Soybean In Wisconsin Research Articles

Multiple herbicide resistance in waterhemp (Amaranthus tuberculatus) accessions from Wisconsin

AbstractA comprehensive, Wisconsin state-wide assessment of waterhemp response to a diverse group of herbicide sites of action has not been conducted. Our objective was to characterize the response of a state-wide collection of waterhemp accessions to postemergence (POST) and preemergence (PRE) herbicides commonly used in corn and soybean in Wisconsin. Greenhouse experiments were conducted with more than 80 accessions from 27 counties. POST treatments included 2,4-D, atrazine, dicamba, fomesafen, glufosinate, glyphosate, imazethapyr, and mesotrione at 1× and 3× label rates. PRE treatments included atrazine, fomesafen, mesotrione, metribuzin, and S-metolachlor at 0.5×, 1×, and 3× label rates. Ninety-eight percent and 88% of the accessions exhibited ≥50% plant survival after exposure to imazethapyr and glyphosate POST 3× rate, respectively. Seventeen percent, 16%, and 3% of the accessions exhibited ≥50% plant survival after exposure to 2,4-D, atrazine, and dicamba, respectively, applied POST at the 1× rate. Survival of all accessions was ≤25% after exposure to 2,4-D or dicamba applied POST at the 3× rate, or glufosinate, fomesafen, and mesotrione applied POST at either rate evaluated. No plant of any accession survived exposure to glufosinate at either rate. Forty-five percent and 3% of the accessions exhibited <90% plant density reduction after exposure to atrazine applied PRE at the 3× rate and fomesafen PRE at the 1× rate, respectively. Plant density reduction of all accessions was ≥96% after exposure to fomesafen applied PRE at the 3× rate, or metribuzin, S-metolachlor, and mesotrione applied PRE at the 1× rate. Our results suggest that waterhemp resistance to imazethapyr and glyphosate applied POST is widespread in Wisconsin, whereas resistance to 2,4-D, atrazine, and dicamba applied POST is present to a lower extent. One accession (A75, Fond du Lac County) exhibited multiple resistance to imazethapyr, atrazine, glyphosate, and 2,4-D when applied POST. Overall, atrazine applied PRE was ineffective for waterhemp control in Wisconsin. Proactive resistance management and the use of effective PRE and POST herbicides are fundamental for waterhemp management in Wisconsin.

First Report of the Root-Lesion Nematode, Pratylenchus alleni, on Soybean in Wisconsin, U.S.A.

