ANALISIS KRITIS ARTIKEL

MATA KULIAH PROTISTA

(Protista Mirip Jamur)

Sasty Alvionita

NIM. 130341614828

I. Biliografi

A. E. Dorrance, Associate Professor, S. A. Berry, Research Assistant, P.

Bowen, Undergraduate Intern, and P. E. Lipps,Professor, Department of Plant Pathology, The

Ohio State University, OARDC, Wooster 44691-4096 (online) diakses tgl. 16 Januari 2014.

II. Tujuan penulis

Tujuan penulis melakukan penelitian ini adalah untuk mengkarakterisasi populasi

Pythium dalam tiga bidang dengan riwayat masalah dari berdiri spesies ini, patogenisitas , dan

sensitivitas metalaksil .

III. Fakta-fakta Unik

1. Abstrak

Pythium spp. yang menyerang jagung dan biji kedelai dari tanah dikumpulkan dari tiga

lokasi di Ohio, Amerika Serikat yang mana pembentukan kedelai dan jagung sangat di

perhatikan. Lima spesies, P. catenulatum, P. irregulare, P. paroecandrum, P. splendens, dan P.

torulosum, telah ditemukan dan sebuah subset dari isolat ini kemudian diuji patogenisitasnya

pada benih jagung dan kedelai serta kepekaan terhadap perlakuan benih metalaksil fungisida .

Ada berbagai baik patogenisitas dan kepekaan terhadap metalaksil di dalam maupun di antara

Pythium spp.

2. Pendahuluan

14 jenis Pythium spp . dapat menyebabkan kerusakan bibit dan kebusukan akar dari

sejumlah ladang termasuk kedelai dan jagung.

Di Ohio, penelitian sebelumnya telah menunjukan bahwa P. arrhenomanes Drechsler, P.

graminicola Subramanian, P. dissotocum Drechsler, dan P. torulosum Coker & F.

terdapat pada akar jagung. Ada berbagai agresivitas pada akar jagung antara isolat yang

dievaluasi dalam studi ini.

Benih Pythium dan bibit kedelai dan jagung yang mana saat ini telah dikelola dengan

menggunakan perawatan benih fungisida . Bahan aktif utama yang digunakan pada

jagung dan benih kedelai adalah metalaksil dan mefenoxam sementara sebelumnya

captan telah digunakan untuk jagung . Metalaksil merupakan fungisida acylalnide yang

menghambat sintesis RNA ribosomal di Peronosporales. Pythium spp . diisolasi dari

wortel , bibit gula bit, dan gandum yang dipamerkan sebagai kepekaan terhadap

metalaksil . Variabilitas ini dianggap bertanggung jawab atas kurangnya pengendalian

penyakit yang terdeteksi di lokasi tertentu .

3. Pengumpulan sampel tanah, Isolasi dan Identifikasi

Tiga tempat yang dipilih adalah di sebelah barat laut Ohio di Defiance , Sandusky , dan

Wood counties . Jenis tanah untuk Defiance dan Wood County adalah tanah liat Hoytville

sementara Sandusky County adalah Brookstone (lempung berlumpur tanah liat)

Ditemukan 129 , 85 , dan 53 isolat dari tanah yang dikumpulkan di Defiance , Sandusky ,

dan Wood County, masing-masing. P. torulosum , P. splendens , dan P. irregulare

mewakili 40% , 38% , dan 22 % dari isolat tanah Defiance County.

Pythium spp . dari tiga lokasi ini berbeda dari yang dilaporkan dari Arkansas , Iowa ,

Minnesota , dan studi sebelumnya di Ohio . P. ultimum tidak menunjukkan dalam

sampling ini atau dari sampel tanaman sakit yang telah dikumpulkan dari lokasi ketika

ladang ini pertama kali terlibat mengalami masalah.

