scholarly journals First Report of Frogeye Leaf Spot (Cercospora sojina) in Wisconsin

Plant Disease ◽  
2002 ◽  
Vol 86 (11) ◽  
pp. 1272-1272 ◽  
Author(s):  
Alemu Mengistu ◽  
N. C. Kurtzweil ◽  
C. R. Grau
Keyword(s):  
Leaf Spot ◽  
Disease Incidence ◽  
Light Output ◽  
Growth Chamber ◽  
Growth Stages ◽  
Cercospora Sojina ◽  
First Report ◽  
Frogeye Leaf Spot ◽  
Pathogenicity Tests ◽  
Leaf Symptoms

Frogeye leaf spot, caused by Cercospora sojina, is an economically important foliar disease of soybean (Glycine max (L.) Merr.) in areas where growing conditions are warm and humid. During a survey conducted in 2000 and 2001 in soybean fields in Wisconsin, reddish brown, circular to angular spots varying in diameter from 1 to 5 mm were observed on soybean leaves in four fields in Dane and Iowa counties, and in five and six fields in Lafayette and Green counties, respectively. Soybean plants were in growth stages between R3 and R5 during sampling. Disease incidence ranged from 30 to 100% with 5 to 10% of leaf area covered with leaf spot in 2000. In 2001, trace levels of the disease were detected in Dane County, but no symptomatic plants were present in the other counties. Symptomatic leaves were collected from all locations in 2000 and Dane county in 2001. Ten leaves were randomly picked from all samples for each year, placed in a 100 × 15 mm petri dish dampened with Whatman No.1 filter paper, and incubated overnight at 24°C. Fungal sporulation developed after 24 h. Fifteen spores were removed from the 10 leaves, placed on acidified potato dextrose agar (APDA), and incubated in the dark at 24°C. Cultures with dark pigmentation and associated conidia and conidiophores were observed after 3 weeks. The conidiophore, spore type, and leaf symptoms correspond to the description of C. sojina (1). Conidiophores were light-to-dark brown, one to four septate, and fasciculate. The conidiophores were also geniculate and measured 52 to 120 x 4 to 6 μm. Conidia were 0 to 10 septate, hyaline, elongate to fusiform, and measured 40 to 60 x 6 to 8 μm. Cultures were maintained on APDA, and spores for inoculations were produced on this medium. Spores from the 2000 cultures were harvested, bulked together, and used for pathogenicity tests. Pathogenicity tests were conducted in a growth chamber using a known susceptible soybean cultivar, Blackhawk. Ten-cm-diameter pots each containing 4 plants was used. Twenty plants were inoculated and 20 served as noninoculated controls. Ten-day-old plants were inoculated with a spore suspension of 3 × 105 spores/ml by spraying inoculum over the entire leaf surfaces with a spray atomizer. Control plants were sprayed similarly with sterile distilled water. Plants were incubated in an enclosed, transparent fiberglass box with a humidifier that provided 95 to 100% humidity. Lighting in the growth chamber was adjusted to 18-h light and 6-h dark during the inoculation period. Plants were removed from the box after 48 h and placed in a growth chamber with a 12-h photoperiod. The light output in the growth chamber was 300 μmol·m-2·s-1 and the temperature was maintained at 24 ± 3°C. The experiment was repeated once. Typical field symptoms appeared on each of the inoculated plant 8 days after inoculation, while the controls expressed no leaf symptoms. C. sojina was reisolated from all symptomatic plants. To our knowledge, this is the first report of C. sojina from soybean in Wisconsin. Reference: (1) D. V. Phillips. Frogeye leaf spot. Page 20 in: Compendium of Soybean Diseases. 4th ed. G. L. Hartman, J. B. Sinclair, and J. C. Rupe, eds. American Phytopathological Society, St. Paul, MN, 1999.

scholarly journals First Report of Frogeye Leaf Spot of Soybean Caused by Cercospora sojina Race 11 in Virginia

