First Report of Corynespora cassiicola-Incited Target Spot on Cotton in Alabama

Target spot symptoms were first observed on dryland and irrigated cotton (Gossypium hirsutum L.) statewide in Alabama in 2011. Leaf spots first appeared in the lower canopy and spread upward through the canopy toward the shoot tips. Individual leaf spots were roughly circular, formed concentric rings of alternating light and dark brown bands, and were up to 10 mm in diameter. Leaves with multiple lesions senesced prematurely. In 2012, target spot symptoms were observed as early as 68 days after planting in Tallapoosa County, Alabama. The possible combination of early disease onset and frequent showers/irrigation triggered rapid premature defoliation in some fields in excess of 75% in susceptible cultivars (Phytogen 499). Estimated yield losses in select cultivars (Deltapine 1050 and Phytogen 499) exceeded 336 kg/ha seed cotton. In 2012, symptomatic leaves were obtained from two separate locations in Alabama (Baldwin and Tallapoosa counties). The fungus was isolated from lesions by single spores plated on antibiotic V8 agar (1) and incubated at 21°C for 2 weeks under 12-h light cycles. Conidiophores arising from the gray, flocculose colonies were simple, erect, cylindrical, brown or olivaceous, unbranched, with two to seven septa. Conidia were borne singly, ranging from subhyaline to olivaceous, obclavate to cylindrical, straight to slightly curved, contained 4 to 15 pseudosepta, and were 50 to 209 μm long and 7 to 15 μm wide. These characteristics were consistent with the original description of Corynespora cassiicola on cotton (2). The internal transcribed spacer region (ITS) of two isolates, one representing each location, was amplified using primers 2234c and 3126t targeting a 550-bp region of the ITS1, 5.8S rRNA gene, and ITS2 (3). Sequences revealed 99% similarity to C. cassiicola in NCBI (Accession Nos. AY238606 and JQ717069). In greenhouse pathogenicity tests, 10 cotton seedlings (Phytogen 499) were inoculated by spraying a fungal suspension (2 × 104 spores/ml) of each of the two isolates prepared from 2-week-old cultures until runoff. Controls were inoculated with sterile water. Cotton seedlings were incubated in a moist chamber at 21°C for 72 h. All plants inoculated with the fungus developed leaf spot symptoms in 6 days. The fungus was reisolated from five inoculated plants. DNA was extracted from each isolate, amplified using primer pair 2234c/3126t, and sequenced. Sequences (550-bp) from all isolates shared 99% similarity to other C. cassiicola sequences in GenBank (Accession Nos. AY238606 and JQ717069). Nucleotide sequence data reported are available in GenBank under Accession Nos. KC544017 to 23. This pathogen has been reported previously to be economically important on a number of other hosts. To our knowledge, this is the first report of C. cassiicola on cotton in Alabama. Given the increasing prevalence of this disease in Alabama, its confirmation is a significant step toward developing management recommendations for growers. References: (1) L. J. Dixon et al. Phytopathology 99:1015, 2009. (2) J. P. Jones. Phytopathology 51:305, 1961. (3) J. Sequerra et al. Mycol. Res. 101:465, 1997.

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First Report of Target Spot of Cotton Caused by Corynespora cassiicola in China

Plant Disease ◽

10.1094/pdis-12-13-1243-pdn ◽

2014 ◽

Vol 98 (7) ◽

pp. 1006-1006 ◽

Cited By ~ 9

Author(s):

Y.-X. Wei ◽

H. Zhang ◽

J.-J. Pu ◽

X.-M. Liu

Keyword(s):

