June 25-27, 2003 - East Lansing, Michigan
Posted online September 24, 2003
Inheritance of mefenoxam resistance in two generations of Phytophthora erythroseptica (Pethybr.). F. M. ABU-EL SAMEN, K. Oberoi, R. J. Taylor, G. A. Secor, and N. C. Gudmestad. Dept. Plant Pathology, North Dakota State University, Fargo, ND 58105. Publication no. P-2004-0001-NCA.
The inheritance of mefenoxam resistance in Phytophthora erythroseptica was investigated using fourteen parental isolates from three mefenoxam-sensitivity phenotypes (sensitive, intermediately-resistant and resistant). Two generations of isolates were tested for mefenoxam sensitivity using the radial growth inhibition assay and calculating EC(50) values. Twenty-four hundred isolates from F1 and F2 progeny isolates were tested. Results demonstrated the lack of segregation for mefenoxam sensitivity among the F1 and F2 progeny isolates from the resistant and sensitive parents. The majority of F1 and F2 progeny isolates from the parents with intermediate resistance were intermediately resistant, but demonstrated substantial quantitative shifts in response to mefenoxam. A few isolates from the F1 progeny were sensitive to mefenoxam. Results from this study did not support the hypothesis that resistance to mefenoxam in P. erythroseptica is under the genetic control of a single gene exhibiting incomplete dominance.
Phenotypic and genotypic variation in Uromyces appendiculatus from a region in a major center of common bean domestication. M. ACEVEDO, A. Alleyne, J. Fenton, and J. R. Steadman. Dept. of Plant Pathology, University of Nebraska-Lincoln, NE 68583. Publication no. P-2004-0002-NCA.
Common bean (Phaseolus vulgaris) was domesticated in two main centers of the Americas, the Andean and Middle American regions. It is thought that isolates of the bean pathogen Uromyces appendiculatus co-evolved within these regions with its only hosts, Phaseolus spp. Isolates of U. appendiculatus from Honduras have higher virulence diversity than rust pathotypes from other regions. The genetic diversity present in U. appendiculatus collected from wild, weedy, landrace and commercial beans from different regions in Honduras may give new insights into the co-adaptation of this pathogen with its host. This study seeks to determine whether the continuum of wild, landrace, and commercial beans has led to genetic diversity and higher levels of virulence in the pathogen. We evaluated single uredinium isolates from Honduras and Argentina for virulence on bean differentials with specific resistance genes and for molecular profiles. In Andean Argentina a wild, landrace and commercial bean proximity continuum does not exist.
Identification of bacteria in onion bulbs after induction of resistance against Alternaria porri. J. ARBOLEYA (1), A. da Rocha (2), J. Jacobs (2), R. Walcott (3), A. Castro (3), R. Hammerschmidt (2), and B. Zandstra (1). (1) Dept. of Horticulture, and (2) Dept. of Plant Pathology, Michigan State University, East Lansing, MI 48824; (3) Dept. of Plant Pathology, University of Georgia, Athens, GA 30602. Publication no. P-2004-0003-NCA.
Alternaria porri infection may provide entrance to bacteria that cause bulb decay in storage. Sour skin, slippery skin, soft rot and center rots are caused by Burkholderia cepacia, B. gladioli pv. alliicola, Erwinia carotovora subsp. carotovora, and Pantoea ananatis, respectively. The objective of this work was to verify the distribution of bacteria in bulbs from a field where resistance activators were tested against A. porri. Plants sowed in 2002 on a Houghton Muck Soil were sprayed with fungicides used to control A. porri; surfactant; Methyl Jasmonate (MeJA); beta-amino-butyric acid; and MeJA plus fungicide. MeJA and fungicides reduced A. porri infection but had no effect on bulb rot. Total DNA was extracted from decayed bulbs. The detection rates of B. cepacia, B. gladioli pv. alliicola, and P. ananatis using the polymerase chain reaction were 11%, 0.8%, and 1.5%, respectively. E. carotovora ssp carotovora was not detected.
Intraspecific comparative genomics to select candidate avirulence genes from Phytophthora infestans. J. I. B. BOS, Z. Liu, T. A. Torto, M. Tian, and S. Kamoun. Department of Plant Pathology, Ohio State University, Ohio Agricultural Research and Development Center, Wooster, OH, USA, 44691, firstname.lastname@example.org. Publication no. P-2004-0004-NCA.
Large scale DNA sequencing approaches promise to impact our understanding of the molecular basis of pathogenicity and host-specificity in Phytophthora by facilitating the isolation of genes encoding effectors with virulence and avirulence functions. As a consequence of co-evolution with host plants, it is likely that Phytophthora effector genes exhibit sequence variation within populations of the pathogen. We used this criteria, along with other features typical of avirulence genes of eukaryotic plant pathogenic microbes, such as secretion, up-regulation during pre-infection and infection stages, and presence of cysteine residues, to identify candidate avirulence genes of Phytophthora infestans from sequence databases. We used PCR amplification of candidate genes of genomic DNA from different P. infestans isolates combined with high throughput sequencing to identify polymorphic genes. These genes were then assayed in functional screens using a potato virus X (PVX)-based expression vector. This approach provides a rapid and efficient alternative to classical positional cloning strategies for identifying avirulence genes that match known resistance genes. In addition, this approach has revealed “orphan” avirulence genes for which corresponding resistance genes have not been previously characterized.
Incorporating disease scouting and Tom-Cast into a foliar blight management program for carrots. R. S. BOUNDS and M. K. Hausbeck. Dept. Plant Pathology, Michigan State University, East Lansing, MI 48824. Publication no. P-2004-0005-NCA.
