First Report of Leaf Spot on Onion Caused by Fusarium acuminatum in Georgia

An unknown disease was observed on shallot onions (Allium cepa L.) in Tattnall County, Georgia, in September of 2012. Disease symptoms included leaf tip die back and scattered light brown lesions on leaves, oval to round in shape, with a size ranging from 0.5 to 2.0 cm. The disease occurred in approximately 1.2 ha of commercial onion fields, and disease incidence ranged from 50 to 70%. Infected leaf tissues from 10 plants were surface sterilized with 0.5% NaOCl and plated on quarter-strength potato dextrose agar (QPDA). The fungus grew on all plates, producing bright orange to rose pigmentation in the medium after incubation at 25°C for 5 days. The fungus produced sickle shaped macroconidia with 3 to 6 septa, 4 to 5 μm wide, and 30 to 54 μm in length. Chlamydospores were formed in chains and averaged 20.4 × 16.8 μm. The fungus was identified as Fusarium sp. based on morphological characteristics (3). Genomic DNA was extracted from single conidial cultures of three representative isolates and the internal transcribed spacer regions of rDNA (ITS1-5.8S-ITS2) were amplified and sequenced with primers ITS1 and ITS4 (2). MegaBLAST analysis of the sequences showed that they were 100% identical to a Fusarium acuminatum isolate (Accession No. JN624894). ITS sequence of an isolate FAON-1 was deposited in GenBank (KC477845). Pathogenicity tests were performed with the three isolates grown on QPDA at 25°C for 7 days. Eight-week-old shallot onion seedlings were inoculated by foliar spray with conidial suspensions at 2 × 106 spores/ml (5 ml per plant). Ten plants were inoculated with each isolate and 10 plants were sprayed with water as a control. The plants were incubated in a humidified chamber at (25 ± 3°C) with >95% relative humidity and 12-h photoperiod for 48 h after inoculation, and then kept in a greenhouse at 22 ± 2°C. Inoculated plants started to show symptoms identical to those observed in the field 7 days after inoculation, and disease incidence reached 100% within 14 days. No disease occurred on the control plants. The fungus was reisolated from the diseased plants and confirmed to be F. acuminatum based on morphological characteristics and molecular identification. Onion was previously reported to be a host of F. acuminatum in Montana (4). To our knowledge, this study is the first report confirming F. acuminatum causing disease on onion in Georgia. Onion is a major vegetable crop in Georgia with an annual production of approximately 5,000 ha (1). Occurrence of leaf spot caused by F. acuminatum and the impact of the disease needs to be considered in developing and implementing disease management programs in onion production. References: (1) S. R. Boatright and J. C. Mckissick, Univ. of Georgia CAES Publication AR-10-02, 2010. (2) M. A. Innes et al. PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA. 1990. (3) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Ames, IA, 2006. (4) C. G. Shaw. Washington State Univ. Agric. Exp. Sta. Bull. 765:12, 1973.

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First Report of Stemphylium botryosum on Spinach in Texas

Plant Disease ◽

10.1094/pdis-06-10-0471 ◽

2010 ◽

Vol 94 (11) ◽

pp. 1377-1377 ◽

Cited By ~ 3

Author(s):

J. D. Reed ◽

J. E. Woodward ◽

K. L. Ong ◽

M. C. Black ◽

L. A. Stein

Keyword(s):