Limiting Factors ◽

Control Treatment ◽

Pathogenicity Test ◽

Corynespora Cassiicola ◽

Single Spore ◽

Internal Transcribed Spacer Region ◽

First Report ◽

Leaf Spots ◽

Target Spot ◽

Initial Symptoms

Cotton (Gossypium hirsutum L.) is one of the most important economic crops in China and fungal diseases are the major limiting factors in its production. In September 2013, cotton plants infected with leaf spots were observed in Sanya, Hainan Province, China. Initial symptoms developed as brick-red dots that led to the formation of irregular to circular lesions with gray centers surrounded by brown borders. Individual leaf spots formed concentric rings of alternating light and dark brown bands. Leaf tissue segments collected from the border between symptomatic and healthy tissue were surface disinfested in 75% ethanol for 1 min, then rinsed three times in sterile water with streptomycin sulfate. Fungal isolates obtained from these segments were purified by the single spore technique on potato dextrose agar (PDA) at 28°C. The initial color of the colonies was olivaceous, turning dark brown after 5 days. Conidiophores were scattered or clustered, brown, straight to curved, unbranched, and glabrous. Conidia had 4 to 12 pseudosepta and were 56 to 230 μm long and 5 to 15 μm wide, brown, straight to slightly curved, obclavate to cylindrical, glabrous, and apex obtuse. These characteristics were consistent with the description of Corynespora cassiicola (Berk. & M.A. Curtis.) C.T. Wei (3). A pathogenicity test was conducted with the four isolates on detached young cotton leaves (two to four true leaf stage). For each isolate, three slightly wounded and three unwounded leaves were inoculated with 5.5-mm-diameter mycelial plugs. For the control treatment, wounded and unwounded leaves were mock inoculated with sterile PDA plugs of the same size. The inoculated leaves were placed in a moist chamber and incubated with a 12-h photoperiod at 28°C. Necrotic lesions appeared on wounded spots after 2 days of incubation and on unwounded leaves 3 days after incubation. All symptoms were similar to those observed in the field. Symptoms were not observed on control leaves. The same fungus was always re-isolated from the diseased tissue according to Koch's postulates. To confirm the identity of the pathogen, DNA was extracted from a 1-week-old culture grown on PDA and the internal transcribed spacer region (ITS) of one isolate (GenBank Accession No. KF924624) was amplified using primers ITS1 and ITS4 (4) and sequenced. BLAST search in GenBank revealed 100% homology with sequences of C. cassiicola (EU364535.1, EU364536.1, FJ852574.1, and FJ852575.1). Based on the symptoms, fungal morphology, ITS sequence comparison, and pathogenicity test, this fungus was identified as C. cassiicola. Target spot of cotton associated with C. cassiicola has been reported in Georgia (2) and Alabama (1). To our knowledge, this is the first report that C. cassiicola can infect cotton in China inducing target spot of cotton (2). This report will establish a foundation for further study of C. cassiicola to aid disease measurement and control. References: (1) K. N. Conner et al. Plant Dis. 97:1379, 2013. (2) A. M. Fulmer et al. Plant Dis. 96:1066, 2012. (3) J. Y. Lu. Page 407 in: Plant Pathogenic Mycology. China Agricultural Press, Beijing, 2000. (4) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA, 1990.

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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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Three novel lineages of ‘Candidatus Liberibacter africanus’ associated with native rutaceous hosts of Trioza erytreae in South Africa

INTERNATIONAL JOURNAL OF SYSTEMATIC AND EVOLUTIONARY MICROBIOLOGY ◽

10.1099/ijs.0.069864-0 ◽

2015 ◽

Vol 65 (Pt_2) ◽

pp. 723-731 ◽

Cited By ~ 38

Author(s):

Ronel Roberts ◽

Emma T. Steenkamp ◽

Gerhard Pietersen

Keyword(s):