Fungal foliar blights of carrots are caused by Alternaria dauci and Cercospora carotae. Traditionally, fungicides are applied every 7 to 14 days, irrespective of prior environmental conditions or disease pressure. This study evaluated the Tom-Cast disease forecaster to time sprays and determined the disease threshold to apply the first spray. Chlorothalonil alternated with azoxystrobin was applied to ‘Early Gold’ carrots in 2001 and 2002. Sprays were initiated prior to blight symptoms, or when foliar blight occurred at a trace, 5%, or 10% level. Subsequent sprays were applied every 10 days or according to Tom-Cast using 15, 20, or 25 disease severity value (DSV) thresholds. Sprays initiated when a trace amount of disease was present and reapplied according to Tom-Cast 15 DSV were equally effective in limiting blight as calendar-based sprays initiated prior to disease detection. In this study, field scouting and the Tom-Cast disease forecaster were reliable management tools while reducing fungicide sprays and production costs.
Evaluation of canola cultivars for resistance to Sclerotinia sclerotiorum using petiole and detached leaf inoculation. C. A. BRADLEY and L. E. del Rio. Department of Plant Pathology, North Dakota State University, Fargo, ND 58105. Publication no. P-2004-0006-NCA.
Sclerotinia stem rot (SSR) can cause considerable economic damage to canola grown in North Dakota and Minnesota when conditions are favorable. Information on cultivar susceptibility to SSR is limited, and observations under field conditions can be inconsistent due to non-uniform disease pressure and differences in cultivar maturity and plant architecture. Twenty canola cultivars were tested under controlled greenhouse and growth chamber conditions for their level of resistance to SSR using a petiole inoculation test (PIT) and a detached leaf assay (DLA). Significant (P < 0.05) differences among cultivars were detected with the PIT under both greenhouse and growth chamber conditions. ‘Hyola 357’ had the lowest AUDPC in both the greenhouse and growth chamber. No significant differences among cultivars were detected using the DLA. Spearman and Pearson correlations between the PIT and the DLA were not significant. Results indicate that the PIT may be an efficient and reliable method to evaluate canola cultivars for their level of resistance to SSR.
BPMV effects on yield and test weight of ten soybean lines. C. L. CIHLAR and M. A. C. Langham. Plant Science Dept., South Dakota State University, Brookings, SD 57007. Publication no. P-2004-0007-NCA.
Ten soybean lines were evaluated for the effects of Bean pod mottle virus (BPMV) (genus: Comovirus, family: Comoviridae) on yield and test weight. Inoculated and non-inoculated four-row plots were paired in a randomized block design with four replications at two locations. Plants were spray-inoculated at the V3-V5 stage with sap extracted from a 1:10 dilution of BPMV-infected Phaseolus vulgaris cv. Provider (0.02M NaKPO(4) buffer, pH 7.2; 1% of silica carbide) at 80 PSI. Yield and test weight were determined for each plot. Other yield parameters included the number of pods per center five nodes and the seed number per pod from eight random plants per plot. BPMV-infected plants demonstrated highly significant differences in yield for cultivar, treatment, cultivar by site, and site by treatment. Comparisons of inoculated vs non-inoculated treatments indicated that no line performed significantly better than any other line in response to BPMV infection. Significant differences were found in test weight for cultivar, site, treatment, and cultivar by treatment. Analyses in progress include comparison of pod numbers, seed set, and visual seed ratings.
Tomato spotted wilt virus severity influenced by acibenzolar-S-methyl, imidacloprid and age of tobacco transplants. A. S. CSINOS (1), N. Martinez-Ochoa (1), and M. G. Stephenson (2). (1) Department of Plant Pathology and (2) Crop and Soil Sciences, University of Georgia, Tifton, GA 31794. Publication no. P-2004-0008-NCA.
Tobacco seedlings 6, 8 or 10 weeks old, not treated or treated with acibenzolar-S-methyl (ASM) plus imidacloprid (I), were transplanted into a field in a randomized complete block design with four replications. Tomato spotted wilt virus (TSWV) incidence was high, killing a large percentage of plants and severely reduced yield of most plots. The youngest of the untreated seedlings, tended to have the highest incidence of TSWV. Vigor tended to be greater on older untreated plants or with ASM and I treated plants of all ages. The percent ELISA positive root samples were greater than the percent symptomatic plants by as much as 67%, suggesting non-symptomatic infections. Yield of plants treated with ASM plus I was up to 107% greater than untreated plants of the same age. As the age of plants increased, severity of TSWV decreased and yields increased. ASM plus I treatments decreased disease and increased yield for all plant ages.
Increase in oxalate oxidase activity in bentgrass response to Sclerotinia homoeocarpa and chemical treatment. A. B. DA ROCHA and R. Hammerschmidt. Dept. of Plant Pathology, Michigan State University, East Lansing, MI 48824 USA. Publication no. P-2004-0009-NCA.
Oxalate oxidase, an enzyme that degrades oxalic acid (OA) to CO(2) and H(2)O(2), has been characterized in some plant species, such as barley, and has also been associated with the responses of barley to pathogens. Although dollar spot, caused by S. homoeocarpa, is one of the primary turfgrass diseases in USA, the interaction between bentgrass and S. homoeocarpa is poorly understood. In this work, we observed that S. homoeocarpa produces OA during the infection process. In order to determine if oxalate oxidase is involved in the response of bentgrass to dollar spot, cultivars Crenshaw, Emerald, and L-93 were inoculated with S. homoeocarpa. Oxalate oxidase activity increased from 12 units/g FW at 24 h.a.i. in the most resistant cultivar (L-93), to 35 units/g FW at 48 h.a.i. The same cultivars were also sprayed with potassium oxalate (KOx), methyl jasmonate (MeJA), or acibenzolar S-methyl (ASM). Oxalate oxidase activity was induced by KOx and MeJA. We are investigating if treatment with KOx or MeJA induces resistance in bentgrass to S. homoeocarpa through increases of oxalate oxidase activity.