Persentase benih yang dibunuh oleh Pythium spp . telah berubah , arcsin dari akar kuadrat

dari persentase dibunuh , sebelum analisis statistik . Analisis varians untuk isolat dalam

setiap lokasi menggunakan Linearized Model Umum di SAS ( SAS Institute , Cary , NC )

ANOVA menunjukkan tes yang sangat signifikan yaitu mengisolasi interaksi untuk tiga

kali piring bioassay agar dapat terselesaikan.

Persentase rata-rata benih membusuk di seluruh isolat adalah 20,9% , 33,7 %, dan 41,7 %

untuk Pythium isolat dari lokasi Defiance untuk Uji 1 , 2 , dan 3 . Namun, terlepas dari

variabilitas , kecenderungan umum adalah serupa dalam tiga eksperimen dan hasil dari

percobaan kedua akan ditampilkan untuk ilustrasi . Sangat sedikit isolat yang diuji yanag

agresif pada kedua jagung dan benih kedelai , tetapi tingkat variabilitas berbeda dengan

lokasinya.

P. splendens isolat dari Sandusky menewaskan 100 % dari benih kedelai dan 13 dari 16

isolat menewaskan 40 sampai 60 % benih jagung . Sebaliknya , 3 dari 5 P. splendens

isolat dari Wood County tidak patogen pada kedelai atau jagung sementara 11 dari 15

yang sangat patogen pada kedelai . Selain itu hanya 7 dari 15 isolat P. splendens dari

Defiance County yang cukup patogen pada tanaman jagung . Semua isolat P. torulosum

yang non - patogen pada kedelai dan hanya beberapa isolat patogen cukup jagung dari

ketiga lokasi . P. catenulatum isolat patogen terutama cukup pada kedua jagung dan

kedelai dari kedua Defiance dan Wood couty.

Pythium spp . dan tingkat pathogenicitya pada kedua jagung dan kedelai benih dari tiga

lokasi di Ohio .

Pythium spp.

No. of

isolates

Corn Soybean

Low Moderate High Low Moderate High

Defiance

P.

catenulatum3 2 1 3

P. irregulare 8 6 2 6 2

P. splendens 15 8 7 4 11

P. torulosum 5 3 2 5

Sandusky

P. splendens 16 13 3 16

P. torulosum 2 2 2

Wood

P.

catenulatum12 1 11 1 10 1

P. irregulare 6 5 1 6

P.

paroecandru

m

2 1 1 1 1

P. splendens 5 3 2 3 1 1

P. torulosum 2 1 1 2

Gb.1 Tingkat patogenisitas ditentukan pada persentase benih jagung atau kedelai yang

membusuk dalam uji lempeng agar. Nol sampai 29, 30-69, dan 70 sampai 100% dari benih

membusuk diklasifikasikan sebagai tingkat rendah, sedang, dan tinggi patogenisitas. Alat tes

diulang tiga kali. Data yang disajikan adalah dari uji kedua.

Hanya delapan tanaman inang terdaftar untuk P. catenulatum di USDA Systematic

Botany dan Mikologi database termasuk Oryza sativa , sebuah rumput yang tidak

diketahui , dan Phaseolus vulgaris . Penelitian ini menguatkan penelitian sebelumnya di

mana dilaporkan perbedaan agresivitas dan patogenisitas isolat antara Pythium . Selain

itu , Brown dan Kennedy melaporkan 9-100 % munculnya dalam tes pot antara P.

ultimum isolat pulih dari kematian benih kedelai dan bibit . Baru-baru ini , Pythium spp .

dari bidang dalam rotasi jagung - kedelai berkisar antara tidak patogen , untuk berbagai

tingkat agresivitas pada kedua jagung dan kedelai , tingginya tingkat agresivitas pada

kedua tanaman.

4. Ketidakpekaan metalaksil

P. irregulare dan satu isolat P. paroecandrum di kedua lokasi . Ada 5 isolat tambahan P.

irregulare yang tumbuh pada kedua konsentrasi media metalaksil , tapi pertumbuhan

lambat.

