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2001 North Central Division Meeting Abstracts

June 19-21, 2001 - Manhattan, Kansas

Posted online October 30, 2001

Analysis of genetic variability among asexual progeny of P. infestans using virulence, RAPD and AFLP markers. F. M. ABU-EL SAMEN, G. A. Secor, and N. C. Gudmestad. Dept. Plant Pathology, North Dakota State University, Fargo, ND 58105. Publication no. P-2002-0001-NCA.

The genotypic variation among twenty-four single zoospore isolates (SZI) of Phytophthora infestans, derived asexually from the parental isolate PI-105P (A2 mating type, US-8 genotype), was assessed with 80 randomly amplified polymorphic DNA (RAPD) primers, and 18 amplified fragment length polymorphic DNA (AFLP) primer pairs. In a previous investigation, these isolates showed high levels of virulence variability and had been differentiated into 14 races. The purpose of this investigation was to determine if the virulence variability observed in this asexual progeny is associated with changes at the DNA level. DNA polymorphism was detected with 51 of the 80 RAPD primers screened, and with all AFLP primer pairs. However, none of the primers distinguished all the SZIs as different genotypes. Cluster analysis using the unweighted pair-group method with arithmetic averages (UPGMA) separated the SZIs into six virulence groups, 11 RAPD groups and seven AFLP groups. No close correlation among RAPD, AFLP, and virulence groups could be established. Results of this study suggested that there is a significant level of genetic variability among SZIs derived asexually from the same parental isolate, and that phenotypic changes in virulence are associated with changes at the DNA level in these isolates.

Transmission of alfalfa mosaic and clover yellow mosaic viruses by the soybean aphid.
R. J. ALLEMAN (1), D. B. Hogg (1), and C. R. Grau (2). (1) Department of Entomology and (2) Department of Plant Pathology, University of Wisconsin-Madison. Publication no. P-2002-0002-NCA.

The soybean aphid (SBA), Aphis glycines, was found to be capable of transmitting alfalfa mosaic virus (AMV) and soybean mosaic virus (SMV) from soybean to soybean in previous laboratory experiments. Objective one of this study was to determine if the SBA transmits AMV from red clover and snap bean to soybean and snap bean, respectively. Objective two was to determine if the SBA transmits clover yellow mosaic virus (CYMV) from red clover to soybean. Transmission studies were conducted by feeding SBA on virus-infected leaves followed by placing 3, 5, or 10 aphids on challenged plants for 3 min before removal. Ten SBA transmitted AMV from red clover to soybean at a rate of 20% and AMV from snap bean to snap bean at a rate of 12%. Three, five, and ten SBA were able to transmit CYMV from red clover to soybean at a rate of 30%, 30%, and 10% respectively. This is the first report of the SBA to transmit AMV from red clover to soybean, AMV from snap bean to snap bean, and CYMV from red clover to soybean. The SBA has the potential to be a significant vector of legume viruses from multiple inoculum sources.

Marker assisted selection for disease resistance in soybean using DNA from seed.
M. BOLTON (1), B. Nelson (1), R. Sparks (2), and A. Santoso (2). Dept. Plant Pathology (1) and Biochemistry and Molecular Biology (2), North Dakota State University, Fargo, ND 58105. Publication no. P-2002-0003-NCA.

Host resistance is the preferred method to control important soybean pathogens such as Heterodera glycines, and Phytophthora sojae. While utilizing a marker assisted selection protocol to detect resistance to these pathogens, a comparison was made between using the standard leaf extracted DNA and seed DNA. The protocol was unsuccessful using seeds, thus experiments were conducted to determine modifications that would allow seeds as the DNA source. The resulting procedure consisted of hydrating seeds, then removing radicals and pressing them onto a blood collection card. Samples were dried and stored at -20 C. Sample disks were removed with a paper punch, and DNA was purified with Gentra solution, washed with ethanol and dried. The DNA was amplified with PCR using primers for simple sequence repeats (SSRs). The resulting product was diluted 1:100 in buffer and 1 µl was reamplified and then electrophoresed in an agarose gel. This protocol resulted in consistent visualization of SSR markers for resistance to both H. glycines and P. sojae.

Identification of perennial wheat lines with resistance to eyespot, Cephalosporium stripe, and wheat streak mosaic.
C. M. COX (1), T. D. Murray (1), and S. S. Jones (2). (1) Dept. Plant Pathology, Washington State University, Pullman, WA 99164; (2) Dept. Crop and Soil Sciences, Washington State University, Pullman, WA 99164. Publication no. P-2002-0004-NCA.

A perennial wheat cropping system for highly erodible agricultural land may provide an alternative to the Conservation Reserve Program and reduce soil erosion while providing a harvestable grain for growers. Twenty-four perennial wheat germplasm lines from crosses between wheat and wheatgrass (Agropyron spp.) were evaluated under controlled environment conditions for resistance to Wheat streak mosaic virus, Cephalosporium gramineum, and Tapesia yallundae, which cause important yield-limiting diseases where perennial wheat will be grown. Perennial wheat lines SS452, SS103, SS237, MT-2, PI 550713, and PI 550715 were resistant to all three pathogens. Eight lines (33%) were resistant to WSMV at 21°C and 25°C; AT3425 was resistant to WSMV at 21°C but not at 25°C. Fourteen lines (58%) were highly to moderately resistant to C. gramineum and 14 out of 22 lines (64%) were resistant to T. yallundae. Agropyron elongatum and A. intermedium are reported as new sources of resistance to T. yallundae.

