First Report of Leaf Spot Disease Caused by Exserohilum rostratum on Pineapple in Hainan Province, China

Pineapple (Ananas comosus (L.) Merr.) is an important perennial monocotyledonous plant that serves as an important fruit crop globally and is also produced in the Hainan Province of China where production in 2009 was 296,600 t. In July 2009, atypical symptoms of a leaf spot disease were observed on mature pineapple leaves in Chengmai County; approximately 15% of plants propagated from suckers became symptomatic after 150 to 300 days, eventually causing a 3 to 10% yield loss. In the initial infection stage, grayish white-to-yellowish white spots emerged on the leaf surfaces that ranged from 1.0 to 2.4 × 0.3 to 0.7 cm; black specks were not always present in the spots. Leaf spots also had distinctive light brown-to-reddish brown banding pattern on the edges. Several spots would often merge to form large lesions, 6.5 to 15.4 × 2.5 to 5.6 cm, covering more than 67% of the leaf surface, which can lead to death of the plant. Infected pineapple leaves collected from an orchard of Chengmai County were surface sterilized (75% ethanol for 30 s, 0.1% HgCl2 for 2 min, and rinsed three times in sterile distilled water). Leaf pieces were placed on potato dextrose agar medium and then incubated at 25°C. The emerging fungal colonies were grayish white to brown. Similar strains were obtained from Qionghai City and Wanning City subsequently. Two isolates, ITF0706-1 and ITF0706-2, were used in confirmation of the identity of the pathogen and in pathogenicity tests. Colonies were fast growing (more than 15 mm per day at 25 to 30°C) with dense aerial mycelia. Conidia were fusiform, pyriform to oval or cylindrical, olive brown to dark brown, 3 to 10 septate (typically 5 to 8), 33.2 to 102.5 × 9.0 to 21.3 μm, with a strongly protruding hilum bulged from the basal cell, which were similar to the Type A conidia described by Lin et al. (3). The strains were subjected to PCR amplification of the internal transcribed spacer (ITS)1-5.8S-ITS2 regions with universal primer pair ITS1/ITS4. The ITS sequence comparisons (GenBank Accession Nos. JN711431 and JN711432) shared between 99.60 and 99.83% identity with the isolate CATAS-ER01 (GenBank Accession No. GQ169762). According to morphological and molecular analysis, the two strains were identified as Exserohilum rostratum (Drechs.) Leonard & Suggs. Pathogenicity experiments were conducted five times and carried out by spraying a conidial suspension (105 CFU/ml) on newly matured leaves of healthy pineapple plants; plants sprayed with sterile water served as the negative control. Plants were incubated in the growth chamber at 20 to 25°C. Symptoms of leaf spot developed on test plants 7 days after inoculation while the control plants remained asymptomatic. Koch's postulates were fulfilled with the reisolation of the two fungal strains. Currently, E. rostratum is one of the most common pathogens on Bromeliads in Florida (2) and has been reported on Zea mays (4), Musa paradisiacal (3), and Calathea picturata (1) in China, but to our knowledge, this is the first report of leaf spot disease caused by E. rostratum on pineapple in Hainan Province of P.R. China. References: (1) L. L. Chern et al. Plant Dis. 95:1033, 2011. (2) R. M. Leahy. Plant Pathol. Circ. No. 393. Florida Department of Agriculture and Consumer Services Division of Plant Industry, 1999. (3) S. H. Lin et al. Australas. Plant Pathol. 40:246, 2011. (4) J. N. Tsai et al. Plant Pathol. Bull. 10:181, 2001.

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First report of banana (Musa acuminate L. AAA Cavendish, cv. Formosana) leaf spot disease caused by Curvularia geniculata in China

Plant Disease ◽

10.1094/pdis-09-21-2001-pdn ◽

2021 ◽

Author(s):

Yanxiang Qi ◽

Yanping Fu ◽

Jun Peng ◽

Fanyun Zeng ◽

Yanwei Wang ◽

...

Keyword(s):