Berbagai kepekaan terhadap metalaksil telah dilaporkan untuk Pythiumisolates dari

wortel , gula bit, dan gandum. Pythium spp . yang kurang sensitif terhadap metalaksil

terdiri 25 sampai 75 % dari populasi di ladang gandum di Pacific Northwest

Hasil ini menunjukkan bahwa penggunaan berulang kali dari satu bahan kimia dapat

menyebabkan sensitivitas penurunan Pythium spp . dan mengurangi tingkat pengendalian

penyakit di lapangan .

5. Kesimpulan

P. catenulatum , P. irregulare , P. paroecandrum , P. splendens , dan P. torulosum

ditemukan dari tiga ladang di Ohio . Isolat dari setiap spesies bervariasi jumlahnya,

patogenisitas , dan kepekaan terhadap metalaksil baik antara dan di dalam lokasi .

Spesies yang diidentifikasi dalam studi ini berbeda dengan yang dilaporkan di negara

bagian lain dari jagung dan kedelai dalam studi sebelumnya dan ini adalah laporan

pertama dari P. catenulatum sebagai patogen jagung dan kedelai biji . Hasil dari

penelitian ini menunjukkan bahwa penggunaan berulang metalaksil atau mefenoxam

sendiri sebagai perlakuan benih untuk mengelola Pythium spp . dapat memilih untuk

strain sensitif spesies ini .

IV. Konsep Utama

Konsep utama dalam artikel ini adalah mengkarakteristikan berbagai jenis P.phytium

spp. melalui penelitian tingkat patogenitas, agretivitas dan juga kepekaan terhadap metalaksil

pada bibit jagung dan kedelai.

V. Pertanyaan yang di ajukan

1. Apa yang menyebabkan P.phytium. spp dapat merusak bibit dan membusukkan akar tanaman

jagung dan kedelai? Bagaimana hal itu bisa terjadi?

2. Mengapa peneliti memlih lokasi pengambilan sampel di bagian Barat laut Ohio? Apa yang

mendasari pngambilan sampel di tempat tersebut?

3. Bagaimana cara kerja metalaksil dan mefenoxam dalam pengujian ketidakpekaan tanaman?

4. Apa faktor yang menyebabkan sebuah isolate tidak dapat tumbuh pada media metalaksil?

5. Apakah di Indonesia dapat di lakukan penelitian serupa, mengingat minimnya sumber daya

manusia, alat penelitian dan juga sumber dana?

VI. Refleksi

Setelah melakuan analisis kritis artikel ini bnyak informasi baru yang saya peroleh namun

banyak hal yang belum saya pahami dari artikel ini, seperti pertanyaan-pertanyaan yang telah

saya ajukan. Artikel ini sangat memotivasi untuk pemunculan ide-ide kreatif pembuatan PKM

(program kreativitas mahasiswa) misalnya pembuatan pestisida alami untuk memberantas

P.phytium spp. tanpa merusak keaneragaman hayati dan rantai makanan serta lingkungan, atau

menemukan musuh alami bagi P.phytium spp. ini agar keberadaanya dapat di kontrol dan tidak

menimbulan kerugian. Banyak pustaka dalam artikel ini yang bisa di jadikan reverensi tugas-

tugas maupun skripsi.

Characterization of Pythium spp. from Three Ohio Fields for Pathogenicity on Corn and Soybean and Metalaxyl Sensitivity

A. E. Dorrance, Associate Professor, S. A. Berry, Research Assistant, P. Bowen, Undergraduate Intern, and P. E. Lipps,Professor, Department of Plant Pathology, The Ohio State University, OARDC, Wooster 44691-4096

Corresponding author: A. E. Dorrance. dorrance.1@osu.edu

Dorrance, A. E., Berry, S. A., Bowen, P., and Lipps, P. E. 2004. Characterization ofPythium spp. from three Ohio fields for pathogenicity on corn and Soybean and metalaxyl sensitivity. Online. Plant Health Progress doi:10.1094/PHP-2004-0202-01-RS.

