First Report of Downy Mildew on Sweet Basil Caused By Peronospora belbahrii in India

Sweet basil (Ocimum basilicum L.; Family Lamiaceae) is an annual aromatic and medicinal plant grown in tropical and subtropical regions of the world. In India, it is cultivated as a commercial crop on ~8,000 ha. Aerial plant parts and essential oil of sweet basil are used in pharmaceutical, perfumery, food industries and in different formulations of traditional Ayurvedic and Unani medicines (Shahrajabian et al. 2020). The leaves have the highest concentrations of secondary metabolites such as terpenes and phenylpropanoids which provide the distinctive aroma (Viuda-Martos et al. 2011). During October 2020, severe foliar disease was observed in experimental fields of sweet basil at Council of Scientific and Industrial Research (CSIR)-Central Institute of Medicinal and Aromatic Plants (CIMAP) in Lucknow, India. Initial symptoms included large, interveinal chlorotic lesions on the adaxial surface of the leaves and black sporulation on the abaxial surface. Within a few days, the abaxial side of leaves turned necrotic, and leaf senescence and defoliation occurred on plants with severe symptoms. Disease incidence was 20 to 30% of plants. The pathogen was characterized morphologically using a light microscope. Sporangiophores were hyaline, dichotomously branched, 186.9 to 423.07 × 6.85 to 9.06 µm and, branched 3 to 5 times with each branch, terminating in two slightly curved branchlets, the longer one 7.05 to 25.31 µm and the shorter one 4.98 to 15.92 µm. Each branchlet had a single sporangium at the tip. Conidia were ellipsoidal to sub-globose, olive-brown in color, and typically measured 25.21 to 33.86 × 17.92 to 26.24 µm, each, without a pedicel. Based on these morphological characteristics, the foliar disease was identified as downy mildew was caused by Peronospora belbahrii (Thines et al. 2009). Eight symptomatic and two asymptomatic plant samples were collected from different locations in the field, and genomic DNA was extracted from the conidia of the eight naturally infected tissues of sweet basil samples as well as leaf tissues from two asymptomatic plants, using the CTAB method. The internal transcribed spacer region was amplified using ITS1 and ITS4 primers. Only eight infected samples amplified products of expected size (~ 700 bp) and two asymptomatic samples showed no amplification. Only five amplified PCR products were sequenced (White et al. 1990). All five sequences were identical and were a 98.1% match with five P. belbahrii isolates (MN450330.1, MN308051.1, MH620351.1, KJ960193, and MF693898). The consensus sequence was deposited into the NCBI database (GenBank Accession No. MW689257). Downy mildew caused by P. belbahrii previously has been reported on sweet basil from several countries (Wyenandt et al. 2015). To confirm the pathogenicity of these isolates on sweet basil (cv. CIM-Saumya), 25 - day-old sweet basil plants were sprayed with a suspension (1 × 105 sporangia/ml) of P. belbahrii. All plants were kept in a growth chamber with a 23/18°C diurnal cycle with 65 to 85% relative humidity for 24 h. Non-inoculated plants treated with sterile water served as a control treatment. After 8 days, typical symptoms of downy mildew appeared on all the inoculated plants while non-inoculated plants remained asymptomatic. Inoculated leaves with symptoms consistent of downy mildew were collected and the causal agent again identified as P. belbahrii on the basis of microscopic examination and ITS rDNA sequence data. To our knowledge, this is the first report of downy mildew caused by P. belbahrii on sweet basil in India. The pathogen has a broad host range and may pose a serious threat to the cultivation of this valuable crop in India. Thus, it is pertinent to develop effective control measures to avoid further spread and mitigate economic loss. References: Shahrajabian, M. H., et al. 2020. Int. J. Food Prop. 23:1961-1970. Wyenandt, C. A., et al. 2015. Phytopathology 105:885. Thines, M., et al. 2009. Mycol. Res. 113:532. White, T. J., et al. 1990. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Viuda-Martos, M., et al. 2011. Food Control. 22:1715.

