First Report of Powdery Mildew Caused by Podosphaera euphorbiae-hirtae on Euphorbia tithymaloides in California

Euphorbia tithymaloides (Euphorbiaceae; known as ‘Jacob's ladder,’ ‘Devil's Backbone’) is a perennial, succulent spurge, grown primarily as a border plant in ornamental landscapes. In June 2011 and February 2012, the California Department of Food and Agriculture Plant Pest Diagnostics Lab, Sacramento, CA, received an unusual powdery mildew sample on greenhouse-grown E. tithymaloides from a Ventura County, CA nursery. Disease incidence at the nursery was 100%. White mycelial patches were present on the stems and on both sides of the leaves. Over time, heavily infected branches defoliated and brownish, roughened, scabby lesions developed on the stems. Hyphae were thin-walled, up to 8 μm wide and developed nipple-shaped appressoria. Ellipsoid-ovoid conidia measured 21.0 to 32.5 × 13 to 18 μm (avg. 26.4 × 13.9 μm, n = 20) and formed in chains. The rDNA internal transcribed spacer (ITS) region was amplified with primers PFITS-F and PF5.8-R (4). The 387-bp sequence (GenBank JX006103) was 99% similar (346/347 bp) to Podosphaera euphorbia-hirtae (AB040306) from Acalypha australis (Euphorbiaceae) (3). Based on ITS similarity and culture morphology, the fungus was identified as P. euphorbiae-hirtae U. Braun & Somani (1,3). Pathogenicity was confirmed through inoculation by gently pressing diseased leaves from the nursery onto the youngest leaves of three plants each of E. tithymaloides cultivars ‘Nano’ and ‘Variegated.’ Leaves of an equal number of control plants were pressed with healthy leaves. Plants were incubated in a dew chamber for 48 h after which they were transferred to a 22°C growth chamber with a 12-h photoperiod. The experiment was repeated once. White powdery mildew colonies formed after 7 days on ‘Variegated’ and 13 days on ‘Nano’. Conidia measured 27.5 to 35.0 × 11 to 15 μm (avg. 30.5 × 12.6 μm, n = 30) which was within the range of P. euphorbia-hirtae. No symptoms developed on the control plants. P. euphorbiae-hirtae has been reported in Asia and the UK on E. tithymaloides and in Asia on A. australis (2). An asexual Oidium stage on Euphorbiaceae in Asia, Africa, Australia, Florida, Puerto Rico, Cuba, and the U.S. Virgin Islands may correspond to P. euphorbiae-hirtae (2). To our knowledge, this is the first report of P. euphorbiae-hirtae in California. Following the 2011 and 2012 detections, all E. tithymaloides plants in the Ventura County, CA nursery were destroyed. A regulatory trace back survey found that the plants were shipped from a Florida supplier, which was also shown to have an outbreak of P. euphorbiae-hirtae. The original source of the Florida E. tithymaloides plants was a 2010 shipment from Costa Rica. The host range of P. euphorbiae-hirtae is restricted to three landscape species in the Euphorbiaceae. References: (1) U. Braun. Beih. Nova Hedwigia 89:143, 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/index.cfm May 1, 2012. (3) T. Hirata. et al. Can. J. Bot. 78:1521, 2000. (4) R. Singh et al. Plant Dis. 93:1348, 2009.

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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 Colletotrichum phormii Causing Anthracnose on New Zealand Flax in the United States

Plant Disease ◽

10.1094/pdis-12-12-1155-pdn ◽

2013 ◽

Vol 97 (8) ◽

pp. 1115-1115 ◽

Cited By ~ 2

Author(s):

M. Serdani ◽

S. Rooney-Latham ◽

K. M. Wallis ◽

C. L. Blomquist

Keyword(s):