AbstractPythium spp. were baited with corn and soybean seed from soils collected from three locations in Ohio where soybean and corn stand establishment was a concern. Five species, P. catenulatum, P. irregulare, P. paroecandrum, P. splendens, and P. torulosum, were recovered and a subset of these isolates was then tested for pathogenicity on corn and soybean seed and sensitivity to the seed treatment fungicide metalaxyl. There was a range of both pathogenicity and sensitivity to metalaxyl within and among the Pythium spp. recovered from the three locations. A more thorough evaluation of the Pythium populations that exist in grain production fields in the north central region of the US is needed to facilitate the development and deployment of broader based seed treatment products.

IntroductionPythium spp. can cause seedling blights and root rots of a number of field crops including

soybean and corn. Fourteen Pythium species have been implicated in causing corn seed and seedling blight (3). In Ohio, earlier studies recovered P. arrhenomanes Drechsler, P. graminicolaSubramanian, P. dissotocum Drechsler, and P. torulosum Coker & F. Patterson from corn roots (6,14). There was a range of aggressiveness on corn roots among the isolates evaluated in these studies (3,6,14).

Pythium aphanidermatum (Edson) Fitzp., P. irregulare Buisman, P. myriotylum Drechs., P. paroecandrum Drechs., P. spinosum Sawada, P. sylvaticum W. A. Campbell & J. W. Hendrix, P. torulosum, and P. ultimumTrow were isolated from dying soybean seedlings or baited from soils in two studies in Iowa (15,19). P. ultimum was attributed to soybean losses in the soybean cultivar Essex in Virginia (9) and from soybeans grown under irrigation in Arkansas (10). In Minnesota, P. ultimum and P. debaryanumAuct. non R. Hesse were the most prevalent species causing damping-off of soybean (2).

Pythium spp. can cause disease individually, but frequently several species are isolated from a single plant. For example, P. irregulare can cause root rot on corn and may provide infection courts for other corn pathogens to colonize tissues later in the season (11). In addition, Pythiumspp. recovered from infected corn or soybean seed or seedlings, or directly

from soil have a range of pathogenicity and aggressiveness when tested in pathogenicity assays (2,6,19).

Pythium seed and seedling blights of soybean and corn are currently managed with the use of fungicide seed treatments. The primary active ingredients used on corn and soybean seed are metalaxyl and mefenoxam while previously captan was used for corn. Metalaxyl is an acylalnide fungicide which inhibits ribosomal RNA synthesis in the Peronosporales (4). Pythium spp. isolated from carrots (18), sugar beet seedlings (1), and wheat (5) exhibited a range of sensitivity to metalaxyl. This variability was thought to be responsible for the lack of disease control detected in certain locations.

During spring of 2000, approximately 40% of the soybean acreage in northwest Ohio required replanting. The majority of this loss was attributed to Phytophthora sojae Kaufmann and Gerdemann; however, questions were raised as to whether Pythium spp. could also be contributing to these losses. Pythium spp. were also recovered from 90% of the soil samples from two intensively sampled fields where thePhytophthora sojae population was high (7). Based on these reports, the objectives of this study were to characterize the Pythium populations in three fields with a history of stand establishment problems for the species present, pathogenicity, and metalaxyl sensitivity.