HomePlant DiseaseVol. 103, No. 8First Report of the Root-Lesion Nematode, Pratylenchus alleni, on Soybean in Wisconsin, U.S.A. PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of the Root-Lesion Nematode, Pratylenchus alleni, on Soybean in Wisconsin, U.S.A.K. Saikai and A. E. MacGuidwinK. SaikaiUniversity of Wisconsin–Madison, Department of Plant Pathology, Madison, WI 53706Search for more papers by this author and A. E. MacGuidwin†Corresponding author: A. E. MacGuidwin; E-mail Address: aem@plantpath.wisc.eduhttp://orcid.org/0000-0002-4807-8953University of Wisconsin–Madison, Department of Plant Pathology, Madison, WI 53706Search for more papers by this authorAffiliationsAuthors and Affiliations K. Saikai A. E. MacGuidwin † University of Wisconsin–Madison, Department of Plant Pathology, Madison, WI 53706 Published Online:13 Jun 2019https://doi.org/10.1094/PDIS-03-19-0501-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Root-lesion nematodes (Pratylenchus spp.) are economically important nematode pathogens on a wide range of crops. In soybean fields in Wisconsin, it is the most common nematode pest present. In 2013, root-lesion nematodes were detected during routine diagnostics from a soil sample collected in a soybean field in Grant Co., WI. Numerous males were observed, and all life stages appeared smaller than what is typical for Pratylenchus penetrans in Wisconsin. Cultures were established by placing a single adult female in a Petri dish containing ‘IOChief’ sweet corn root explants growing on Gamborg’s B5 medium without auxins or cytokinin. After 3 months, infected root pieces in agar were transferred to new in vitro root cultures on Gamborg’s B5 medium to continue to increase the population. Nematodes were collected for morphological and molecular identification by incubating roots on a Baermann funnel for 48 h. Morphometric data were collected for 25 females and 25 males; measurements are presented as means (range). The body length of females was 482.1 μm (427.8 to 540.6 μm), with a maximum body width of 20.3 μm (18.4 to 22.6 μm). Values of a, b, and c ratios were 23.8 (21.8 to 26.3), 5.1 (4.5 to 6.0), and 20.1 (16.0 to 23.6), respectively. The height of the head was 2.3 μm (1.9 to 2.7 μm), with two lip annules. The stylet length was 14.1 μm (13.4 to 15.1 μm) with anteriorly flattened knobs. The lateral field was marked with four lines at midbody. The vulva percentage was 79% (77 to 81%). Females had a round spermatheca filled with sperm and a postuterine sac with a length of 13.3 μm (8.7 to 19.9 μm) that was slightly shorter than the body width at the vulva. The female tail was subcylindrical or slightly conical with a smooth tail tip and a tail length of 24.2 μm (20.8 to 31.7 μm) with 20 annules (16 to 25). Males were shorter with a body length of 418.0 μm (373.2 to 518.4 μm) and stylet length of 12.6 μm (11.5 to 14.0 μm). The spicules were arched, 16.5 μm long (12.8 to 19.4 μm), and the length of the gubernaculum was 4.0 μm (3.0 to 5.3 μm). The isolate was identified as Pratylenchus alleni based on morphological characters (Castillo and Vovlas 2007; Handoo and Golden 1989). Molecular characterization was based on 18S rDNA (Chizhov et al. 2006), the D2 to D3 expansion region of 28S rDNA (Subbotin et al. 2008), and cytochrome c oxidase subunit I (Derycke et al. 2010) from five specimens. The 28S sequence (GenBank accession no. MK037385) was 99% identical to P. alleni reported in Canada (Dauphinais et al. 2018) with a difference of two nucleotides. The 18S sequence (GenBank accession no. MK035844) was 98% similar to P. scribneri, but the COI sequence (GenBank accession no. MK045330) was only 84% similar to P. scribneri. There were no sequences for either loci for P. alleni available in GenBank. DNA samples of a Canadian isolate of P. alleni obtained from Agriculture and Agri-Food Canada, Saint-Jean-sur-Richelieu Research and Development Centre (Saint-Jean-sur-Richelieu, Canada) were 99 and 100% identical to the 18S and COI sequences of the Wisconsin isolate, respectively. Therefore, we identified the Wisconsin isolate as P. alleni based on the morphological and molecular data. Three soybean plants of cultivar ‘Corsoy’ were inoculated with 1,000 mixed-stage nematodes of the isolate and grown at 24°C with a 14-h photoperiod in pasteurized loamy sand soil. The reproductive factor (final population density/initial population density) 3 months after inoculation was 3.8, and many lesions were observed on roots. To our knowledge, this is the first report of P. alleni on soybean in Wisconsin. Further investigation about the economic impact of this species to soybean production and its distribution in Wisconsin are planned.The author(s) declare no conflict of interest.

First Report of Aster Yellows Phytoplasma in Soybean in Michigan.