Leaf Spot ◽

Disease Incidence ◽

Morphological Characteristics ◽

Universal Primers ◽

Leaf Spot Disease ◽

Leaf Margin ◽

Conidial Suspension ◽

Tropical Fruit ◽

First Report ◽

Spot Disease

Banana (Musa acuminate L.) is an important tropical fruit in China. During 2019-2020, a new leaf spot disease was observed on banana (M. acuminate L. AAA Cavendish, cv. Formosana) at two orchards of Chengmai county (19°48ʹ41.79″ N, 109°58ʹ44.95″ E), Hainan province, China. In total, the disease incidence was about 5% of banana trees (6 000 trees). The leaf spots occurred sporadically and were mostly confined to the leaf margin, and the percentage of the leaf area covered by lesions was less than 1%. Symptoms on the leaves were initially reddish brown spots that gradually expanded to ovoid-shaped lesions and eventually become necrotic, dry, and gray with a yellow halo. The conidia obtained from leaf lesions were brown, erect or curved, fusiform or elliptical, 3 to 4 septa with dimensions of 13.75 to 31.39 µm × 5.91 to 13.35 µm (avg. 22.39 × 8.83 µm). The cells of both ends were small and hyaline while the middle cells were larger and darker (Zhang et al. 2010). Morphological characteristics of the conidia matched the description of Curvularia geniculata (Tracy & Earle) Boedijn. To acquire the pathogen, tissue pieces (15 mm2) of symptomatic leaves were surface disinfected in 70% ethanol (10 s) and 0.8% NaClO (2 min), rinsed in sterile water three times, and transferred to potato dextrose agar (PDA) for three days at 28°C. Grayish green fungal colonies appeared, and then turned fluffy with grey and white aerial mycelium with age. Two representative isolates (CATAS-CG01 and CATAS-CG92) of single-spore cultures were selected for molecular identification. Genomic DNA was extracted from the two isolates, the internal transcribed spacer (ITS), large subunit ribosomal DNA (LSU rDNA), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), translation elongation factor 1-alpha (TEF1-α) and RNA polymerase II second largest subunit (RPB2) were amplified and sequenced with universal primers ITS1/ITS4, LROR/LR5, GPD1/GPD2, EF1-983F/EF1-2218R and 5F2/7cR, respectively (Huang et al. 2017; Raza et al. 2019). The sequences were deposited in GenBank (MW186196, MW186197, OK091651, OK721009 and OK491081 for CATAS-CG01; MZ734453, MZ734465, OK091652, OK721100 and OK642748 for CATAS-CG92, respectively). For phylogenetic analysis, MEGA7.0 (Kumar et al. 2016) was used to construct a Maximum Likelihood (ML) tree with 1 000 bootstrap replicates, based on a concatenation alignment of five gene sequences of the two isolates in this study as well as sequences of other Curvularia species obtained from GenBank. The cluster analysis revealed that isolates CATAS-CG01 and CATAS-CG92 were C. geniculata. Pathogenicity assays were conducted on 7-leaf-old banana seedlings. Two leaves from potted plants were stab inoculated by puncturing into 1-mm using a sterilized needle and placing 10 μl conidial suspension (2×106 conidia/ml) on the surface of wounded leaves and equal number of leaves were inoculated with sterile distilled water serving as control (three replicates). Inoculated plants were grown in the greenhouse (12 h/12 h light/dark, 28°C, 90% relative humidity). Necrotic lesions on inoculated leaves appeared seven days after inoculation, whereas control leaves remained healthy. The fungus was recovered from inoculated leaves, and its taxonomy was confirmed morphologically and molecularly, fulfilling Koch’s postulates. C. geniculata has been reported to cause leaf spot on banana in Jamaica (Meredith, 1963). To our knowledge, this is the first report of C. geniculata on banana in China.

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First Report of a Leaf Spot Disease of Bells-of-Ireland (Moluccella laevis) Caused by Cercospora apii in California

Plant Disease ◽

10.1094/pdis.2003.87.2.203a ◽

2003 ◽

Vol 87 (2) ◽

pp. 203-203

Author(s):

S. T. Koike ◽

S. A. Tjosvold ◽

J. Z. Groenewald ◽

P. W. Crous

Keyword(s):

Leaf Spot ◽

Sequence Data ◽

Disease Incidence ◽

Leaf Spot Disease ◽

Conidial Suspension ◽

Internal Transcribed Spacer Region ◽

First Report ◽

Spot Disease ◽

Leaf Spots ◽

Initial Symptoms

Bells-of-Ireland (Moluccella laevis) (Lamiaceae) is an annual plant that is field planted in coastal California (Santa Cruz County) for commercial cutflower production. In 2001, a new leaf spot disease was found in these commercially grown cutflowers. The disease was most serious in the winter-grown crops in 2001 and 2002, with a few plantings having as much as 100% disease incidence. All other plantings that were surveyed during this time had at least 50% disease. Initial symptoms consisted of gray-green leaf spots. Spots were generally oval in shape, often delimited by the major leaf veins, and later turned tan. Lesions were apparent on both adaxial and abaxial sides of the leaves. A cercosporoid fungus having fasciculate conidiophores, which formed primarily on the abaxial leaf surface, was consistently associated with the spots. Based on morphology and its host, this fungus was initially considered to be Cercospora molucellae Bremer & Petr., which was previously reported on leaves of M. laevis in Turkey (1). However, sequence data obtained from the internal transcribed spacer region (ITS1, ITS2) and the 5.8S gene (STE-U 5110, 5111; GenBank Accession Nos. AY156918 and AY156919) indicated there were no base pair differences between the bells-of-Ireland isolates from California, our own reference isolates of C. apii, as well as GenBank sequences deposited as C. apii. Based on these data, the fungus was subsequently identified as C. apii sensu lato. Pathogenicity was confirmed by spraying a conidial suspension (1.0 × 105 conidia/ml) on leaves of potted bells-of-Ireland plants, incubating the plants in a dew chamber for 24 h, and maintaining them in a greenhouse (23 to 25°C). After 2 weeks, all inoculated plants developed leaf spots that were identical to those observed in the field. C. apii was again associated with all leaf spots. Control plants, which were treated with water, did not develop any symptoms. The test was repeated and the results were similar. To our knowledge this is the first report of C. apii as a pathogen of bells-of-Ireland in California. Reference: (1) C. Chupp. A Monograph of the Fungus Genus Cercospora. Cornell University Press, Ithaca, New York, 1954.