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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 Downy Mildew Caused by Peronospora belbahrii on Sweet Basil (Ocimum basilicum) in Cyprus

Plant Disease ◽

10.1094/pdis-07-13-0759-pdn ◽

2014 ◽

Vol 98 (2) ◽

pp. 283-283 ◽

Cited By ~ 5

Author(s):

L. Kanetis ◽

A. Vasiliou ◽

G. Neophytou ◽

S. Samouel ◽

D. Tsaltas

Keyword(s):

Downy Mildew ◽

Disease Incidence ◽

Infected Plant ◽

Morphological Characteristics ◽

Ocimum Basilicum ◽

First Report ◽

Consensus Sequences ◽

Sweet Basil ◽

Plastic Bags ◽

Necrotic Spots

Sweet basil (Ocimum basilicum L.) is an economically important annual aromatic plant, grown mostly for culinary use for both fresh and dry consumption and as a source of essential oil. In Cyprus, approximately 4 ha are grown annually, either in greenhouses as a year-round crop or in open fields from April to November, and the majority of the production is exported to the European market. During May 2012, a sweet basil cv. Genovese Gigante greenhouse operation in the area of Limassol was severely affected by a foliar disease, causing almost 100% crop losses. Within a few days, a similar, heavy disease incidence was also reported from a nearby greenhouse facility on the Genovese-type cultivars Superbo, Aroma 2, and Bonazza, as well as on Thai basil (O. basilicum var. thyrsiflorum). Successively, destructive hits of similar symptomatology have been reported from other areas and since then the disease appears to have been well-established in the country, causing major economic damages. It is also noteworthy to mention that in greenhouse infections the disease remains active even during winter, considering the mild environmental conditions and the monoculture fashion followed. Symptoms appeared on the leaves initially as interveinal, zonal, chlorotic lesions, followed by the appearance of a fuzzy, purplish sporulation on the abaxial side. Progressively, infected leaves curled and sporadic necrotic spots were evident and finally abscised. Light microscopic examination of infected samples revealed the presence of straight, hyaline sporangiophores (n = 15) typical of downy mildew, 210 to 590 μm long (mean = 350.7 μm; SD ± 117.5 μm) × 12 to 15 μm wide (mean = 13.1 μm; SD ± 1.4 μm). Sporangiophores were monopodially branched three to five times, terminating with curved branchlets bearing single sporangia at their tips. The sporangia (n = 25) were purplish-grey, ovoid to subglobose, and measured 32 to 22 μm in length (mean = 27.2 μm; SD ± 2.8 μm) and 30 to 10 μm in breadth (mean = 21.7 μm; SD ± 4.8 μm). Based on these morphological characteristics, the causal agent was identified as Peronospora belbahrii Thines (1,4). Furthermore, genomic DNA was extracted from infected plant tissue from eight different samples according to Dellaporta et al. (2). The complete ITS rDNA region was amplified and sequenced using primers ITS5 and ITS4 (3). Two of the consensus sequences were deposited in GenBank (Accession Nos. KF419289 and KF419290) and a BLAST analysis in the NCBI database revealed 99% similarity to all of the P. belbahrii sequences and other Peronospora sp. previously reported on sweet basil (Accession Nos. AY831719, DQ479408, FJ394336, and FJ436024). In a pathogenicity trial, five 40-day-old potted sweet basil plants were spray-inoculated with a sporangial suspension (1 × 105 sporangia/ml) until runoff, bagged for 24 h, and placed in a growth chamber at 18°C. Subsequently, the plastic bags were removed and the plants were kept at 22°C with a 16-h photoperiod and 80% relative humidity. Additionally, five plants were water-sprayed and served as controls. Typical downy mildew symptoms appeared 6 to 8 days after inoculation, while the uninoculated plants remained disease-free. To our knowledge, this is first report of downy mildew on sweet basil in Cyprus. References: (1) L. Belbahri et al. Mycol. Res. 109:1276, 2005. (2) S. L. Dellaporta et al. Plant Mol. Biol. Rep., 1:19, 1983. (3) G. Nagy and A. Horvat, Plant Dis. 93:1999, 2009. (4) M. Thines et al. Mycol. Res. 113:532, 2009.

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First Report of Colletotrichum capsici Causing Anthracnose on Alocasia macrorrhizos in China

Plant Disease ◽

10.1094/pdis-06-20-1228-pdn ◽

2020 ◽

Author(s):

HaiYan Ben ◽

JianFei Huo ◽

YuRong Yao ◽

Wei Gao ◽

WanLi Wang ◽

...