During the summer of 2012, soybean plants in a commercial field in Clinton County, Michigan, exhibited symptoms characteristic of phytoplasmal diseases (1,2). Symptoms included extensive top dieback, stunting, purple stem surfaces, internal necrosis, leaf vein discoloration, and bud proliferation. Approximately 80% of plants in a half hectare along the southern edge of the field were symptomatic, although the majority of plants in the 4-ha field appeared symptomless. Total genomic DNA was extracted from one symptomatic and one asymptomatic leaf sample using a Qiagen DNeasy Plant Mini Kit (Qiagen, Germantown, MD) according to manufacturer's instructions. The DNA was used as template in direct PCR primed by the phytoplasma-universal primers P1/P7 followed by nested PCR primed by P1/AYint (3). Reactions containing template DNA from the symptomatic plant yielded ribosomal RNA gene amplicons of 1.8 kbp (P1/P7-primed) and 1.6 kbp (P1/AYint-primed), respectively. Reactions containing template DNA from the asymptomatic plant or water did not yield amplicons. The products of PCRs primed by P1/P7 were purified using PureLink PCR Purification kit (Life Technologies, Carlsbad, CA) and cloned in a pGem T-Easy vector system (Promega, Madison, WI). Three separate clones were sequenced using the sequencing primers M13For, M13Rev, SAYF nt 755, (5'-AAAGCGTGGGGAGCAAACAG), and SAYR nt 1159, (5'-TTTGACGTCGTCCCCACCTT). The sequences of all three clones were identical. A consensus (Sequencher 4.1, Gene Codes Corporation, Ann Arbor, MI) nucleotide sequence of 1,830 bp was deposited in GenBank under the accession number KF528320. A BLASTn similarity search revealed that the sequence shared 100% identity to rDNA of aster yellows phytoplasma (AF222063). Additionally, analysis of the 16Sr group/subgroup classification, based on in silico RFLP analyses using iPhyClassifier (4), indicated that the soybean phytoplasma is a member of subgroup 16SrI-B aster yellows phytoplasma subgroup. In a phylogenic tree deduced using the neighbor joining algorithm, the phytoplasma consensus sequence obtained from soybean in Michigan clustered with other group 16SrI (aster yellows phytoplasma) strains. While aster yellows phytoplasma has been previously reported in soybean in Wisconsin (2), to our knowledge, this is the first report of aster yellows in soybean in Michigan.

First Report of Sudden Death Syndrome of Soybean in Wisconsin.

In August of 2006, soybean (Glycine max (L.) Merr.) plants collected from Columbia, Dane, Green Lake, Walworth, Jefferson, and Waushara counties in southern Wisconsin exhibited symptoms typical of sudden death syndrome (SDS) caused by Fusarium virguliforme O'Donnell & Aoki [synonym F. solani (Mart.) Sacc. f. sp. glycines] (1). Foliar symptoms ranged from chlorotic spots to severe interveinal chlorosis and necrosis. Taproots of symptomatic plants were necrotic and stunted and stems exhibited a light tan discoloration, but never the dark brown discoloration typical for brown stem rot, a disease with similar foliar symptoms. Isolations from root and crown tissue of symptomatic plants were made using one-quarter-strength potato dextrose agar (PDA) amended with 100 ppm of streptomycin. Slow-growing, white-to-cream fungal colonies with blue and turquoise sporodochia were observed. Spores produced in sporodochia grown on PDA ranged in size from 32.5 to 70 μm long (average 53.1 μm) and 3 to 6 μm wide (average 4.4 μm) and with 3-5 septa (mode of 3). Isolates were characteristic of F. virguliforme based on colony morphology, spore morphology and size, and the absence of microconidia (3). The identity of F. virguliforme was confirmed by PCR amplification and DNA sequencing of the ITS, BT1, Act, and EF1B regions. All isolate sequences exhibited single nucleotide polymorphisms that matched the sequences of these regions of F. virguliforme. Koch's postulates were conducted to confirm that the causal agent of the observed symptoms was F. virguliforme. Inoculum of single-spore isolates was produced on sterilized sorghum seed. After 14 days of incubation at 20 to 22°C and a 12-h photoperiod, the sorghum seed was assayed to determine colonization incidence by transferring seeds to PDA. In all trials, sorghum seed was 100% infested. Infested sorghum seeds (35) were placed in potting soil at 2 cm beneath each seed of the susceptible soybean cv. Williams 82 (4). Noninfested sorghum seed was used for a noninoculated control. Three trials were performed, each using 15 replicates of several fungal isolates and 15 replicates of the noninoculated control. Plants were grown in water baths located in a greenhouse (trial 1) and in a growth chamber (trial 2) and both maintained at an average temperature of 25°C with a 14-h photoperiod (2). The third trial was conducted in the growth chamber without a water bath with the same temperature and light regimen. In all environments, inoculated plants developed chlorotic spots 14 days after planting. After 21 days, symptoms progressed to a range of chlorotic mottling to interveinal chlorosis and necrosis. Foliar and root symptoms that resembled those on the original plant samples infected with F. virguliforme appeared on 88% of inoculated plants. Isolates that resembled the original F. virguliforme were recovered from 75% of inoculated plants and from 88% of plants showing symptoms. No symptoms were observed and no isolates were recovered from noninoculated plants. There was a statistically significant difference between inoculated and control plants (P < 0.001) based on the presence of symptoms and isolation success using the Goodman χ2 analysis. The confirmation of the presence of SDS in five counties suggests that the disease is widespread in Wisconsin and could become a serious threat to soybean production in the future.

