Cercospora Sojina Research Articles

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

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).

Registration of ‘NC‐Burton’ Soybean

‘NC‐Burton’ soybean [Glycine max (L.) Merr.] (Reg. No. CV‐504, PI 664026) was cooperatively developed and released by North Carolina State University (NCSU) and the North Carolina Agricultural Research Service, and it was first tested in North Carolina yield trials in 2003. NC‐Burton is a determinate, maturity‐group‐V, high‐yielding, conventional cultivar adapted to the northern and central regions of eastern North Carolina. It was derived from the cross of the high‐yielding line TN93‐99 and the soybean cyst nematode–resistant cultivar ‘Fowler’. In the NCSU breeding trials (11 environments), NC‐Burton averaged 3466 kg ha−1, or 441 kg ha−1 more than the check cultivar ‘5601T’ under full‐season conditions. In eight average‐ to high‐yield environments in the North Carolina Official Variety Trials, NC‐Burton had a significantly higher seed yield (4091 kg ha−1) than 5601T in narrow (19‐cm) row spacing. Seed protein content was lower but the oil content was similar to that of 5601T. NC‐Burton is resistant to stem canker (caused by Diaporthe phaseolorum var. meridionalis), frogeye leaf spot (caused by Cercospora sojina Hara), and bacterial pustule [caused by Xanthomonas campestris pv. glycines (Nakano) Dye].

Registration of ‘NC‐Tinius’ Soybean

‘NC‐Tinius’ soybean [Glycine max (L.,) Merr.] (Reg. No. CV‐503, PI 664027) was cooperatively developed and released by North Carolina State University (NCSU) and the North Carolina Agricultural Research Service. It was first tested in North Carolina yield trials in 2003. NC‐Tinius is a determinate, maturity‐group‐V, conventional cultivar. It is a high‐yielding conventional line adapted to the northern and central regions of eastern North Carolina. It was derived from the cross of the low‐palmitate and low‐linolenate conventional line TN99‐76,077 to a high‐yielding conventional line V91‐3036. In the NCSU breeding trials (11 environments), NC‐Tinius averaged 3443 kg ha−1, or 353 kg ha−1 more than ‘5601T’, under full‐season conditions. In eight average‐ to high‐yield environments in the North Carolina Official Variety Trials, NC‐Tinius produced significantly higher yields (4031 kg ha−1) than did the standard cultivar 5601T in narrow (19 cm) row spacing. Seed protein and oil contents were similar to those of 5601T. NC‐Tinius is resistant to Soybean mosaic virus (G1), frogeye leaf spot (caused by Cercospora sojina Hara), bacterial pustule [caused by Xanthomonas campestris pv. glycines (Nakano) Dye], and stem canker (caused by Diaporthe phaseolorum var. meridionalis) and is moderately resistant to sudden death syndrome (caused by Fusarium solani f. sp. glycines).

Resistance to Frogeye Leaf Spot in Selected Soybean Accessions in MG I through MG VI

Frogeye leaf spot (FLS) caused by Cercospora sojina Hara is a disease of soybean [Glycine max (L.) Merr.] that causes significant seed yield loss in warm, humid environments worldwide. The Rcs3 gene in soybean has been reported to condition resistance to all known races of C. sojina. The objectives of this study were to: (i) identify maturity group (MG) I to VI accessions resistant to C. sojina race 11 by field screening at two locations; and (ii) determine if the FLS resistance of the symptomless soybean accessions is likely to be conditioned by the Rcs3 allele. A total of 260 accessions including 12 differentials were evaluated for reaction to race 11 in field trials in Missouri and Illinois during 2009, and 20 accessions that did not develop symptoms were retested in 2010 to validate their resistance. The 20 accessions remained resistant and were tested for the potential presence of Rcs3 allele using molecular markers; and none was predicted to carry the Rcs3 allele. These accessions may contain novel loci for FLS resistance and may be used to broaden the base for developing soybean cultivars with frogeye leaf spot resistance. Accepted for publication 16 April 2012. Published 21 May 2012.