United States ◽

New Zealand ◽

Sequence Similarity ◽

Disease Incidence ◽

Its Region ◽

The United States ◽

Production Costs ◽

Santa Cruz ◽

California Department ◽

First Report

Phormium colensoi Hook.f. (syn. P. cookianum), New Zealand flax, (family Xanthorrhoeaceae) is popular in ornamental landscapes in the United States because of its sturdy blade-like foliage available in diverse colors. In February 2012, the Oregon State University Plant Clinic received three potted plants of P. colensoi ‘Black Adder’ from a commercial nursery in Santa Cruz County, California. The margins and midribs of several leaves had brown lesions that were variable in size, and fusiform to ellipsoidal in shape. Embedded in the lesions were black acervuli without setae that exuded salmon-colored spore masses under moist conditions. Conidia were hyaline, cylindrical to fusiform, straight to slightly curved, and 22.4 to 35.2 × 4.0 to 6.4 (average 24.7 × 4.9) μm. Based on morphology, the fungus was confirmed by USDA-APHIS National Identification Services to be Colletotrichum phormii (Henn.) D.F. Farr & Rossman (2). In March 2012, the California Department of Food and Agriculture Plant Pest Diagnostic Lab received additional samples from the same nursery lot (25% disease incidence) from which a similar fungus was recovered. rDNA sequences of the internal transcribed spacer (ITS) region from the California isolate (GenBank KC122681), amplified using primers ITS1 and ITS4 (2), were 100% identical to multiple species of Colletotrichum, including C. phormii by a BLAST query (JQ948446 through JQ948453). ITS sequence similarity alone is not sufficient to address Colletotrichum taxonomy and must be used in combination with host range and morphology (1). Pathogenicity of C. phormii (isolate CDFA986) was tested on three ‘Black Adder’ plants, which were inoculated with 6-mm agar plugs from a 14-day-old culture grown on half strength potato dextrose agar (PDA). Leaves were wound-inoculated along the midrib using colonized plugs (4). Five leaves per plant were inoculated with C. phormii plugs and five leaves per plant were treated with uncolonized PDA agar plugs as controls. Plants were sprayed with water and incubated in plastic bags at 22°C with a 12-h photoperiod. After 48 h, the bags and caps were removed and plants were kept under the same conditions. Two weeks later, water-soaked lesions had developed on the inoculated leaves. Lesions expanded along the midrib and became fusiform in shape after 21 to 28 days. C. phormii was isolated from lesion margins of all the inoculated leaves, but not from control leaves. This experiment was repeated once with similar results. Another Colletotrichum species, C. gloeosporiodes, also occurs on Phormium spp., but differs from C. phormii in morphology and symptom expression. Subsequent nursery and landscape surveys showed that anthracnose caused by C. phormii occurs on several P. colensoi cultivars as well as on P. tenax in five California counties including Santa Cruz, Yolo, Sacramento, San Luis Obispo, and Solano. C. phormii is also reported to infect P. colensoi and P. tenax in New Zealand, Europe, the United Kingdom, Australia, and South Africa (2,3). To our knowledge, this is the first report of C. phormii causing anthracnose on Phormium in North America. This disease could impact the American nursery trade and New Zealand flax production due to crop loss and increased production costs for pest management. References: (1) J. Crouch et al. Mycologia 101:648, 2009. (2) D. F. Farr et al. Mycol. Res. 110:1395, 2006. (3). H. Golzar and C. Wang. Australas. Plant Pathol. 5:110, 2010. (4) L. E. Yakabe et al. Plant Dis. 93:883, 2009.