Reaction of dry bean cultivars of the Northern Plains to anthracnose.
L. E. DEL RIO, R. S. Lamppa, and P. L. Gross. Dept. Plant Pathology, North Dakota State University, Fargo, ND 58105. Publication no. P-2002-0005-NCA.

Some of the germplasm used by the North Dakota bean breeding program originated from Michigan, where races 7 and 73 of Colletotrichum lindemuthianum, causal agent of anthracnose, are prevalent. More recently, race 89 was identified in Manitoba. Although these races have not been detected in the Northern Plains, navy, pinto, and kidney beans are at risk of an anthracnose epidemic. Thus, 30 dry bean cultivars widely grown in North Dakota and Minnesota were evaluated for their reaction to these three races. Most kidney beans were highly susceptible to race 7, but resistant to races 73 and 89. 'Isles' was the only kidney bean resistant to all three races, while 'Drake' showed resistance to races 7 and 73. All pinto beans were highly susceptible to races 73 and 89 and moderately susceptible to race 7. 'Maverick', the most popular pinto cultivar, was moderately resistant to race 7. Navy cultivars 'Newport' and 'Envoy' were resistant to all three races, however, 'Norstar', the most popular navy bean, was highly susceptible. The use of germplasm resistant to race 89 in the breeding program, and screening of all advanced lines for reaction to this race is recommended.

Partial host range characterization of a bean pod mottle virus isolate from South Dakota.
D. C. DOXTADER and M. A. C. Langham. Plant Science Dept., South Dakota State University, Brookings, SD 57007. Publication no. P-2002-0006-NCA.

Bean pod mottle virus
(BPMV), family: Comovirdiae, genus: Comovirus, was first identified in South Dakota in 1998. Preliminary studies indicated that the South Dakota isolate differed from an Arkansas BPMV strain due to a partial identity reaction with the Arkansas strain in double diffusion tests. Host range studies comparing the two isolates were conducted in the greenhouse. Fifty test plants for each species per isolate were mechanically inoculated. Similar symptom expression was observed in greenbean (Phaseolus vulgarius) cv. Provider, lambsquarters (Chenopodium amarathicolor), and tobacco (Nicotiana tobacum) cv. Kentucky 16. Alfalfa (Medicago sativa) had a 2% infection rate with both strains. The South Dakota BPMV isolate did not infect greenbean cv. Tendergreen but all of the plants inoculated with the Arkansas strain were symptomatic. Cowpea (Vigna unguiculata) cv. Monarch demonstrated chlorotic local lesions inoculated with the South Dakota strain and necrotic local lesions with the Arkansas strain. Common lambsquarters (Chenopodium quinoa) were systemically infected only by the South Dakota strain. The host range comparison demonstrates differences between the two isolates that may contribute to epidemiological differences.

The use of Aphanomyces euteiches isolates to detect resistance genes in peas.
G. L. FOREMAN (1), C. R. Grau (1), and D. K. Malvick (1). (1) Dept. Plant Pathology, University of Wisconsin, Madison, WI 53706. Publication no. P-2002-0007-NCA.

The soil borne pathogen, Aphanomyces euteiches, (Ae), the cause of root rot of peas is common in many regions of the United States. Resistance of peas to Ae appears to be a multigenic trait and interacts strongly with environmental factors. In a controlled environment, ten experimental pea lines were challenged with three isolates of the pathogen (P54, B16, AeOR5) at 2,500 zoospores/ml to characterize the pea lines for disease reaction and the isolates for virulence phenotype. Previously, phenotypic selection for disease resistance took place involving repeated cycles of selection, selfing superior genotypes, and generation advance. In this study the level of resistance for five previously selected pea lines was determined and genetic gain was tested against the Ae isolates. Pea line MN314-P54C3 went through three cycles of selection against Ae isolate P54 and expressed moderate resistance to isolate P54 and high resistance to isolate B16. Pea breeding families are bulked at the F4 generation, thus, are potentially heterogeneous for genes that confer resistance to Ae. Knowledge of pea line x isolate interactions may allow breeders to probe putative heterogeneous pea populations with specific isolates of Ae to identify resistance genes. High and stable resistance to a greater number of Ae isolates would be of great value in pea production.

Use of satellite images to detect soybean stress caused by soybean cyst nematode.
J. GUAN (1), F. W. Nutter, Jr. (1), T. Rosburg (2), G. L. Tylka (1), and C. C. Marett (1). (1) Dept. Plant Pathology, Iowa State University, Ames, IA 50011; (2) Dept. Biology, Drake University, Des Moines, IA 50311. Publication no. P-2002-0008-NCA.