Keyword(s):

Disease Incidence ◽

Morphological Characteristics ◽

Asia Pacific ◽

Stem Rot ◽

Perennial Herb ◽

Broad Host Range ◽

Distilled Water ◽

First Report ◽

Colletotrichum Capsici ◽

Initial Symptoms

Alocasia macrorrhizos (Linnaeus) G. Don is a perennial herb in the Araceae family. It is native to South Asia and the Asia-Pacific and has long been cultivated as it is an economically important medicinal and ornamental plant. During July 2012 and 2013, severe outbreaks of leaf spot and stem rot disease on this plant occurred in a greenhouse of Shunyi district, in Beijing, China (117°05’E, 40°13’N). The disease incidence was greater than 30%. The leaf spots first appeared as yellow dots. As lesions expanded, the symptoms were circular to subcircular, light brown lesions with darker brown edges, Around the lesions the leaf tissue was chlorotic causing the formation of a yellow halo (Suppl. Fig1). Initial symptoms on the stems were brown, round or fusiform spots . As the disease progressed, lesions enlarged and merged together. When humidity was high, black acervuli with grey brown cirrhus of conidia were rapidly produced in lesions. Infected plants eventually withered or collapsed from the stem rot (Suppl. Fig2). Infected tissues were surface-sterilized in 1% NaOCl for 1 min, washed three times with distilled water, and placed on potato dextrose agar (PDA). Colonies on PDA, growing at 25°C in darkness, showed grayish brown and grey brown conidial masses produced from acervuli with black seta (Suppl. Fig3). Acervuli (n=30) were dark brown to black and approximately round, 121 to 210 μm in diameter, averaging 166.5 μm (Suppl. Fig4). Setae (n=30) scattered in acervuli, black, septate, 94.4 to 128.4×3.4 to 4.7 μm, base inflated, and narrower toward the top (Suppl. Fig5). Conidiophores (n=50) were phialidic, hyaline, unicellular. Conidia (n=50) were hyaline, monospora, falcate, base obtuse, apices acute, and 20.5 to 24.7 ×2.8 to 3.4 μm (Suppl. Fig6). Six monoconidial isolates were made, and the morphological characteristics of the fungus were similar to those of Colletotrichum capsici (Syd.) Butler & Bisby (Mordue, 1971). In the greenhouse (25 to 30 °C, relative humidity 98%), pathogenicity tests were conducted by spraying a 106 spores /mL suspension on leaves and stems of 10 healthy potted A. macrorrhizos plants (3-year-old). A control was included that consisted of ten plants sprayed with sterile distilled water. All treated plants were covered with a plastic bag and removed 48 h later. After 12 days, all inoculated leaves and stems appeared with typical Anthracnose symptoms, whereas control plants remained healthy. The fungus was reisolated from diseased tissues, fulfilling Koch´s postulates. The ITS region of a representative isolate was amplified and sequenced using the primers ITS1/ITS4 (White et al. 1990).The obtained ITS sequence (GenBank Accession No. KJ018793.1) showed 100% similarity to Colletotrichum capsici (Accession No. HQ271469.1 and DQ454016.1). Colletotrichum capsici is synonymous to Colletotrichum truncatum. Colletotrichum capsici is a major phytopathogen with a broad host range which causes anthracnose disease. The first report of C. capsici as a pathogen of Alocasia macrorrhizos was reported in India in 1979 (Mathur, 1979). To our knowledge, this is the first record of C. capsici causing anthracnose on A. macrorrhizos in China.

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First Report of a Peronospora Species on Sweet Basil in South Africa

Plant Disease ◽

10.1094/pd-90-1115a ◽

2006 ◽

Vol 90 (8) ◽

pp. 1115-1115 ◽

Cited By ~ 18

Author(s):

A. McLeod ◽

S. Coertze ◽

L. Mostert

Keyword(s):