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First Report of Powdery Mildew Caused by Erysiphe heraclei on Peucedanum japonicum in Korea

Plant Disease ◽

10.1094/pdis-09-14-0895-pdn ◽

2015 ◽

Vol 99 (1) ◽

pp. 161-161 ◽

Cited By ~ 1

Author(s):

I. Y. Choi ◽

S. H. Hong ◽

S. E. Cho ◽

J. H. Park ◽

H. D. Shin

Keyword(s):

Powdery Mildew ◽

Organic Farming ◽

Disease Incidence ◽

Morphological Characteristics ◽

Its Region ◽

Petroselinum Crispum ◽

Width Ratio ◽

First Report ◽

Potted Plants ◽

Powdery Mildews

Peucedanum japonicum Thunb., belonging to the family Apiaceae, is distributed in many Asian countries, including Korea. This plant was recently developed as an edible green and is cultivated under organic farming in Korea. In June 2013, plants showing typical symptoms of powdery mildew were found with approximately 50% disease incidence in polyethylene-film-covered greenhouses in Iksan City, Korea. Symptoms first appeared as circular white colonies, which subsequently showed abundant mycelial growth on the leaves, often covering the whole surface. Infected plants were unmarketable mainly due to signs of white fungal growths and reddish discoloration on the leaves. The same symptoms were found on P. japonicum in poly-tunnels in Iksan City and Jinan County of Korea in 2014. Voucher specimens (n = 3) were deposited in the Korea University Herbarium (KUS). Appressoria were lobed, and solitary or in opposite pairs. Conidiophores were cylindrical, 80 to 145 × 8 to 10 μm, and composed of three to four cells. Foot-cells of conidiophores were straight to substraight, cylindrical, and 25 to 63 μm long. Singly produced conidia were oblong-elliptical to oblong, occasionally ovate, 35 to 50 × 13 to 16 μm with a length/width ratio of 2.3:3.1, with angular/rectangular wrinkling of outer walls, and lacked distinct fibrosin bodies. Germ tubes were produced on the perihilar position of conidia. Primary conidia were apically conical, basally truncate, and generally smaller than the secondary conidia. No chasmothecia were found. These structures are typical of the powdery mildew Pseudoidium anamorph of the genus Erysiphe. The specific measurements and morphological characteristics were consistent with those of E. heraclei DC. (2). To confirm the identification, the complete internal transcribed spacer (ITS) region of rDNA from KUS-F27872 was amplified with primers ITS1/ITS4 and sequenced. The resulting 560-bp sequence was deposited in GenBank (Accession No. KM491178). The obtained ITS sequence shared >99% similarity with those of E. heraclei from apiaceous hosts, e.g., Daucus carota (KC480605), Pimpinella affinis (AB104513), and Petroselinum crispum (KF931139). Pathogenicity was confirmed through inoculation by gently dusting conidia onto leaves of five healthy potted plants. Five non-inoculated plants served as controls. Inoculated plants developed symptoms after 6 days, whereas the control plants remained symptomless. The fungus present on the inoculated plants was identical in morphology to those observed in the field. Powdery mildew of P. japonicum caused by E. heraclei has been reported in Japan (4), and numerous reports of E. heraclei on various species of Peucedanum plants have been made in most part of Europe and East Asia (Japan and far eastern Russia) (1,3). However, this is the first report of powdery mildew caused by E. heraclei on P. japonicum in Korea. Occurrence of powdery mildews is a threat to the quality and marketability of this plant, especially in organic farming. 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 August 18, 2014. (4) S. Tanda and C. Nakashima. J. Agric. Sci., Tokyo Univ. Agric. 47:54, 2002.

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First Report of Oidium longipes as the Causal Agent of Petunia Powdery Mildew in the United Kingdom

Plant Disease ◽

10.1094/pdis-09-10-0680 ◽

2011 ◽

Vol 95 (3) ◽

pp. 361-361 ◽

Cited By ~ 1

Author(s):

L. Kiss ◽

Z. Bereczky

Keyword(s):