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First Report of Leaf Spot Disease Caused by Epicoccum nigrum on Lablab purpureus in India

Plant Disease ◽

10.1094/pdis-07-13-0798-pdn ◽

2014 ◽

Vol 98 (2) ◽

pp. 284-284 ◽

Cited By ~ 12

Author(s):

S. Mahadevakumar ◽

K. M. Jayaramaiah ◽

G. R. Janardhana

Keyword(s):

Leaf Spot ◽

Leaf Surface ◽

Disease Incidence ◽

Leaf Spot Disease ◽

Post Inoculation ◽

Conidial Suspension ◽

Lablab Purpureus ◽

First Report ◽

Spot Disease ◽

Epicoccum Nigrum

Lablab purpureus (L.) Sweet (Indian bean) is an important pulse crop grown in arid and semi-arid regions of India. It is one of the most widely cultivated legume species and has multiple uses. During a September 2010 survey, we recorded a new leaf spot disease on L. purpureus in and around Mysore district (Karnataka state) with 40 to 80% disease incidence in 130 ha of field crop studied, which accounted for 20 to 35% estimated yield loss. The symptoms appeared as small necrotic spots on the upper leaf surface. The leaf spots were persistent under mild infection throughout the season with production of conidia in clusters on abaxial leaf surface. A Dueteromyceteous fungus was isolated from affected leaf tissues that were surface sterilized with 2% NaOCl2 solution then washed thrice, dried, inoculated on potato dextrose agar (PDA) medium, and incubated at 28 ± 2°C at 12 h alternate light and dark period for 7 days. The fungal colony with aerial mycelia interspersed with dark cushion-shaped sporodochia consists of short, compact conidiophores bearing large isodiametric, solitary, muricate, brown, globular to pear shaped conidia (29.43 to 23.92 μm). Fungal isolate was identified as Epicoccum sp. based on micro-morphological and cultural features (1). Further authenticity of the fungus was confirmed by PCR amplification of the internal transcribed spacer (ITS) region using ITS1/ITS4 universal primer. The amplified PCR product was purified, sequenced directly, and BLASTn search revealed 100% homology to Epicoccum nigrum Link. (DQ093668.1 and JX914480.1). A representative sequence of E. nigrum was deposited in GenBank (Accession No. KC568289.1). The isolated fungus was further tested for its pathogenicity on 30-day-old healthy L. purpureus plants under greenhouse conditions. A conidial suspension (106 conidia/ml) was applied as foliar spray (three replicates of 15 plants each) along with suitable controls. The plants were kept under high humidity (80%) for 5 days and at ambient temperature (28 ± 2°C). The appearance of leaf spot symptoms were observed after 25 days post inoculation. Further, the pathogen was re-isolated and confirmed by micro-morphological characteristics. E. nigrum has been reported to cause post-harvest decay of cantaloupe in Oklahoma (2). It has also been reported as an endophyte (3). Occurrence as a pathogen on lablab bean has not been previously reported. To our knowledge, this is the first report of the occurrence of E. nigrum on L. purpureus in India causing leaf spot disease. References: (1) H. L. Barnet and B. B. Hunter. Page 150 in: Illustrated Genera of Imperfect Fungi, 1972. (2) B. D. Bruten et al. Plant Dis. 77:1060, 1993. (3) L. C. Fávaro et al. PLoS One 7(6):e36826, 2012.