South Africa ◽

Downy Mildew ◽

Sequence Data ◽

Pcr Amplification ◽

Its Sequence ◽

Western Cape ◽

Crop Failure ◽

First Report ◽

Sweet Basil ◽

Initial Symptoms

Sweet basil (Ocimum basilicum) is an herbaceous aromatic annual plant of the family Lamiaceae grown for its flavoring and fragrances that can be used fresh or dried. In South Africa, sweet basil is grown on a commercial scale. Downy mildew has recently been reported as one of the most destructive diseases of sweet basil in Switzerland, France, and Italy (1–3). The identity of the downy mildew species infecting sweet basil has been controversial and has been indicated as Peronospora lamii, a presumably undescribed (unnamed) Peronospora species, as well as a few species of which the status as distinct species is mostly unclear or doubtful (1). The distinction between P. lamii and the unnamed Peronospora species has been based on their sporangial dimensions, with P. lamii having sporangial dimensions with a length and width range of 16 to 26 × 15 to 23 μm (average 21 × 18 μm) and the unnamed Peronospora species having sporangial dimensions of 20 to 35 × 15 to 25 μm (average 28 × 22 μm) (1) or 23 to 36 × 18 to 29 μm (average 29 × 23 μm) (2). Additionally, internal transcribed spacer (ITS) sequence data has also been used to show that P. lamii and the unnamed Peronospora species on basil are not similar (1). In the Western Cape Province of South Africa, a sweet basil sample was received at the Stellenbosch University Plant Disease Clinic in 2005 from a grower in the region who experienced almost 50% crop failure under greenhouse-grown conditions. Initial symptoms were chlorotic leaves that subsequently developed a brown sporulation on the abaxial side. Microscopic observations of the brown sporulation were consistent with a Peronospora species. The sporangiophores branched two to five times with lengths ranging from 130 to 290 μm (average 194 μm). Sporangiophores terminated with dichotomously branched denticels bearing single detachable sporangia. Sporangia measured 26 to 34 × 20 to 28 μm (average 30 × 24 μm) and were elliptical and brown. The sporangia were similar in shape, color, and size range as that previously reported for a unnamed Peronospora species on sweet basil (1,2). Sequence analyses were also conducted on two isolates by first extracting DNA from spores that were washed from leaves using the Wizard SV genomic DNA purification system (Promega, Madison, WI), followed by polymerase chain reaction (PCR) amplification and sequencing of the ITS1, 5.8S, and ITS2 regions using primers ITS6 and ITS4 (4). The sequences of the two isolates were identical (GenBank Accession No. DQ479408). BLAST analyses of the sequences revealed a 99% similarity to the unnamed Peronospora species that was isolated from sweet basil in Switzerland and Italy (1). The sequences of the South African isolates only had low homology to P. lamii. To our knowledge, this is the first report of a Peronospora species on sweet basil in South Africa that on the basis of morphology and ITS sequence data is similar to the unnamed Peronospora species recently described in Switzerland and Italy on sweet basil (1). References: (1) L. Belbahri et al. Mycol. Res. 109:1276, 2005. (2) A. Garibaldi et al. Plant Dis. 88:312, 2004. (3) A. Garibaldi et al. Plant Dis. 89:683, 2005. (4) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds., Academic Press, San Diego, 1990.

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First Report of Downy Mildew Caused by Peronospora belbahrii on Basil (Ocimum spp.) in Ontario

Plant Disease ◽

10.1094/pdis-01-13-0026-pdn ◽

2013 ◽

Vol 97 (9) ◽

pp. 1248-1248 ◽

Cited By ~ 6

Author(s):

C. Saude ◽

S. Westerveld ◽

M. Filotas ◽

M. R. McDonald

Keyword(s):