Common features between non-host and host resistance of bentgrass to Sclerotinia homoeocarpa. A. B. DA ROCHA, J. Klepaski, and R. Hammerschmidt. Dept. Plant Pathology, Michigan State University, East Lansing, MI 48824. Publication no. P-2004-0010-NCA.
Dollar spot, caused by Sclerotinia homoeocarpa, is one of the primary diseases of turfgrass in the USA. However, little is known about the mechanisms involved in resistance of bentgrass to dollar spot. The objective of this work was to study non-host interactions between bentgrass and Colletotrichum graminicola, Colletotrichum orbiculare, or Sclerotinia sclerotiorum, and compare it to a compatible interaction where cultivar L-93 shows resistance to S. homoeocarpa isolate VCG-B. Leaf blades of L-93 were inoculated with the cited fungi. The number of penetration sites and deposition of lignin and callose were examined with the microscope 48 hours post inoculation. C. graminicola was restricted at the surface of the leaf blades, but C. orbiculare was able to penetrate into the epidermis. Lignification was observed in response to C. orbiculare. Bentgrass also showed lignification and necrosis after S. sclerotiorum penetration. Lignification was also observed when L-93 was infected with S. homoeocarpa, indicating that lignin deposition may be a common feature in both non-host and host resistance.
Survival of mycelium of Phytophthora infestans after exposure to temperatures below 3°C. S. I. DZENGELESKI, W. W. Kirk, and R. Hammerschmidt. Dept. Plant Pathology, Michigan State University, East Lansing, MI 48824. Publication no. P-2004-0011-NCA.
Over the past decade in North America, there has been a decrease in A1, metalaxyl sensitive isolates of Phytophthora infestans, e.g. US1, in favor of A2, metalaxyl insensitive isolates, e.g. US8. The US-8 genotype also appears to be more cold tolerant and aggressive on potato plants than US-1 genotype. The objective of this study is to characterize the effect of cold temperatures on survival of mycelium from different genotypes of P. infestans in vitro and in vivo. Mycelium of P. infestans from Michigan and Mexico, grown on rye agar were exposed to temperatures from -5 to +3°C for periods of 1 to 5 days. After cold treatment, the cultures were maintained at 24°C for 27 days. Recovery was estimated using digital image analysis. Preliminary results indicate that cultures survive better when exposed to the warmer temperatures (+3 and 0°C) and for shorter durations (1 and 2 days). We will investigate the development of P. infestans on three varieties of whole tubers in storage at -3, 0, and +3°C.
Identification of sources of resistance to Sclerotinia sclerotiorum in common bean. M. ENDER (1), A. B. da Rocha (2), R. Hammerschmidt (2), and J. D. Kelly (1). (1) Dept. of Crop and Soil Sciences; (2) Dept. of Plant Pathology, Michigan State University, East Lansing, MI 48824. Publication no. P-2004-0012-NCA.
White mold, caused by S. sclerotiorum, is one of the most destructive diseases of common bean. A strategy to increase resistance of cultivated bean is to introgress resistance genes from related landraces and wild species. The response of five bean genotypes to S. sclerotiorum and the activity of defense-related enzymes was determined. Bean PI 318695 (wild) and PI 313850 (landrace) and varieties Tacana, Raven and Bunsi were inoculated with S. sclerotiorum. Disease severity and the activity of peroxidase, beta-1,3-glucanase and chitinase were evaluated at 48 hours post inoculation. PI 313850 was the most resistant, followed by PI 318695 and Tacana. PI 313850 also showed the highest peroxidase activity after infection, while Tacana had the highest glucanase activity. Chitinase activity was similar in all genotypes after inoculation. Crosses were made between Tacana and the two PI accessions and putative resistant progenies were identified in greenhouse tests.
Characterization and distribution of Phytophthora capsici from irrigation water near Michigan cucurbit fields. A first report of Phytophthora capsici in irrigation water in Michigan. A. J. GEVENS and M. K. Hausbeck. Dept. Plant Pathology, Michigan State University, East Lansing, MI 48824. Publication no. P-2004-0013-NCA.
Phytophthora capsici causes fruit rot of cucurbit and solanaceous crops in Michigan. Recently, growers have sustained economic losses as a result of this disease. Pear and cucumber baits were used at 5 locations to detect P. capsici in water used for irrigation. Locations included a well-fed pond, a naturally-fed pond, a stream, and 2 rivers. P. capsici was isolated weekly from 4 of the 5 locations from Aug. 7 until Sept. 27, 2002. Isolates of P. capsici from 3 of the 5 locations were characterized for compatibility type (CT) and tested for sensitivity to the fungicide mefenoxam. The ratio of CT of 30 isolates recovered from the stream was 1:1 for A1:A2. Nine isolates were fully insensitive (I), 16 were intermediately sensitive (IS) and 5 were sensitive (S) to mefenoxam. A river yielded 8 isolates with a 3:5 ratio of A1:A2 CT that were nearly equally divided among the I, IS, and S categories. Twenty-one isolates from a naturally-fed pond were in a 9:5 ratio of A1:A2 CT. Seven isolates did not mate with either A1 or A2 CT. Six isolates were IS and 15 were S.
Soybean green stem caused by selected strains of bean pod mottle virus. Y.-K. GOH (1), J. S. Russin (1), S. A. Ghabrial (2), J. P. Bond (1), and M. E. Schmidt (1). (1) Southern Illinois University, Carbondale, IL; (2) University of Kentucky, Lexington, KY. Publication no. P-2004-0014-NCA.