Soybean Yield Response to Pyraclostrobin and Drainage Water Management

Although pyraclostrobin {carbamic acid, [2,[[[1‐(4‐chlorophenyl)‐1H‐pyrazol‐3‐yl]oxy]methyl]phenyl]methoxy‐,methyl ester} has been used to protect soybean [Glycine max (L.) Merr.] from foliar diseases, its interaction with drainage water management (DWM) systems was unknown. Field research during two wet years (95 to 97 mm greater than the past decade) evaluated the effects of pyraclostrobin application timing (R3, R5, R3+R5, and R3+R5+lambda‐cyhalothrin) and DWM system (nondrained and drainage only [DO] or drainage plus subirrigation [DSI] at 6.1 and 12.2 m drain tile spacings) on soybean yield, grain quality, and severity of Septoria brown spot (SBS) (Septoria glycines) and frogeye leaf spot (FLS) (Cercospora sojina). Grain yields increased 18 to 22% with DO or DSI at 6.1 and 12.2 m spacings compared to a nonfungicide treated, nondrained control. In the absence of drainage, pyraclostrobin with or without lambda‐cyhalothrin increased yields 20 to 27% compared to the nondrained, nonfungicide treated control. The combination of DWM and pyraclostrobin increased grain yields up to 36%. Pyraclostrobin plus lambda‐cyhalothrin at R3+R5 increased yield 8 to 12% except with DO at 12.2 m compared to similar nonfungicide‐treated DWM systems. A DWM and pyraclostrobin interaction was detected for grain oil and protein concentration, but differences were minimal. Pyraclostrobin with or without lambda‐cyhalothrin reduced severity of SBS and FLS 2 to 8% depending on the year, but DWM did not affect severity of these diseases. The greatest synergistic yield increase on a claypan soil occurred when foliar disease management and DWM systems were used together in years with higher than normal rainfall.

ダイズ斑点病 (病原菌Cercospora sojina Hara) の種子伝染

ダイズ斑点病 (病原菌Cercospora sojina Hara) の種子伝染

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

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.

Differential Responses of Soybean Cultivars to Cercospora sojina Isolates, the Causal Agent of Frogeye Leaf Spot in Korea

During the summer of 2005, specimens of soybean cultivars (Daepung, Daewon, Hwanggeum and Taegwang) showing frogeye leaf spot (FLS) were obtained from various areas in Korea. Eight isolates identified as Cercospora sojina were inoculated on the adaxial leaf surfaces of 63 Korean soybean cultivars; the disease responses to each isolate were evaluated 14 days and 21 days after inoculation. Based on the disease responses (resistant or susceptible) of the cultivars by the isolates, a set of cultivars (Anpeong, Bogwang, Cheongdu No. 1, Cheongja No. 3, Dachae, Daemang, Jangwon, Namhae, Sowon, Taegwang) were selected and inoculated with seven isolates for further testing pathogenic variance. Interestingly, 6 out of 7 tested C. sojina isolates revealed differential ability in infecting different soybean cultivars. This result may indicate the possibility of new race occurrence or pathogenic variation; this also presents evidence for prevalent FLS occurrence during humid and hot weather in Korea.

Identification of Soybean Accessions Resistant to Cercospora sojina by Field Screening, Molecular Markers, and Phenotyping

Frogeye leaf spot (FLS) of soybean [Glycine max (L.) Merr.], caused by Cercospora sojina K. Hara, has been a problem in the southern United States for many years. Cultivars resistant to FLS have been developed for planting in this area, and resistance in many of these cultivars is conditioned by the Rcs3 allele at the Rcs3 locus, which provides immunity to all known races of the pathogen. Frogeye leaf spot has recently become a greater problem in the northern United States, and few C. sojina resistant cultivars and breeding lines adapted to this area have been identified. The objectives of this study were to (i) identify maturity group (MG) 00 to VII accessions resistant to C. sojina race 11 by field screening at multiple locations over years and (ii) determine if FLS resistance in these accessions is likely to be conditioned by the Rcs3 allele. A total of 522 accessions were evaluated for reaction to race 11 in field trials in Missouri and Illinois during 2006 and 2007, and 84 of these lines did not develop symptoms of FLS and were field screened for reaction to natural inoculum in Tennessee during 2008. Nine accessions of the 84 lines were susceptible. The remaining 75 were subsequently tested for the possible presence of Rcs3 using five molecular markers located within 2 cM of the gene. Of these 75 accessions, only PI 437726, PI 438302B, and PI 494851 had the Rcs3 haplotype of the cultivar Davis, the source of Rcs3 The soybean accessions predicted not to have the Rcs3 allele and with no FLS symptoms in field trials may also be useful in developing soybean cultivars with resistance to FLS.