Downy Mildew ◽

Disease Incidence ◽

Morphological Characteristics ◽

Its Region ◽

Research Field ◽

Research Station ◽

Marketable Yield ◽

First Report ◽

Sweet Basil ◽

High Disease Severity

Basil (Ocimum spp.) is one of the most commercially significant fresh culinary herb crops worldwide. In Ontario, basil is grown both in the field and in the greenhouse. In the summer of 2011, basil plants grown in a research field at the Simcoe Research Station in Norfolk County, Ontario, Canada (44°15′N, 77°35′W), were infected with downy mildew. Infected leaves exhibited interveinal chlorotic lesions on the upper surface and clear to black sporulation on the abaxial leaf surfaces. Leaf senescence and defoliation occurred at high disease severity, which reduced marketable yield. Basil downy mildew symptoms were severe on leaves of cultivars Genovese and Sweet Basil, with 40 to 100% disease incidence. Based on morphological characteristics, the basil downy mildew causal agent was identified as Peronospora belbahrii Thines (4). Infected leaves were collected and microscopic observations of the sporulating lesions were carried out and the structures measured. Sporangiophores (n = 20) were hyaline with relatively long, straight trunks and were monopodially branched, with a length of 150 to 360 μm (average 285 μm). Sporangiophores ended with two slightly curved branchlets, the longer one measuring 15 to 27 μm (average 19 μm) and the shorter one 5 to 15 μm (average 9 μm). Sporangia (n = 50) were round, or slightly ovoid, olive to brown in color, and measured 29 × 25 μm (25 to 35 × 20 to 30 μm). Genomic DNA was extracted from 10 isolates and the nuclear ribosomal internal transcribed spacer (ITS) region was amplified with ITS4 and ITS5 primers and sequenced. The sequences of the 10 isolates were nearly identical. A BLAST search of the NCBI database with the ITS sequences (GenBank Accession No. KC756923) revealed a 98 to 100% similarity to the sequences of P. belbahrii (HQ730979, FJ436024, and HQ702191) isolated from sweet basil in Florida (3), California (1), and Hungary (2), respectively. To confirm pathogenicity, 5-week-old ‘Genovese’ seedlings were sprayed with a suspension of 1 × 105 sporangia/ml. Plants were kept in a growth chamber maintained at 23/18°C, 60 to 85% relative humidity, and 12/12 h light/dark. Non-inoculated plants served as controls. Basil downy mildew symptoms developed after 8 days on the inoculated plants and the pathogen was identified in association with symptoms consistent with downy mildew. The non-inoculated controls remained healthy. In North America, the occurrence of basil downy mildew has been reported since 2007 (3) and the disease has spread into several U.S. states. To our knowledge, this is the first report of downy mildew on sweet basil in Canada. References: (1) C. L. Blomquist et al. Plant Dis. 93:968, 2009. (2) G. Nagy and A. Horvath. Plant Dis. 95:1034, 2011. (3) P. D. Roberts et al. Plant Dis. 98:199, 2009. (4) M. Thines et al. Mycol. Res. 113:532, 2009.

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Evaluation of a Disease Warning System for Downy Mildew of Grapes

Plant Disease ◽

10.1094/pdis.2000.84.5.549 ◽

2000 ◽

Vol 84 (5) ◽

pp. 549-554 ◽

Cited By ~ 57

Author(s):

L. V. Madden ◽

M. A. Ellis ◽

N. Lalancette ◽

G. Hughes ◽

L. L. Wilson

Keyword(s):

Linear Model ◽

Downy Mildew ◽

Environmental Conditions ◽

Generalized Linear Model ◽

Disease Incidence ◽

Warning System ◽

Plasmopara Viticola ◽

Effective Control ◽

Subsequent Infection ◽

Grape Downy Mildew

An electronic warning system for grape downy mildew— based on models for the infection of leaves of Vitis lambrusca, production of sporangia by Plasmopara viticola in lesions, and sporangial survival—was tested over 7 years in Ohio. Grapevines were sprayed with metalaxyl plus mancozeb (Ridomil MZ58) when the warning system indicated that environmental conditions were favorable for sporulation and subsequent infection. Over the 7 years, plots were sprayed from one to four times according to the warning system, and from four to 10 times according to the standard calendar-based schedule (depending on the date of the initiation of the experiment). The warning system resulted in yearly reductions of one to six sprays (with median of three sprays). Disease incidence (i.e., proportion of leaves with symptoms) in unsprayed plots at the end of the season ranged from 0 to 86%, with a median of 68%. Incidence generally was very similar for the warning-system and standard-schedule treatments (median of 7% of the leaves with symptoms), and both of these incidence values were significantly lower (P < 0.05) than that found for the unsprayed control, based on a generalized-linear-model analysis. Simplifications of the disease warning system, where sprays were applied based only on the infection or sporulation components of the system, were also effective in controlling the disease, although more fungicide applications sometimes were applied. Effective control of downy mildew, therefore, can be achieved with the use of the warning system with fewer sprays than a with a standard schedule.

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First Report of Anthracnose of Papaya (Carica papaya L.) Caused by Colletotrichum siamense in China

Plant Disease ◽

10.1094/pdis-10-20-2154-pdn ◽

2021 ◽

Author(s):

Yujie Zhang ◽

Wenxiu Sun ◽

Ping Ning ◽

Tangxun Guo ◽

SuiPing Huang ◽

...