South Africa ◽

Phylogenetic Analysis ◽

16S Rrna ◽

16S Rrna Gene ◽

Sequence Data ◽

Rrna Gene ◽

Gene Sequences ◽

16S Rrna Gene Sequences ◽

Nucleotide Sequence Data ◽

Trioza Erytreae

Greening disease of citrus in South Africa is associated with ‘Candidatus Liberibacter africanus’ (Laf), a phloem-limited bacterium vectored by the sap-sucking insect Trioza erytreae (Triozidae). Despite the implementation of control strategies, this disease remains problematic, suggesting the existence of reservoir hosts to Laf. The current study aimed to identify such hosts. Samples from 234 trees of Clausena anisata, 289 trees of Vepris lanceolata and 231 trees of Zanthoxylum capense were collected throughout the natural distribution of these trees in South Africa. Total DNA was extracted from samples and tested for the presence of liberibacters by a generic Liberibacter TaqMan real-time PCR assay. Liberibacters present in positive samples were characterized by amplifying and sequencing rplJ, omp and 16S rRNA gene regions. The identity of tree host species from which liberibacter sequences were obtained was verified by sequencing host rbcL genes. Of the trees tested, 33 specimens of Clausena, 17 specimens of Vepris and 10 specimens of Zanthoxylum tested positive for liberibacter. None of the samples contained typical citrus-infecting Laf sequences. Phylogenetic analysis of 16S rRNA gene sequences indicated that the liberibacters obtained from Vepris and Clausena had 16S rRNA gene sequences identical to that of ‘Candidatus Liberibacter africanus subsp. capensis’ (LafC), whereas those from Zanthoxylum species grouped separately. Phylogenetic analysis of the rplJ and omp gene regions revealed unique clusters for liberibacters associated with each tree species. We propose the following names for these novel liberibacters: ‘Candidatus Liberibacter africanus subsp. clausenae’ (LafCl), ‘Candidatus Liberibacter africanus subsp. vepridis’ (LafV) and ‘Candidatus Liberibacter africanus subsp. zanthoxyli’ (LafZ). This study did not find any natural hosts of Laf associated with greening of citrus. While native citrus relatives were shown to be infected with Laf-related liberibacters, nucleotide sequence data suggest that these are not alternative sources of Laf to citrus orchards, per se.

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Redescription of Anopheles oswaldoi (Peryassú, 1922) (Diptera: Culicidae), with formal lectotype designation

Zootaxa ◽

10.11646/zootaxa.1588.1.2 ◽

2007 ◽

Vol 1588 (1) ◽

pp. 31-51 ◽

Cited By ~ 6

Author(s):

MAYSA TIEMI MOTOKI ◽

YVONNE-MARIE LINTON ◽

FREDDY RUIZ ◽

CARMEN FLORES-MENDOZA ◽

MARIA ANICE MUREB SALLUM

Keyword(s):

Adult Female ◽

Male Genitalia ◽

Sequence Data ◽

Original Description ◽

Instar Larva ◽

Morphological Characters ◽

Fourth Instar Larva ◽

Internal Transcribed Spacer Region ◽

Dna Sequence Data ◽

Molecular Identity

Anopheles (Nyssorhynchus) oswaldoi (Peryassú, 1922) comprises a species complex in South America. To fully characterize other taxa within the Oswaldoi Complex, it is essential to fix the identity of the nominotypical member. Given that the no type was designated in the original description, a lectotype is formally designated from the remaining syntypes in the Museu Nacional do Rio de Janeiro. These and other recently collected specimens from the type locality (Espírito Santo, Brazil) and the State of São Paulo, Brazil were used to redescribe the species using morphological characters of the adult female, male and male genitalia, and the fourth-instar larva and pupa. The larva, pupa, and male genitalia are illustrated. Diagnostic morphological characters of the adult female and male genitalia are provided to distinguish An. oswaldoi s.s. from the morphologically similar An. konderi, An. galvaoi, and An. ininii. DNA sequence data from the second nuclear internal transcribed spacer region (ITS2) are included to fix the molecular identity of An. oswaldoi s.s.