Soybean cyst nematode (SCN) (Heterodera glycines), the most important pathogen of soybean in the United States, causes significant yield losses annually. Remote sensing may provide a fast, nondestructive, objective, and affordable method to quantify plant stresses for crops grown over large areas. The main goal of this research was to investigate whether satellite images can be used to detect and quantify plant stress caused by SCN. Landsat 7 Enhanced Thematic Mapper images were obtained for five dates during the 2000 growing season. ERDAS IMAGINE and ArcView (GIS) were used to analyze satellite images. Linear regression was used to relate soybean yield, protein and oil concentrations, and initial and final SCN population densities to satellite image intensities. Satellite image intensities explained up to 47% of the variation in soybean yield, 80% of the variation in protein, 81% of the variation in oil, and 58% and 54% of the variations in initial and final SCN population densities, respectively.

Case study in biology education: An ongoing search for "real science" in non-majors labs.
M. H. HOEFNAGELS. Departments of Botany/Microbiology and Zoology, University of Oklahoma, Norman, OK 73019. Publication no. P-2002-0009-NCA.

The purpose of this poster is to open a dialog about general biology instruction, beginning with a summary of our non-majors course (Concepts in Biology) at the University of Oklahoma. Each semester our 5-credit Concepts course enrolls 70-80 students, most of whom need a lab science for a general education requirement. The course includes lecture, discussions based on assigned readings, online quizzes, and a weekly laboratory. Along with a case study of our course's strengths and weaknesses, I will focus specifically on the Concepts lab. The faculty and graduate students who teach the course would like to provide a meaningful, interesting experience in science. Yet we face significant constraints, including large sections (up to 40 students), lab manuals that do not challenge students or promote true scientific thinking, limited space for computers and microscopes, and limited funds for new equipment. Since the theme of this meeting is "Developing Useful Collaborations," I hope to use our experience as a springboard to share ideas with others who teach general biology or introductory plant pathology.

Stunting of 10 accessions of Medicago truncatula by Xanthomonas axonopodis alfalfae.
J. L. HORNING, D. L. Stuteville, and F. F. White. Dept. Plant Pathology, Kansas State University, Manhattan, KS 66506. Publication no. P-2002-0010-NCA.

Medicago truncatula
is a model plant for genetic studies that may be applicable to related legume species. M. truncatula, which is closely related to M. sativa (alfalfa), is well suited for biological studies due to the relatively small diploid genome. Xanthomonas axonopodis alfalfae causes bacterial leaf spot and stunting in alfalfa. The goal of this project was to determine it’s ability to stunt plants in accessions of M. truncatula. Approximately 16-hour-old inoculum was diluted to a concentration of 2.4-3.2 × 10(^8) CFU/ml. A 1.0 µl aliquot containing 2.4-3.2 × 10(^5) CFU, was used to inoculate plants at the cotyledon stage. One plant was inoculated with buffer-nutrient broth as a control for every plant inoculated with the bacterial suspension. The plants were placed in a growth chamber at 30°C with a 24-hour photoperiod. Petiole length was measured to determine the extent of stunting. Two weeks after inoculation, seedlings of PI accessions 292436, 566886, 566887, 566888, 566889, 566890, 566891, and seed lot A-17-1 were stunted (p<0.005) by X. a. alfalfae; seedlings of PI 384648 and 566892 were not stunted (p>0.07).

Aggressiveness of spring dead spot pathogens to bermudagrass cultivars exposed to low temperatures.
F. B. IRIARTE (1), J. D. Fry (2), D. L. Martin (3), and N. A. Tisserat (1). (1) Dept. Plant Pathology, and (2) Division of Horticulture, Kansas State University, Manhattan, KS 66506 and (3) Dept. Horticulture and Landscape Architecture, Oklahoma State University, Stillwater, OK 74078. Publication no. P-2002-0011-NCA.

Spring dead spot (SDS) disease of bermudagrass primarily is caused by Ophiosphaerella herpotricha in the southern Great Plains and by O. korrae in the southeastern United States. We studied the aggressiveness of these fungi to selected bermudagrass cultivars following cold temperature treatments. One susceptible (Tifgreen), two resistant (Midlawn, Guymon) and one cultivar (Champion) with undetermined field resistance to SDS were inoculated with O. herpotricha or O. korrae isolates. Inoculated grass was incubated at 25°C (non-acclimated) or 4°C (cold-acclimated) for 1 mo and then exposed to -2° to -8°C for 2 to 8 hr. Shoot survival was determined 1 mo after exposure to subfreezing temperatures. Inoculated, cold-acclimated plants exhibited greater shoot mortality than similarly treated non-acclimated plants. In cold acclimated plants, O. herpotricha caused more shoot death than O. korrae at all freezing temperatures tested. No differences in shoot mortality were detected among cultivars inoculated with the same pathogen. In general, shoot mortality on inoculated, non-acclimated plants was relatively light and was not affected by lowering the freezing temperature from -2° to -6°C. O. korrae caused similar or more shoot death than O. herpotricha on all non-acclimated cultivars.