Keyword(s):

Carica Papaya ◽

Disease Incidence ◽

Aerial Mycelium ◽

Postharvest Disease ◽

Distilled Water ◽

First Report ◽

Surface Samples ◽

Initial Symptoms ◽

Colletotrichum Siamense ◽

Pathogenicity Tests

Papaya (Carica papaya L.) is a rosaceous plant widely grown in China, which is economically important. Anthracnose caused by Colletotrichum sp. is an important postharvest disease, which severely affects the quality of papaya fruits (Liu et al., 2019). During April 2020, some mature papaya fruits with typical anthracnose symptoms were observed in Fusui, Nanning, Guangxi, China with an average of 30% disease incidence (DI) and over 60% DI in some orchards. Initial symptoms of these papayas appeared as watery lesions, which turned dark brown, sunken, with a conidial mass appearing on the lesions under humid and warm conditions. The disease severity varied among fruits, with some showing tiny light brown spots, and some ripe fruits presenting brownish, rounded, necrotic and depressed lesions over part of their surface. Samples from two papaya plantations (107.54°E, 22.38°N) were collected, and brought to the laboratory. Symptomatic diseased tissues were cut into 5 × 5 mm pieces, surface sterilized with 2% (v/v) sodium hypochlorite for 1 minute, and rinsed three times with sterilized water. The pieces were then placed on potato dextrose agar (PDA). After incubation at 25°C in the dark for one week, colonies with uniform morphology were obtained. The aerial mycelium on PDA was white on top side, and concentric rings of salmon acervuli on the underside. A gelatinous layer of spores was observed on part of PDA plates after 7 days at 28°C. The conidia were elliptical, aseptate and hyaline (Zhang et al., 2020). The length and width of 60 conidia were measured for each of the two representative isolates, MG2-1 and MG3-1, and these averaged 13.10 × 5.11 μm and 14.45 × 5.95 μm. DNA was extracted from mycelia of these two isolates with the DNA secure Plant Kit (TIANGEN, Biotech, China). The internal transcribed spacer (ITS), partial actin (ACT), calmodulin (CAL), chitin synthase (CHS), β-tubulin 2 (TUB2) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) regions were amplified by PCR and sequenced. The sequences were deposited into GenBank with accessions MT904003, MT904004, and MT898650 to MT898659. BLASTN analyses against the GenBank database showed that they all had over 99% identity to the type strain of Colletotrichum siamense isolate ICMP 18642 (GenBank accession numbers JX010278, GQ856775, JX009709, GQ856730, JX010410, JX010019) (Weir et al., 2012). A phylogenetic tree based on the combined ITS, ACT, CAL, CHS, TUB2 and GAPDH sequences using the Neighbor-joining algorithm also showed that the isolates were C. siamense. Pathogenicity tests were conducted on 24 mature, healthy and surface-sterilized papaya fruits. On 12 papaya fruits, three well separated wounded sites were made for inoculation, and for each wounded site, six adjacent pinhole wounds were made in a 5-mm-diameter circular area using a sterilized needle. A 10 µl aliquot of 1 × 106 conidia/ml suspension of each of the isolates (MG2-1 and MG3-1) was inoculated into each wound. For each isolate, there were six replicate fruits. The control fruits were inoculated with sterile distilled water. The same inoculation was applied to 12 non-wound papaya fruits. Fruits were then placed in boxes which were first washed with 75% alcohol and lined with autoclaved filter paper moistened with sterilized distilled water to maintain high humidity. The boxes were then sealed and incubated at 28°C. After 10 days, all the inoculated fruits showed symptoms, while the fruits that were mock inoculated were without symptoms. Koch's postulates were fulfilled by re-isolation of C. siamense from diseased fruits. To our knowledge, this is the first report of C. siamense causing anthracnose of papaya in China. This finding will enable better control of anthracnose disease caused by C. siamense on papaya.

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First Report of a Leaf Spot on Snow Lotus Caused by Alternaria carthami in China

Plant Disease ◽

10.1094/pdis-92-2-0318b ◽

2008 ◽

Vol 92 (2) ◽

pp. 318-318

Author(s):

S. Zhao ◽

G. Xie ◽

H. Zhao ◽

H. Li ◽

C. Li

Keyword(s):