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First Report of Curvularia gladioli Causing a Leaf Spot on Gladiolus grandiflorus in Brazil

Plant Disease ◽

10.1094/pdis-12-12-1118-pdn ◽

2013 ◽

Vol 97 (6) ◽

pp. 847-847 ◽

Cited By ~ 5

Author(s):

D. P. Torres ◽

M. A. Silva ◽

D. B. Pinho ◽

O. L. Pereira ◽

G. Q. Furtado

Keyword(s):

Leaf Spot ◽

Central Cell ◽

Post Inoculation ◽

Intermediate Cell ◽

Conidial Suspension ◽

Single Spore ◽

Internal Transcribed Spacer Region ◽

First Report ◽

The Third ◽

Leaf Spots

Gladiolus (Iridaceae) is a popular bulbous plant grown worldwide as an ornamental garden plant or cut flower due to its attractive color, size, and flower shape. In April 2012, leaf spots were observed on plants of Gladiolus grandiflorus varieties T-704 and Amsterdam growing in a production area of cut flowers located in the city of Viçosa, Minas Gerais. The oval to round leaf spots were brown with a dark border surrounded by a halo of yellow tissue. Infected leaf samples were deposited in the herbarium at the Universidade Federal de Viçosa (VIC31897). A fungus was isolated from the leaf spots and a single-spore pure culture was initiated and grown on corn meal carrot agar (CCA) medium in petri dishes incubated at 25°C under a 12-h photoperiod for 4 weeks. A sporulating single-spore culture was deposited at the Coleção de Culturas de fungos fitopatogênicos “Prof. Maria Menezes” (UFRPE, Brazil) code CMM 4055. On CCA medium, the fungal isolate initially appeared white, becoming dark after 14 days. Thirty conidia and conidiophores were measured for identification to species. The septate, smooth to pale brown conidiophores were present singly or in groups. The simple, straight or flexuous conidiophores were 42.5 to 82.5 × 3.5 to 7.5 μm and some had a geniculate growth pattern. The majority of conidia were curved at the third (central) cell from the base, which was usually enlarged compared to the end cells. The cells at each end of the 3-distoseptate conidia were pale brown, the intermediate cell brown or dark brown, and the third (central) cell was often the darkest. The basal cell had a protuberant hilum. Conidia were smooth and 20.0 to 33.5 × 10 to 17.5 μm. These characteristics matched well with the description of Curvularia gladioli (1). To confirm this identification, DNA was extracted using a Wizard Genomic DNA Purification Kit and the internal transcribed spacer region (ITS) of rDNA was amplified using ITS1 and ITS4 primers and the partial 28S rDNA region using primers LR0R and LR5. The sequences were deposited in GenBank as accession nos. JX995106 and JX995107, respectively. The ITS sequence matched sequence AF071337, C. gladioli, with 100% identity. This pathogen was first identified as C. lunata, but based on the characteristic of the hilum, spore size, and pathogenicity testing, the fungus was renamed C. trifolii f. sp. gladioli (3). Due to the explicit curvature of the conidia at the third cell and molecular data, the fungus was reclassified as C. gladioli (1,2). To confirm Koch's postulates, 1-month-old healthy plants of G. grandiflorus var. T-704 and Amsterdam (five plants each) were inoculated with a conidial suspension (2 × 104 conidia mL–1) by spraying the foliage and then placed on a growth chamber at 25°C. The control plants were sprayed with distilled water. Symptoms were consistent with those initially observed and all plants developed leaf spots by 4 days post-inoculation. C. gladioli was consistently recovered from the symptomatic tissue and control plants remained symptomless. To our knowledge, this is the first report of C. gladioli causing leaf spot on G. grandiflorus in Brazil. Due to a lack of chemical fungicides for management of this pathogen, further studies to evaluate the susceptibility of the main varieties of gladiolus grown in Brazil to C. gladioli may be necessary. References: (1) G. H. Boerema and M. E. C. Hamers. Neth. J. Plant Pathol. 95:1, 1989. (2) D. S. Manamgoda et al. Fungal Divers. 56:131, 2012. (3) J. A. Parmelee. Mycologia 48:558, 1956.