Plant Disease ◽  
2011 ◽  
Vol 95 (7) ◽  
pp. 878-878 ◽  
Author(s):  
M. L. Rosso ◽  
A. Vazquez ◽  
K. M. Rainey
Keyword(s):  
Leaf Spot ◽  
Dominant Gene ◽  
Lima Bean ◽  
Growth Stages ◽  
Single Dominant Gene ◽  
Cercospora Sojina ◽  
First Report ◽  
Frogeye Leaf Spot ◽  
Humidity Chamber ◽  
Soybean Leaves

Frogeye leaf spot of soybean (FLS) (Glycine max (L.) Merr.), caused by Cercospora sojina Hara, was first detected in Virginia in 1942 (1). During the 2008 growing season, a FLS survey was conducted in soybean fields in Virginia. This was the first FLS race survey conducted in Virginia. Typical frogeye leaf spot symptoms, as reported by Phillips (4), were observed on soybean leaves in Westmoreland County. During 2008, Westmoreland County planted 7,365 ha of soybean. Symptomatic leaves were collected from V06-1891, V06-1365, V05-4394, V04-8405, and Hutcheson cultivars from plants in growth stages R5 to R6. Leaves were placed in a moist chamber for 24 h at 21°C with 12-h light to induce sporulation. C. sojina was only recovered from V06-1365. Conidia were removed from the leaves, placed into V8 juice agar amended with rifampicin (10 mg ml–1) and ampicillin (0.25 g liter–1) and incubated at 21°C with 12-h light. Cultures with dark pigmentation and presence of conidia were observed after 3 weeks. Conidia matched the description of C. sojina (4). Conidia had three to nine septa, were hyaline, elongate to fusiform, and measured 3 to 6 × 25 to 40 μm. Race identification was conducted using the set of differentials reported by Mian et al. (3). Spores for inoculation were produced on soybean stem lima bean agar (SSLBA) media. Tencentimeter-diameter pots, each containing four plants, were used. The test was conducted twice in a complete randomized design with three replications. Seedlings were inoculated at the V3 growth stage with a spore suspension of 6 × 104 spores/ml. Control plants were sprayed with sterile distilled water. Plants were placed in a greenhouse bench humidity chamber at 21°C for 72 h. Disease rating was conducted 14 days after inoculation. Since the resistance to FLS is known to be controlled by single dominant genes, the FLS was scored as a qualitative trait (i.e., resistant versus susceptible) as previously done by Mian et al. (2). Plants that showed numerous, large, spreading lesions were classified as susceptible and each plant was given a score of 1. Plants that showed no lesions or only small lesions or flecks were classified as resistant and each plant was given a score of 0. Control plants remained healthy. On the basis of the reaction response of the isolate on the set of differentials and comparison with the proposed race designations of Mian et al. (3), the isolate was classified as race 11. Race 11 shows compatible reaction (susceptibility) on the soybean cv. Lincoln, which is the source of Rcs1 resistance gene, and incompatible reactions (resistance) on cvs. Peking, Davis, and Kent. The latter two cultivars are sources of the Rcs3 and Rcs2 genes, respectively. Successful development of soybean cultivars with FLS resistance not only depends on knowledge of the presence of resistance genes, but also on the understanding of the pathogen population structure. To our knowledge this is the first report of C. sojina race 11 from soybean in Virginia. Resistance to this race is conditioned by Rcs2, Rcs3, and the single dominant gene in Peking (3). We recommend use of Rcs3 and Rcs2 genes and the single dominant gene in Peking for resistance to FLS in Virginia. References: (1) S. B. Fenn. Plant Dis. Rep. 26:383, 1942. (2) M. A. R. Mian et al. Crop Sci. 39:1687, 1999. (3) M. A. R. Mian et al. Crop Sci. 48:14, 2008. (4) D. V. Phillips. Page 20 in: Compendium of Soybean Diseases. 4th ed. The American Phytopathological Society. St. Paul, MN, 1999.