Leaf Spot ◽

Spinacia Oleracea ◽

Disease Incidence ◽

Morphological Characteristics ◽

Tween 80 ◽

Growing Season ◽

Control Treatment ◽

Infected Leaf ◽

First Report ◽

Stemphylium Botryosum

During the 2009 to 2010 growing season, symptoms of an unknown leaf spot were observed on spinach (Spinacia oleracea L.) in production fields in southwest Texas. Approximately 500 ha were affected, especially cvs. Rakaia and Viceroy. Disease incidence was 30 and 2% for Rakaia and Viceroy, respectively. Diseased plants exhibited small (1 to 3 mm in diameter), tan, necrotic lesions with a circular to oval shape and were void of any signs of a pathogen. Symptomatic leaves were surface sterilized in 1.5% NaOCl for 1 min, rinsed with sterile water, and air dried. Leaf sections (~1 cm2) were cut and placed on acidified potato dextrose agar (APDA), or APDA supplemented with streptomycin (SAPDA). Fungal mycelia growing from the edges of infected leaf sections were transferred to PDA and incubated at 25°C with a 12-h/12-h light/dark cycle. After 14 days of incubation, dark brown mycelia giving rise to unbranched conidiophores bearing brown, deeply septate, ovoid conidia were observed. Conidia measured 16.8 to 27.3 × 13.1 to 19.6 μm. On the basis of these morphological characteristics, the fungus was identified as Stemphylium botryosum (3). Cultures were transferred to clarified V8 juice agar to obtain inoculum for pathogenicity tests. Eight-week-old plants (n = 20) of spinach cvs. Hybrid 310, Wintergreen, Ashley, and Rakaia were sprayed until runoff with a suspension containing 0.001% Tween 80 and 1 × 104 conidia/ml. Noninoculated plants served as a control treatment. Plants were placed in a growth chamber and incubated in the dark at 25°C and 95% relative humidity. Following 36 h of incubation, plants were transferred to a plastic enclosure and maintained at 23 ± 4°C. After 7 to 10 days, tan, oval-shaped lesions were observed on all inoculated spinach plants. All control plants, with the exception of Rakaia, failed to develop symptoms. Isolates of S. botryosum were recovered on SAPDA from symptomatic leaves, confirming Koch's postulates. Previous reports have shown that S. botryosum can be transmitted from infected seed (1), thus, additional plants of each cultivar (n = 36) were grown in the greenhouse to determine the potential for seedborne contamination. After 8 weeks, leaf spot symptoms identical to those observed on the original plants developed on 75% of the Rakaia plants, while symptom development on the other cultivars was negligible. Isolates of S. botryosum were only recovered from symptomatic Rakaia leaves. Similar field observations were made during the 2001 to 2002 growing season; however, attempts to isolate S. botryosum in that season were unsuccessful. Recent outbreaks of Stemphylium leaf spot have been reported in Arizona (4), California (3), Delaware and Maryland (2), and Washington (1). To our knowledge, this is the first report of S. botryosum on spinach in Texas. While the origin of inoculum causing the disease in Texas is unknown, S. botryosum may have been seedborne (2). The implementation within the past few years of very high density plantings of spinach (1.9 to 3.7 million seeds/ha) may lead to an increase in incidence and severity of this disease in Texas. References: (1) L. J. du Toit and M. L. Derie. Plant Dis. 85:920, 2001. (2) K. L. Everts and D. K. Armentrout. Plant Dis. 85:1209, 2001. (3) S. T. Koike et al. Plant Dis. 85:126, 2001. (4) S. T. Koike et al. Plant Dis. 89:1359, 2005.

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First Report of Epicoccum tobaicum Associated with Leaf Spot on Flowering Cherry in South Korea

Plant Disease ◽

10.1094/pdis-12-20-2711-pdn ◽

2021 ◽

Author(s):

Viet-Cuong Han ◽

Nan Hee Yu ◽

Hyeokjun Yoon ◽

Youn Kyoung Son ◽

Buoung Hee Lee ◽

...

Keyword(s):