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First Report of Leaf Spot Disease Caused by Exserohilum rostratum on Bottle Gourd in India

Plant Disease ◽

10.1094/pdis-02-18-0315-pdn ◽

2018 ◽

Vol 102 (10) ◽

pp. 2042-2042 ◽

Cited By ~ 1

Author(s):

M. Choudhary ◽

H. R. Sardana ◽

M. N. Bhat ◽

M. S. Gurjar

Keyword(s):

Leaf Spot ◽

Bottle Gourd ◽

Leaf Spot Disease ◽

First Report ◽

Spot Disease ◽

Exserohilum Rostratum

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First Report of Bacterial Leaf Spot Disease of Broussonetia papyrifera Caused by Pseudomonas syringae pv. actinidiae in China

Plant Disease ◽

10.1094/pdis-07-20-1527-pdn ◽

2020 ◽

Author(s):

Li Li ◽

Hui Pan ◽

Lei Deng ◽

Dandan Feng ◽

Caihong Zhong

Keyword(s):

Leaf Spot ◽

Science And Technology ◽

Effective Control ◽

Economic Losses ◽

Leaf Spot Disease ◽

Broussonetia Papyrifera ◽

Bacterial Leaf Spot ◽

First Report ◽

Spot Disease ◽

Plant Pathol

Broussonetia papyrifera (paper mulberry) is a deciduous tree with a number of uses and is native to northeastern Asia. Because of its fast-growing nature and high tolerance to dust, smoke, and high temperatures, paper mulberry is regarded as an important and economically-valuable component of a biologically diverse community and is used extensively in several areas including medicine, animal husbandry, paper making, weaving, afforestation and light industry (Mei et al. 2016). From June to August of 2019, symptoms on paper mulberry trees were observed in Shiniushan village, Sanhua town, Xishui County, Hubei province of China. Typical symptoms on leaves included small, angular, brown spots surrounded by yellow haloes. These spots coalesced into necrotic areas. The incidence was around 30%, which threatened the survival and reduced the yield of paper mulberry. In order to identify the causal pathogenic organism, leaf samples from 10 different infected trees were collected every two weeks and isolations made over three months. Several circular, flat, granulated colonies with entire margins were isolated on King’s B medium (KB). The biochemical and physiological characteristics of thirty typical strains were tested and listed as following: gram negative, aerobic, rod shaped, and non-fluorescent on King’s B medium; positive for carbohydrate utilization (sucrose, glucose, fructose and arabinose), levan production, hypersensitive on tobacco, potato and tomato; and negative for oxidase, arginine dehydrolase, tyrosinase and urease activity, gelatin liquefaction, and reduction of nitrate. Psa pathovar-specific primers PsaF1/PsaR2 (280bp product ) identified two representative strains as Psa (Rees-George et al. 2010). BLAST analysis further confirmed that the 16S rDNA region amplified by primers 27F/1492R (NCBI accession nos. MT472100 and MT472101) shared 99.84% and 99.77% identity with the Psa type strain ICMP 18884 (CP011972) respectively (Weisburg et al. 1991). For ten typical strains, pathogenicity was confirmed by spraying a bacterial suspension (108 cfu/mL) onto fifty one-year seedlings of B. papyrifera, five seedlings repetitions for each strain. Symptoms of infection similar to those observed initially in the field were detected within 7 days after incubation at 25°C with 80–85% humidity. No symptoms were observed on control plants. The pathogen was re-isolated from symptomatic leaves and re-identified as Psa by morphological characteristics and sequencing. To our knowledge, this is the first report of Psa causing bacterial leaf spot disease on B. papyrifera, China. Psa has been reported as a pathogen causing bacterial canker of kiwifruit worldwide, resulting in severe economic losses to kiwifruit growers (McCann & Li, 2017). As a host of Psa, B. papyrifera may be a source of inoculum for nearby kiwifruit orchards, and consequently effective control measures should be taken to manage this disease. Funding: This study was supported by the National Natural Science Foundation of China (31701974; 31901980), Science and technology program funded by Wuhan Science and Technology Bureau (2018020401011307). References: Mei et al. 2016. Eur J Plant Pathol. 145: 203. McCann & Li et al. 2017. Genome Biol Evol. 9: 932. Rees-George et al. 2010. Plant Pathol. 59: 453 Weisburg et al. 1991. J Bacteriol. 173: 697.

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First Report of Tomato Gray Leaf Spot Disease Caused by Stemphylium solani in Malaysia

Plant Disease ◽

10.1094/pdis-03-12-0223-pdn ◽

2012 ◽

Vol 96 (8) ◽

pp. 1226-1226

Author(s):

A. Nasehi ◽

J. B. Kadir ◽

M. A. Zainal Abidin ◽

M. Y. Wong ◽

F. Mahmodi

Keyword(s):