United Kingdom ◽

Powdery Mildew ◽

Its Region ◽

Its Sequences ◽

Nuclear Ribosomal Dna ◽

Herbarium Specimens ◽

First Report ◽

The United Kingdom ◽

The Uk ◽

Solanaceous Plants

In autumn 2009, during a survey of powdery mildews of solanaceous plants in the United Kingdom, petunia (Petunia × hybrida) plants showing typical symptoms of powdery mildew infections were repeatedly collected in East Malling, Rochester, and Sandringham, UK. Leaves, stems, and petals of the collected plants, grown as outdoor ornamentals, were covered by dense, sporulating, white mycelium. Conidia were ellipsoid-cylindrical, measured 20 to 30 × 10 to 15 μm, and were produced in chains. Germ tubes arose from the ends of conidia and terminated in simple, unlobed apices. Some of the conidiophores were extremely long, up to 250 μm, because the second or third cell, or sometimes the foot cell, was up to 105 to 170 μm long. Other conidiophores were shorter, with no exceptionally long cells, but all of them exhibited a few characteristics in common: their width increased from base to top, sometimes enlarging considerably at a particular point of the foot cell, and basal septa were usually located 7 to 30 μm from the point of branching. Hyphal appressoria were nipple shaped. The teleomorph stage was not found. On the basis of these characteristics, the fungus was identified as Oidium longipes, a recently described (4) and little known pathogen of petunia and other solanaceous plants (1,3). To support the identification of this fungus, DNA was extracted from conidia collected with sterile brushes from single leaves collected in Sandringham, East Malling, and Rochester with a Qiagen DNeasy Plant Kit (Qiagen, Hilden, Germany), and the internal transcribed spacer (ITS) region of the nuclear ribosomal DNA was amplified and determined as described in Jankovics et al. (2). The three identical ITS sequences, deposited in GenBank under Accession Nos. HM156495, HM156496, and HM156497, were identical to several ITS sequences of O. longipes, such as AF250777, EU327324, and EU327325. This has also supported that the disease was caused by this species. Herbarium specimens were deposited under the Accession Nos. HAL 2373F, HAL 2374F, and HAL 2375F at the Herbarium of Martin Luther University, Halle, Germany. To our knowledge, this is the first report of O. longipes in the UK. References: (1) A. Bolay. Cryptogam. Helv. 20:1, 2005. (2) T. Jankovics et al. Phytopathology 98:529, 2008. (3) L. Kiss et al. Plant Disease 92:818, 2008. (4) M. E. Noordeloos and W. M. Loerakker. Persoonia 14:51, 1989.

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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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First report of Colletotrichum siamense Causing Blossom Blight on Thai basil (Ocimum basilicum L.) in Malaysia

Plant Disease ◽

10.1094/pdis-06-20-1371-pdn ◽

2020 ◽

Author(s):

Siti Izera Ismail ◽

Nur Adlina Rahim ◽

Dzarifah Zulperi

Keyword(s):