Seasonal Progression, Symptom Development, and Yield Effects of Alfalfa mosaic virus Epidemics on Soybean in Wisconsin.

The occurrence of Alfalfa mosaic virus (AMV) has increased in Wisconsin soybean fields in conjunction with the establishment of the soybean aphid (Aphis glycines). Field studies were conducted to determine the seasonal incidence of AMV-infected plants, progression of symptom severity caused by AMV, and the effect of AMV on soybean yield and seed quality. An isolate of AMV, collected from field-grown soybean, was introduced into plots by mechanical inoculation of plants at the V1 growth stage. The goal of the experiment was to achieve an incidence of AMV-infected plants of 0, 50, and 100% in 2002, and 0, 10, 25, 50, 75, and 100% in 2003. Severity of foliar symptoms was rated, and leaf samples were collected for serological assay (enzyme-linked immunosorbent assay [ELISA]) to estimate the incidence of AMV-infected plants from growth stages VC to R5. The maximum incidence of AMV-infected plants was 49% at growth stage R5, yet detection of the virus by ELISA dropped dramatically thereafter in both years. Incidence of AMV-infected plants accounted for 53 to 67% of the variability observed for severity of foliar symptoms in 2002 and 2003, respectively. Maximum yield loss ranged from 32% in 2002 to 48% in 2003 based on the difference in yield between noninoculated plots and plots with the highest incidence of AMV-infected plants. Incidence of AMV-infected plants explained 31% of the variation in yield in 2002 and 26% in 2003. An AMV incidence of 30% or greater was required for yield loss caused by AMV. Results of this study suggest that AMV has the potential to lower soybean yield and warrants further study.

Seasonal Progression and Agronomic Impact of Tobacco streak virus on Soybean in Wisconsin.

Pod necrosis and dieback of terminal portions of stems, commonly called bud blight, are observed in soybean fields and associated with Tobacco streak virus (TSV), an understudied virus of soybean. Furthermore, many TSV-infected plants are asymptomatic. The objectives of this study were to characterize the distribution and seasonal progress of TSV-infected plants in both natural and controlled epidemics, and the agronomic impact of TSV on soybean in plots with controlled introduction of inoculum. Incidence of TSV-positive samples ranged from 17 to 56% in a general survey. In the presence of natural sources of inoculum, the incidence of TSV-infected plants ranged from 10 to 95% depending on cultivar and location, and peaked at growth stage R2, but detection dropped dramatically at R5. During 2001, significant yield loss and incidence of mottled seed were associated with TSV, but results were confounded by a high incidence of SMV. In 2002, SMV was controlled by cultivar selection, and a 25% reduction in grain yield was attributable to TSV. The incidence of mottled seed and green stem syndrome were low in the presence of TSV. Reductions in plant density and final plant height contributed to reduced yields. However, no significant differences were found in seed number per plant and 100-seed weight. Data indicate that plant mortality was the main mechanism by which TSV caused yield loss in induced epidemics.

First Report of Soybean dwarf virus on Soybean in Wisconsin.