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First Report of Embellisia hyacinthi Causing a Leaf Spot and Bulb Skin Spot Disease on Scilla peruviana in California

Plant Disease ◽

10.1094/pdis-11-10-0845 ◽

2011 ◽

Vol 95 (3) ◽

pp. 356-356

Author(s):

S. Rooney-Latham ◽

C. L. Blomquist ◽

D. G. Fogle ◽

E. G. Simmons

Keyword(s):

Leaf Spot ◽

Apical Cell ◽

Leaf Spot Disease ◽

Adaxial Side ◽

Internal Transcribed Spacer Region ◽

California Department ◽

First Report ◽

Spot Disease ◽

Leaf Spots ◽

Food And Agriculture

The genus Scilla (Hyacinthaceae) includes more than 50 species of perennial, flowering bulbs grown in landscapes worldwide. In December 2000 and May 2009, an unknown leaf spot disease on Scilla peruviana was submitted to the California Department of Food and Agriculture Plant Pest Diagnostic Lab. Samples were collected during routine phytosanitary inspections of production fields in Santa Cruz County in 2000 and Monterey County in 2009. The disease was detected before plants flowered in one field at each location each year and appeared to have a scattered distribution. Foliar spots were large, elliptical to oblong with grayish black centers and brown margins. Yellow halos surrounded many of the spots. Examination of the bulb material revealed small necrotic patches on the outer bulb scales. A rapidly growing fungus was isolated on one-half-strength acidified potato dextrose agar (APDA) from the sporulating leaf spots and necrotic patches on the bulbs. The colonies were greenish gray and became dark olivaceous with age. Dictyospores, which formed on simple to branched, geniculate conidiophores, were oblong, fusiform or obclavate and usually had a triangular apical cell. They were initially hyaline, turning olivaceous brown with age. Conidia measured 14 to 39 × 8 to 13 μm (average 24.6 × 9.9 μm) typically with two to four (but up to seven) thick, transverse septa and one to two longitudinal septa. Morphologically, the fungus matched the description of Embellisia hyacinthi de Hoog & Miller (1,3). To confirm pathogenicity, four leaves of four S. peruviana plants were inoculated by taking colonized mycelial plugs from 2-week-old cultures and placing them in a plastic screw-cap lid filled with sterile water. The water plus mycelial plug suspension in the lid was then clipped to the adaxial side of a pushpin-wounded leaf (4). Plants were placed in a dark dew chamber at 20°C for 48 h and then moved to a growth chamber at 20°C with a 12-h photoperiod. After 48 h, the clips, caps, and plugs were removed. An equal number of control plants were wounded and mock inoculated with noncolonized APDA agar plugs and the experiment was repeated. Leaf lesions were visible 3 days after clip removal and expanded to an average of 26 × 10 mm, 14 days after inoculation. Sporulation was observed in the lesions after 5 to 7 days and the fungus was isolated from all inoculated leaves. No symptoms developed on the control leaves. DNA sequencing of the internal transcribed spacer region of the isolate (GenBank Accession No. HQ425562) using primers ITS1 and ITS4 matched the identity of E. hyacinthi (2,4). E. hyacinthi has been reported as a foliar and bulb pathogen on Hyacinthus, Freesia, and Scilla in Japan and Europe including Great Britain. Bulbs infected with E. hyacinthi are generally less sound and less valuable than noninfected bulbs (1). To our knowledge, this is the first report of the disease on S. peruviana in California. References: (1) G. S. de Hoog and P. J. Muller. Neth. J. Plant Pathol. 79:85, 1973. (2) B. Pryor and D. M. Bigelow. Mycologia 95:1141, 2003. (3) E. Simmons. Mycotaxon 17:216, 1983. (4) L. E. Yakabe et al. Plant Dis. 93:883, 2009.

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First Report of Leaf Spot on Gerbera jamesonii Caused by Corynespora cassiicola in China

Plant Disease ◽

10.1094/pdis-12-11-1081-pdn ◽

2012 ◽

Vol 96 (6) ◽

pp. 915-915

Author(s):

Z. R. Shi ◽

M. M. Xiang ◽

Y. X. Zhang ◽

J. H. Huang

Keyword(s):