Glyceollin, a soybean phytoalexin with medicinal properties

This review covers the biosynthesis of glyceollin and its biological activities including antiproliferative/antitumor action (toward B16 melanoma cells, LNCaP prostate cancer cells, and BG-1 ovarian cancer cells), anti-estrogenic action (through estrogen receptors α- and β-), antibacterial action (toward Erwinia carotovora, Escherichia coli, Bradyrhizobium japonicum, Sinorhizobium fredii ), antinematode activity, and antifungal activity (toward Fusarium solani, Phakospora pachyrhizi, Diaporthe phaseolorum, Macrophomina phaseolina, Sclerotina sclerotiorum, Phytophthora sojae, Cercospora sojina, Phialophora gregata, and Rhizoctonia solani). Other activities include insulinotropic action and attenuation of vascular contractions in rat aorta.

Preliminary Mapping of Soybean Dominant Locus <em>Hrcs7</em> Conferring Resistance to <em>Cerocospara sojina</em> Race 7

Molecular marker-assisted selection can significantly improved resistance breeding efficiency. The soybean frogeye leaf spot (FLS) is caused by the fungus Cercospora sojina Hara. In order to find the resistant markers linked to C. sojina race 7 in soybean, we carried out the resistant genetic ananlysis and the resistant locus mapping. The F 2 population derived from the cross of 'Gang 95144-1' and 'Gongjiao 9723-6' was employed to analyze the resistance genetics. it was sure that the resistance conferring to FLS was controlled by one major dominant gene.. Bulk Segregant Analysis (BSA) and Simple Sequence Repeat (SSR) method were used to map the resistant locus. Among the 600 selected SSR primers, there were four primer pairs exhibiting the polymorphisms between DNA bulk of resistant and susceptible as well as both parents. Segregation distribution of the SSR markers, satt 414 and satt384, were conformed significantly to be as 1:2:1.of Mendel Segregation. The marker, satt411 and satt384 were assigned to link with the resistant locus based on estimation of MAPMAKER/EXP 3.0 software. The linkage order and distance would be Satt384 -5.7cM - Satt411 -7.9cM - Hrcs7 . The resistant locus was integrated to soybean linkage group E based on the Cregen ' s genetic linkage map of soybean.Molecular marker-assisted selection can significantly improved resistance breeding efficiency. The soybean frogeye leaf spot (FLS) is caused by the fungus Cercospora sojina Hara. In order to find the resistant markers linked to C. sojina race 7 in soybean, we carried out the resistant genetic ananlysis and the resistant locus mapping. The F 2 population derived from the cross of 'Gang 95144-1' and 'Gongjiao 9723-6' was employed to analyze the resistance genetics. it was sure that the resistance conferring to FLS was controlled by one major dominant locus named Hrcs7 .. Bulk Segregant Analysis (BSA) and Simple Sequence Repeat (SSR) method were used to map the resistant locus. Among the 600 selected SSR primers, there were four primer pairs exhibiting the polymorphisms between DNA bulk of resistant and susceptible as well as both parents. Segregation distribution of the SSR markers, satt 414 and satt384, were conformed significantly to be as 1:2:1.of Mendel Segregation. The marker, satt411 and satt384, were assigned to link with the resistant locus based on estimation of MAPMAKER/EXP 3.0 software. The linkage order and distance would be Satt384 -5.7cM -Satt411 -7.9cM - Hrcs7 . The resistant locus was integrated to soybean linkage group E based on the Cregen ' s genetic linkage map of soybean.

Soybean Response to Preplant and Foliar‐Applied Potassium Chloride with Strobilurin Fungicides