scholarly journals First Report of the Soybean Frogeye Leaf Spot Fungus (Cercospora sojina) Resistant to Quinone Outside Inhibitor Fungicides in North America

Plant Disease ◽  
2012 ◽  
Vol 96 (5) ◽  
pp. 767-767 ◽  
Author(s):  
G. R. Zhang ◽  
M. A. Newman ◽  
C. A. Bradley
Keyword(s):  
Leaf Spot ◽  
Management Practices ◽  
The United States ◽  
Conidial Germination ◽  
Cercospora Sojina ◽  
Soybean Field ◽  
Qoi Fungicides ◽  
First Report ◽  
Quinone Outside Inhibitor ◽  
Frogeye Leaf Spot

Quinone outside inhibitor (QoI; also known as strobilurin) fungicides sometimes are applied to soybean (Glycine max) fields to help manage frogeye leaf spot of soybean (caused by Cercospora sojina) in the United States. In August 2010, soybean leaflets exhibiting severe frogeye leaf spot symptoms were collected from a field in Lauderdale County, TN that had been treated twice with pyraclostrobin during that growing season. The field had been planted into soybean annually since at least 2008, and a QoI fungicide had been applied to the field in each of those years. Fifteen single-spore isolates of C. sojina were recovered from the affected soybean leaflets. These isolates were identified as C. sojina based on the observed symptoms on the soybean leaflets and the morphology and size of conidiophores and conidia (3). In addition, DNA was extracted from the cultures, PCR amplification of the small subunit rDNA and internal transcribed spacer (ITS) region was conducted (2), and the resulting PCR product was sequenced at the Keck Biotechnology Center at the University of Illinois, Urbana. The resulting nucleotide sequences were compared with sequences deposited in the nucleotide database ( http://www.ncbi.nlm.nih.gov ) and showed highest homology to sequences of C. sojina. The isolates were tested for their sensitivity to technical-grade formulations of the QoI fungicides azoxystrobin, pyraclostrobin, and trifloxystrobin with an in vitro conidial germination assay with fungicide + salicylhydroxamic acid (SHAM)-amended potato dextrose agar as described by Bradley and Pedersen (1). The effective concentration at which 50% conidial germination was inhibited (EC50) was determined for all 15 C. sojina isolates, with mean values of 3.1644 (2.7826 to 4.5409), 0.3297 (0.2818 to 0.6404), and 0.8573 (0.3665 to 2.5119) μg/ml for azoxystrobin, pyraclostrobin, and trifloxystrobin, respectively. When compared with previously established mean EC50 values of C. sojina baseline isolates (4), EC50 values of the C. sojina isolates collected from the Lauderdale County, TN soybean field were approximately 249- to 7,144-fold greater than the EC50 values of the baseline isolates. These results indicate that all isolates recovered from the Lauderdale County, TN soybean field were highly resistant to QoI fungicides. To our knowledge, this is the first report of QoI fungicide resistance occurring in C. sojina, and surveys for additional QoI fungicide-resistant C. sojina isolates are needed to determine their prevalence and geographic distribution. In light of these findings, soybean growers in Tennessee and adjacent states should consider utilizing alternative frogeye leaf spot management practices such as planting resistant cultivars, rotating to nonhost crops, and tilling affected soybean residue (3). References: (1) C. A. Bradley and D. K. Pedersen. Plant Dis. 95:189, 2011. (2) N. S. Lord et al. FEMS Microbiol. Ecol. 42:327, 2002. (3) D. V. Phillips. Page 20 in: Compendium of Soybean Diseases. 4th ed. G. L. Hartman et al., eds. The American Phytopathological Society, St. Paul, MN, 1999. (4) G. Zhang et al. Phytopathology (Abstr.) 100(suppl.):S145, 2010.

scholarly journals Frogeye Leaf Spot of Soybean Caused by Cercospora sojina in Northwestern Argentina