Leaf Spot ◽

Control Measures ◽

Control Treatment ◽

Leaf Spot Disease ◽

Corynespora Cassiicola ◽

Gerbera Jamesonii ◽

Cut Flower ◽

Single Spore ◽

Internal Transcribed Spacer Region ◽

First Report

Gerbera (Gerbera jamesonii Bolus ex. Hook f.) is a popular cut flower and flowering potted plant. In August 2011, a new leaf spot disease was observed on double-type Gerbera growing in outdoor ground beds in Guangzhou, Guangdong Province, China. Approximately 30% of about 20,000 Gerbera plants in the Guangzhou ground beds were affected. Leaf spots were round or irregular with grayish centers surrounded by dark brown borders and ranged from 5 to 15 mm in diameter. Leaves with multiple lesions became blighted. A fungus was isolated from the lesions and single-spore isolates plated on potato dextrose agar (PDA) produced gray, floccose colonies, which reached 65 mm on PDA after 7 days at 28°C. Conidiophores were brown or olivaceous, cylindrical, straight and unbranched, two to seven septations, and 25 to 83 × 4 to 7 μm. Conidiogenous cells were olivaceous or brown, cylindrical, and 11 to 21 × 4 to 6 μm. Conidia were borne singly or in chains of two to five, brown, cylindrical, straight to slightly curved, two to eight pseudosepta, and 30 to 90 × 5.5 to 11.5 μm (mean 70.4 × 7.3 μm), with a conspicuous hilum. These characteristics were consistent with the description of Corynespora cassiicola (Berk. & M.A. Curtis.) C.T. Wei (1). The internal transcribed spacer region (ITS) of one isolate (GenBank Accession No. JN853778) was amplified using primers ITS4 and ITS5 (3) and sequenced. A BLAST search in GenBank revealed highest similarity (99%) to sequences of C. cassiicola (AY238606.1 and FJ852715.1). Pathogenicity tests were conducted on 10 potted double-type Gerbera plants. Five wounded and five unwounded leaves on each plant were inoculated with 5-mm mycelial plugs from the periphery of 5-day-old cultures of the isolated fungus. The plugs were put on the leaf surface and secured with sterile wet cotton. Sterile PDA plugs were used as the control treatment on different leaves of the same plants that were inoculated. Plants were covered with plastic bags and incubated in a growth chamber with 12 h of light at 28°C. Necrotic lesions appeared on wounded leaves after 2 to 3 days of incubation and on unwounded leaves 5 to 7 days after incubation. Symptoms on wounded and unwounded leaves were similar to those observed in the field, whereas control leaves inoculated with sterile PDA plugs remained symptomless. C. cassiicola was consistently reisolated from these lesions. Although there are approximately 644 reported hosts of C. cassiicola (2), to our knowledge, this is the first report of C. cassiicola leaf spot on G. jamesonii. Because the disease caused damage to the foliage and affected the flowering of the plants, control measures may need to be implemented for the production of Gerbera in cut flower nurseries. References: (1) M. B. Ellis. CMI Mycol. Pap. 65:15, 1957. (2) D. F. Farr and A. Y. Rossman. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved from http://nt.ars-grin.gov/fungaldatabases/ , 21 November 2011. (3) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, 1990.

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Developing a greenhouse protocol for evaluating resistance to Corynespora cassiicola in cotton

Plant Disease ◽

10.1094/pdis-08-20-1675-re ◽

2021 ◽

Author(s):

Carly Moore ◽

Nancy Sharma ◽

Kira L. Bowen ◽

Jenny Koebernick

Keyword(s):