Soybean dwarf virus (SbDV) causes widespread economic losses on soybean (Glycine max (L.) Merr.) in Japan (4), and has been reported on soybean in Virginia (2), in various legumes in the southeastern United States (1), and in peas in California (3). During late July and early August of 2003, soybean plants in Wisconsin were surveyed for SbDV. In 286 soybean fields at the R2-R4 growth stage, the uppermost fully unfurled leaf was collected from 10 plants at each of five sites. Samples were collected at random without regard to symptoms. SbDV symptom information was not recorded. Samples were stored on ice until frozen at -80°C. Five fields in four Wisconsin counties (Columbia, Lafayette, Sauk, and Waushara) tested positive for SbDV using double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). DAS-ELISA testing was conducted with reagents from Agdia, Inc (Elkhart, IN) following the manufacturer's protocol. Absorbance was read at 405 nm with a Stat Fax 2100 microplate reader (Awareness Technology, Inc., Palm City, FL) or visually evaluated. DAS-ELISA did not discriminate between strains of SbDV. The presence of SbDV was confirmed, and strain identity was inferred as dwarfing strain using reverse transcription-polymerase chain reaction (RT-PCR). Total RNA was extracted from homogenized leaf tissue, reverse transcribed, and amplified with the SuperScript One Step RT-PCR System (Invitrogen, Carlsbad, CA) and SbDV-specific primers (5'-CTGCTTCTGGTGATTACACTGCCG-3' and 5'-CGCTTTCATTTAACGYCATCAAAGGG-3'). Size of the RT-PCR products (110 bp) was consistent with the dwarfing strain, SbDV-D. All locations that tested positive for SbDV showed soybean aphids, Aphis glycines Matsumura (Homoptera: Aphididae), on 100% of soybean plants. Several aphid species have been reported to vector SbDV, but at this time, vector relations in the Wisconsin infections are unknown. To our knowledge, this is the first report of SbDV infecting soybean in Wisconsin.

Occurrence of Soybean Stem Canker (Diaporthe phaseolorum var. meridionalis) in Wisconsin.

Soybean (Glycine max) developed symptoms characteristic of stem canker during the 2000 to 2003 growing seasons in Wisconsin. Symptoms were widespread in 2003 and were associated with yield losses of ≈1% statewide and as much as 25% in individual fields. Affected plants expressed dieback of foliage beginning at growth stage R3 and progressed until the R6 growth stage. Dark brown lesions were frequently observed at a single node on the lower portion of stems of plants expressing foliage dieback. Fungi were isolated from symptomatic plants collected from seven growers' fields in Rock, Sauk, Veron, and Walworth counties and the Arlington and Marshfield Agricultural Research Stations. Stems with lesions were cut into ≈5-mm pieces, surface disinfested with a 0.5% NaOCl solution for 3 min, rinsed three times in sterile distilled water, and placed on water agar (WA) or potato dextrose agar (PDA) at pH 4.5. Hy-phal tips from colonies of interest were excised and placed on acidified PDA at 25°C under continuous light for 25 to 30 days. In addition to Diaporthe phaseolorum var. caulivora (the cause of northern stem canker), four isolates of D. phaseolorum var. meridionalis (the cause of southern stem canker) were isolated. Colonies of D. phaseolorum var. meridionalis isolates were white, lanose, and became tan with age as previously described for D. phaseolorum var. meridionalis (1). Pycnidia with alpha conidia (no beta conidia) and perithecia with 3.1 to 3.4 × 9.5 to 9.8 μm ascospores formed on oat flakes on acidified WA after 30 days. Stromata were brown to black and irregularly shaped. Four isolates of D. phaseolorum var. meridionalis were tested for pathogenicity in a controlled environment using a cut stem inoculation method (2). Stems of 3-week-old seedlings of cv. Sturdy were cut at the midpoint between the second and third node, and a PDA mycelial plug (4 mm in diameter) was placed on the surface of the cut stems. This method was used to inoculate 15 plants in three replicates for each isolate tested. Inoculated plants were placed in a mist chamber in the dark at 25°C for 4 days and later moved to a greenhouse with a 16-h photoperiod at 24 ± 3°C for 3 days. All plants challenged by this method exhibited stem lesions that were 2 to 3 cm long and of similar color to lesions observed in field-grown plants. For each isolate tested, D. phaseolorum var. meridionalis was reisolated from three randomly selected symptomatic plants. Negative controls with a PDA plug did not produce lesions. To our knowledge, this is the first report of D. phaseolorum var. meridionalis on soybean in Wisconsin. The significance of this report relates to the potential spread of D. phaseolorum var. meridionalis beyond its known southern range in the United States.