Bean pod mottle virus (BPMV) is widespread in southern Illinois soybean fields. A two-year survey showed that BPMV was present in >80% of soybean fields in this region. A relationship between BPMV and delayed maturity (i.e., green stem) is suspected but not proven. Strains collected from soybean differed in leaf symptom severity in greenhouse tests. In a screen house study, the soybean cultivar Essex(Rsv1) exhibited the green stem symptoms at harvest maturity and reduced seed quality when inoculated with severe (CB-B and Crawford) or intermediate (Ky G7 and CB-4) strains of BPMV, but only when inoculated at early growth stages (V2-V4). Yield was reduced only by severe strains inoculated at V2-V4. Mild strains (Ullin and Shelby) had no effects on soybean plants. Leaf symptom ratings correlated directly with green stem ratings. Greenhouse studies using severe strains of BPMV to screen for resistance to both foliar symptoms and green stem in selected soybean varieties are ongoing. The inheritance of these traits will be studied in segregating populations.
Inheritance of anthracnose resistance in cultivar Widusa. M. C. GONÇALVES-VIDIGAL* (1), V. Vallejo, and J. D. Kelly (2). (1) Maringá State University, PR, Brazil, 87020-900; (2) Dep. Crop & Soil Science, Michigan State University, 48823. Publication no. P-2004-0015-NCA.
The bean cultivar Widusa was crossed with Michigan Dark Red Kidney (MDRK), Cornell 49242, TO, BAT 93, TU, and PI 207262 and their F(1) and F(2) were evaluated with races 7, 65, and 73 of Colletotrichum lindemuthianum. F(1) and F(2) plants from cross Widusa x MDRK showed the 3:1 ratio of resistant to susceptible plants, when inoculated with race 7. This indicates that Widusa carries 1 dominant gene for resistance to race 7. Allelism tests in F(2) populations derived from crosses with Widusa and Cornell 49242, TO, TU, and BAT 93, showed segregation ratio of 15R:1S when plants were inoculated with races 7 or 73. In the cross Widusa x PI 207262, the F(2) segregated as 63R:1S, showing that 3 independent dominant genes confer resistance to race 73. According to these results, the anthracnose resistance gene in Widusa is independent of Co-2, Co-4, Co-4(^3), Co-5, and Co-9 genes. In cross Widusa and MDRK, no susceptible F(2) plants were found when inoculated with race 65, suggesting that Widusa carries an allele at the Co-1 locus. The authors propose that the anthracnose resistance allele in Widusa be named Co-1(^5).
*Financial from Capes.
An unknown Phytophthora species isolated from soybean in Illinois. E. GRUNDEN and D. K. Malvick. Department of Crop Sciences, University of Illinois at Urbana-Champaign, Urbana, IL 61801. Publication no. P-2004-0016-NCA.
Phytophthora rot is a significant disease of soybean caused primarily by Phytophthora sojae. While using cv. Sloan soybean to isolate P. sojae from Illinois soybean fields with a history of seedling disease in 22 counties, an unknown Phytophthora sp. was isolated at a frequency of 70% from two east-central counties. This unknown species grows five times faster on potato dextrose agar and 1.5 times faster on dilute V8 agar than P. sojae, and produces larger oogonia (48.6 micrometers diam.) than P. sojae (36.2 micrometers diam.). The unknown isolates kill soybean seedlings in standard greenhouse race tests using 12 differentials, but do not match the characteristics of any reported races of P. sojae. Sequences of the ITS region of nrDNA from three isolates of the unknown most closely match P. medicaginis and P. cryptogea. However, the diameter of oogonia, production of sporangia, and homothallism suggest the unknown is neither of these two species. Studies to characterize this unknown Phytophthora sp. and its potential to damage soybeans are in progress.
Using high-resolution satellite images to assess soybean yield losses caused by leaf blight in Argentina. J. GUAN (1), X. B. Yang (1), A. Ivancovich (2), and F. W. Nutter, Jr. (1). (1) Dept. Plant Pathology, Iowa State Univeristy, Ames, IA 50011; (2) INTA Pergamino, Argentina. Publication no. P-2004-0017-NCA.
Soybean leaf blight, caused by Cercospora kikuchii, is a major disease in northern Argentina. Field experiments were conducted at Itin (Province of Chaco, Argentina) to estimate yield losses caused by leaf blight and to quantify the relationships between satellite image intensity and soybean yield. Five fungicide treatments (a mixture of azoxystrobin and difenoconazole applied at different growth stages) were used to generate a range of disease intensity levels. Soybean yield and IKONOS satellite images (1 m resolution) for the different fungicide treatments were obtained. ArcGIS software was used to extract satellite image intensity from each corresponding soybean plot and linear regression was used to relate satellite image intensity to soybean yield. Yield losses caused by soybean leaf blight were 14.8% and satellite image intensity explained more than 85% of the variation in soybean yield. This research indicates that IKONOS satellite images have tremendous potential to estimate soybean yield losses over large areas.
Fungal pathogens causing tomato fruit rot and their control with chemical fungicides. L. J. GUTIERREZ. Dept. of Plant Pathology, Graduate Research Associate, The Ohio State University, Wooster, OH 44691. Publication no. P-2004-0018-NCA.
The fungal pathogens causing tomato fruit rot and the chemical control employed to control these agents were investigated to determine the range of these causal agents and the efficacy of the commonly used chemical fungicides. Over 100 fungi were isolated from tomato fruit exhibiting fruit rot symptoms. A sub-sample was characterized using 18S and ITS rDNA sequencing, which identified Colletotrichum, Fusarium, and Phomopsis in the collection. The wide range of fungi isolated from rotting tomato fruit indicates the potential for more organisms to cause tomato fruit rot than previously reported. The isolates were also tested in vitro for sensitivity to the commonly used fungicides, mancozeb, chlorothalonil, fixed copper, and azoxystrobin at three concentrations. Patterns indicate the potential for tolerance to azoxystrobin and fixed copper. Further investigation is necessary to determine the pathogenicity of the isolated fungi and the significance of fungicide sensitivity and tolerance in vitro and in situ.