Genetic interactions of Arabidopsis general resistance and Pseudomonas virulence.
Li Kang, Xiaoyan Tang, and Jian-Min Zhou. Kansas State University. Publication no. P-2002-0012-NCA.

The long history of association has driven the evolution of elaborate and interrelated defense mechanisms in plants and virulence mechanisms in pathogens. Thus genetic interactions between plant defense mutants and pathogen virulence/pathogenicity mutants can be utilized to establish a genetic framework of plant-pathogen interactions. We have previously isolated 10 Arabidopsis mutants that supported the growth of the nonhost bacterium Pseudomonas syringae pv. phaseolicola. Additional nho mutants are isolating by using a luciferase imaging system that monitors bacterial growth in planta. The nho1 mutant supports the growth of a number of nonhost Pseudomonas strains. nho1 also partially restores the virulence of the P. s. tomato DC3000 hrcC and hrpS mutants. Thus, the NHO1 function seems to interact with the bacterial pathogenicity functions. Here we show that this interaction is specific to the hrp pathway, because the nho1 mutant does not support the growth of a Pseudomonas strain defective in the production of alginate, an exopolysaccharide required for the virulence. Interestingly, deletion on CEL of P. s. t. DC3000 seems to complement the nho1 mutation.

The spatiotemporal genetic structure of Phytophthora capsici in Michigan and implications for control.
K. H. LAMOUR and M. K. Hausbeck. Dept. of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48824. Publication no. P-2002-0013-NCA.

Phytophthora capsici
isolates were recovered from pepper and cucurbit hosts at seven locations in Michigan from 1998 to 2000. Isolates were characterized for compatibility type, mefenoxam sensitivity, and AFLP marker profiles. In total, 94 AFLP bands were resolved. Individual populations were highly variable. Within populations, 39 to 49 percent of the AFLP bands were polymorphic and estimated heterozygosities ranged from 0.16 to 0.19. Of the 646 isolates fingerprinted, 70 percent (454) had unique AFLP profiles. No clones were recovered among years or locations. Pairwise population F(ST)’s ranged from 0.18 to 0.40. There was no correlation between genetic distance and geographical distance. UPGMA cluster analysis indicates discrete clusters based on location with no clustering based on year of sampling. AMOVA partitioned variability as 40 percent among and 60 percent within populations. The overall estimated F(ST) was 0.34. These data suggest that long distance dispersal is rare and that the sexual stage plays a significant role in survival and maintaining genetic diversity.

Identification of races of Pseudomonas syringae pv. phaseolicola present in North Dakota.
R. S. LAMPPA, P. L. Gross, and L. E. del Río. Dept. Plant Pathology, North Dakota State University, Fargo, ND 58105. Publication no. P-2002-0014-NCA.

Halo blight, caused by Pseudomonas syringae pv. phaseolicola (Psp), is considered an important disease affecting dry bean production in North Dakota. However, despite its prevalence in the fields, the race composition of its populations is not known. Between 1995 and 2000, a total of 161 Psp isolates was retrieved from plant material from eleven North Dakota counties: Dickey, Foster, Grand Forks, Griggs, Nelson, Richland, Sargent, Steele, Stutsman, Traill, and Walsh. The identity of the isolates was ascertained by standard biochemical methods and pathogenicity tests. Race identification was conducted by inoculation of eight differential cultivars. A total of 148 isolates were identified as Psp race 6. Race 6 was detected in samples from all counties surveyed, while Psp race 2 was detected in samples from Sargent, Foster and Stutsman County only. The race identification of 10 isolates could not be established. This is the first report on the identity of races of Pseudomonas syringae pv. phaseolicola present in North Dakota.

Prevalence and agronomic effects of viruses in Wisconsin soybeans.
M. E. LEE (1), N. C. Kurtzweil (1), and C. R. Grau (1). (1) Department of Plant Pathology, University of Wisconsin-Madison, Madison, WI 53706. Publication no. P-2002-0015-NCA.

Surveys were conducted in 1999 and 2000 to assess the prevalence of soybean mosaic virus (SMV), alfalfa mosaic virus (AMV), bean pod mottle virus (BPMV), tobacco streak virus (TSV), tobacco ringspot virus (TRSV), and bean yellow mosaic virus (BYMV). In 1999, a survey of 14 locations showed a greater incidence of viruses in the south, east and central parts of the state. BPMV was detected for the first time in Wisconsin. In 143 samples, SMV was most commonly detected (30%), followed by AMV (28%), TSV (19%), BYMV (7%), TRSV (6%), and BPMV (3%). In more intensive surveys of 3 locations, overall incidence of SMV was 7%, AMV 4%, TSV 3%, TRSV 3%, BYMV 2%, and BPMV 1%. In surveys of 4 locations in 2000, incidence of SMV was 54%, AMV 13%, TSV 18%, and BPMV 38% (BPMV 2 locations only). Yield loss associated with virus-like symptoms was estimated at 7 bu/acre in Arlington, WI. Mottling of seed was associated with high incidence of SMV, but was variety dependent. The higher incidence of viruses in 2000 may be related to an increase in insect activity, especially the bean leaf beetle (Cerotoma trifurcata) and the soybean aphid (Aphis glycines).