Leaf Spot ◽

Disease Incidence ◽

Gray Leaf Spot ◽

Leaf Spot Disease ◽

Conidial Suspension ◽

Internal Transcribed Spacer Region ◽

First Report ◽

Spot Disease ◽

Pcr Product ◽

Morphological Criteria

In June 2011, tomatoes (Solanum lycopersicum) in major growing areas of the Cameron Highlands and the Johor state in Malaysia were affected by a leaf spot disease. Disease incidence exceeded 80% in some severely infected regions. Symptoms on 50 observed plants initially appeared on leaves as small, brownish black specks, which later became grayish brown, angular lesions surrounded by a yellow border. As the lesions matured, the affected leaves dried up and became brittle and later developed cracks in the center of the lesions. A survey was performed in these growing areas and 27 isolates of the pathogen were isolated from the tomato leaves on potato carrot agar (PCA). The isolates were purified by the single spore technique and were transferred onto PCA and V8 agar media for conidiophore and conidia production under alternating light (8 hours per day) and darkness (16 hours per day) (4). Colonies on PCA and V8 agar exhibited grey mycelium and numerous conidia were formed at the terminal end of conidiophores. The conidiophores were up to 240 μm long. Conidia were oblong with 2 to 11 transverse and 1 to 6 longitudinal septa and were 24 to 69.6 μm long × 9.6 to 14.4 μm wide. The pathogen was identified as Stemphylium solani on the basis of morphological criteria (2). In addition, DNA was extracted and the internal transcribed spacer region (ITS) was amplified by universal primers ITS5 and ITS4 (1). The PCR product was purified by the commercial PCR purification kit and the purified PCR product sequenced. The resulting sequences were 100% identical to published S. solani sequences (GenBank Accestion Nos. AF203451 and HQ840713). The amplified ITS region was deposited with NCBI GenBank under Accession No. JQ657726. A representative isolate of the pathogen was inoculated on detached 45-day-old tomato leaves of Malaysian cultivar 152177-A for pathogenicity testing. One wounded and two nonwounded leaflets per leaf were used in this experiment. The leaves were wounded by applying pressure to leaf blades with the serrated edge of a forceps. A 20-μl drop of conidial suspension containing 105 conidia/ml was used to inoculate these leaves (3). The inoculated leaves were placed on moist filter paper in petri dishes and incubated for 48 h at 25°C. Control leaves were inoculated with sterilized distilled water. After 7 days, typical symptoms for S. solani similar to those observed in the farmers' fields developed on both wounded and nonwounded inoculated leaves, but not on noninoculated controls, and S. solani was consistently reisolated. To our knowledge, this is the first report of S. solani causing gray leaf spot of tomato in Malaysia. References: (1) M. P. S. Camara et al. Mycologia 94:660, 2002. (2) B. S. Kim et al. Plant Pathol. J. 15:348, 1999. (3) B. M. Pryor and T. J. Michailides. Phytopathology 92:406, 2002. (4) E. G. Simmons. CBS Biodiversity Series 6:775, 2007.

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First Report of Gray Leaf Spot of Mango (Mangifera indica) Caused by Pestalotiopsis mangiferae in Taiwan

Plant Disease ◽

10.1094/pdis-91-12-1684b ◽

2007 ◽

Vol 91 (12) ◽

pp. 1684-1684 ◽

Cited By ~ 6

Author(s):

Y. Ko ◽

K. S. Yao ◽

C. Y. Chen ◽

C. H. Lin

Keyword(s):