Plant Disease ◽  
2001 ◽  
Vol 85 (7) ◽  
pp. 801-801 ◽  
Author(s):  
L. D. Ploper ◽  
V. González ◽  
M. R. Gálvez ◽  
M. R. Devani ◽  
F. Ledesma ◽  
...  
Keyword(s):  
Leaf Area ◽  
Leaf Spot ◽  
Leaf Surface ◽  
Disease Incidence ◽  
Growing Season ◽  
Conidial Suspension ◽  
Cercospora Sojina ◽  
Northwestern Argentina ◽  
Resistant Cultivars ◽  
Frogeye Leaf Spot

Frogeye leaf spot of soybean (Glycine max (L.) Merr.), caused by Cercospora sojina Hara, was first detected during the 1997-98 growing season at low incidence and severity (<1% of the leaf diseased) levels in the provinces of Tucumán, Salta, Jujuy, Catamarca, and Santiago del Estero in northwestern Argentina. During the 1998-1999 growing season, disease incidence increased and disease severity grew to 10% of the leaf surface diseased on highly susceptible cultivars in a few locations. An outbreak of frogeye leaf spot occurred throughout northwestern Argentina during the 1999-2000 growing season. Frogeye leaf spot was severe on susceptible cultivars in the provinces of Salta, Santiago del Estero and Catamarca with the greatest intensity in the northeastern part of the Province of Tucumán. Symptoms on leaves were circular lesions that ranged in size from 1 to 5 mm, were reddish-brown to gray or tan, and were bordered by a narrow, reddish-brown to purple margin. Conidiophores and conidia of C. sojina developed on the abaxial leaf surface (1,2). Severely diseased leaves were desiccated and dropped during the R6 stage of growth. Lesions also developed on stems, pods, and seeds. Field surveys indicated that this disease reduced the yields of the highly susceptible cultivars Anta 82 RR, Coker 6738, and A 6445 RG by 48, 34, and 25%, respectively. C. sojina was cultured from diseased tissue on PDA acidified with 0.2% lactic acid and maintained on V-8 juice agar amended with streptomycin sulfate (100 mg/l). Conidia were elongated, dark, 38 to 62 × 5 to 9 μm, with 2 to 6 septa, and borne on dark conidiophores with 1 to 4 septa. Pathogenicity tests were conducted on seedlings of the susceptible cultivars A 6445 RG and Coker 6738 and on the resistant cultivars A 8000 RG and Shulka. Seedlings were inoculated at the V3 growth stage by spraying the leaves with a conidial suspension (4 × 104 conidia/ml) using a hand-held atomizer. Control plants were sprayed with sterile distilled water. Plants were placed in a moist chamber at 26°C for 2 days and then transferred to a greenhouse bench where they were kept at 25 to 30°C. Symptoms identical to those observed in the field became visible after 7 to 10 days. Ratings were made 14 days after inoculation by estimating the percentage of leaf area affected using a standard area diagram. Lesions covered 60 to 65% of the leaf area of susceptible cultivars, but less than 2% on resistant cultivars. Control plants remained healthy. C. sojina was reisolated from lesions on leaves of susceptible plants. Above-average rainfall and high relative humidity in northwestern Argentina during the first three months of 2000 may have encouraged the severe outbreak of frogeye leaf spot of soybean. The outbreak was aggravated by the widespread use of notillage systems in the region and the large hectarage planted with susceptible cultivars. References: (1) S.G. Lehman J. Agric. Res. 36:811–833, 1928. (2) D. V. Philips and J. T. Yorinori. 1989. Frogeye leaf spot. Pages 19–21 in: Compendium of Soybean Diseases, 3rd ed. APS Press, St. Paul, MN.

scholarly journals First Report of Ramularia didyma Causing a Leaf Spot on Ranunculus (Ranunculus asiaticus) Hybrids in California

Plant Disease ◽  
2011 ◽  
Vol 95 (7) ◽  
pp. 872-872 ◽  
Author(s):  
C. L. Blomquist ◽  
C. Y. Warfield
Keyword(s):  
Leaf Spot ◽  
Large Scale ◽  
Disease Incidence ◽  
The United States ◽  
Growth Chamber ◽  
Scale Production ◽  
Cut Flower ◽  
Ranunculus Asiaticus ◽  
Pathogenicity Tests ◽  
San Mateo County