Potassium chloride (KCl) preplant or foliar applied with fungicides to soybean [Glycine max (L.) Merr.] may allow farmers to increase yields when soil K availability is reduced and/or when Septoria brown spot (SBS) (Septoria glycines), frogeye leaf spot (FLS) (Cercospora sojina), or sudden death syndrome (SDS) (Fusarium solani (Mart.) Sacc. f. sp. glycines) are present. Interactions between fertilizer and fungicide management programs have not been examined in the central United States. Our objective was to evaluate the effect of preplant‐ and foliar‐applied KCl alone or combined with pyraclostrobin, azoxystrobin, or azoxystrobin plus lambda‐cyhalothrin on soybean response and severity of SBS, FLS, and SDS. Experiments were conducted in northeastern (Novelty) and southeastern (Qulin) Missouri in 2006 and 2007 on soils with low to medium K. Leaf K concentrations increased 1.4 to 6.1 g kg−1 following preplant KCl compared to nontreated or foliar KCl. Leaf Cl concentrations increased significantly with preplant KCl at Qulin and foliar KCl at R4 at Qulin and Novelty. At Novelty, preplant KCl reduced the severity of SBS and FLS up to 6%, and increased yield 340 kg ha−1, while foliar KCl increased yield 110 kg ha−1 An R4 application of strobilurin fungicides increased yields 230 to 360 kg ha−1 at Novelty. At Qulin, soybean yield increased 390 kg ha−1 with preplant KCl, while there were variable effects of fungicides on the severity of SBS, FLS, or SDS, and no yield increase due to fungicides or foliar KCl. Foliar applications of KCl were no substitute for preplant KCl.

Simple and Reliable DNA Extraction Method for the Dark Pigmented Fungus, Cercospora sojina

This study used a modified cetyltrimethylammonium bromide (CTAB) method to efficiently extract DNA from the plant pathogenic fungus Cercospora sojina. Total DNA yield obtained by this method was approximately 1 mg/g of mycelia (fresh weight), and the mean ratio of A260/A280 and A260/A230 were 2.04 and 2.1, respectively. The results of random amplified polymorphic DNA (RAPD) analysis, digestion with restriction enzymes, and Southern hybridization indicated that polysaccharides were effectively removed by this method, and the resulting DNA was sufficient for use in subsequent molecular analysis.

Severe Outbreaks of Soybean Frogeye Leaf Spot Caused by Cercospora sojina in the Pampean Region, Argentina.

Frogeye leaf spot of soybean (Glycine max (L.) Merr.) caused by Cercospora sojina Hara was reported to be severe from 1998 to 1999 in northwest Argentina (2). Although the disease was detected at low prevalence (5 to 25%), incidence, and severity in the Pampean Region from 2005 to 2008, no severe outbreaks have been recorded in the provinces of Córdoba, Santa Fe, and Buenos Aires. During the 2008-2009 growing season, disease spread rapidly throughout most soybean-growing areas of the Pampean Region. Disease was observed on almost all varieties of maturity group (MG) III, IV, and V. Symptoms on leaves were circular, reddish brown-to-gray spots (1 to 6 mm) and bordered by typical, narrow, reddish purple margins. Morphology of the fungi was examined on infected tissues. Conidiophores were light-to-dark brown, fasciculate, geniculate, and measured 110 to 203 μm long. Conidia were 1 to 9 septate, hyaline, elongate to fusiform, and measured 26 to 111 (47.3 ± 14.7) × 5.2 to 7.4 μm (6.1 ± 0.7). Pathogenicity tests were conducted on seedlings of a susceptible cultivar by spraying leaves of each of 80 plants at the V3 growth stage with 18 ml of a conidial suspension (3 × 104 conidia/ml) with a hand-held atomizer. Plants were covered with plastic bags and placed in a greenhouse at 28 to 30°C for 48 h. The plastic bags were removed and plants were maintained in high humidity at the same temperature. The same number of noninoculated plants was used as controls. After 10 to 12 days, all inoculated plants showed typical symptoms. Koch's postulates were fulfilled by isolating C. sojina from inoculated plants. Control plants remained healthy. Foliar lesions and morphological characteristics of the pathogen were consistent with C. sojina (1). Disease assessments were made for the middle and upper canopy from 15 arbitrarily collected plants. Soybean plants were in growth stages between R3 and R5 during the survey. Incidence (percentage of plants affected) and severity (percentage of leaf area affected with lesions) were visually estimated from each of the 30 soybean-production fields located in Monte Cristo, Alta Gracia, Jesús María, W. Escalante, Monte Buey, (10 fields, Córdoba Province), Venado Tuerto, Villa Cañás, Cristophersen, María Teresa, (12 fields, Santa Fe Province), Pergamino, Rojas, and Salto (8 fields, Buenos Aires Province). Incidence was 100% in all fields from Córdoba and Santa Fe. Incidence in Buenos Aires was 0 to 100%. Highest severity levels were quantified from fields in Córdoba (severity of 30 to 60%). Lesions also developed on stems and pods. In samples from Buenos Aires, severity levels were ≤10% in the eight soybean fields. Number of lesions per leaflet was recorded from central leaflets in samples from Monte Cristo, Alta Gracia, Venado Tuerto, and María Teresa with 20 to 55 typical lesions per leaflet. Since the disease was always more important in northwest Argentina, genetic resistance is more commonly available in varieties of MG VII to VIII, so most of the varieties of MG III, IV, and V frequently planted in Pampean Region are susceptible. This fact in combination with rainfall, warm temperatures, and high relative humidity in no-till fields during this summer have encouraged the severe outbreak of frogeye leaf spot, especially in the province of Córdoba and in some regions of Santa Fe.