Leaf Spot ◽

Mangifera Indica ◽

Gray Leaf Spot ◽

Leaf Spot Disease ◽

Continuous Exposure ◽

Conidial Suspension ◽

Tropical Fruit ◽

First Report ◽

Spot Disease ◽

Initial Symptoms

Mango (Mangifera indica L.; family Anacardiaceae) is one of the world's most important fruit crops and is widely grown in tropical and subtropical regions. Since 2001, a leaf spot disease was found in mango orchards of Taiwan. Now, the disease was observed throughout (approximately 21,000 ha) Taiwan in moderate to severe form, thus affecting the general health of mango trees and orchards. Initial symptoms were small, yellow-to-brown spots on leaves. Later, the irregularly shaped spots, ranging from a few millimeters to a few centimeters in diameter, turned white to gray and coalesced to form larger gray patches. Lesions had slightly raised dark margins. On mature lesions, numerous black acervuli, measuring 290 to 328 μm in diameter, developed on the gray necrotic areas. Single conidial isolates of the fungus were identified morphologically as Pestalotiopsis mangiferae (Henn.) Steyaert (2,3) and were consistently isolated from the diseased mango leaves on acidified (0.06% lactic acid) potato dextrose agar (PDA) medium incubated at 25 ± 1°C. Initially, the fungus grew (3 mm per day) on PDA as a white, chalky colony that subsequently turned gray after 2 weeks. Acervuli developed in culture after continuous exposure to light for 9 to 12 days at 20 to 30°C. Abundant conidia oozed from the acervulus as a creamy mass. The conidia (17.6 to 25.4 μm long and 4.8 to 7.1 μm wide) were fusiform and usually straight to slightly curved with four septa. Three median cells were olivaceous and larger than the hyaline apical and basal cells. The apical cells bore three (rarely four) cylindrical appendages. Pathogenicity tests were conducted with either 3-day-old mycelial discs or conidial suspension (105 conidia per ml) obtained from 8- to 10-day-old cultures. Four leaves on each of 10 trees were inoculated. Before inoculation, the leaves were washed with a mild detergent, rinsed with tap water, and then surface sterilized with 70% ethanol. Leaves were wounded with a needle and exposed to either a 5-mm mycelial disc or 0.2 ml of the spore suspension. The inoculated areas were wrapped with cotton pads saturated with sterile water and the leaves were covered with polyethylene bags for 3 days to maintain high relative humidity. Wounded leaves inoculated with PDA discs alone served as controls. The symptoms described above were observed on all inoculated leaves, whereas uninoculated leaves remained completely free from symptoms. Reisolation from the inoculated leaves consistently yielded P. mangiferae, thus fulfilling Koch's postulates. Gray leaf spot is a common disease of mangos in the tropics and is widely distributed in Africa and Asia (1–3); however, to our knowledge, this is the first report of gray leaf spot disease affecting mango in Taiwan. References: (1) T. K. Lim and K. C. Khoo. Diseases and Disorders of Mango in Malaysia. Tropical Press. Malaysia, 1985. (2) J. E. M. Mordue. No. 676 in: CMI Descriptions of Pathogenic Fungi and Bacteria. Surrey, England, 1980. (3) R. C. Ploetz et al. Compendium of Tropical Fruit Diseases. The American Phytopathological Society. St. Paul, MN, 1994.

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First Report of Leaf Spot Disease of Peony Caused by Seimatosporium botan in China

Plant Disease ◽

10.1094/pdis-10-10-0735 ◽

2011 ◽

Vol 95 (2) ◽

pp. 226-226

Author(s):

Y. B. Duan ◽

Z. Z. Yu ◽

Y. B. Kang

Keyword(s):

Basal Cell ◽

Leaf Spot ◽

Apical Cell ◽

Leaf Spot Disease ◽

Conidial Suspension ◽

Internal Transcribed Spacer Region ◽

Humid Atmosphere ◽

First Report ◽

Spot Disease ◽

Initial Symptoms

Tree peony (Paeonia suffruticosa Andrews), a perennial ligneous deciduous shrub in the Paeoniaceae family, is known for its beautiful and charming flowers. It is regarded as the flower symbol of China and is cultivated throughout the country. In August 2008, a previously unknown leaf spot was observed on peony cultivated in the Mountain Peony Garden located in the Luoyang area of Henan Province, China. In 2009, the leaf spot disease was observed in some gardens in the city of Luoyang, China. Initial symptoms appeared as small, round or irregular, brown, necrotic lesions in the middle of leaves. These lesions gradually enlarged up to 1 cm in diameter and were circular or irregular, brown to dark brown, and brown on the margins. In a humid atmosphere, black, sessile, discoid acervuli developed on the lesions, and the lesions sometimes became waxy-like, eventually coalesced, and nearly covered the entire leaf. Conidia produced in acervuli had two morphologically different types. One type had a single basal appendage, ellipsoid to fusiform, transversely three septate, 16 to 20 × 5 to 7 μm, smooth, basal cell obconic with a truncate base, subhyaline, 3 to 5 μm long; two central cells subcylindrical to dolioform, brown to dark brown, 8 to 10 μm long, apical cell conical with rounded apex, concolorous with the central cells, 4 to 5 μm long, basal appendage filiform, unbranched, excentric, 4 to 8 μm long. The other type had a single appendage at both ends, fusiform to subcylindrical, transversely three septate, 16 to 20 × 4 to 5 μm, smooth; basal cell obconic with a truncate base, subhyaline, 4 to 5 μm long; two central cells subcylindrical to dolioform, pale brown, 8 to 11 μm long; apical cell conical with an acute apex, hyaline to subhyaline, 4 to 5 μm long; basal appendage filiform, unbranched, excentric, 4 to 8 μm long; apical appendage filiform, unbranched, 4 to 8 μm long. Single conidial isolates of both types of conidia yielded identical colonies, which produced both types of conidia on potato dextrose agar (PDA), thus showing that both types of conidia belonged to the same fungus. Colonies on PDA were slimy in appearance, yellow to villous with an irregular taupe margin; reverse brown to grayish brown. Cultural and conidial characteristics of the isolates were similar to those of Seimatosporium botan (1). The DNA sequence for the fungus showed internal transcribed spacer region (ITS1-5.8S-ITS2) sequences (GenBank Accession No. HM067840) with 93% sequence identity to S. discosioides (Accession Nos. EF600970.1 and EF600969.1). This is the first submission of a S. botan sequence to GenBank. To determine pathogenicity, 20 healthy leaves of P. suffruticosa were inoculated by spraying a conidial suspension of S. botan onto the foliage. Ten leaves were sprayed with sterile water and served as controls. Plants were covered with plastic for 24 h to maintain high relative humidity. After 15 days, the symptoms described above were observed on leaves in all inoculated plants, whereas symptoms did not develop on the control plants. The pathogen was reisolated from inoculated leaves, fulfilling Koch's postulates. On the basis of morphology and ITS region sequences, we conclude that S. botan is the causal agent of leaf spots of P. suffruticosa. There is a report of S. botan on P. suffruticosa stems in Japan (1), but to our knowledge, this is the first report of leaf spot disease of peony caused by S. botan in China. References: (1) S. Hatakeyama et al. Mycoscience 45:106, 2004.