Ranunculus or Persian buttercups (Ranunculus asiaticus) are colorful, cool-season perennials or annuals grown as landscape bedding plants and for field-grown bulb and cut flower production in mild winter climates. In March of 2008, tan-to-brown lesions were observed on the foliage of containerized ranunculus growing in a greenhouse at a production and retail nursery in coastal San Mateo County, CA. Approximately 15% of the approximately 150 cv. Bloomingdale mixed shade ranunculus plants had leaf spot symptoms. Symptomatic plants were generally clustered together on two benches, with a double-flowered purple cultivar with picotee markings having the highest disease incidence and severity. Angular to round, necrotic lesions ranged between 0.25 and 1.0 cm in diameter and were often surrounded by chlorotic tissue. Whitish sporulation was observed on abaxial and adaxial sides of the larger lesions. Conidiophores were hyaline, aseptate, measured 45 to 75 × 3 to 5 μm (56 × 3.7 μm average), and were produced in fascicles on the leaf surface. One-celled fusiform to cylindrical conidia measured 22.5 to 30.0 × 9.0 to 15 μm (25.4 × 11.9 μm average) and two-celled conidia measured 26.0 to 47.5 × 10 to 14 μm (35.3 × 12.1 μm average). Most conidia were hyaline, although a few were pale brown. Morphologically, the fungus matched the description of Ramularia didyma Unger (1). Small (3-mm2) pieces were taken from the margin of the lesion, disinfested with 0.6% sodium hypochlorite for 2 min, and placed at room temperature on carrot piece agar. Colonies were white and grew slowly to approximately 3.5 cm in 25 days. No conidia were produced in culture. To conduct pathogenicity tests, the foliage of nine mixed-color ranunculus plants grown from tubers for 7 weeks at 16°C in a growth chamber were sprayed with an aqueous suspension of mycelia. Inoculum was produced by grinding five, 3.5-cm colonies on carrot piece agar in 120 ml of water with a mortar and pestle. The foliage of an equal number of plants was sprayed with water. Plants were incubated in a dew chamber at 20°C for 48 h in the dark and then moved into a growth chamber with a 12-h photoperiod where relative humidity was maintained at ~95% by placing plants over a tray of water and covering each plant group with a plastic tent. Small, angular spots developed on approximately half of the inoculated plants 20 days later when the fungus was reisolated from the lesions. No symptoms were observed on the noninoculated control plants. Sporulation was observed on diseased lesions following misting of plants and incubation in sealed plastic bags for an additional week. Pathogenicity tests were repeated with mycelia with similar results. Sequence of the internal transcribed spacer regions of the rDNA was deposited into GenBank (Accession No. HQ442297). The sequence matched R. coleosporii and R. carthami with 96% identity. R. didyma has been reported to cause a leaf spot on Ranunculus spp. in the United States (Delaware, Iowa, Indiana, Maryland, New York, and Vermont). To our knowledge, this is the first confirmed report of R. didyma on Ranunculus asiaticus in California. Introduction of this pathogen into commercial production fields could cause significant economic loss. The closest large-scale production fields are located approximately 430 miles south of San Mateo County near Carlsbad, CA where more than 50 acres of ranunculus are grown for cut flower and tuber production. Reference: (1) J. B. Ellis and B. M. Everhart. J. Mycol. 1:79, 1885.

scholarly journals Outbreaks of Soybean Frogeye Leaf Spot in Iowa

Plant Disease ◽  
2001 ◽  
Vol 85 (4) ◽  
pp. 443-443 ◽  
Author(s):  
X. B. Yang ◽  
M. D. Uphoff ◽  
S. Sanogo
Keyword(s):  
Disease Severity ◽  
Leaf Spot ◽  
Performance Test ◽  
Disease Incidence ◽  
Central City ◽  
Cercospora Sojina ◽  
East Central ◽  
Production Region ◽  
Frogeye Leaf Spot ◽  
Winter Temperatures