South Korea ◽

Leaf Spot ◽

Disease Incidence ◽

Morphological Characteristics ◽

Leaf Spot Disease ◽

Infected Leaf ◽

First Report ◽

Leaf Spots ◽

Plastic Bag ◽

Flowering Cherry

Flowering cherry (FC, Prunus x yedoensis Matsumura; Somei-yoshino cherry) is an ornamental tree, planted across South Korea and producing stunning flowers in spring. The seasonal blooms are annually celebrated during cherry blossom festivals in many locations across the country. The leaf spot disease is among the most common and important diseases affecting FC trees every year, resulting in premature defoliation and reduced flowering of cherry blossoms in the following year. In May 2018, brown spots (2 to 5 mm), circular to irregular and with dark borders were observed on FC leaves in Hadong, Gyeongsangnamdo, South Korea (35°07'48.9"N, 127°46'53.8"E), with a disease incidence of 55%. Single lesions often coalesced and were sometimes perforated, leaving shot holes. Sampled leaves were surface sterilized with 1% NaOCl for 1 min and 70% ethanol for 30 s, and then rinsed twice with sterile distilled water. About 2-mm-long infected leaf pieces from the margins of lesions were put onto water agar (WA, 1.5% agar) plates and incubated at 25oC for 72 h. Mycelia grown from symptomatic tissue were transferred to PDA plates, and five similar fungal isolates were obtained from hyphal tips. They produced a strong reddish-orange diffusible pigment on PDA after 5 d and exudates after 8 d. Conidia were globular to pear-shaped, dark, verrucose, multicellular, and 14.8 to 23.5 μm in diameter (av. = 18.7 μm, n = 30) for isolate JCK-CSHF10. These morphological characteristics were consistent with the Epicoccum genus. Three loci, ITS, tub2, and rpb2, from three isolates JCK-CSHF8, JCK-CSHF9, and JCK-CSHF10 were amplified using the primer pairs ITS1F/LR5 (Gardes and Bruns 1993; Vilgalys and Hester 1990), Btub2Fd/Btub4Rd (Woudenberg et al. 2009), and RPB2-5F2/RPB2-7cR (Liu et al. 1999; Sung et al. 2007), respectively. The ITS, tub2, and rpb2 sequences of the three isolates were deposited in Genbank (MW368668-MW368670, MW392083-MW392085, and MW392086-MW392088, respectively), showing 99.6 to 100% identity to E. layuense (E33), a later synonym for E. tobaicum (Hou et al. 2020). The phylogenetic tree using concatenated sequences of the three loci placed the three isolates in a cluster of E. tobaicum (CBS 232.59, CGMCC 3.18362, and CBS 384.36; Hou et al. 2020). Taken together, the three isolates were identified as E. tobaicum. The pathogenicity of JCK-CSHF10 was tested on 15 healthy leaves on three FC trees (cv. Somei-yoshino, 1.2 m in height) kept in a greenhouse. Five-mm-diameter plugs from 7-d-old fungal cultures grown on PDA or mycelia-free PDA plugs as controls were placed on the abaxial side of a leaf at three points, previously wounded by a sterile needle (Zlatković et al. 2016). Inoculation sites were covered with moist cotton plugs. Trees were then covered with a clear plastic bag and maintained in high humidity at 25oC in darkness for 24 h, followed by a 12-h photoperiod. Brown spots appeared on inoculated leaves after 7 d, identical to those observed in the field, while control leaves remained symptomless. This experiment was repeated three times. A fungus with the same morphology as JCK-CSHF10 was recovered from lesions, thus confirming Koch’s postulates. E. layuense (syn. E. tobaicum) has been reported as a leaf spot-causing agent on Perilla sp. (Chen et al. 2017) and Camellia sinensis (Chen et al. 2020). To date, there is no report on the occurrence of E. tobaicum from leaf spots on FC. To our knowledge, this is the first report of E. tobaicum causing leaf spot on FC in South Korea.

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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 Leaf Spot Disease Caused by Colletotrichum gloeosporioides on Chinese Bean Tree in China

Plant Disease ◽

10.1094/pdis-03-12-0261-pdn ◽

2013 ◽

Vol 97 (1) ◽

pp. 138-138 ◽

Cited By ~ 1

Author(s):

B. Z. Fu ◽

M. Yang ◽

G. Y. Li ◽

J. R. Wu ◽

J. Z. Zhang ◽

...

Keyword(s):