Identification of Soybean Genotypes Resistant to Cercospora sojina by Field Screening and Molecular Markers.

Frogeye leaf spot (FLS) of soybean, caused by Cercospora sojina, has been a problem in the southern United States for many years and has recently become a greater problem in the northern United States. Cultivars resistant to FLS have been developed for planting in the southern United States and resistance in many of these cultivars is conditioned by the Rcs3 gene. This gene conditions immunity to all known races and isolates of the pathogen. Resistance to C. sojina in soybean genotypes (cultivars and breeding lines) adapted to north-central U.S. production region is unknown. The objectives of this study were to (i) identify maturity group (MG) III, IV, and V soybean genotypes resistant to C. sojina race 11 by field screening at multiple locations over years and (ii) determine whether FLS resistance in these genotypes is likely to be conditioned by the Rcs3 gene. In total, 1,350 genotypes were evaluated for resistance to race 11 in field trials, and 13 MG III, 45 MG IV, and 15 MG V genotypes did not develop symptoms of FLS. Of these, 54 were subsequently tested for the possible presence of Rcs3 using five molecular markers located within 2 centimorgans (cM) of the gene. None of the MG III genotypes tested had the Rcs3 haplotype of cv. Davis, the source of Rcs3; six of the MG IV genotypes and seven of the MG V genotypes had the Rcs3 haplotype. This is the first report of the presence of the Rcs3 haplotype in LN 97-15076 and S99-2281. The soybean genotypes predicted to have the Rcs3 gene and other genotypes with no FLS symptoms in field trials may be useful in developing soybean cultivars with broad resistance to FLS and adapted to the northern United States.

Similarity, Pattern, and Grouping of Soybean Fungal Diseases in the United States: Implications for the Risk of Soybean Rust.

Ten biological or ecological characteristics of pathogens/diseases were used to quantitatively describe 34 soybean (Glycine max) fungal diseases in the United States. These characteristics included optimal temperatures for disease development, host ranges, characteristics of disease cycle, and the pathogens' survival capacity. Gower's general similarity coefficients for pairs of diseases were determined and used in principal coordinate analysis (PCoA) to project the diseases into a two-dimensional space, in which significant patterns were identified for some of the characteristic variables, e.g., means of pathogen dispersal. Similarity coefficients indicated that soybean rust (Phakopsora pachyrhizi) resembled soybean downy mildew (Peronospora manshurica) and Leptosphaerulina leaf spot (Leptosphaerulina trifolii). Cluster analysis with multiscale bootstrapping identified two major clusters with high significance level (P > 0.95). In a loose cluster (P = 0.86), soybean rust was grouped with brown spot (Septoria glycines), frogeye leaf spot (Cercospora sojina), Phyllosticta leaf spot (Phyllosticta sojicola), purple seed stain (Cercospora kikuchii), downy mildew, and Leptosphaerulina leaf spot. Estimated soybean yield losses in the United States from 1996 to 2005 and the geographical distribution information of the diseases in this cluster implied that the potential geographical distribution range of soybean rust may include most U.S. soybean production regions and that yield losses would be light in the north but moderate in the south if environmental conditions are conducive.

Characterization and Survival of Cercospora sojina in Ohio

Frogeye leaf spot (FLS) of soybean, caused by Cercospora sojina, has increased in incidence and severity during the last 3 years in Ohio and caused substantial economic losses for the first time during 2006. FLS is common in the southern United States but has only recently been reported to cause losses in the north-central region. This study evaluated several traits of the fungus which may have contributed to the increase in disease incidence such as: the ability of C. sojina to overwinter and sporulate on infested soybean debris; optimum temperatures for mycelial growth; races (pathotypes) present in Ohio; and pathogenicity on cultivars with Rcs gene(s) for FLS resistance. Conidia of C. sojina were recovered from soybean debris collected at two locations from December to May 2007-2008. The optimum temperature for mycelial growth of all isolates evaluated in this study including those from Louisiana and southern Illinois was 25°C. The 50 isolates of C. sojina collected in Ohio were able to infect a mean of 4.9 of 12 differentials and had a total of 20 different pathotypes. The Rcs3 gene conferred resistance to all of the Ohio isolates. Survival of C. sojina in the field during the winters of 2005 to 2007 contributed to the increase of C. sojina during the 2005, 2006, and 2007 production seasons in Ohio. Accepted for publication 11 April 2009. Published 12 May 2009.