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First report of Alternaria alternata causing leaf spot on Oat (Avena sativa) in India

Plant Disease ◽

10.1094/pdis-02-21-0322-pdn ◽

2021 ◽

Author(s):

Boda Praveen ◽

Prasanna Kumar M.K. ◽

Devanna Pramesh ◽

PALANNA K B ◽

Buela P.P. ◽

...

Keyword(s):

Avena Sativa ◽

Leaf Spot ◽

Leaf Spot Disease ◽

Post Inoculation ◽

Conidial Suspension ◽

Cultural Characteristics ◽

Leaf Quality ◽

First Report ◽

Spot Disease ◽

Pathogenicity Assay

Oat (Avena sativa L.) is an important cereal crop grown worldwide primarily for food and animal feed. In November 2019, a leaf spot disease was observed on the oat plants at Mandya (12.5218° N, 76.8951° E), Karnataka, India. The disease incidence on plants was ranged between 43 to 57 percent. Initially, the symptoms appeared on leaves as small dark-brown spots surrounded by a yellow halo later turned to irregular necrotic spots with a yellow halo. A total of thirty leaves showing typical symptoms were collected from ten plants (three leaves per plant), cut into an area of 4-5 mm pieces at the junction of infected and healthy tissues. Cut tissues were soaked in 75% ethanol for 45 seconds, followed by 1% sodium hypochlorite solution for 1 min, rinsed five times in sterile distilled water, air dried, and placed on PDA and incubated at 25 ± 1 ℃. After 7 days of incubation, greyish fungal colonies appeared on PDA. Single-spore isolation method was employed to recover the pure cultures for five isolates. The colonies initially produced light-greyish aerial mycelia, then turned to dark-greyish upon maturity. Conidia were obclavate to pyriform and measured 17.34 to 46.97 µm long, 5.38 to 14.31 µm wide with 0 to 3 longitudinal, and 1 to 6 transverse septa with short beak (2.73 to 10.17µm) (n = 50.) Based on the morpho-cultural characteristics, the isolates were identified as Alternaria spp., and PCR assay using species-specific primers (AAF2/AAR3; Konstantinova, et al. 2002) confirmed the taxonomic identity of all five isolates as A. alternata. To further confirm the identity, the internal transcribed spacer (ITS), small subunit (SSU), glyceraldehyde-3-phosphate dehydrogenase (gapdh), RNA polymerase second largest subunit (rpb2), Alternaria major allergen (Alt a1), endopolygalacturonase (endoPG), an anonymous gene region OPA10-2, KOG1058 and translation elongation factor 1-alpha (tef1) of two isolates MAAS-1 and MAAS-2 were PCR amplified using the primers described previously (Woudenberg et al. 2015; Praveen et al. 2020) and the resultant PCR products were sequenced and deposited in NCBI GenBank (ITS: MW487388, MW741962, SSU: MW506220, MW752854, gapdh: MW506221, MW752855, rpb2: MW506222, MW752856, Alt a1: MW506223, MW752857, endoPG: MW506224, MW752858, OPA10-2: MW506225, MW752859, KOG1058: MW506226, MW752860, and tef1: MW506227, MW752861) which showed (99.62%, 99.81%), (100%, 100%), (100%, 99.66%), (100%, 100%), (99.58%, 99.15%), (99.55%, 99.32%), (99.53%, 99.68%), (99.23%, 99.56%) and (99.17%, 99.58%) identity with ITS (AF347031), SSU (KC584507), gapdh (AY278808), rpb2 (KC584375), Alt a1 (AY563301), endoPG (JQ811978), OPA10-2 (KP124632), KOG1058 (KP125233) and tef1 (KC584634) genes/genomic regions of type strain CBS916.96 of A. alternata respectively, confirming the identity of MAAS-1 as A. alternata. For pathogenicity assay, the conidial suspension (2 × 106 conidia/ml) of MAAS-1 isolate was artificially sprayed until runoff on ten healthy oat plants (cv. Kent, 35 days old) and ten plants sprayed with sterile water served as control. All plants were covered with polyethylene covers and kept under the greenhouse at 28 ± 1 ℃. The pathogenicity assay was repeated three times. After six days post-inoculation, small dark-brown spots with light-yellow halo appeared on leaves of MAAS-1inoculated plants. In comparison, no symptoms were observed on control plants. The fungal pathogen was re-isolated from the artificially infected plants and confirmed as A. alternata based on morpho-cultural characteristics and PCR assays. The leaf spot disease of Oat caused by A. alternata has already been reported from China (Chen et al. 2020); to our knowledge, it is the first report of A. alternata causing leaf spot on Oat in India. The leaf spot disease is an emerging threat to oat cultivation, and it reduces the grain yield and leaf quality; therefore, its management is essential for increasing productivity.