Disease Incidence ◽

Its Region ◽

Ocimum Basilicum ◽

Distilled Water ◽

Single Spore ◽

First Report ◽

Plastic Bags ◽

Colletotrichum Siamense ◽

Primer Sets ◽

Acca Sellowiana

Thai basil (Ocimum basilicum L.) is widely cultivated in Malaysia and commonly used for culinary purposes. In March 2019, necrotic lesions were observed on the inflorescences of Thai basil plants with a disease incidence of 60% in Organic Edible Garden Unit, Faculty of Agriculture in the Serdang district (2°59'05.5"N 101°43'59.5"E) of Selangor province, Malaysia. Symptoms appeared as sudden, extensive brown spotting on the inflorescences of Thai basil that coalesced and rapidly expanded to cover the entire inflorescences. Diseased tissues (4×4 mm) were cut from the infected lesions, surface disinfected with 0.5% NaOCl for 1 min, rinsed three times with sterile distilled water, placed onto potato dextrose agar (PDA) plates and incubated at 25°C under 12-h photoperiod for 5 days. A total of 8 single-spore isolates were obtained from all sampled inflorescence tissues. The fungal colonies appeared white, turned grayish black with age and pale yellow on the reverse side. Conidia were one-celled, hyaline, subcylindrical with rounded end and 3 to 4 μm (width) and 13 to 15 μm (length) in size. For fungal identification to species level, genomic DNA of representative isolate (isolate C) was extracted using DNeasy Plant Mini Kit (Qiagen, USA). Internal transcribed spacer (ITS) region, calmodulin (CAL), actin (ACT), and chitin synthase-1 (CHS-1) were amplified using ITS5/ITS4 (White et al. 1990), CL1C/CL2C (Weir et al. 2012), ACT-512F/783R, and CHS-79F/CHS-345R primer sets (Carbone and Kohn 1999), respectively. A BLAST nucleotide search of ITS, CHS-1, CAL and ACT sequences showed 100% similarity to Colletotrichum siamense ex-type cultures strain C1315.2 (GenBank accession nos. ITS: JX010171 and CHS-1: JX009865) and isolate BPDI2 (CAL: FJ917505, ACT: FJ907423). The ITS, CHS-1, CAL and ACT sequences were deposited in GenBank as accession numbers MT571330, MW192791, MW192792 and MW140016. Pathogenicity was confirmed by spraying a spore suspension (1×106 spores/ml) of 7-day-old culture of isolate C onto 10 healthy inflorescences on five healthy Thai basil plants. Ten infloresences from an additional five control plants were only sprayed with sterile distilled water and the inoculated plants were covered with plastic bags for 2 days and maintained in a greenhouse at 28 ± 1°C, 98% relative humidity with a photoperiod of 12-h. Blossom blight symptoms resembling those observed in the field developed after 7 days on all inoculated inflorescences, while inflorescences on control plants remained asymptomatic. The experiment was repeated twice. C. siamense was successfully re-isolated from the infected inflorescences fulfilling Koch’s postulates. C. siamense has been reported causing blossom blight of Uraria in India (Srivastava et al. 2017), anthracnose on dragon fruit in India and fruits of Acca sellowiana in Brazil (Abirami et al. 2019; Fantinel et al. 2017). This pathogen can cause a serious threat to cultivation of Thai basil and there is currently no effective disease management strategy to control this disease. To our knowledge, this is the first report of blossom blight caused by C. siamense on Thai basil in Malaysia.

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Effective Management of Cucumber Powdery Mildew with Essential Oils

Agriculture ◽

10.3390/agriculture11111177 ◽

2021 ◽

Vol 11 (11) ◽

pp. 1177

Author(s):

Yasser S. Mostafa ◽

Mohamed Hashem ◽

Ali M. Alshehri ◽

Saad Alamri ◽

Ebrahem M. Eid ◽

...

Keyword(s):

Powdery Mildew ◽

Essential Oils ◽

Disease Incidence ◽

Its Region ◽

Dry Weight ◽

Positive Control ◽

Powdery Mildew Fungus ◽

Membrane Injury ◽

Cucumber Powdery Mildew

This research evaluated the efficacy of essential oils in the management of cucumber powdery mildew. Essential oils of lemongrass, lemon, thyme, peppermint, abundance blend, purification blend, and thieves blend were tested in vitro and under greenhouse conditions in two separate experiments. The effects of essential oils were tested against powdery mildew disease at concentrations of 1.0–2.5 mL/L, and the consequent impact of the oils on plant growth was evaluated. Powdery mildew fungus, Podosphaera xanthii, was identified using sequencing of the ITS region. The essential oils significantly reduced disease incidence up to 77.3% compared with the positive control (p < 0.5). Moreover, the essential oils increased the plant length (up to 187 cm), leaf area (up to 27.5 cm2), fresh weight (up to 123 g), dry weight (up to 22.5 g), number of flowers (16.3), and metabolite content compared with the positive control (p < 0.5). Cell membrane injury decreased significantly in the oil-treated pants (p < 0.5), indicating the protective effect of essential oils. This study recommends the application of essential oils in an appropriate dose (2.5 mL/L) to protect cucumber plants against powdery mildew. Overdose of the oils (more than 2.5 mL/L) should be avoided due to adverse effects.