Isolation and characterization of tomato mutants suppressing spontaneous cell death mediated by Pto overexpression.
J. X. Li, J. M. Zhou, and X. Y. Tang. Dept. Plant Pathology, Kansas State University, Manhattan, KS 66506. Publication no. P-2002-0016-NCA.

The Pto gene confers specific disease resistance to Pseudomonas syringae pv tomato strain expressing the cognate avirulence gene avrPto The Pto/AvrPto-mediated resistance requires Prf. Overexpression of Pto in tomato using the CaMV 35S promoter resulted in spontaneous cell death which also requires the functional Prf gene. We mutagenized the seeds of the Pto overexpression plants and screened for mutants that suppressed the spontaneous cell death. From ~ 670 M(2) families, six putative mutants were identified that showed very minor or no spontaneous cell death. To testify whether the mutations occurred to the Pto transgene and/or endogenous Prf gene, we designed specific primers to amplify the Pto transgene and the Prf gene from all the mutants. Sequence analysis of the PCR products did not reveal any mutation in either the Pto transgene or endogenous Prf gene. RNA blot analysis did not reveal alteration on the expression of the Pto transgene and the Prf gene in the mutants. These results suggested that all the mutants are truly novel mutants. Genetic characterization of these mutants and analysis of the defense responses and disease resistance of these mutants will be reported.

Round-up Ready gene transfer from transgenic to non-transgenic field-grown soybeans.
S. LI (1), B. Dunker (1), W. PEDERSEN, and G. Hartman (1,2). (1) Dept. of Crop Sciences, University of Illinois; (2) USDA/ARS, 1101 W. Peabody Dr., Urbana, IL 61801. Publication no. P-2002-0017-NCA.

The goal of this research was to determine the frequency of Roundup Ready gene transfer from Roundup Ready soybean to non-Roundup Ready soybean via pollen movement and to provide recommendations to seed producers and growers on how to minimize this contamination. In 1999, non-Roundup Ready cultivars were planted at several distances from Roundup Ready soybean cultivars. Seeds were harvested from the non-Roundup Ready cultivars, planted in 2000, and 21-day-old seedlings were sprayed with Roundup Ultra®. Of 168,000 plants tested, only 47 plants survived the herbicide treatment. Laboratory tests confirmed the presence of the Roundup Ready gene in the surviving plants. In 2000, field experiments included repeating the experiment from 1999, which involved testing the distance pollen moves from a known Roundup Ready source. In addition, the role of insects in pollen movement was studied in a wildlife area that had high insect populations and in insect-proof cages with very low insect populations and with soybean male sterile lines. Finally, hybrid corn was evaluated as a potential physical barrier to soybean pollen movement . Results from these experiments provided information on how far soybean pollen moves, the role of insects in movement of soybean pollen, and the effectiveness of corn as barrier to soybean pollen.

Adjuvants and efficacy of Folicur and Tilt fungicides for control of Fusarium head blight in spring grains.
M. MCMULLEN, J. Jordahl, and S. Meyer. Dept. Plant Pathology, North Dakota State University, Fargo, ND 58105. Publication no. P-2002-0018-NCA.

Folicur (tebuconazole) and Tilt (propiconazole) fungicides have special use registrations for control of Fusarium head blight (FHB) in ND. The Folicur label recommends addition of a spray surfactant; the Tilt label does not. Field and greenhouse studies at Fargo determined if adjuvants improved Folicur and Tilt performance against FHB. Applications were at early flowering in wheat and at early heading in barley. Field studies relied on natural inoculum, while Fusarium graminearum spores were sprayed onto grain heads at heading to early flowering stages in the greenhouse. Field results on spring wheat and durum showed that Induce, a non-ionic surfactant, improved FHB control with Folicur, and Induce and Herbimax, a petroleum oil, improved control with Tilt. Greenhouse studies with spring wheat and barley indicated that an experimental adjuvant added to Folicur provided slightly better control of FHB than did Induce or Silwet, a silicone surfactant, while the addition of Silwet to Tilt provided slightly better FHB control than did additions of Induce or two experimental adjuvants.

Stem rust resistance in spring wheat germplasm resistant to Fusarium head blight.
J. D. Miller (1) and R. W. STACK (2). (1) USDA-ARS, NCRL, Fargo, ND 58105; (2) Dept. of Plant Pathology, North Dakota State Univ., Fargo, ND 58105. Publication no. P-2002-0019-NCA.