Irrigation System ◽

Disease Onset ◽

Genetic Resistance ◽

Leaf Wetness ◽

Corynespora Cassiicola ◽

Optimum Temperature ◽

Gossypium Hirsutum L ◽

Breeding Lines ◽

Target Spot ◽

Cotton Genotypes

Target spot, caused by Corynespora cassiicola, has re-emerged as a disease of economic importance in cotton (Gossypium hirsutum L.) in the southeastern U.S. While this pathogen affects other economically important crops, relatively little is known about C. cassiicola on cotton, especially with regard to conditions conducive for disease development and sources of genetic resistance. Therefore, in order to more efficiently screen cotton genotypes for resistance, a greenhouse protocol is needed. Optimum temperature and conducive leaf wetness duration were determined in growth chamber trials. Temperature range for disease onset as well as greatest lesion counts occurred between 20 and 28°C. Generally, with ≥ 24 h leaf wetness at these temperatures, disease onset was noted as rapidly as 1 day after inoculation on a cultivar that was previously determined to be susceptible to target spot. A mist irrigation system was used to maintain prolonged periods of leaf wetness in the greenhouse. In greenhouse trials, inoculation of cotyledons with 4 × 104 conidia/ml allowed differentiation of five selected genotypes with disease reactions that reflected their field rankings. The current protocol will be useful for evaluating cotton breeding lines for resistance to target spot.

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First Report of Target Spot of Broadleaf Tobacco Caused by Rhizoctonia solani (AG-3) in Connecticut

Plant Disease ◽

10.1094/pdis-04-12-0335-pdn ◽

2012 ◽

Vol 96 (9) ◽

pp. 1378-1378 ◽

Cited By ~ 1

Author(s):

J. A. LaMondia ◽

C. R. Vossbrinck

Keyword(s):

Rhizoctonia Solani ◽

Sequence Data ◽

Its Region ◽

Anastomosis Group ◽

Growth Chamber ◽

First Report ◽

Potted Plants ◽

Plastic Bags ◽

Target Spot ◽

Half Strength

In June 2011, 15 transplant beds of broadleaf cigar wrapper tobacco (Nicotiana tabacum L., cv. C9) plants in Hartford County, Connecticut, were observed with almost every plant diseased. Leaf lesion symptoms ranged from small (2 to 3 mm) water-soaked spots to larger (2 to 3 cm) lesions. Disease was subsequently observed, also at nearly 100% incidence in a 10-hectare field on that farm and at additional broadleaf tobacco farms from two other towns in Hartford County and one town in Tolland County. Lesions exhibited a pattern of concentric rings, necrotic centers and tears in the centers, and margins that often resulted in a shot-hole appearance. Some lesions had chlorotic halos. Rhizoctonia solani Kuhn (Thanatephorus cucumeris A. B. Frank) was isolated from the margins of lesions that had been surface sterilized in 0.5% NaOCl for 30 s and then rinsed in sterile distilled water and placed on the surface of half-strength potato dextrose agar (PDA). Multiple isolations were made and the pathogen was identified on the basis of mycelial characteristics including multinucleate cells, septate hyphae wider than 7 μm, and hyphal branches occurring at approximately right angles, constricted at the base (4). Eight-week-old potted tobacco plants were each inoculated by spraying with a mycelial suspension (1 × 105 CFU) of an isolate of R. solani recovered from tobacco onto leaves, or with water alone (five plants each). The plants were placed in plastic bags in a 24°C growth chamber and misted. After 2 days, the bags were removed and the potted plants placed in trays filled to a depth of 1 cm with water in the growth chamber. After 8 days, the pathogen was reisolated from all inoculated plants exhibiting water-soaked spots as disease symptoms. Leaves inoculated with water or half-strength PDA plugs alone were asymptomatic. DNA was liberated from hyphae of the R. solani isolate by bead beating in STE buffer using 0.15 mm zirconium beads. Two microliters of the eluate was used to amplify the ITS region. Amplified DNA was purified in a Qiagen QIAquick PCR purification kit and submitted to the Yale science hill genomic facility for standard Sanger dideoxy sequencing. The sequence was exactly the same as an isolate from Massachusetts that we sequenced in 2010 (GenBank Accession No. HQ241274). The ITS sequence confirmed our identification of this new isolate as R. solani anastomosis group (AG) 3. This disease has been previously reported on tobacco from South America, South Africa, and the southern United States (1), Canada (3), and Massachusetts (2). Conditions were very conducive for disease because 2011 was a very wet year in Connecticut. To our knowledge, this is the first report of this disease in broadleaf cigar wrapper tobacco in Connecticut. The sequence data suggested that it may have been introduced to Connecticut from Massachusetts. We have found the target spot pathogen distributed across the tobacco producing area of Connecticut. This constitutes a serious threat as there are no systemic fungicides currently registered for control of this disease in broadleaf tobacco. References: (1) J. S. Johnk et al. Phytopathology 83:854, 1993. (2) J. A. LaMondia and C. R. Vossbrinck, Plant Dis. 95:496, 2010. (3) R. D. Reeleder et al., Plant Dis., 80:712. (4) B. Sneh et al. Identification of Rhizoctonia species. The American Phytopathological Society, St. Paul, MN, 1991.