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First Report of Mucor spp. Causing Root Rot of Radix pseudstellariae in Guizhou Province of China

Plant Disease ◽

10.1094/pdis-07-20-1634-pdn ◽

2020 ◽

Author(s):

Hongmiao Wu ◽

Jiachun Wu ◽

Feng Li ◽

Ling Zheng ◽

Jingkai Fan ◽

...

Keyword(s):

Root Rot ◽

Disease Incidence ◽

Acid Soils ◽

Its Region ◽

Significant Loss ◽

Day Length ◽

Guizhou Province ◽

First Report ◽

Chinese Medicinal Plants ◽

Branched Chains

Radix pseudostellariae L. is one of the most common and highly-prized Chinese medicinal plants with various pharmacological effects, and mainly produced in acid soils in the Guizhou and Fujian provinces of southwestern and southeastern China, respectively (Wu et al. 2020). However, consecutive monoculture of R. pseudostellariae results in severe root rot and decline in biomass and quality of underground tubers. Root tubers of R. pseudostellariae are typically planted in December and harvested in next June. Root rot commonly starts developing in May. The disease incidence of root rot was ranging from 37 to 46% in root portions and basal stem of R. pseudostellariae under the consecutive monoculture fields in Shibing County, Guizhou Province, China (108°12ʹE, 27°03ʹN) (Li et al. 2017). Severe root rot was observed in Shibing County in May 2018. Infected plants displayed curly, withered, and yellow leaves, blight, retarded growth, root rot, and yield losses. Abundant whitish mycelia were observed on roots and surrounding soil. Two fungal isolates, designated GZ20190123 and GZ20190124, were obtained from symptomatic roots cultured on potato dextrose agar (PDA). The optimum temperature range for growth of the two isolates was 25 to 30°C. The optimum pH range for the growth of GZ20190123 was 5 to 5.5, whereas GZ20190124 grew better between pH 5 to 8.5. The mean mycelial growth rates of GZ20190123 and GZ20190124 at 30°C were 2.1 and 1.5 cm/day, respectively. Conidia of the two isolates were ovoid or obclavate and were produced in single or branched chains. The internal transcribed spacer (ITS) region was amplified with primers ITS1 and ITS4 (White et al. 1990). The sequences were deposited in GenBank as accession No. MN726736 for GZ20190123 and MN726738 for GZ20190124. Sequence comparison revealed 99% (GZ20190123) and 97% (GZ20190124) identity with previously reported isolate xsd08071 of Mucor racemosus Bull. (accession No. FJ582639.1) and isolate BM3 of Mucor fragilis Bainier (accession No. MK910058.1), respectively, which was confirmed by phylogenetic analysis. The two isolates were tested for pathogenicity on R. pseudostellariae. Six roots of R. pseudostellariae were surface-sterilized with 75% ethanol and stab inoculated with mycelia using a sterile toothpick for each isolate. Sterile distilled water was stab inoculated to twelve roots to serve as the control. Treated roots were incubated in a greenhouse with 16 h day length [light intensity 146.5 μmol/(m2·s)] and day/night temperature 26°C/18°C. The inoculated roots showed the expected symptoms on roots and sprouts 7 days after inoculation, whereas the control roots with sprouts did not show any symptom. The fungi were re-isolated from the diseased roots and confirmed as expected M. racemosus or M. fragilis based on the ITS sequences, which satisfied Koch’s postulates. Thus, isolate GZ20190123 was identified as M. racemosus and GZ20190124 as M. fragilis. Previously, M. racemosus and M. fragilis have been reported as a pathogen on tomato (Kwon and Hong 2005) and grape (Ghuffar et al. 2018), respectively. To our knowledge, this is the first report of M. racemosus and M. fragilis causing root rot of R. pseudostellariae in southwestern China, where the disease could cause a significant loss to production of this important medicinal plant.