Since 1993, Fusarium Head Blight (FHB) has caused serious loss of spring wheat yield and quality. Among the best sources of resistance to FHB are certain spring wheat lines which are very susceptible (S) to wheat stem rust (WSR). WSR is a disease threat potentially as serious as FHB. The widespread use of germplasm resistant to FHB, but S to WSR raises the spectre of a possible future WSR epidemic. We selected 14 breeding source lines resistant to FHB and tested them for reaction to 14 pathotypes of WSR including past and present prevalent pathotypes and several potentially threatening ones. Most of the FHB source lines were of an intermediate type -- S to some WSR cultures and R to others. Four lines were R to all 14 WSR cultures in the test; three of these lines were from China and one was from Brazil. A strain of Sumai3 that has been widely used for FHB resistance breeding in the spring wheat region was S to 13 of the WSR cultures and showed a mixture of R and S to the fourteenth. Lines derived from FHB resistant parent sources must be thoroughly screened for WSR reaction prior to release.

Reaction of snap bean cultivars to two isolates of alfalfa mosaic virus from Wisconsin.
A. M. Mondjana, N. C. Kurtzweil, and C. R. GRAU. Dept. Plant Pathology, University of Wisconsin, Madison, WI 53706. Publication no. P-2002-0020-NCA.

Virus-like symptoms were observed in snap bean fields located near Belgium and Cambria, Wisconsin, in 2000. Symptoms were characterized by leaf distortion, mottling and mosaic patterns on leaves, stunting, pod distortion, and pod necrosis. Bean samples tested positive for alfalfa mosaic virus (AMV) using an enzyme-linked immuno-sorbent assay and a local lesion assay on Phaseolus vulgaris cv. Bountiful. Etiology studies were performed in a greenhouse to verify pathogenicity of AMV from snap beans. The inoculated plants developed symptoms similar to those observed in the field. Another study was conducted to determine the reaction of six snap bean cultivars to the snap bean AMV isolates. The isolates equally reduced plant development and productivity in all cultivars. Neither isolate was seed transmitted. The host range and symptomatology indicated that the snap bean AMV isolates are different from AMV isolates from alfalfa, kura clover, and soybean. Data support the conclusion that the snap bean AMV isolates constitute a new strain or strains of AMV.

Quantifying soybean cyst nematode injury and its qualitative and quantitative impact on soybean yield using remote sensing.
A. J. A. MOREIRA (1), F. W. Nutter, Jr. (1), G. L. Tylka (1), J. Guan (1), and C. C. Marett (1). (1) Dept. Plant Pathology, Iowa State University, Ames, IA 50011. Publication no. P-2002-0021-NCA.

Soybean cyst nematode (SCN), Heterodera glycines, is an important yield-limiting factor wherever soybean Glycine max is cultivated. Annual yield losses caused by SCN currently exceed 1 billion dollars in the US. Remote sensing may promote a fast, nondestructive, and economic way to detect soybean stress caused by SCN. Using a hand-held, multispectral radiometer, the percentage of sunlight reflected from the canopy of a SCN-infested soybean field was measured every 10-14 days during the 2000 growing season. Geo-referenced maps of percentage of reflectance, yield, soy oil, soy protein, and initial and final SCN population densities were generated using ArcView software. Information generated from those maps was regressed on percentage of reflectance (810 nm). Reflectance data explained up to 91% of the variation in soybean yield, 54% of the variation in soy protein, 36% of the variation in soy oil, and 61% and 44% of the variation in the initial and final SCN population densities, respectively.

Preferential genotypes of the soybean brown stem rot pathogen Phialophora gregata influenced by crop rotation.
P. PEDERSEN (1), C. R. Grau (2), W. Chen (3), and J. G. Lauer (1). (1) Dept. of Agronomy and (2) Plant Pathology, University of Wisconsin-Madison; (3) Illinois Nat. Hist. Surv., Champaign. Publication no. P-2002-0022-NCA.

Phialophora gregata
(Pg) is characterized by two genotypes (A or B) using genotype specific PCR primers. The two genotypes preferentially infect susceptible and resistant cultivars, respectively. It is not known if management practices affect the ability of each genotype to infect soybean (SB). We compared the frequency of pathogen genotypes in plants of a BSR resistant SB cultivar (AG2301) grown in seven different rotation sequences of corn (C). Stems were sampled at harvest and assayed for genotype of Pg by PCR. Pg was detected in 77% of the samples. Of those samples, genotype A and genotype B were detected in 33% and 58% of the samples, respectively. Both genotypes were found in 9% of the samples. Genotype B was most frequently detected in an annual rotation of C and SB and rotations with consecutive years of SB, but genotype A was most frequently detected in first year SB following five years of C (P<0.025). Further research is needed to determine survival abilities of genotypes A and B in a non-host environment.

Differential gene expression in wheat roots in response to infection by the “take-all” fungus Gaeumannomyces graminis var. tritici.
T. D. SAMUELS (1), A. C. Guenzi (1), L. L. Singleton (2), and W. Bockus (3). (1) Dept. Plant and Soil Sciences; (2) Dept. of Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK 74078; (3) Dept. of Plant Pathology, Kansas State University, Manhattan, KS 66506. Publication no. P-2002-0023-NCA.