Mating type and mefenoxam sensitivity of over wintering Phytophthora capsici. S. HILL (1), K. Lamour (2), and M. K. Hausbeck (1). (1) Dept. of Plant Pathology, Michigan State University, East Lansing, MI 48824; (2) Dept. of Entomology and Plant Pathology, University of Tennessee, Knoxville, TN 37996. Publication no. P-2004-0019-NCA.
Phytophthora capsici causes crown, root and fruit rot on squash, pepper and cucumber crops in Michigan. Insensitivity of P. capsici to the fungicide mefenoxam has been documented in commercial fields, but has not been studied in a controlled plot. Cucumbers were planted in a plot with no previous history of cucurbits or P. capsici at the Michigan State University Muck Soils Research Farm, Bath, Michigan. The plot was infested via overhead irrigation with P. capsici zoospores of compatible types (CT) A1 and A2 sensitive (S) and fully insensitive (I) to mefenoxam, respectively. Diseased fruit were observed seven weeks after inoculation and incorporated in the soil at the end of the growing season. The next spring, cucumbers were planted in the same plot and fruit became diseased naturally in August. Sixteen cucumbers with sporulating P. capsici were sampled and isolates were recovered. Six were A1 CT with five IS and one I to mefenoxam. The remaining ten isolates were A2 CT with one S, eight IS and one I to mefenoxam.
Induced resistance in potato to common scab. E. C. HOLLISTER (1), R. Hammerschmidt (1), D. S. Douches (2), and W. W. Kirk (1). (1) Dept. Plant Pathology; (2) Dept. Crop and Soil Sciences, Michigan State University, East Lansing, MI 48824. Publication no. P-2004-0020-NCA.
Common scab of potato, caused by Streptomyces scabies, is an important disease with a limited number of effective control measures, which include use of host resistance and maintaining adequate soil moisture. The successful control of other diseases with resistance activators suggests that this approach may be useful in controlling common scab. The objective of this study was to investigate the effects of two resistance activators (chitosan and harpin) and application timing on common scab incidence and severity. Field experiments were conducted using a common scab-susceptible cultivar to evaluate the effects of the resistance activators and different application methods on common scab development and PR protein production. In 2001, in-furrow and foliar treatments of harpin and chitosan had over 30 percent of harvested tubers in the disease free category. In 2002, chitosan in-furrow treatments had slightly more disease free tubers than the control. In 2003, another trial will be conducted to determine inter-annual variability for each elicitor and application method on scab incidence.
Spatial structuring of dollar spot epidemics. B. J. HORVATH and J. M. Vargas, Jr. Department of Plant Pathology, Michigan State University, E. Lansing, MI 48824. Publication no. P-2004-0021-NCA.
Dollar spot is a severe turfgrass pathogen caused by the pathogen Sclerotinia homoeocarpa F.T. Bennett. This fungus is not known to produce sexual or asexual spores, and therefore, its primary mode of transport is via infected grass clippings on equipment and humans. A basic understanding of the epidemiology of this pathogen is needed. The objective for this project was to quantify the spatial structure of dollar spot incidence and determine its temporal stability. The study area was established on a mixed sward of creeping bentgrass and annual bluegrass in E. Lansing, MI. Dollar spot foci were counted at 223 locations within the study area. Variograms of disease incidence were constructed for each date and showed clear spatial structuring at relatively small scales (~0-10 m). Closer examination of the variogram model parameters showed that the nugget and sill parameters were proportional to each other, and that the range parameter remained fairly constant within each season. Between 50 and 60 percent of the total population variance in each year was spatially structured. This indicates that the spatial structure of dollar spot remains relatively unchanged regardless of disease severity, suggesting that the factor primarily responsible for the spatial pattern is one that does not move about in space.
Dissection of nonhost resistance of Arabidopsis to Phytophthora infestans. E. HUITEMA, S. Dong, W. Hamada, and S. Kamoun. Dept. Plant Pathology, The Ohio State University-OARDC, Wooster, OH 44691 USA. Publication no. P-2004-0022-NCA.
Phytophthora infestans, a plant pathogenic oomycete, causes late blight on the Solanaceous plants potato and tomato. Control of late blight has proven difficult partly due to a lack of sustainable sources of genetic resistance. A number of plant species however, are fully resistant to all known strains of P. infestans (nonhosts), and could potentially reveal novel defense genes and pathways. We initiated a number of studies aimed at exploiting Arabidopsis nonhost resistance to Phytophthora and establishing a model system for understanding nonhost resistance to oomycete pathogens. Here, we provide an update on various aspects of this research. (1) Kinetic PCR technology was used to compare quantitative changes in P. infestans biomass during infection of wild-type and mutant Arabidopsis plants and to assess the impact of defense pathways in nonhost resistance of Arabidopsis. (2) DNA microarrays were used to profile changes in gene expression in Arabidopsis following inoculation with P. infestans. (3) P. infestans genes were evaluated for their ability to induce defense responses in Arabidopsis. This work is helping us to dissect the molecular basis of nonhost resistance of Arabidopsis to this economically important pathogen.
Evaluation of early maturing soybean cultivars for partial resistance to Phytophthora sojae. H. JIA and J. E. Kurle. Dept. of Plant Pathology, University of Minnesota, St. Paul, MN 55108. Publication no. P-2004-0023-NCA.