Leaf Spot ◽

Colletotrichum Gloeosporioides ◽

Disease Incidence ◽

Phylogenetic Analyses ◽

Morphological Characteristics ◽

Leaf Spot Disease ◽

First Report ◽

Spot Disease ◽

Rdna Its ◽

Its Sequence Analysis

Chinese bean tree, Catalpa fargesii f. duciouxii (Dode) Gilmour, is an ornamental arbor plant. Its roots, leaves, and flowers have long been used for medicinal purposes in China. During July 2010, severe outbreaks of leaf spot disease on this plant occurred in Kunming, Yunnan Province. The disease incidence was greater than 90%. The symptoms on leaves began as dark brown lesions surrounded by chlorotic halos, and later became larger, round or irregular spots with gray to off-white centers surrounded by dark brown margins. Leaf tissues (3 × 3 mm), cut from the margins of lesions, were surface disinfected in 0.1% HgCl2 solution for 3 min, rinsed three times in sterile water, plated on potato dextrose agar (PDA), and incubated at 28°C. The same fungus was consistently isolated from the diseased leaves. Colonies of white-to-dark gray mycelia formed on PDA, and were slightly brown on the underside of the colony. The hyphae were achromatic, branching, septate, and 4.59 (±1.38) μm in diameter on average. Perithecia were brown to black, globose in shape, and 275.9 to 379.3 × 245.3 to 344.8 μm. Asci that formed after 3 to 4 weeks in culture were eight-spored, clavate to cylindrical. The ascospores were fusiform, slightly curved, unicellular and hyaline, and 13.05 to 24.03 × 10.68 to 16.02 μm. PCR amplification was carried out by utilizing universal rDNA-ITS primer pair ITS4/ITS5 (2). Sequencing of the PCR products of DQ1 (GenBank Accession No. JN165746) revealed 99% similarity (100% coverage) with Colletotrichum gloeosporioides isolates (GenBank Accession No. FJ456938.1, No. EU326190.1, No. DQ682572.1, and No. AY423474.1). Phylogenetic analyses (MEGA 4.1) using the neighbor-joining (NJ) algorithm placed the isolate in a well-supported cluster (>90% bootstrap value based on 1,000 replicates) with other C. gloeosporioides isolates. The pathogen was identified as C. gloeosporioides (Penz.) Penz. & Sacc. (teleomorph Glomerella cingulata (Stoneman) Spauld & H. Schrenk) based on the morphological characteristics and rDNA-ITS sequence analysis (1). To confirm pathogenicity, Koch's postulates were performed on detached leaves of C. fargesii f. duciouxii, inoculated with a solution of 1.0 × 106 conidia per ml. Symptoms similar to the original ones started to appear after 10 days, while untreated leaves remained healthy. The inoculation assay used three leaves for untreated and six leaves for treated. The experiments were repeated once. C. gloeosporioides was consistently reisolated from the diseased tissue. C. gloeosporioides is distributed worldwide causing anthracnose on a wide variety of plants (3). To the best of our knowledge, this is the first report of C. gloeosporioides causing leaf spots on C. fargesii f. duciouxii in China. References: (1) B. C. Sutton. Page 1 in: Colletotrichum: Biology, Pathology and Control. CAB International. Wallingford, UK, 1992. (2) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, 1990. (3) J. Yan et al. Plant Dis. 95:880, 2011.

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Screening of different plant extracts against leaf spot (Cercospora arachidicola and Cercosporidium personatum) of groundnut (Arachis hypogaea L.)

Bangladesh Journal of Agricultural Research ◽

10.3329/bjar.v38i3.16976 ◽

2013 ◽

Vol 38 (3) ◽

pp. 491-503 ◽

Cited By ~ 1

Author(s):

MH Hossain ◽

I Hossain

Keyword(s):

Plant Extracts ◽

Leaf Spot ◽

Growth Parameters ◽

Disease Incidence ◽

Foliar Spray ◽

Plain Water ◽

Infected Leaf ◽

Cercospora Arachidicola ◽

Cercosporidium Personatum ◽

Almost All

A study was undertaken to evaluate effectiveness of foliar spray with 33 plant extracts against leaf spot (Tikka) of groundnut caused by Cercospora arachidicola and Cercosporidium personatum. Bavistin and BAU-Biofungicide were included in the experiment as checks and spray of plain water represented control. Almost all treatments gave considerable reduction in disease incidence and increase in growth parameters, pod and haulm yield compared to control. The most effective materials were Bavistin 50 WP, BAU-Biofungicide, leaf extract of neem, tomato, datura black, and datura white. The materials decreased spot number per leaf, defoliation per plant, incidence of leaf spot, and number of infected leaf per plant by 35.45 -60.07, 42.06-72.20, 51.9763.58, and 38.33 to 46.89 % and increased pod yield and haulm yield by 64.37-111.41 and 32.35- 74.71 %, respectively. The materials may be recommended against the disease after economic analysis. DOI: http://dx.doi.org/10.3329/bjar.v38i3.16976 Bangladesh J. Agril. Res. 38(3): 491-503, September 2013

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First Report of a Chaetomella sp. Causing a Leaf Spot on Sansevieria trifasciata in China

Plant Disease ◽

10.1094/pdis-10-12-0993-pdn ◽

2013 ◽

Vol 97 (7) ◽

pp. 992-992 ◽

Cited By ~ 4

Author(s):

Y. L. Li ◽

Z. Zhou ◽

W. Lu ◽

J. R. Ye

Keyword(s):