Leaf Spot ◽

Disease Incidence ◽

Leaf Spot Disease ◽

Tianshan Mountain ◽

Causal Organism ◽

Saussurea Involucrata ◽

First Report ◽

Spot Disease ◽

Initial Symptoms ◽

Snow Lotus

Snow lotus (Saussurea involucrata Karel. & Kir. ex Sch. Bip.) is an economically important medicinal herb increasingly grown in China in recent years. In June of 2005, a leaf spot disease on commercially grown plants was found in the QiTai Region, south of the Tianshan Mountain area of Xinjiang, China at 2,100 m above sea level. Disease incidence was approximately 60 to 70% of the plants during the 2006 and 2007 growing seasons. Initial symptoms appeared on older leaves as irregularly shaped, minute, dark brown-to-black spots, with yellow borders on the edge of the leaflet blade by July. As the disease progressed, the lesions expanded, causing the leaflets to turn brown, shrivel, and die. A fungus was consistently isolated from the margins of these lesions on potato dextrose agar. Fifty-eight isolates were obtained that produced abundant conidia in the dark. Conidia were usually solitary, rarely in chains of two, ellipsoid to obclavate, with 6 to 11 transverse and one longitudinal or oblique septum. Conidia measured 60 to 80 × 20 to 30 μm, including a filamentous beak (13 to 47 × 3.5 to 6 μm). According to the morphology, and when compared with the standard reference strains, the causal organism of leaf spot of snow lotus was identified as Alternaria carthami (1,4). Pathogenicity of the strains was tested on snow lotus seedlings at the six-leaf stage. The lower leaves of 20 plants were sprayed until runoff with conidial suspensions of 1 × 104 spores mL–1, and five plants sprayed with sterile distilled water served as controls. All plants were covered with a polyethylene bag, incubated at 25°C for 2 days, and subsequently transferred to a growth chamber at 25°C with a 16-h photoperiod. Light brown lesions developed within 10 days on leaflet margins in all inoculated plants. The pathogen was reisolated from inoculated leaves, and isolates were deposited at the Key Oasis Eco-agriculture Laboratory of Xinjiang Production and Construction Group, Xinjiang and the Institute of Biotechnology, Zhejiang University. No reports of a spot disease caused by A. carthami on snow lotus leaves have been found, although this pathogen has been reported on safflower in western Canada (3), Australia (2), India (1), and China (4). To our knowledge, this is the first report of a leaf spot caused by A. carthami on snow lotus in China. References: (1) S. Chowdhury. J. Indian Bot. Soc. 23:59, 1944. (2) J. A. G. Irwin. Aust. J. Exp. Agric. Anim. Husb. 16:921, 1976. (3) G. A. Petrie. Can. Plant Dis. Surv. 54:155, 1974. (4) T. Y. Zhang. J. Yunnan Agric. Univ.17:320, 2002.

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The First Report of Downy Mildew Caused by Peronospora belbahrii on Sweet Basil in Greenhouses in the Czech Republic

Plant Disease ◽

10.1094/pdis-07-13-0747-pdn ◽

2014 ◽

Vol 98 (11) ◽

pp. 1579-1579 ◽

Cited By ~ 3

Author(s):

I. Šafránková ◽

L. Holková

Keyword(s):

Czech Republic ◽

Downy Mildew ◽

Width Ratio ◽

Specific Sequence ◽

The Czech Republic ◽

First Report ◽

Sweet Basil ◽

Potted Plants ◽

Length Width ◽

Necrotic Spots

Sweet basil (Ocimum basilicum L.) is an aromatic plant that is cultivated as a pot plant in greenhouses or in fields in the Czech Republic. The plants are intended for direct consumption or for drying. In April of 2012, the first large chlorotic from the middle necrotic spots occurred gradually on leaves of pot plants O. basilicum cv. Genovese in greenhouses in Central Bohemia. The characteristic gray to brown furry growth of downy mildew appeared on abaxial surfaces of leaves in the place of chlorotic spots within 3 to 4 days. The infested leaves fell off in the late stages of pathogenesis. The infestation gradually manifested itself in ever-younger plants and in July, cotyledons and possibly the first true leaves were already heavily infected and damaged and these plants rapidly died. The plant damage reached 80 to 100%, so it was necessary to stop growing the plants in the greenhouse at the end of July. The causal agent was isolated and identified as Peronospora belbahrii Thines by means of morphological and molecular characters (2,3). Conidiophores were hyaline, straight, monopodial, 280 to 460 μm, branched three to five times, ended with two slightly curved branchlets with a single conidia on each branchled tip. The longer branchlets measured 13 to 24 μm (average 18.2 μm), the shorter one 4 to 15 μm (average 9.7 μm). Conidia were rounded or slightly ovoid, from brownish to dark brownish, measured 22 to 31 × 20 to 28 μm (length/width ratio 1.2). A pathogen-specific sequence was detected with the help of the pathogen ITS rDNA specific primers in symptomatic leaves (1). DNA from plant tissues was isolated using the DNeasy plant Mini Kit (Qiagen, Germany) following the standard protocol. PCR was performed using KAPA2G Robust HotStar kit (Kapa Biosystems, United States) according to the conditions recommended in Belbahri et al. (1). The specific products were visualized by electrophoresis through 1.5% agarose gels. Leaves of 20-day-old potted plants O. basilicum ‘Genovese’ were inoculated by spraying with 5 × 105 conidia/ml of the pathogen. Each pot contained 10 plants. Sterilized distilled water was applied to control plants. Plants were covered with polyethylene bags during the entire incubation period to maintain high humidity, and kept at a temperature of 22 to 24°C. Typical disease symptoms appeared on leaves 5 to 9 days after inoculation. Control plants were symptomless. P. belbahrii was re-isolated from the lesions of inoculated plants, thus fulfilling Koch's postulates. Downy mildew on sweet basil was reported in countries in Africa, Europe, and South and North America (4). To our knowledge, this is the first report of downy mildew on sweet basil in the Czech Republic. References: (1) L. Belbahri et al. Mycol. Res. 109:1276, 2005. (2) Y.-J. Choi et al. Mycol. Res. 113:1340, 2009. (3) M. Thines et al. Mycol. Res. 113:532, 2009. (4) C. A. Wyenandt et al. HortScience 45:1416, 2010.