Frogeye leaf spot of soybean, caused by Cercospora sojina, is typically a disease of warm and humid regions (2). Although the disease was reported in the Midwest in the 1920s (1), no outbreaks have been recorded in Iowa. Outbreaks of frogeye leaf spot occurred during 1999 in soybean fields in Ames and Grand Junction in central Iowa. During the 2000 growing season, the disease occurred in southwestern, southcentral, central, southeastern, and east-central Iowa. Occurrences of the disease with severity (reduction of green leaf area) greater than 50% were observed in production soybean fields at Grand Junction in central Iowa and Central City in eastern Iowa. In a 12-ha no-till field planted with cv. Asgrow 2501, the disease was noticeable and uniformly distributed in the entire field in mid July. Disease severity in this field was greater than 70% by the end of August. Disease incidence, however, was less than 10% in three adjacent soybean fields. In a soybean performance test at a central Iowa location where the disease occurred in 1999 and 2000, the disease was observed on all 80 varieties, with four having a severity equal to or greater than 40%. Fourteen entries had less than a 10% disease severity and 19 entries had a disease severity equal to or greater than 30%. Infected leaves in these locations had typical lesions of frogeye leaf spot, which appeared as reddish brown margins surrounding light brown or ash gray centers. On the infected tissues, hyaline, straight, and multiseptate conidia from clustered conidiophores were found, isolated, and identified to C. sojina. The relatively warm winter temperatures in 1998 to 1999 and 1999 to 2000 were associated with frogeye leaf spot epidemics. Because of the seedborne nature of C. sojina, efforts are warranted to monitor and survey the occurrence of frogeye leaf spot in Iowa, an important seed production state in the northern soybean production region. References: (1) K. Athow and A. H. Probst. Phytopathology 42:660–662, 1952. (2) D. V. Phillips. 1999. Pages 20–21 in: Soybean Disease Compendium. Hartman et al. eds, American Phytopathological Society. St. Paul, MN.

scholarly journals First Report of Races 11 and 12 of Cercospora sojina, the Causal Agent of Soybean Frogeye Leaf Spot, in Argentina

Plant Disease ◽  
2012 ◽  
Vol 96 (7) ◽  
pp. 1067-1067 ◽  
Author(s):  
M. Scandiani ◽  
M. Ferri ◽  
B. Ferrari ◽  
N. Formento ◽  
M. Carmona ◽  
...  
Keyword(s):  
Leaf Spot ◽  
Buenos Aires ◽  
Causal Agent ◽  
Light Cycle ◽  
Santa Fe ◽  
Cercospora Sojina ◽  
First Report ◽  
Soybean Cultivars ◽  
Frogeye Leaf Spot ◽  
Entre Rios