Leaf Spot ◽

Disease Incidence ◽

Morphological Characteristics ◽

Leaf Tissue ◽

Aerial Mycelium ◽

Control Treatment ◽

Distilled Water ◽

First Report ◽

Potted Plants ◽

Fungal Isolates

Sansevieria trifasciata originates from tropical West Africa. It is widely planted as a potted ornamental in China for improving indoor air quality (1). In February 2011, leaves of S. trifasciata plants in an ornamental market of Anle, Luoyang City, China, were observed with sunken brown lesions up to 20 mm in diameter, and with black pycnidia present in the lesions. One hundred potted plants were examined, with disease incidence at 20%. The symptomatic leaves affected the ornamental value of the plants. A section of leaf tissue from the periphery of two lesions from a plant was cut into 1 cm2 pieces, soaked in 70% ethanol for 30 s, sterilized with 0.1% HgCl2 for 2 min, then washed five times in sterilized distilled water. The pieces were incubated at 28°C on potato dextrose agar (PDA). Colonies of two isolates were brown with submerged hyphae, and aerial mycelium was rare. Abundant and scattered pycnidia were reniform, dark brown, and 200 to 350 × 100 to 250 μm. There were two types of setae on the pycnidia: 1) dark brown setae with inward curved tops, and 2) straight, brown setae. Conidia were hyaline, unicellular, cylindrical, and 3.75 to 6.25 × 1.25 to 2.50 μm. Morphological characteristics suggested the two fungal isolates were a Chaetomella sp. To confirm pathogenicity, six mature leaves of a potted S. trifasciata plant were wounded with a sterile pin after wiping each leaf surface with 70% ethanol and washing each leaf with sterilized distilled water three times. A 0.5 cm mycelial disk cut from the margin of a 5-day-old colony on a PDA plate was placed on each pin-wounded leaf, ensuring that the mycelium was in contact with the wound. Non-colonized PDA discs were placed on pin-wounded leaves as the control treatment. Each of two fungal isolates was inoculated on two leaves, and the control treatment was done similarly on two leaves. The inoculated plant was placed in a growth chamber at 28°C with 80% relative humidity. After 7 days, inoculated leaves produced brown lesions with black pycnidia, but no symptoms developed on the control leaves. A Chaetomella sp. was reisolated from the lesions of inoculated leaves, but not from the control leaves. An additional two potted plants were inoculated using the same methods as replications of the experiment, with identical results. To confirm the fungal identification, the internal transcribed spacer (ITS) region of rDNA of the two isolates was amplified using primers ITS1 and ITS4 (2) and sequenced. The sequences were identical (GenBank Accession No. KC515097) and exhibited 99% nucleotide identity to the ITS sequence of an isolate of Chaetomella sp. in GenBank (AJ301961). To our knowledge, this is the first report of a leaf spot of S. trifasciata caused by Chaetomella sp. in China as well as anywhere in the world. References: (1) X. Z. Guo et al. Subtropical Crops Commun. Zhejiang 27:9, 2005. (2) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, CA, 1990.

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First Report of Ascochyta rabiei Causing Ascochyta Blight of Chickpea in Argentina

Plant Disease ◽

10.1094/pdis-02-12-0153-pdn ◽

2012 ◽

Vol 96 (9) ◽

pp. 1375-1375 ◽

Cited By ~ 3

Author(s):

G. Viotti ◽

M. A. Carmona ◽

M. Scandiani ◽

A. N. Formento ◽

A. Luque

Keyword(s):