Take-all [Gaeumannomyces graminis var. tritici (Ggt)] is regarded as the most damaging root disease affecting wheat worldwide. Control of take-all has been suggested to increase yield up to 10 to 50%. Procedures for studying the infection process under controlled conditions were developed. Seeds were sterilized with 1% AgNO(3) (30s), rinsed with sterile-deionized water, placed on sterile filter paper in a cold room (4.5°C) without light for 48 h. Imbibed seeds were then aseptically transferred to 1/5X PDA medium at 25°C without light for 48 hours. Seedlings with roots approximately 2.0 to 3.0 cm long were transferred to fresh 1/5 strength PDA medium (control) or to a Ggt lawn (14d) (treatment) and placed back into a 25°C incubator without light. A time course for infection was determined with light microscopy. Results indicated that at 12 h Ggt had colonized the root surface, at 24 hours root hairs were penetrated, and at 48 hours root hairs collapsed and the fungus had penetrated the epidermis and cortex. These times are currently being used to sample tissue and create normalized cDNA libraries by suppression-subtraction hybridization. Gene expression profiles obtained from this research will provide insight into the host-pathogen interaction with the hope of eventually developing resistance to this soilborne fungal pathogen.

Quantifying the spatial and temporal dynamics of Soybean mosaic virus (SMV) in transgenic soybeans.
T. A. STEINLAGE (1), J. H. Hill (1), and F. W. Nutter, Jr. (1). (1) Dept. Plant Pathology, Iowa State University, Ames, IA 50011. Publication no. P-2002-0024-NCA.

Soybean mosaic virus
(SMV) causes a serious disease of soybeans, and is found in all major growing regions worldwide. The virus is vectored by over 30 species of aphids in a non-persistent manner. Six soybean lines were generated by Agrobacterium-mediated transformation with the coat-protein gene of SMV strain N. Field plots of each line were established with point sources of aphid-transmissible SMV strain AL-5 in 1999 and 2000. Plots were divided into quadrats, and plant samples within quadrats were bulked together for testing by biotin-avidin ELISA. The Gompertz model was the most appropriate for quantifying and comparing the temporal spread of SMV in the six soybean lines over both years. Two lines (3-24 and 7B-11) had lower infection rates and lower final pathogen incidences, compared to the untransformed control. Ordinary runs analysis revealed clustering of infected quadrats in lines with the highest rates of pathogen progress for both years. Harvested soybeans showed significantly less seed-coat mottling in 3-24 and 7B-11, compared to the untransformed control.

Reaction of switchgrass cultivars to seed smut caused by Tilletia maclaganii.
D. L. STUTEVILLE (1), R. L. Wynia (2), and J. M. Row (2). (1) Dept. Plant Pathology, Kansas State University, Manhattan, KS 66506; (2) USDA-NRCS, Manhattan, KS 66502. Publication no. P-2002-0025-NCA.

Seed smut caused by Tilletia maclaganii (Berk) G. P. Clinton is common and reduces yields in seed production fields of 'Blackwell' switchgrass (Panicum virgatum L.) in Kansas. To determine the reaction of other cultivars, in May 1998 we artificially infested two-year-old stands with teliospores. Smutted panicles first appeared in June 1999. In June 2000, the smut was prevalent in the cultivars Blackwell, Cave-in-Rock, Pathfinder, Shelter, Summer and accession 9006010, but did not occur in the cultivar Kanlow.

Susceptibility of hard red spring wheat and durum wheat to common root rot.
D. J. TOBIAS (1), N. Balbyshev (1), N. Riveland (2), and R. W. Stack (1). (1) Department of Plant Pathology, North Dakota State University, Fargo, ND 58105; (2) NDSU Williston Research Center, Williston, ND 58801. Publication no. P-2002-0026-NCA.

Hard red spring wheat and durum wheat cultivars were tested for susceptibility to common root rot (CRR) at Williston, ND in a field plot with high natural inoculum of Cochliobolus sativus. Incidence and severity of CRR were determined for 42 spring wheat and 30 durum cultivars. There were 8 replicate blocks; in each replicate at least 24 plants of each entry of spring wheat and durum were individually scored for CRR using the subcrown internode index method where individual plants are scored into clean, slight, moderate or severe disease categories. Samples for disease scoring were collected when plants were in soft dough stage. In this study, reactions of susceptible and resistant checks were fairly consistent with long term results since 1987. No cultivars were immune to C. sativus infection but significant varietal differences in root rot reaction were observed for both spring wheat and durum.

Comparison of Rp3 rust resistance gene family members.
C. WEBB, H. Trick, and S. Hulbert. Department of Plant Pathology, Kansas State University, Manhattan, KS 66506. Publication no. P-2002-0027-NCA.

In maize, Rp3 confers resistance to common rust caused by the fungal pathogen Puccinia sorghi. We have identified a nucleotide binding site-leucine rich repeat (NBS-LRR) gene family that maps to the rp3 locus. Gel blot experiments suggest that there are at least six tightly linked family members at the locus, at least five of which are transcribed in the Rp3-A haplotype. We are comparing Rp3 gene family members from different Rp3-carrying haplotypes to determine which member carries the gene conferring rust resistance. One recombinant Rp3 haplotype, Rp3-AD4, exhibits an intermediate resistance phenotype compared to its rust resistant parents Rp3-A and Rp3-D. On gel blots, it displays a unique HpaII restriction fragment relative to the parents. A lambda library from the Rp3-AD4 line was constructed. Partial DNA sequence analysis was conducted on those clones carrying putative full-length genes to classify them into six different groups. The coding regions of representatives from each of the six classes were completely sequenced and compared. One candidate clone is currently being used in complementation experiments to determine if it confers rust resistance.