Phytophthora root and stem rot, caused by Phytophthora sojae, is among the most damaging diseases of soybean in the United States. Race specific resistance has been effective in limiting losses to P. sojae. However, new races with virulence for available sources of resistance have appeared with increasing frequency over the past 40 years. Use of cultivars possessing partial resistance is a promising alternative for limiting yield loss to P. sojae. Little information is available on the resistance or partial resistance characteristic of early Maturity Group (MG) Plant Introductions (PIs) in MGs 000, 00, 0, I. Our objective was to find early MG standard check cultivars that can be utilized in screening PIs for partial resistance. Using the inoculum layer method, we compared 24 cultivars in MGs 00-II and 4 standard check cultivars in MGs II and III for partial resistance to the combination of P. sojae races 7 and 25. Three of 24 early MG cultivars exhibited partial resistance equal to or greater than the check cultivar, Conrad (P > 0.05), and will be used in screening the early MG PIs.
Evaluation of an in vitro fungicide sensitivity assay for predicting fungicide efficacy against dollar spot in the field. Y. JO, A. L. Mikuszewski, J. W. Rimelspach, and M. J. Boehm. Dept. Plant Pathology, The Ohio State University, Columbus, OH 43210. Publication no. P-2004-0024-NCA.
Dollar spot is the most widespread and chronic disease of golf course turf in Ohio. Resistance in Sclerotinia homoeocarpa to benzimidazole, demethylase inhibitor and dicarboximide fungicides has been reported. A recent survey of dollar spot isolates from 42 golf courses in Ohio using an in vitro fungicide sensitivity assay revealed that 48% of the isolates were insensitive to thiophanate-methyl, 50% were moderately or strongly insensitive to propiconazole and 11% were moderately insensitive to iprodione. The goal of this work was to evaluate the in vitro assay used previously as a predictor of fungicide efficacy in the field. Two replicated field trials were conducted at various sites from which S. homoeocarpa had been previously collected and screened using the in vitro assay. Results from the first trial showed that the in vitro assay was a good predictor of thiophanate-methyl and iprodione efficacy in the field. The in vitro assay also worked well for predicting propiconazole efficacy for sensitive and strongly insensitive isolates but not for isolates with ED(50) values between 0.03 and 0.04 ug/ml a.i. Results from the second field study, conducted at 16 locations with various in vitro fungicide sensitivity profiles between April and June 2003, will be presented.
Plant population and row spacing affects Sclerotinia stem rot severity in soybean. J. KURLE (1) and S. Naeve (2). (1) Dept. of Plant Pathology, 495 Borlaug Hall, St. Paul, MN 55108; (2) Dept of Agronomy and Plant Genetics, 411 Borlaug Hall, St. Paul, MN 55108. Publication no. P-2004-0025-NCA.
Sclerotinia stem rot (SSR) of soybean, caused by Sclerotinia sclerotiorum, has become an important disease of soybean in the north central United States. The increased occurrence of SSR is associated with crop management practice changes that promote rapid formation of a dense crop canopy. Among these changes are narrowed row spacings and increased plant populations. A field study planted at multiple locations in Minnesota from 1999 through 2002 examined the effect of row spacing, plant population, and soybean variety on SSR severity. The study relied on natural inoculum present at each location. Measurable SSR occurred only in 1999 and 2002 at five locations and ranged from 4 to 21%. Plant population (PP) affected disease severity significantly at four locations (P < 0.11), row spacing (RS) at two locations (P < 0.14), and the interaction of RS x PP at one location (P = 0.11). Disease severity tended to increase either as RS decreased or as PP increased; however, the relative effect of both factors differed among varieties and locations.
Analysis of the role of candidate genes in inoculum development of Fusarium graminearum. Y. LETOURNEAU, L. Velasquez, and F. Trail. Department of Plant Biology, Michigan State University, East Lansing, MI 48824. Publication no. P-2004-0026-NCA.
The Fusarium graminearum (Gibberella zeae) genome sequence has been recently released. The combination of this valuable information with gene prediction software has provided theoretical coding sequences that can be targeted for disruption. Genes with a possible role in perithecium formation and ascospore dispersal have been targeted for disruption. The effect of disruption of trehalose-6-phosphate synthase will be presented. In Magnaporta grisea the disruption of this gene has considerably reduced sporulation and has affected the generation of turgor pressure in appressoria. In addition, several putative light-dependent genes have been disrupted. The effect of these gene disruptions on spore discharge and perithecium formation in F. graminearum will be presented.
Analysis of expressed sequence tags of Fusarium solani f. sp. glycines during infection of soybean. S. LI (1), A. G. Hernandez (2), L. Liu (2), G. L. Hartman (1,3), L. L. Domier (1,3), and P. A. Schweitzer (2). (1) Univ. of Illinois, Dept. of Crop Sciences, Urbana, IL 61801; (2) Univ. of Illinois, W.M. Keck Center; (3) USDA-ARS, Urbana, IL 61801. Publication no. P-2004-0027-NCA.
Fusarium solani f. sp. glycines (Fsg) causes soybean sudden death syndrome (SDS). To identify soybean and Fsg genes preferentially expressed during infection, a normalized directionally-cloned cDNA library was constructed from cultured Fsg and Fsg-infected soybean roots. Fsg and Fsg-infected soybean mRNAs were differentially tagged at the 3(prime)-end for sequence identification. The normalized cDNA library was then subtracted with the cDNA prepared from non-inoculated healthy soybean roots. Initially, 178 cDNA clones were sequenced. Of these, 89 sequences were from cultured Fsg and 78 were from Fsg-infected soybean roots. Ninety-seven (55%) of the expressed sequence tags (EST) significantly matched entries in the National Center for Biotechnology Information non-redundant protein database, 53 were similar to previously identified plant genes, 42 to fungal genes, and two to animal and bacterial genes. Additional EST analysis will provide information on Fsg gene expression during the infection of soybean roots.