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First Report of Fruit Rot of Melon Caused by Fusarium asiaticum in China

Plant Disease ◽

10.1094/pdis-08-20-1857-pdn ◽

2020 ◽

Author(s):

Fangmin Hao ◽

Quanyu Zang ◽

Weihong Ding ◽

Erlei Ma ◽

Yunping Huang ◽

...

Keyword(s):

Disease Incidence ◽

Elongation Factor ◽

Morphological Characteristics ◽

Its Region ◽

Fruit Rot ◽

Post Inoculation ◽

Basal Cells ◽

First Report ◽

Fusarium Asiaticum ◽

Sterile Needle

Melon (Cucumis melo L.) is a member of the Cucurbitaceae family, an important economical and horticultural crop, which is widely grown in China. In May 2020, fruit rot disease with water-soaked lesions and pink molds on cantaloupe melons was observed in several greenhouses with 50% disease incidence in Ningbo, Zhejiang Province in China. In order to know the causal agent, diseased fruits were cut into pieces, surface sterilized for 1 min with 1% sodium hypochlorite (NaClO), 2 min with 75% ethyl alcohol, rinsed in sterile distilled water three times (Zhou et al. 2018), and then placed on potato dextrose agar (PDA) medium amended with streptomycin sulfate (100 μg/ml) plates at 25°C for 4 days. The growing hyphae were transferred to new PDA plates using the hyphal tip method, putative Fusarium colonies were purified by single-sporing. Twenty-five fungal isolates were obtained and formed red colonies with white aerial mycelia at 25°C for 7 days, which were identified as Fusarium isolates based on the morphological characteristics and microscopic examination. The average radial mycelial growth rate of Fusarium isolate Fa-25 was 11.44 mm/day at 25°C in the dark on PDA. Macroconidia were stout with curved apical and basal cells, usually with 4 to 6 septa, and 29.5 to 44.2 × 3.7 to 5.2 μm on Spezieller Nährstoffarmer agar (SNA) medium at 25°C for 10 days (Leslie and Summerell 2006). To identify the species, the internal transcribed spacer (ITS) region and translational elongation factor 1-alpha (TEF1-α) gene of the isolates were amplified and cloned. ITS and TEF1-α was amplified using primers ITS1/ITS4 and EF1/EF2 (O’Donnell et al. 1998), respectively. Sequences of ITS (545 bp, GenBank Accession No. MT811812) and TEF1-α (707 bp, GenBank Acc. No. MT856659) for isolate Fa-25 were 100% and 99.72% identical to those of F. asiaticum strains MSBL-4 (ITS, GenBank Acc. MT322117.1) and Daya350-3 (TEF1-α, GenBank Acc. KT380124.1) in GenBank, respectively. A phylogenetic tree was established based on the TEF1-α sequences of Fa-25 and other Fusarium spp., and Fa-25 was clustered with F. asiaticum. Thus, both morphological and molecular characterizations supported the isolate as F. asiaticum. To confirm the pathogenicity, mycelium agar plugs (6 mm in diameter) removed from the colony margin of a 2-day-old culture of strain Fa-25 were used to inoculate melon fruits. Before inoculation, healthy melon fruits were selected, soaked in 2% NaClO solution for 2 min, and washed in sterile water. After wounding the melon fruits with a sterile needle, the fruits were inoculated by placing mycelium agar plugs on the wounds, and mock inoculation with mycelium-free PDA plugs was used as control. Five fruits were used in each treatment. The inoculated and mock-inoculated fruits were incubated at 25°C with high relative humidity. Symptoms were observed on all inoculated melon fruits 10 days post inoculation, which were similar to those naturally infected fruits, whereas the mock-inoculated fruits remained symptomless. The fungus re-isolated from the diseased fruits resembled colony morphology of the original isolate. The experiment was conducted three times and produced the same results. To our knowledge, this is the first report of fruit rot of melon caused by F. asiaticum in China.

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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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