Soil Sample Collection, Isolation, and IdentificationThree fields were chosen in northwest Ohio with a history of soybean stand establishment

problems in Defiance, Sandusky, and Wood counties. The soil type for both Defiance and Wood County fields was Hoytville clay while the Sandusky County field type was a Brookstone silty clay loam. From each field, 10 to 25 soil samples over a 2- to 5-ha area were collected for a total of approximately 30 to 40 liters of soil. The soil from each field was air dried, ground in a burr mill, mixed, and divided into 15-cm-diameter pots and stored at room temperature until assays were made. The pots were saturated for 24 hours, allowed to drain, placed in plastic bags and incubated for two weeks at room temperature at 18.3°C (65°F). Pots were planted with 15 seeds per pot of either corn hybrid Pfister 2295 or soybean cultivar Sloan, and three pots with each host plant were placed in growth chambers set at 12.8°C (55°F) or 18.3°C (65°F). Three and five days after planting corn and soybean seeds, respectively, pots were placed in 10-liter (2.5-gal) buckets of water in which the water level was approximately 1 cm above the soil surface in the pots. These were then placed in the growth chamber for 24 hours to saturate soil. Pots were removed from the buckets and allowed to drain for 24 hours in the growth chamber. Soybean and corn seeds were then removed from the soil and washed under running tap water with soap (Tide, Proctor & Gamble, Cincinnati, OH) until the visible soil was removed. Seeds were cut in half with a sterile knife and placed between 3 to 5 layers of sterile paper toweling. A rolling pin was used to roll over the paper toweling to remove excess water from seeds. The seeds were then placed on PIBNC media (16). Hyphal tip transfers were made from mycelia growing from the seeds onto cornmeal agar within 2 to 3 days and stored at 15°C (60°F) until used. Isolates were transferred onto water agar, lima bean 10 agar (10 g lima beans, 15 g agar per liter) or onto sterile grass blades floated in sterile water for identification (17). All Pythium species were identified based on morphological characteristics of hyphae, antheridia, oospores, and sporangia using the keys of Middleton (12) and Waterhouse (17).

Five species, P. catenulatum, P. irregulare, P. paroecandrum, P. splendens H. Braun, and P. torulosum (Fig. 1), were recovered from soils in Ohio using both corn and soybean seed as bait but the number of isolates and the percentage of each species was different for each of the three

field locations. There were 129, 85, and 53 isolates recovered from soils collected in Defiance, Sandusky, and Wood County, respectively. P. torulosum, P. splendens, and P. irregulare represented 40, 38, and 22% of the isolates recovered from the Defiance County soil (Fig. 2). P. splendenswas the predominant species (72%) recovered from both soybean and corn seed from the Sandusky soil, while P. catenulatum and P. splendenscomprised 20 and 14% of the isolates from Wood County soil, respectively. More isolates were recovered from corn seed than soybean seed in Defiance and Sandusky County soils.

A B

C D

E FFig. 1. Pythium spp. recovered from three Ohio fields with a history of stand establishment problems: (A) oogonium of P. catenulatum with multiple diclinous and monoclinous antheridia; (B) irregularly swollen sporangia of P. catenulatumproduced in water cultures; (C) oogonium of P. irregulare with a single irregular wall projection and a diclinous antheridium; (D) oogonium of P. paroecandrum with single, flatly applied, sessile antheridium; (E) common

terminal, spherical sporangium of P. splendens; and (F) a single, stalked antheridium attached to an oogonium of P. torulosum containing an immature plerotic oospore.

Fig. 2. Percentage of isolates recovered from soils collected from three locations in Ohio: (A) Defiance; (B) Sandusky; and (C) Wood counties. Pythium spp. were recovered from soil through the use of baiting techniques using corn and soybean seed.

Pythium spp. recovered from these three locations were different than those reported from Arkansas, Iowa, Minnesota, and previous studies in Ohio. P. ultimum was not recovered in this sampling nor was it recovered from diseased plant samples collected from these locations when these fields were first implicated as having stand establishment problems (data not shown).

