv. Qingyanchunbai No. 1). Five non-inoculated plants served as a control treatment. Inoculated plants were isolated from non-inoculated plants in separate rooms in a greenhouse at 20 ± 2°C. Inoculated plants developed signs and symptoms after 10 days, whereas the control plants remained symptomless. The fungus present on the inoculated plants was identical morphologically to that originally observed on diseased plants, thus fulfilling Koch's postulates. Though many Brassica spp. have been known to be infected with E. cruciferarum throughout the world, powdery mildew of Chinese cabbage caused by E. cruciferarum has been reported only in Finland, Germany, and Korea (1,3). To our knowledge, this is the first report of powdery mildew caused by E. cruciferarum on Chinese cabbage in China. Though occurrence of the powdery mildew on Chinese cabbage was noticed in an experimental breeding plot, this finding poses a potential threat to production of this vegetable in China. References: (1) U. Braun. The Powdery Mildews (Erysiphales) of Europe. Gustav Fischer Verlag, Jena, Germany, 1995. (2) U. Braun and R. T. A. Cook. Taxonomic Manual of the Erysiphales (Powdery Mildews), CBS Biodiversity Series No. 11. CBS, Utrecht, 2012. (3) H. J. Jee et al. Plant Pathol. 57:777, 2008. (4) S. Matsuda and S. Takamatsu. Mol. Phylogen. Evol. 27:314, 2003.

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First Report of Powdery Mildew Caused by Erysiphe pulchra on Cornus florida in Italy

Plant Disease ◽

10.1094/pdis-93-3-0320c ◽

2009 ◽

Vol 93 (3) ◽

pp. 320-320 ◽

Cited By ~ 2

Author(s):

A. Garibaldi ◽

D. Bertetti ◽

M. L. Gullino

Keyword(s):

Powdery Mildew ◽

Its Region ◽

The United States ◽

Deciduous Tree ◽

Herbarium Specimens ◽

Pathogenicity Test ◽

Cornus Florida ◽

First Report ◽

Flowering Dogwood ◽

Young Leaves

Cornus florida L. (Cornaceae), flowering dogwood, is a small deciduous tree whose showy inflorescences, clusters of bright red fruits and red and purple leaves in autumn, make it a much appreciated ornamental. During the summer of 2008, severe outbreaks of a previously unknown powdery mildew were observed in several gardens and nurseries in Piedmont (northern Italy). Young leaves were covered with dense, white mycelia and conidia, especially on the adaxial surface. As the disease progressed, infected leaves turned red. Conidia were hyaline, elliptical, borne singly, and measured 32 to 46 × 15 to 20 (average 38 × 17) μm. Conidiophores measured 68 to 77 × 8 to 9 (average 73 × 8) μm, with a cylindrical foot cell measuring 26 to 37 × 8 to 10 (average 31 × 9) μm, followed by two shorter cells. Fibrosin bodies were absent. No chasmothecia were observed. The ITS region (internal transcribed spacer) of rDNA was amplified using primers ITS4/ITS6 and sequenced. The 627-bp sequence (Accession No. EU FJ436989 in GenBank) has 99% identity with Erysiphe pulchra. As proof of pathogenicity, diseased leaves were pressed against leaves of three healthy 3-year-old plants. Three noninoculated plants served as controls. Inoculated and noninoculated plants were maintained outdoors at 13 to 21°C. After 15 days, typical powdery mildew colonies 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 the presence of powdery mildew on C. florida caused by E. pulchra in Italy. Powdery mildew of dogwood, caused by Microsphaera (Erysiphe) pulchra, has been reported in the United States (3) and Japan (1). In Italy, a powdery mildew caused by an Oidium sp. has been reported on C. sanguinea (2). Herbarium specimens of this disease are available at AGROINNOVA Collection, University of Torino, Italy. References: (1) T. Kobayashi. Index of Fungi Inhabiting Woody Plants in Japan. Host, Distribution, and Literature. Zenkoku-Noson-Kyoikai Publishing Co., Ltd., Tokyo, 2007. (2) G. Sicoli et al. Inf. Agrario 56/48:84, 2000. (3) V. L. Smith. Plant Dis. 83:782, 1999.

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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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