During the growing seasons of 2008 to 2009 and 2009 to 2010, severe outbreaks of soybean (Glycine max (L.) Merr.) frogeye leaf spot, a disease caused by Cercospora sojina Hara, occurred in several areas in Argentina (1). Two surveys were conducted in soybean fields, one in 2008 that included the provinces of Buenos Aires, Córdoba, and Santa Fe, and another that was performed in 2009 in the same provinces plus three others: Entre Ríos, Santiago del Estero, and Tucumán. In both surveys, plants presented circular lesions with reddish brown-to-gray spots and bordered by typical, narrow, reddish purple margins (3). To promote sporulation and to enable identification of the causal agent, leaves of diseased plants were collected and placed in a moist chamber for 24 h with a 12-h light cycle at 25°C. Conidia were plated on potato dextrose agar medium amended with streptomycin and were incubated at 25°C and 12 h of fluorescent light. Isolated cultures sporulated in 10 days and, on the basis of their morphology, were identified as C. sojina. A total of 147 isolates were deposited at the Culture Collection of CEREMIC (Centro de Referencia de Micología). They produced one- to nine-septate hyaline, elongate to fusiform conidia that measured 54.9 ± 16.2 × 5.7 ± 1.0 μm. Six isolates of C. sojina, each representing a province, were inoculated on a set of 12 differential soybean cultivars: Lee, Davis, Hood, Richland, Lincoln, Kent, Tracy, S 100, Palmetto, Peking, CNS, and Blackhawk (2). Fifteen plants of each differential were sprayed at V3 growth stage with a suspension of 6 × 104 conidia/ml. The test was conducted twice in a complete randomized design with three replicates. Control plants were sprayed with sterile distilled water. After inoculation, plants were placed in a greenhouse bench humidity chamber at 26 to 28°C for 72 h. Disease was rated 14 days after inoculation; plants with numerous lesions were considered susceptible and each of the 15 plants was given a score of 1. Plants with small or no lesions were classified as resistant and given a score of 0. Control plants remained healthy. The pathogen was reisolated from symptomatic plants and morphological characteristics were consistent with C. sojina. Based on the response of the differentials to each isolate and on the race designations, the isolates from Buenos Aires, Córdoba, Santa Fe, and Tucumán belong to race 11, while those from Santiago del Estero and Entre Ríos province to race 12. The finding of these two races threatening soybean cultivars in Argentina may be indicative of additional races. Thus, the incorporation of multiple resistance genes may reduce the impact of the disease on soybean. To our knowledge, this is the first report of the identification of races of C. sojina in Argentina. References: (1) M. A. Carmona et al. Plant Dis. 93:966, 2009. (2) M. A. R. Mian et al. Crop Sci. 48:14, 2008. (3) D.V. Phillips. Page 20 in: Compendium of Soybean Diseases. 4th ed. APS Press, St. Paul, MN, 1999.

scholarly journals Characterization of Quinone Outside Inhibitor Fungicide Resistance in Cercospora sojina and Development of Diagnostic Tools for its Identification

Plant Disease ◽  
2015 ◽  
Vol 99 (4) ◽  
pp. 544-550 ◽  
Author(s):  
F. Zeng ◽  
E. Arnao ◽  
G. Zhang ◽  
G. Olaya ◽  
J. Wullschleger ◽  
...  
Keyword(s):  
Cytochrome B ◽  
Leaf Spot ◽  
Fungicide Resistance ◽  
Cytochrome B Gene ◽  
Diagnostic Tools ◽  
Polymerase Chain Reaction Primer ◽  
Cercospora Sojina ◽  
Qoi Fungicides ◽  
Quinone Outside Inhibitor ◽  
Frogeye Leaf Spot

Frogeye leaf spot of soybean, caused by the fungus Cercospora sojina, reduces soybean yields in most of the top-producing countries around the world. Control strategies for frogeye leaf spot can rely heavily on quinone outside inhibitor (QoI) fungicides. In 2010, QoI fungicide-resistant C. sojina isolates were identified in Tennessee for the first time. As the target of QoI fungicides, the cytochrome b gene present in fungal mitochondria has played a key role in the development of resistance to this fungicide class. The cytochrome b genes from three QoI-sensitive and three QoI-resistant C. sojina isolates were cloned and sequenced. The complete coding sequence of the cytochrome b gene was identified and found to encode 396 amino acids. The QoI-resistant C. sojina isolates contained the G143A mutation in the cytochrome b gene, a guanidine to cytosine transversion at the second position in codon 143 that causes an amino acid substitution of alanine for glycine. C. sojina-specific polymerase chain reaction primer sets and TaqMan probes were developed to efficiently discriminate QoI-resistant and -sensitive isolates. The molecular basis of QoI fungicide resistance in field isolates of C. sojina was identified as the G143A mutation, and specific molecular approaches were developed to discriminate and to track QoI-resistant and -sensitive isolates of C. sojina.

scholarly journals First Report of Alternaria Leaf Spot Caused by Alternaria sp. on Highbush Blueberry (Vaccinium corymbosum) in South Korea