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First Report of Leaf Spot of Phoenix theophrasti Caused by Paraconiothyrium variabile in Greece

Plant Disease ◽

10.1094/pdis-01-13-0114-pdn ◽

2013 ◽

Vol 97 (9) ◽

pp. 1250-1250

Author(s):

E. K. Ligoxigakis ◽

I. A. Papaioannou ◽

E. A. Markakis ◽

M. A. Typas

Keyword(s):

Leaf Spot ◽

Rrna Genes ◽

Leaf Spot Disease ◽

28S Rrna ◽

Conidial Suspension ◽

First Report ◽

Spot Disease ◽

Initial Symptoms ◽

Palm Species ◽

Paraconiothyrium Variabile

In the spring of 2011, a severe leaf spot disease of Phoenix theophrasti was observed in the vicinity of Heraklion (Crete), Greece. Initial symptoms were small, round-ovoid spots of varying shades of brown on the leaves, later being transformed into oblong streaks (average dimensions 7.3 ± 1.0 × 3.3 ± 0.5 mm), surrounded by dark brown rings. As the disease progressed, the expanding streaks often coalesced to form enlarged necrotic lesions. Similar symptoms were also detected on petioles and leaf bases. Extended spotting and blighting occasionally resulted in leaf death. A filamentous fungus was consistently isolated onto potato dextrose agar plates from the periphery of the characteristic lesions, with cultures invariably producing brick to cinnamon colonies with sparse aerial mycelium, subglobose and dark brown superficial pycnidial conidiomata on pine needles, 1- to 3-celled hyaline conidiophores, and hyaline, subcylindrical to ellipsoidal, 1-celled, smooth- and thin-walled conidia, with average dimensions of 3.5 ± 0.6 × 1.7 ± 0.4 μm (n = 100). Total DNA of two isolates was extracted and used for PCR amplification and sequencing of the ITS1-5.8S-ITS2 region, together with parts of the flanking 18S and 28S rRNA genes (4). Both sequences (GenBank Accession Nos. JX456476 and JX456477) were 100% identical to deposited Paraconiothyrium variabile ITS sequences (EU295640 to 48, JN983440 and 41, and JF934920), and were clustered together as a single group with these sequences with good support by phylogenetic analysis that included representatives of the relative P. brasiliense and P. africanum species. Based on the morphological, molecular, and phylogenetic analyses, the pathogen was identified as P. variabile Riccioni, Damm, Verkley & Crous (2). To prove pathogenicity, 10 P. theophrasti 2-year-old seedlings were sprayed with a conidial suspension of the fungus (107 conidia ml–1, 10 ml per plant), while five additional control plants were treated with sterile distilled water. All plants were maintained in the greenhouse at 15 ± 5°C, with 90% humidity. Characteristic leaf spots were evident 4 weeks post inoculation on the older leaves, and P. variabile was consistently reisolated from all inoculated plants. No symptoms were observed on control plants. Paraconiothyrium variabile has been isolated from various woody host plants such as Prunus persica, P. salicina, and Malus sp. in South Africa (1,2), Actinidia chinensis and A. deliciosa in Italy (2), Laurus nobilis in Turkey (2), and Salix matsudana in China (3). To our knowledge, this is the first report of P. variabile naturally infecting and causing a leaf spot disease on a palm species. Palms are extensively used as ornamentals throughout Greece and the occurrence of P. variabile can potentially result in economic loss to the local ornamental industry. References: (1) M. Cloete et al. Phytopathol. Mediterr. 50:S176, 2011. (2) U. Damm et al. Persoonia 20:9, 2008. (3) H. Gao et al. Afr. J. Biotechnol. 10:4166, 2011. (4) M. P. Pantou et al. Mycol. Res. 109:889, 2005.

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