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

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.

Identification of aster yellows phytoplasmas in soybean in Wisconsin based on RFLP analysis of PCR-amplified products (16S rDNAs)

Phytoplasmas have been detected for the first time by molecular methods in soybeans in Wisconsin. Nested polymerase chain reaction (PCR) using a combination of two phytoplasma-specific "universal" primer pairs (P1/P7-R16F2n/R16R2 and R16mF2/R16mR1-R16F2n/R16R2) amplified 16S rDNA (with expected fragment size of 1.2 kilobases) in soybean leaf tissue in 48 of 121 plants tested. Restriction fragment length polymorphism analysis of nested PCR products indicated that only 2 of these samples contained phytoplasmas. Gram-positive bacterial 16S rDNA genes were detected in 46 PCR positive samples. This was confirmed by culturing bacteria and direct PCR of soybean seed. In the two soybean samples, phytoplasmas belonging to the aster yellows phytoplasma group (16SrI), subgroup 16SrI-A, and a newly established subgroup, 16SrI-O, were identified. Phylogenetic analysis using partial 16S rDNA sequences (1.2 kilobases) from representative phytoplasma strains clustered soybean phytoplasmas into two distinct phylogenetic lineages that are consistent with the two subgroups defined by restriction fragment length polymorphism analysis. No correlation between the presence of phytoplasmas and the occurrence of "green-stem syndrome" in soybeans in Wisconsin was detected.

First Report of Root Rot of Soybeans Caused by Corynespora cassiicola in Wisconsin

Corynespora cassiicola (Berk. & M. A. Curtis) C. T. Wei was isolated from diseased soybean plants (Glycine max) collected in two fields near Racine and Arlington, WI. Plants sampled at seedling emergence (VC), late vegetative (V5), and mid-reproductive (R5) stages exhibited reddish to dark brown longitudinal lesions on the exterior of the tap root extending vertically on the hypocotyl to the soil line, and extensive necrosis of lateral roots. Sample size at each growth stage was 144 plants per site. Roots were surface sterilized in 0.5% sodium hypochlorite for 2 min and sections of symptomatic tissue placed on water agar (12 g/liter) containing 100 μg of streptomycin per ml. Sporulation occurred on lesions and on mycelium that had grown out from the plant tissue onto the water agar following a 2-week incubation at 24°C under fluorescent light (280 μmol s-1 m-2). Incidence of isolation of C. cassiicola at both sites was 40% of plants sampled at growth stage VC, 67% at V5, and 78% at R5. Conidia characteristic of C. cassiicola were particularly abundant on the surface of necrotic lateral root tissue. Elongated conidia produced on water agar were 151 ± 5 μm × 15 ± 0.5 μm with an average of 13 ± 0.4 cells separated by hyaline pseudosepta (1). To confirm pathogenicity, a 1-cm lateral slice into each of four 5-day-old soybean seedling roots was made and a plug of agar taken from the margin of a colony of C. cassiicola grown on potato dextrose agar was placed in each wound and incubated for 14 days at 24°C in a growth chamber. Symptoms similar to those of diseased field plants were observed and C. cassiicola was reisolated from all plants inoculated with C. cassiicola; all controls treated with agar alone had no symptoms and C. cassiicola was recovered from none of the noninoculated controls. This is the first report of root rot caused by C. cassiicola on soybean in Wisconsin. Reference: (1) W. L. Seaman and R. A. Shoemaker. Can. J. Bot. 43:1461, 1965.

Variation in Morphological, Cultural, and Pathological Characteristics ofPhialophora gregataandAcremoniumsp. Recovered from Soybean in Wisconsin

Variation in Morphological, Cultural, and Pathological Characteristics of<i>Phialophora gregata</i>and<i>Acremonium</i>sp. Recovered from Soybean in Wisconsin