Disease Incidence ◽

Ascochyta Blight ◽

Morphological Characteristics ◽

Pathogenic Fungi ◽

Ascochyta Rabiei ◽

Infected Leaf ◽

Buenos Aires Province ◽

Conidial Suspension ◽

First Report ◽

Plastic Bags

In November 2011, lesions similar to those reported for Ascochyta blight (1) were observed on Cicer arietinum L. (chickpea) plants growing in three commercial fields located at Río Primero and Río Segundo (Cordoba Province) and Lobería (Buenos Aires Province), Argentina. Disease incidence (percentage of plants affected) was 100% in all fields surveyed. Plants showed leaves, petioles, stems, and pods with brown lesions. Symptoms on leaves and pods were circular to oval (2 to 14 mm) while in the stems the lesions were elongated (2 to 30 mm). Seeds appeared small and shriveled with brown discoloration. Morphology of the fungi was examined on infected tissues. Numerous black pycnidia measuring 94.6 to 217.9 μm (145.9 ± 28.8 μm), arranged in concentric rings, were observed within of all the lesions. Conidia were predominantly aseptate, straight, hyaline with blunt ends, and measured 9.3 to 12.9 (11.3 ± 1.12) × 3.3 to 5.0 μm (4.2 ± 0.51). Morphological characteristics of the pathogen were similar to those described for Ascochyta rabiei (Pass.) Labrousse (teleomorph Didymella rabiei (Kovacheski) v. Arx (= Mycosphaerella rabiei Kovacheski)) (2). Fungus from infected leaf tissues was isolated on potato dextrose agar. Pathogenicity tests were conducted on seedlings of the susceptible cultivar by spraying leaves of each of 100 seedling plants with 10 ml of a conidial suspension (2 × 104 conidia/ml) of the isolated pathogen with a handheld atomizer. Plants were covered with plastic bags and placed in a growing chamber at 20 to 25°C for 3 days. The plastic bags were removed and the plants were maintained in high humidity at the same temperature. Noninoculated plants were used as controls. After 5 days, all inoculated plants showed typical symptoms. Foliar and stem lesions symptoms were similar to those originally observed in the field. Control plants remained healthy. Koch's postulates were fulfilled by isolating A. rabiei from inoculated plants. The colonies and the morphology of conidia were the same as those of the original isolates. To our knowledge, this is the first report of A. rabiei infecting chickpeas in Argentina. The outbreak of Ascochyta blight in Argentina is of concern because of its severity and the possibility that the pathogen was introduced on seed. This report underscores the need for further research on effective management programs for Ascochyta blight. References: (1) B. Bayaa and W. Chen. Compendium of Chickpea and Lentil Diseases and Pests The American Phytopathological Society, St. Paul, MN, 2011. (2) E. Punithalingam and P. Holliday. Page 337 in: CMI Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1972.

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First Report of White Leaf Spot of Dry Bean Caused by Pseudocercosporella albida in North America

Plant Disease ◽

10.1094/pdis.2003.87.12.1537c ◽

2003 ◽

Vol 87 (12) ◽

pp. 1537-1537

Author(s):

L. E. del Río ◽

C. A. Bradley ◽

R. S. Lamppa

Keyword(s):

North America ◽

Leaf Spot ◽

Disease Incidence ◽

Infected Plant ◽

Leaf Spot Disease ◽

Dry Bean ◽

First Report ◽

White Leaf ◽

Electron Microscopes ◽

The Impact

In August 2002, white leaf spot disease was observed on red kidney bean (Phaseolus vulgaris L.) at three fields near Staples, MN. Disease incidence in these fields, calculated as the proportion of plants showing visible symptoms, ranged from 20 to 100%. Symptoms and signs consisted of abundant, white sporulation on the abaxial side of leaves that was limited by secondary veins, resulting in angular-shaped lesions. Corresponding with fungal growth, yellow, angular spots were observed on the upper leaf surface. In older leaves, lesions coalesced, covering most of their surface, while younger leaves were relatively free of symptoms. Heavily diseased plants senesced faster and defoliated earlier than nonsymptomatic plants. Identification of the pathogen was conducted by direct observation of infected plant tissues with light and electron microscopes. Conidia were hyaline, filiform, rounded at their apex, and with no visible scar at their point of attachment to the conidiophore. Conidia had one to four septa, were 57 to 68 μm long, and approximately 2.4 μm in diameter. Conidia were produced at the tip of colorless, short conidiophores that emerged through stomata in groups of five or more. These traits are in agreement with the description of Pseudocercosporella albida (Matta & Belliard) Deighton (1,2). A sample of infected tissues has been deposited at the U.S. National Fungus Collection (BPI 842303) at Beltsville, MD. The impact of this disease on bean yields in Minnesota was not estimated. However, in the cool highlands of Colombia, where white leaf spot is endemic, yields can be reduced by as much as 47% (3). To our knowledge, this is the first report of the presence of this pathogen on dry bean in North America. References: (1) F. C. Deighton. Trans. Br. Mycol. Soc. 66:547, 1976. (2) A. Matta and L. Belliard. Phytopathol. Mediterr. 12:102, 1973. (3) H. F. Schwartz et al. Plant Dis. 65:494, 1981.