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First Report of Downy Mildew Caused by Plasmopara obducens on Impatiens in California

Plant Disease ◽

10.1094/pdis.2004.88.8.909b ◽

2004 ◽

Vol 88 (8) ◽

pp. 909-909 ◽

Cited By ~ 14

Author(s):

S. N. Wegulo ◽

S. T. Koike ◽

M. Vilchez ◽

P. Santos

Keyword(s):

United States ◽

Downy Mildew ◽

Disease Incidence ◽

Leaf Tissue ◽

The United States ◽

Plant Diseases ◽

Single Type ◽

First Report ◽

Commercial Grower ◽

Impatiens Walleriana

During February 2004, diseased double impatiens (Impatiens walleriana) plants were received from a commercial grower in southern California. The upper surfaces of symptomatic leaves were pale yellow with no distinct lesions. Diseased leaves later wilted, and severely affected leaves abscised from the stem. At the nursery, only double impatiens plants in the Fiesta series were infected, and some cultivars were more heavily infected than others. Disease incidence in cv. Sparkler Hot pink was nearly 100%. The interior of infected leaves was colonized by coenocytic mycelium. A conspicuous white growth was observed only on the underside of leaves. Sporangiophores were hyaline, thin walled, emergent from stomata, and had slightly swollen bases. Sporangiophore branching was distinctly monopodial. Smaller sporangiophore branches were arranged at right angles to the supporting branches, and tips of branches measured 8 to 14 μm long. Sporangia were ovoid and hyaline with a single pore on the distal ends. Distal ends of sporangia were predominantly flat but occasionally had a slight papilla. Short pedicels were present on the attached ends. Sporangia measured 19.4 to 22.2 (-25.0) μm × 13.9 to 16.7 (-19.4) μm. Oospores were not observed in leaf tissue. On the basis of symptoms and morphology of the organism, the pathogen was identified as Plasmopara obducens J. Schröt. Pathogenicity tests were done on double type cvs. Fiesta, Tioga Red, and Tioga Cherry Red and on single type cvs. Cajun Watermelon and Accent Lilac. Plants were spray inoculated with sporangiospore suspensions (1 × 104 sporangiospores per milliliter), incubated for 24 h in a dew chamber (18 to 20°C), and then maintained in a greenhouse (22 to 24°C). Symptoms and signs of downy mildew developed after 12 days only on inoculated cv. Fiesta plants, and the pathogen morphology matched that of the originally observed pathogen. Nontreated control plants did not develop downy mildew. To our knowledge, this is the first report of downy mildew on impatiens in California. P. obducens is one of two causal agents of downy mildew of impatiens (2,4). The other pathogen, Bremiella sphaerosperma, has dichotomous sporangiophore branching and causes lesions with well-defined margins (2,4). In the United States, the disease has been recorded in the eastern and northeastern states and in Indiana, Minnesota, Mississippi, Montana, and Wisconsin (3). In Canada, the disease has been recorded in Manitoba and Quebec (1). References: (1) I. L. Conners. An Annotated Index of Plant Diseases in Canada and Fungi Recorded on Plants in Alaska, Canada, and Greenland. Research Branch, Canada Department of Agriculture, Publication 1251, 1967. (2) O. Constantinescu. Mycologia 83:473, 1991. (3) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, 1989. (4) G. W. Wilson. Bull. Torrey Bot. Club 34:387, 1907.

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