Pto(^G50S) functions as a dominant negative mutant to suppress 35S::Pto induced cell death.
Fangming Xiao, Jianxiong Li, Xiaoyan Tang, and Jian-min Zhou. Plant Pathology Department, Kansas State University, Manhattan, KS 66506. Publication no. P-2002-0028-NCA.

The tomato resistance gene Pto confers resistance to Pseudomonas syringae pathovar tomato containing corresponding avirulent gene avrPto. The resistance is triggered by the recognition of AvrPto by Pto in plant cell. Pto also directly interacts with several proteins (Ptis) in yeast two-hybrid system. Overexpression of Pto in the transgenic tomato plants leads to spontaneous cell death, accumulation of salicylic acid, constitutive expression of a large number of defense-related genes, and broad-spectrum resistance to bacterial and fungal pathogens. We created several Pto mutants that were unable to interact with Ptis but still interacted normally with AvrPto. One of these mutants, Pto(^G50S) did not interact with Pti1, Pti4/5/6. 35S::Pto(^G50S) transgenic plants did not develop cell death or show enhanced resistance to virulent P.s.t. When crossed with 35S::Pto, 35S::Pto(^G50S) suppressed all the phenotypes controlled by 35S::Pto, including spontaneous cell death, accumulation of SA, resistance to virulent P.s.t. This indicates that Pto(^G50S) is a dominant negative mutant. Macro array analysis of 78 genes constitutively expressed in 35S::Pto showed that most of the defense-related genes constitutively expressed in 35S::Pto plants were also suppressed by 35S::Pto(^G50S). However, 35S::Pto(^G50S) plants are resistant to P.s. tomato (avrPto). The implication of the results on Pto's role in gene-for-gene and general defense will be discussed.

Differential gene expression in bermudagrass associated with Ophiosphaerella herpotricha infection
. YAN ZHANG (1), Arron C. Guenzi (1), Michael Anderson (1), Charles Taliaferro (1), Dennis Martin (2), and Ned Tisserat (3). (1) Dept. of Plant and Soil Sciences and (2) Dept. of Horticulture and Landscape Architecture, Oklahoma State University, Stillwater, OK 74078; (3) Dept. of Plant Pathology, Kansas State University, Manhattan, KS 66506. Publication no. P-2002-0029-NCA.

Bermudagrass, Cynodon dactylon, is extensively used for turf and forage in the southern United States. Spring dead spot (SDS), caused by Ophiosphaerella herpotricha, is a serious disease of bermudagrass. The objective of this research was to identify bermudagrass genes conferring response and resistance to SDS. Differentially expressed gene transcripts were selected from two sets of samples (resistant vs. susceptible cultivars; infected vs. non-infected tissues) by Suppression Subtractive Hybridization (SSH) to create normalized cDNA libraries. Two SSH libraries that contain 834 fungal-induced gene transcripts were created. Putative function of ninety-eight clones was determined by database mining. Six categories of genes involved in host-pathogen interactions were identified: 1) anti-microbial, 2) general stress responses, 3) low molecular weight defense signals, 4) high molecular weight signal regulation, 5) cell maintenance, and 6) development. EST sequences were submitted to GenBank dbEST. Preliminary results indicated disease resistance was associated with a complex defense response that involved an integrated set of genes. These results will help elucidate the molecular mechanisms of the plant defense system and provide insights into developing cultivars with superior resistance.

Incidence of bean pod mottle virus and soybean mosaic virus in Nebraska.
A. D. ZIEMS, L. G. Gielser, and L. C. Lane. Dept. Plant Pathology, University of Nebraska, Lincoln, NE 68583-0772. Publication no. P-2002-0030-NCA.

Soybeans are produced on 4.6 million acres in Nebraska. Soybean viruses are an important production issue in regards to seed quality and yield. Bean pod mottle virus (BPMV) and soybean mosaic virus (SMV) are present in Nebraska, but the incidence status of each has not been determined. As the prevalence of BPMV in the North Central Region of the United States increases, the importance of measuring its incidence becomes more critical to soybean production in the area. Surveys of BPMV and SMV in Nebraska were initiated in 2000. During the 2000 growing season, 197 soybean leaf samples were randomly collected in 32 counties in Nebraska. Using ELISA, BPMV was found to be the most prevalent virus in this survey and was detected in 69.5% of the samples, distributed in 24 of the 32 sampled counties. SMV was found only in the eastern third of Nebraska in 3.5% of the samples, distributed in 3 of the 32 sampled counties. Within county incidence ranged from 0 to 100% for BPMV; BPMV was the most prevalent in the eastern third of Nebraska. The high incidence of BPMV appears to be associated with high populations of bean leaf beetles, which vector the virus.