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First report of leaf spot disease caused by Stemphylium eturmiunum on American sweetgum (Liquidambar styraciflua L.) in China

Plant Disease ◽

10.1094/pdis-09-20-1877-pdn ◽

2021 ◽

Author(s):

Yun-fei Mao ◽

Li Jin ◽

Huiyue Chen ◽

Xiang-rong Zheng ◽

Minjia Wang ◽

...

Keyword(s):

Leaf Spot ◽

Disease Incidence ◽

Morphological Characteristics ◽

Liquidambar Styraciflua ◽

Leaf Spot Disease ◽

Distilled Water ◽

Conidial Suspension ◽

First Report ◽

Wood Processing ◽

Light Yellow

American sweetgum (Liquidambar styraciflua L.) is an important tree for landscaping and wood processing. In recent years, leaf spots on American sweetgum with disease incidence of about 53% were observed in about 1200 full grown plants in a field (about 8 ha) located in Pizhou, Jiangsu Province, China. Initially, dense reddish-brown spots appeared on both old and new leaves. Later, the spots expanded into dark brown lesions with yellow halos. Symptomatic leaf samples from different trees were collected and processed in the laboratory. For pathogen isolation, leaf sections (4×4mm) removed from the lesion margin were surface sterilized with 75% ethanol for 20s and then sterilized in 2% NaOCl for 30s, rinsed three times in sterile distilled water, incubated on potato dextrose agar (PDA) at 25 °C in the darkness. After 5 days of cultivation, the pure culture was obtained by single spore separation. 6 isolate samples from different leaves named FXA1 to FXA6 shared nearly identical morphological features. The isolate FXA1 (codes CFCC 54675) was deposited in the China Center for Type Culture Collection. On the PDA, the colonies were light yellow with dense mycelium, rough margin, and reverse brownish yellow. Conidiophores (23–35 × 6–10 µm) (n=60) were solitary, straight to flexuous. Conidia (19–34 × 10–21 µm) (n=60) were single, muriform, oblong, mid to deep brown, with 1 to 6 transverse septa. These morphological characteristics resemble Stemphylium eturmiunum (Simmons 2001). Genomic DNA was extracted from mycelium following the CTAB method. The ITS region, gapdh, and cmdA genes were amplified and sequenced with the primers ITS5/ITS4 (Woudenberg et al. 2017), gpd1/gpd2 (Berbee et al. 1999), and CALDF1/CALDR2 (Lawrence et al. 2013), respectively. A maximum likelihood phylogenetic analysis based on ITS, gapdh and cmdA (accession nos. MT898502-MT898507, MT902342-MT902347, MT902336-MT902341) sequences using MEGA 7.0 revealed that the isolates were placed in the same clade as S. eturmiunum with 98% bootstrap support. All seedlings for pathogenicity tests were enclosed in plastic transparent incubators to maintain high relative humidity (90%-100%) and incubated in a greenhouse at 25°C with a 12-h photoperiod. For pathogenicity, the conidial suspension (105 spores/ml) of each isolate was sprayed respectively onto healthy leaves of L. styraciflua potted seedlings (2-year-old, 3 replicate plants per isolate). As a control, 3 seedlings were sprayed with sterile distilled water. After 7 days, dense reddish-brown spots were observed on all inoculated leaves. In another set of tests, healthy plants (3 leaves per plant, 3 replicate plants per isolate) were wound-inoculated with mycelial plugs (4×4mm) and inoculated with sterile PDA plugs as a control. After 7 days, brown lesions with light yellow halo were observed on all inoculation sites with the mycelial plugs. Controls remained asymptomatic in the entire experiment. The pathogen was reisolated from symptomatic tissues and identified as S. eturmiunum but was not recovered from the control. The experiment was repeated twice with the similar results, fulfilling Koch’s postulates. S. eturmiunum had been reported on tomato (Andersen et al. 2004), wheat (Poursafar et al. 2016), garlic (L. Fu et al. 2019) but not on woody plant leaves. To our knowledge, this is the first report of S. eturmiunum causing leaf spot on L. styraciflua in the world. This disease poses a potential threat to American sweetgum and wheat in Pizhou.