Study of regional-scale seasonal distribution pattern of wheat powdery mildew in China with geostatistics. X. LI (1), X. B. Yang (1), J. Y. Tang (2), and W. C. Liu (2). (1) Dept. of Plant Pathology, Iowa State University, Ames, IA 50011; (2) Ministry of Agriculture, Beijing 100026, China. Publication no. P-2004-0028-NCA.
We studied the regional-scale seasonal distribution patterns of wheat powdery mildew (Erysiphe graminis f. sp. tritici) in China. Two disease data sets for 1980-1993 and 1997-1998 were analyzed with geostatistics to detect autocorrelation among widely dispersed locations. Based on autocorrelation results, ordinary Kriging was used to interpolate and map the disease distributions over monitored areas. No autocorrelation was detected in 1980-1993, perhaps due to the small number of sampling points collected over a large area or due to the low level of epidemics. In 1997-1998, disease incidence and prevalence had significant autocorrelation within the range of 220 to 550 km. The autocorrelation suggests that possible regional-scale factors, especially climate variables, affected the spread and progress of the disease these years.
Occurrence and races of Aphanomyces euteiches in Illinois alfalfa fields. D. MALVICK, M. Montez-Ellis, and A. T. Dyer. Department of Crop Sciences, University of Illinois, Urbana, IL 61801. Publication no. P-2004-0029-NCA.
Alfalfa is the fourth largest crop in Illinois based on land in production. Among the factors that may cause poor stand establishment is Aphanomyces root rot caused by Aphanomyces euteiches. Two races of A. euteiches (R1 and R2) kill alfalfa seedlings and cause decline of mature plants in slowly-drained soils. The objectives of this study were to determine the distribution and relative frequency of both races of A. euteiches in Illinois alfalfa fields. Soil samples (n = 103) were collected from 35 alfalfa fields in 19 counties concentrated in the primary alfalfa production areas of Illinois. Aphanomyces euteiches (311 isolates) was isolated from 85% of the samples, including all counties, using cultivar Saranac as a baiting host. Race phenotype of 140 isolates was characterized on cv. Saranac. (susceptible to R1 and R2) and cv. WAPH-1 (resistant to R1 and susceptible to R2). Approximately 60% of the isolates were R1 and 40% were R2. Both races were isolated from 67% of the counties, whereas only R1 or R2 was isolated from 17% of the counties. Aphanomyces euteiches is a common pathogen and may be best managed in Illinois with cultivars having resistance to both R1 and R2.
Development of a less complex medium for production of Sporidesmium sclerotivorum. F. M. MATHEW and L. E. del Río. Dept. Plant Pathology, North Dakota State University, Fargo, ND 58105. Publication no. P-2004-0030-NCA.
Sporidesmium sclerotivorum, (SS) is a parasite of the sclerotia of Sclerotinia sclerotiorum. SS has been identified as a biocontrol agent with potential for commercialization; however, establishing an efficient system to mass-produce the inoculum has proved difficult. SS grows slowly on SM-4, a complex medium made of glucose, nitrogen sources, salts and vitamins and buffered at pH 5.3. A common microbiological medium based on peptone, yeast extract and glucose (PYG) buffered at pH 5.9 supported faster growth. The addition of Fe(^2+) to PYG to stimulate sporulation is currently under study. Nitrogen sources such as Casamino acids, L-Glutamine, and aspartic acid used either alone, or in combination, with glucose and peptone, did not improve growth of SS.
Effect of date of planting on the incidence of Stewart’s disease of corn in Iowa. B. MENELAS and F. W. Nutter, Jr. Dept. Plant Pathology, Iowa State University, Ames, IA 50011. Publication no. P-2004-0031-NCA.
Altering the date of planting to avoid exposure to pathogen populations is one potential disease management alternative that might be used to improve the management of Stewart’s disease of corn. To determine the effect of planting date on the incidence of Stewart’s disease in Iowa, the susceptible sweet corn variety Jubilee was planted on 5 sequential weekly planting dates at Boone, IA in 2001 and Crawfordsville, IA in 2002. In 2001, final disease incidence on 15 Aug ranged from 0 (last planting) to 3.7% (first planting). In 2002, final disease incidence on 2 Aug ranged from 26.7 (last planting) to 48.7% (first planting). The logistic model best described the change in disease incidence with respect to time. Coefficients of determination (R(^2)) ranged from 0.61 in 2001 to 0.98 in 2002. In 2002, there was a significant negative linear relationship between date of planting and incidence of Stewart’s disease on both the first disease assessment (6 June: Y = 43.59 - 0.2646(X), R(^2) = 0.81) and the last assessment (2 Aug: Y = 116.98 - 0.6386(X), R(^2) = 0.65). This information indicates that delaying planting may help to reduce the incidence of Stewart’s disease in sweet corn.
Quantifying the acquisition and transmission feeding periods of the corn flea beetle in the Stewart’s disease of corn pathosystem. B. MENELAS and F. W. Nutter, Jr. Dept. Plant Pathology, Iowa State University, Ames, IA 50011. Publication no. P-2004-0032-NCA.