Pathogenicity assays. A petri dish assay, similar to that used previously for evaluations of pathogenicity and aggressiveness ofRhizoctonia and Pythium on soybean (13,19), was used. A 5-mm colonized lima bean agar plug of the Pythium isolate was placed in the center of a 15-mm petri plate containing 20 ml water agar. After 3 days, 10 seeds of either corn or soybean previously surface disinfested for 1 min in 10% Clorox (The Clorox Company, Oakland, CA) and rinsed with sterile distilled water were equally placed 3 mm from the edge of the plate. Plates were examined for fungal colonization of seeds after 2 and 7 days. At 7 days, the number of seeds that were killed by Pythium or germinated per plate was recorded. The pathogenicity assays were completed 3 times for 39, 27, and 31 Pythium isolates from Defiance, Sandusky, and Wood County soils, respectively. The isolates from each county were compared in the same assay. Seeds colonized by seed-borne pathogens were not included in the counts. The percentage of seeds killed by the Pythium spp. was transformed, arcsin of the square root of the percentage

killed, prior to statistical analysis. Analysis of variance for the isolates within each location was completed using the General Linearized Model in SAS (SAS Institute, Cary, NC).

The ANOVA indicated a highly significant test × isolate interaction for the three times the agar plate bioassay was completed. The isolates that caused high or low levels of disease were consistent across the three experiments, but isolates that caused 20 to 70% seed rot in the plate assays were variable. The average percentage of rotted seeds across isolates was 20.9, 33.7, and 41.7% for the Pythium isolates from the Defiance location for Test 1, 2, and 3; respectively. However, in spite of the variability, the general trends were similar across the three experiments and the results from the second experiment are shown for illustration. Very few of the isolates tested were highly aggressive on both corn and soybean seed, but the degree of variability differed by location (Table 1). The P. splendens isolates from Sandusky killed 100% of the soybean seed and 13 of the 16 isolates killed 40 to 60% of the corn seed. In contrast, 3 of the 5 P. splendens isolates from Wood County were not pathogenic on soybean or corn while 11 of 15 were highly pathogenic on soybean. Additionally only 7 of 15 P. splendens isolates from Defiance County were moderately pathogenic on corn. All of the isolates of P. torulosum were non-pathogenic on soybean and only a few isolates were moderately pathogenic on corn from all three locations. P. catenulatum isolates were mainly moderately pathogenic on both corn and soybean from both Defiance and Wood counties.

Table 1. Pythium spp. and levels of pathogenicitya on both corn and soybean seeds from three locations in Ohio.

Pythium spp.No. ofisolates

Corn Soybean

Low Moderate High Low Moderate High

Defiance

P. catenulatum

3 2 1 3

P. irregulare 8 6 2 6 2

P. splendens 15 8 7 4 11

P. torulosum 5 3 2 5

Sandusky

P. splendens 16 13 3 16

P. torulosum 2 2 2

Wood

P. catenulatum

12 1 11 1 10 1

P. irregulare 6 5 1 6

P. paroecandrum

2 1 1 1 1

P. splendens 5 3 2 3 1 1

P. torulosum 2 1 1 2a Levels of pathogenicity were determined on the percentage of corn or soybean seed rotted in an

agar plate assay. Zero to 29, 30 to 69, and 70 to 100% of the seeds rotted were classified as low, moderate, and high levels of pathogenicity, respectively. The assays were repeated three times. Data presented is from the second assay.

This is the first report of P. catenulatum as a pathogen of corn and soybean seed. This species was first identified from water containing plant debris in North Carolina and Missouri (12). Only eight host plants are listed for P. catenulatum in the USDA Systematic Botany and Mycology Database including Oryza sativa, an unknown grass, and Phaseolus vulgaris (8). This study corroborates earlier studies where differences in aggressiveness and pathogenicity among Pythium isolates were reported (2,6,19). Additionally, Brown and Kennedy (2) reported 9 to 100% emergence in pot assays among P. ultimum isolates recovered from dying soybean seed and seedlings. More recently, Pythium spp. recovered from fields in a corn-soybean rotation ranged from not pathogenic, to varying levels of aggressiveness on both corn and soybeans, to high levels of aggressiveness on both crops (19).