Plant Disease ◽  
2014 ◽  
Vol 98 (10) ◽  
pp. 1434-1434
Author(s):  
J.-H. Kwon ◽  
D.-W. Kang ◽  
M.-G. Cheon ◽  
J. Kim
Keyword(s):  
South Korea ◽  
Leaf Spot ◽  
Disease Incidence ◽  
Vaccinium Corymbosum ◽  
Its Rdna ◽  
Universal Primers ◽  
Conidial Suspension ◽  
First Report ◽  
Representative Isolate ◽  
Alternaria Sp

In South Korea, the culture, production, and consumption of blueberry (Vaccinium corymbosum) have increased rapidly over the past 10 years. In June and July 2012, blueberry plants with leaf spots (~10% of disease incidence) were sampled from a blueberry orchard in Jinju, South Korea. Leaf symptoms included small (1 to 5 mm in diameter) brown spots that were circular to irregular in shape. The spots expanded and fused into irregularly shaped, large lesions with distinct dark, brownish-red borders. The leaves with severe infection dropped early. A fungus was recovered consistently from sections of surface-disinfested (1% NaOCl) symptomatic leaf tissue after transfer onto water agar and sub-culture on PDA at 25°C. Fungal colonies were dark olive and produced loose, aerial hyphae on the culture surfaces. Conidia, which had 3 to 6 transverse septa, 1 to 2 longitudinal septa, and sometimes also a few oblique septa, were pale brown to golden brown, ellipsoid to ovoid, obclavate to obpyriform, and 16 to 42 × 7 to 16 μm (n = 50). Conidiophores were pale to mid-brown, solitary or fasciculate, and 28 to 116 × 3 to 5 μm (n = 50). The species was placed in the Alternaria alternata group (1). To confirm the identity of the fungus, the complete internal transcribed spacer (ITS) rDNA region of a representative isolate, AAVC-01, was amplified using ITS1 and ITS4 primers (2). The DNA products were cloned into the pGEM-T Easy vector (Promega, Madison, WI) and the resulting pOR13 plasmid was sequenced using universal primers. The resulting 570-bp sequence was deposited in GenBank (Accession No. KJ636460). Comparison of ITS rDNA sequences with other Alternaria spp. using ClustalX showed ≥99% similarity with the sequences of A. alternata causing blight on Jatropha curcas (JQ660842) from Mexico and Cajannus cajan (JQ074093) from India, citrus black rot (AF404664) from South Africa, and other Alternaria species, including A. tenuissima (WAC13639) (3), A. lini (Y17071), and A. longipes (AF267137). Two base substitutions, C to T at positions 345 and 426, were found in the 570-bp amplicon. Phylogenetic analysis revealed that the present Alternaria sp. infecting blueberry grouped separately from A. tenuissima and A. alternata reported from other hosts. A representative isolate of the pathogen was used to inoculate V. corymbosum Northland leaves for pathogenicity testing. A conidial suspension (2 × 104 conidia/ml) from a single spore culture and 0.025% Tween was spot inoculated onto 30 leaves, ranging from recently emerged to oldest, of 2-year-old V. corymbosum Northland plants. Ten leaves were treated with sterilized distilled water and 0.025% Tween as a control. The plants were kept in a moist chamber with >90% relative humidity at 25°C for 48 h and then moved to a greenhouse. After 15 days, leaf spot symptoms similar to those observed in the field developed on the inoculated leaves, whereas the control plants remained asymptomatic. The causal fungus was re-isolated from the lesions of the inoculated plants to fulfill Koch's postulates. To our knowledge, this is the first report of Alternaria sp. on V. corymbosum in South Korea. References: (1) E. G. Simmons. Page 1797 in: Alternaria: An Identification Manual. CBS Fungal Biodiversity Centre, Utrecht, The Netherlands, 2007. (2) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, 1990. (3) M. P. You et al. Plant Dis. 98:423, 2014.

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

Plant Disease ◽  
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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