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First Report of Corynespora cassiicola Causing Leaf Spot of Cassava in China

Plant Disease ◽

10.1094/pdis-94-7-0916a ◽

2010 ◽

Vol 94 (7) ◽

pp. 916-916 ◽

Cited By ~ 1

Author(s):

X.-B. Liu ◽

T. Shi ◽

C.-P. Li ◽

J.-M. Cai ◽

G.-X. Huang

Keyword(s):

Leaf Spot ◽

Morphological Characteristics ◽

Its Region ◽

Pathogenic Fungi ◽

Commonwealth Mycological Institute ◽

Corynespora Cassiicola ◽

Single Spore ◽

First Report ◽

Leaf Spots ◽

Main Vein

Cassava (Manihot esculenta) is an important economic crop in the tropical area of China. During a survey of diseases in July and September of 2009, leaf spots were observed on cassava plants at three separate plantations in Guangxi (Yunfu and Wuming) and Hainan (Baisha) provinces. Circular or irregular-shaped leaf spots were present on more than one-third of the plants. Spots were dark brown or had white papery centers delimited by dark brown rims and surrounded by a yellow halo. Usually, the main vein or small veinlets adjacent to the spots were dark. Some defoliation of plants was evident at the Wuming location. A fungus was isolated from symptomatic leaves from each of the three locations and designated CCCGX01, CCCGX02, and CCCHN01. Single-spore cultures of these isolates were incubated on potato dextrose agar (PDA) for 7 days with a 12-h light/dark cycle at a temperature of 28 ± 1°C. Conidiophores were straight to slightly curved, unbranched, and pale to light brown. Conidia were formed singly or in chains, obclavate to cylindrical, straight or curved, subhyaline-to-pale olivaceous brown, 19.6 to 150.3 μm long and 5.5 to 10.7 μm wide at the base, with 4 to 13 pseudosepta. Morphological characteristics of the specimen and their conidia were similar to the descriptions for Corynespora cassiicola (2). The isolate CCCGX01 was selected as a representative for molecular identification. Genomic DNA was extracted by the cetyltrimethylammoniumbromide protocol (3) from mycelia and used as a template for amplification of the internal transcribed spacer (ITS) region of rDNA with primer pair ITS1/ITS4. The sequence (GenBank Accession No. GU138988) exactly matched several sequences (e.g., GenBank Accession Nos. FJ852715, EF198117, and AY238606) of C. cassiicola (1). Young, healthy, and fully expanded green leaves of cassava cv. SC205 were surface sterilized. Ten leaves were inoculated with 10-μl drops of 104 ml suspension of conidia and five leaves were inoculated with the same volume of sterile water to serve as controls. After inoculation, leaves were placed in a dew and dark chamber for 36 h at 25°C and subsequently transferred to the light for 5 days. All inoculated leaves with isolates showed symptoms similar to those observed in natural conditions, whereas the controls remained symptom free. The morphological characteristics of reisolated conidia that formed on the diseased parts were identical with the nature isolates. To our knowledge, this is the first report of leaf spot caused by C. cassiicola on cassava in China. References: (1) L. J. Dixon et al. Phytopathology 99:1015, 2009. (2) M. B. Ellis et al. Corynespora cassiicola. No. 303 in: CMI Description of Pathogenic Fungi and Bacteria. Commonwealth Mycological Institute, Kew, UK 1971. (3) J. R. Xu et al. Genetics 143:175, 1996.

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