Metalaxyl InsensitivitySensitivity to metalaxyl was measured at 5 and 100 µg/ml. Technical grade metalaxyl

(Gustafson LLC, Plano, TX) was dissolved in dimethylsulfoxide (DMSO) and added to V8 juice agar after autoclaving. DMSO, at the same volume as treatments, was added to the control. A 5-mm colonized, agar plug of the Pythium isolate to be tested was transferred from the actively growing margin of a 3- to 4-day-old culture to the center of the plate. Each isolate was evaluated at 0, 5, and 100 µg/ml, using three replicate plates. After 2 days, the length from the plug to the end of the mycelium was measured. Linear growth on metalaxyl-amended media was expressed as a percent of growth on control plates and used in the analysis.

All three locations had Pythium isolates that grew on metalaxyl-amended medium at 100 µg/ml. Although the majority of these isolates grew at this concentration, growth was 1 to 30% of the unamended control (Fig. 3). This included 30 of 39, 27 of 27, and 13 of 31 isolates tested for Defiance, Sandusky, and Wood locations, respectively. Only 5 of the 39 isolates tested in Defiance County and 7 of the 31 from Wood County did not grow on metalaxyl-amended medium at the 5-µg/ml concentration. Interestingly, these were all P. irregulare and one isolate of P. paroecandrum at both locations. There were 5 additional isolates of P. irregulare that grew on both concentrations of metalaxyl-amended medium, but growth was slow.

Fig. 3. Metalaxyl sensitivity at (A) 5 µg and (B) 100 µg of a subset of Pythiumspp. recovered from soils collected from three locations in Ohio. Metalaxyl was added to V8-juice agar and growth of isolates was measured after 2 days.

A range in sensitivity to metalaxyl has been reported for Pythiumisolates recovered from carrots (18), sugar beet (1), and wheat (5).Pythium spp. that were less sensitive to metalaxyl comprised 25 to 75% of the populations in wheat fields in the Pacific Northwest (5). This variation in levels of sensitivity could account for the development of Pythium root rot in some fields. However, Brantner and Windels (1) suggested that use of metalaxyl as a seed treatment posed a limited risk for development of populations of metalaxyl-insensitive isolates because only a small proportion of the Pythium population within sugar beet production fields are exposed to this seed treatment fungicide and other crops in the rotational sequence do not have seed treatment applied. All corn, most soybeans, and a smaller proportion of wheat seed planted in Ohio are treated with metalaxyl or the closely-related compound mefenoxam, which has the same mode of action. In addition, during the 1980s some of the fields in these counties had metalaxyl applied in-furrow to controlPhytophthora sojae on soybean. At this time, no populations of P. sojaewith insensitivity to metalaxy have been detected in Ohio (Dorrance,unpublished data). There are a number of seed treatment fungicide compounds with different modes of action that do have some efficacy towards Pythium spp. These results suggest that repeated use of one chemical may result in decreased sensitivity of Pythium spp. and reduced levels of disease control in the field.

ConclusionP. catenulatum, P. irregulare, P. paroecandrum, P. splendens, and P. torulosum were

recovered from the three fields in Ohio. Isolates of each species varied in number, pathogenicity, and sensitivity to metalaxyl both between and within locations. The species identified in this study are different from those reported in other states from corn and soybean in earlier studies and this is the first report of P. catenulatum as a pathogen of corn and soybean seed. The results

from this study indicate that repeated use of metalaxyl or mefenoxam alone as a seed treatment to manage Pythium spp. may be selecting for insensitive strains of these species. Variation in species composition and pathogenicity will pose additional challenges for the development of more biologically based seed treatments which may have narrow host ranges. A more thorough evaluation of the Pythium populations that exist in grain production fields in the north-central region is needed to facilitate the development and deployment of broader based biological and chemical seed treatments.

AcknowledgmentsWe would like to thank Ohio State University County Extension Agents B. Clevenger, D.