Registration of S99‐2281 Soybean Germplasm Line with Resistance to Frogeye Leaf Spot and Three Nematode Species

Soybean [Glycine max (L.) Merr.] germplasm line S99‐2281 (Reg. No. GP‐361, PI 654356) was developed at the University of Missouri–Delta Center and released by the University of Missouri Agricultural Experiment Station. It is an F4 plant selection composited in the F5 generation from the cross of N90‐516 × S92‐1069. S99‐2281 is a productive, early group V (relative maturity 5.2) soybean line with broad resistance to soybean cyst nematode (Heterodera glycines Ichinohe) HG types (races), southern root knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood], and reniform nematode [Rotylenchulus reniformis (Linford and Oliveira)]. It also carries the Rcs3 gene for resistance to all known races of frogeye leaf spot, caused by Cercospora sojina K. Hara. In combined analyses over 3 yr, S99‐2281 yielded 3 and 7% more than ‘Manokin’ in southeast Missouri trials (15 tests) and in Uniform Group IVs Tests–Southern States (39 tests), respectively. It will be useful as an elite parent in soybean breeding programs to develop productive soybean cultivars with broad resistance to frogeye leaf spot and resistance to multiple nematode species.

Registration of ‘N8101’ Small‐Seeded Soybean

‘N8101’ soybean [Glycine max (L.) Merr.] (Reg. No. CV‐498, PI 654355) was cooperatively developed and released by the USDA‐ARS and the North Carolina Agricultural Research Service in February 2008 as a small‐seeded Maturity Group VIII conventional cultivar. N8101 is the first publicly released small‐seeded soybean cultivar in its maturity group and has potential use in the Japanese soyfoods market. It was derived from the cross of small‐seeded germplasm NC114 and a small‐seeded cultivar N7101. N8101 is adapted to the southeastern United States between 30 and 36° N latitude. In 22 USDA regional trials, N8101 exhibited a 100‐seed weight of 7.3 g, 5.4 g less than that of control variety, ‘Prichard RR’. Yield of N8101 was approximately 92% of that produced by Prichard RR (2712 kg ha−1). Over seven additional trials in North Carolina, N8101 had a 100‐seed weight of 6.5 g, 1.4 g less than that of small‐seeded Maturity Group VII cultivar N7103. Seed protein content was similar to that of Prichard RR, and seed carbohydrate composition was similar to that of N7103. N8101 is resistant to shattering, Soybean mosaic virus, frogeye leaf spot (Cercospora sojina Hara), and bacterial pustule [Xanthomonas campestris pv. glycines (Nakano) Dye]. The reduced yield of N8101 compared with commodity‐type cultivars limits its use to specialty purposes.

Frogeye Leaf Spot of Soybean: A Review and Proposed Race Designations for Isolates of Cercospora sojina Hara

Frogeye leaf spot (FLS), caused by Cercospora sojina K. Hara, is a common disease of soybean [Glycine max (L.) Merr.] in most soybean‐growing countries of the world. Significant yield losses of soybean (10–60%) have been attributed to FLS under hot and humid growing conditions. The FLS in the southern United States has been kept under control by planting resistant cultivars. Cercospora sojina is a dynamic pathogen with extensive virulence or race diversity. The current number of C. sojina isolates at the University of Georgia collection is 93. Assigning race designations to this large number of isolates has been difficult because of the lack of a well‐defined set of differentials. To facilitate future studies of the genetics of soybean resistance to FLS and the identification and comparison of existing and future races of C. sojina, we have reassessed both the soybean differentials and the C. sojina races. Based on the reactions of 93 isolates of C. sojina on 38 putative soybean differentials, we propose a core set of 12 differentials and 11 races that represent the major diversity among the 93 C. sojina isolates. The definition of these 12 differentials and 11 races should provide the foundation for the identification and comparison of additional soybean resistance genes and new races of C. sojina