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First report of leaf spot caused by Colletotrichum fructicola on Dalbergia hupeana in China

Plant Disease ◽

10.1094/pdis-08-21-1842-pdn ◽

2021 ◽

Author(s):

Yang Zhou ◽

Rou Ye ◽

Qin Ying ◽

Yang Zhang ◽

Linping Zhang

Keyword(s):

Phylogenetic Tree ◽

Leaf Spot ◽

Disease Incidence ◽

Morphological Characteristics ◽

Jiangxi Province ◽

Leaf Spot Disease ◽

Sterile Water ◽

First Report ◽

Spot Disease ◽

Colletotrichum Fructicola

Dalbergia hupeana is a kind of wood and medicinal tree widely distributed in southern China. Since 2019, a leaf spot disease was observed on the leaves of D. hupeana in Gangxia village, Luoting town in Jiangxi Province, China (28°52′53″N, 115°44′58″E). The disease incidence was estimated to be above 50%. The symptoms began as small spots that gradually expanded, developing a brown central and dark brown to black margin. The spots ranged from 4 to 6 mm in diameter. Leaf pieces (5 × 5 mm) from lesion margins were surface sterilized in 70% ethanol for 30 s followed by 2% NaOCl for 1 min and then rinsed three times with sterile water. Tissues were placed on potato dextrose agar (PDA) and incubated at 25°C. Pure cultures were obtained by monosporic isolation. Fifteen strains with similar morphological characterizations were isolated, and three representative isolates (JHT-1, JHT-2, and JHT-3) were chosen and used for further study. Colonies on PDA of three isolates were grayish-green with white edges and dark green on the reverse side. Conidia were transparent, cylindrical with rounded ends, and measured 3.6-5.3 µm × 9.5-15.2 µm (3.7 ± 0.2 × 13.6 ± 1.1 µm, n = 100). Appressoria were dark brown, globose or subcylindrical, and ranged from 6.2-9.2 µm× 5.1-6.8 µm (7.9 ± 0.4 × 5.9 ± 0.3 µm, n=100). The morphological characteristics of the three strains were consistent with the description of species in the Colletotrichum gloeosporioides complex (Weir et al. 2012). The internal transcribed spacer (ITS) regions, actin (ACT), calmodulin (CAL), chitin synthase (CHS-1) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and beta-tubulin 2 (TUB2) were amplified from genomic DNA for the three isolates using primers ITS1/ITS4, ACT-512F/ACT-783R, CL1/CL2, CHS-79F/CHS-345R, GDF/GDR and T1/Bt2b (Weir et al. 2012), respectively. The sequences were deposited in GenBank (Accession Nos. MZ482016 - MZ482018 for ITS; MZ463636 - MZ463638 for ACT; MZ463648- MZ463650 for CAL; MZ463639 - MZ463641 for CHS-1; MZ463642 - MZ463644 for GAPDH; MZ463645 - MZ463647 for TUB2). A neighbor-joining phylogenetic tree was constructed with MEGA 7.0 using the concatenation of multiple sequences (ITS, ACT, GAPDH, TUB2, CHS-1, CAL) (Kumar et al. 2016). According to the phylogenetic tree, three isolates fall within the Colletotrichum fructicola clade (boot support 99%). Based on morphological characteristics and phylogenetic analysis, three isolates were identified as C. fructicola. The pathogenicity of three isolates was conducted on two-yr-old seedlings (30 cm tall) of D. hupeana. Healthy leaves were wounded with a sterile needle and then inoculated with 10 μL spore suspension (106 conidia per mL). Controls were treated with sterile water. All plants were covered with transparent plastic bags and incubated in a greenhouse at 28°C with a 12 h photoperiod (relative humidity > 80%). Within five days, the inoculated leaves developed lesions similar to those observed in the field, whereas controls were asymptomatic. The experiments repeated three times showed similar results. The infection rate was 100%. C. fructicola was re-isolated from the lesions, whereas no fungus was isolated from control leaves. C. fructicola can cause leaf diseases in a variety of hosts, including Aesculus chinensis (Sun et al. 2020), Peucedanum praeruptorum (Ma et al. 2020), and Mandevilla × amabilis (Sun et al. 2020). C. brevisporum and C. gigasporum were also reported to infect Dalbergia odorifera (Chen et al. 2021; Wan et al. 2018). However, This is the first report of C. fructicola associated with leaf spot disease on D. hupeana in China. These results will help to develop effective strategies for appropriately managing this newly emerging disease.

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