Frobose, and C. Hutson for identifying problem fields. We would also like to thank M. Ellis and R. Riedel for critically reviewing this manuscript. Salaries and research support provided by State and Federal Funds appropriated to the Ohio Agricultural Research and Development Center, the Ohio State University.

Literature Cited1. Brantner, J. R., and Windels, C. R. 1998. Variability in sensitivity to metalaxyl in vitro,

pathogenicity, and control of Pythium spp. on sugar beet. Plant Dis. 82:896-899.2. Brown, G. E., and Kennedy, B. W. 1965. Pythium pre-emergence damping-off of soybean in

Minnesota. Plant Dis. Rep. 49:646-647.3. Chen, W. 1999. Pythium root rot and feeder root necrosis. Pages 11-12 in: Compendium of

Corn Diseases. 3rd ed. D. G. White, ed. American Phytopathological Society, St. Paul, MN.4. Cohen, Y., and Coffey, M. D. 1986. Systemic fungicides and the control of oomycetes. Annu.

Rev. Phytopathol. 24:311-338.5. Cook, R. J., and Zhang, B. X. 1985. Degrees of sensitivity to metalaxyl within

the Pythium spp. pathogenic to wheat in the Pacific Northwest. Plant Dis. 69:686-688.6. Deep, I. W., and Lipps, P. E. 1996. Recovery of Pythium arrhenomanes and its virulence to

corn. Crop Prot. 15:85-90.7. Dorrance, A. E., McClure, S. A., and deSilva, A. 2003. Pathogenic diversity of Phytophthora

sojae in Ohio soybean fields. Plant Dis. 87:139-146.8. Farr, D. F., Rossman, A. Y., Palm, M. E., and McCray, E. B. 2004. Online. Fungal Databases,

Systematic Botany & Mycology Laboratory, ARS, USDA.9. Griffin, G. J. 1990. Importance of Pythium ultimum in a disease syndrome of cv. Essex

soybean. Can. J. Plant Pathol. 12:135-140.10. Kirkpatrick, M. T. 1999. The effect of Pythium spp. on soybeans subjected to periodic soil

flooding. M.S. Thesis, University of Arkansas.11. Mao, W., Carroll, R. B., and Whittington, D. P. 1998. Association of Phoma

terrestris, Pythium irregulare, and Fusarium acuminatum in causing red root rot of corn. Plant Dis. 82:337-342.

12. Middleton, J. T. 1943. The taxonomy, host range and geographic distribution of the genus Pythium. Mem. Torrey Bot. Club 20:1-171.

13. Muyolo, N. G., Lipps, P. E., and Schmitthenner, A. F. 1993. Anastomosis grouping and variation in virulence among isolates of Rhizoctonia solaniassociated with dry bean and soybean in Ohio and Zaire. Phytopathology 83:438-444.

14. Rao, B., Schmitthenner, A. F., Caldwell, R., and Ellett, C. W. 1978. Prevalence and virulence of Pythium species associated with root rot of corn in poorly drained soil. Phytopathology 68:1557-1563.

15. Rizvi, S. S. A., and Yang, X. B. 1996. Fungi associated with soybean seedling disease in Iowa. Plant Dis. 80:57-60.

16. Schmitthenner, A. F., and Bhat, R. G. 1994. Useful Methods for StudyingPhytophthora in the Laboratory. Ohio Agric. Res. Dev. Cent. Spec. Circ. 143.

17. Waterhouse, G. M. 1967. Key to Pythium Pringsheim. Mycological Papers no. 109. Commonwealth Mycological Institute, Kew, England.

18. White, J. G., Stanghellini, M. E., and Ayoubi, L. M. 1988. Variation in the sensitivity to metalaxyl of Pythium spp. isolated from carrot and other sources. Ann. Appl. Biol. 113:269-277.

19. Zhang, B. Q., and Yang, X. B. 2000. Pathogenicity of Pythium populations from corn-soybean rotation fields. Plant Dis. 84:94-99.