Effective management of Stewart’s disease, caused by Pantoea stewartii, depends on understanding pathogen-vector interactions. The purpose of this study was to quantify the probability of P. stewartii acquisition and transmission by corn flea beetles (CFB) Chaetocnema pulicaria as a function of time. Under greenhouse conditions, CFBs were allowed to feed 6, 12, 24, 36, 48, and 72 hr on corn seedlings previously inoculated with a rifampicin-resistant strain of P. stewartii to determine acquisition time. To determine transmission time, CFBs infested with P. stewartii were allowed to feed on healthy corn seedlings for periods of 3, 6, 12, 24, 36, 48, and 72 hr. Acquisition of P. stewartii by CFBs (rifampicin-amended media) occurred within 6 hr and the mean time for acquisition by 50% of CFBs was 38.3 ± 10.1 hr. The minimum time required for CFBs to transmit P. stewartii was 3 hr and the mean time for transmission by 50% of CFBs was 28.3 ± 5.4 hr. This is the first study to quantify pathogen acquisition / transmission dynamics in this pathosystem.
Effect of host plant resistance and managed fungicide applications on late blight development in potatoes. J. B. MUHINYUZA (1), W. W. Kirk (1), R. Hammerschmidt (1), and D. Douches (2). (1) Dept. Plant Pathology, Michigan State University, East Lansing, MI 48824; (2) Dept. Crop and Soil Sciences, Michigan State University, East Lansing, MI 48824. Publication no. P-2004-0033-NCA.
The appearance of new strains of P. infestans resistant to Phenylamides has increased continued research to find new compounds for control of potato late blight. Fluazinam, a protectant fungicide with residual activity is active in relatively small doses to inhibit spore germination and infection. When applied on potato foliage in combination with cultivar resistance, fluazinam is able to control late blight at reduced rate and increased spray intervals. Four rates 33, 50, 66 and 100% of fluazinam were applied on 5, 7, 10 and 15-day application intervals in 2001 and 2002 and examined for foliar late blight control. The results of this study showed that reduced amounts of fluazinam were either partially or fully effective at all application rates tested on all cultivars compared to the non-treated controls at P = 0.05. On susceptible cultivars, applications of fluazinam at 10 or 15-day intervals were partially effective for controlling foliar late blight at the doses tested. All cultivars treated at full and half rates of fluazinam effectively protected foliage against late blight on a 5-day spray interval and was partially effective at all other rates and application intervals. Application of fluazinam at reduced rate and frequencies could successfully be used in a control program using host resistance.
Comparison of aggressiveness and growth rate among different races of Phytophthora sojae. X. F. NIU and X. B. Yang. Dept. Plant Pathology, Iowa State University, Ames, IA 50011. Publication no. P-2004-0034-NCA.
Studies were conducted to determine fitness parameters of races of Phytophthora sojae isolated from Iowa soybean fields. Single-zoospore isolates of four races were cultured on V8 agar at 25°C, and colony diameter was measured daily for 5 days. After 6 days, eight 1-cm(^2) plugs from each colony were cultured using salt washing method for zoospore production and quantification. Infection aggressiveness was determined by inoculating soybean leaves (Cultivar Sloan, universal susceptible) with zoospore suspensions with series of concentration, then quantifying lesion development after 6, 10, 15, and 30 hour of incubation in a moist chamber. Significant differences among races were observed for colony diameter, zoospore production, and infection aggressiveness. Further research is needed to determine whether these differences are associated with observed changes in prevalence of these races in Iowa soybean fields since 1994.
Two undescribed species in the Ceratocystis fimbriata complex on Ficus and Colocasia from Asia and Polynesia. A. PASURA and T. C. Harrington. Dept. of Plant Pathology, Iowa State University, Ames, IA 50011. Publication no. P-2004-0035-NCA.
Ceratocystis fimbriata causes economically important diseases on a broad range of crops worldwide, especially in the Americas. We examined isolates and herbarium specimens from fig (Ficus caricae) in Japan and taro (Colocasia esculenta) in China and Polynesia. Phylogenetic analyses of ITS and MAT-2 DNA sequences showed the taro and fig isolates and specimens to be closely related but distinct from each other and from isolates of the North American and Latin American clades of C. fimbriata. Morphological study showed that fig isolates produced larger perithecial bases and longer perithecial necks than did taro isolates and specimens, and both differed from isolates of the American clades. Mating experiments demonstrated that taro isolates are interfertile with each other but not with fig isolates. Fig and taro isolates showed host specialization to their respective hosts in an inoculation experiment in a growth chamber. These results support the hypothesis that fig and taro isolates from Asia and Polynesia represent two undescribed species in the C. fimbriata complex.
Petiole inoculation (PI) to characterize the reaction of soybean germplasm to Sclerotinia sclerotiorum (Ss) in a field environment. A. J. PELTIER, N. C. Kurtzweil, and C. R. Grau. Dept. Plant Pathology, University of Wisconsin, Madison, WI 53706. Publication no. P-2004-0036-NCA.
Field screens of soybean germplasm for physiological resistance to Ss are complicated by many factors. Microclimates unfavorable for infection, uneven inoculum distribution and the inability to separate ‘escape phenomenon’ from physiological resistance all contribute to the unreliability of natural field screens. A PI was used to evaluate 19 soybean lines for physiological resistance. Interaction phenotypes were characterized using area under wilt progress curves (AUWPC). Three experiments were performed. One field experiment was planted in May and another in August, the third was conducted in the Biotron, a controlled-environment facility. Low coefficients of variation as well as the wide AUPWC separation of susceptible (BSR-101) and resistant (NK S19-90) checks afforded confidence in the August and Biotron experiment results. A Spearman’s rank correlation (corrected for ties) showed that AUWPC ranks were significantly correlated (P < 0.001) for August and Biotron experiments. The PI may help to quantify the role of physiological resistance to Ss in soybean.
Identification of genes expressed during hyphal differentiation in the head scab fungus, Fusarium graminearum. W. QI (1), C. Kwon (1), and F. Trail (1,2). (1) Department of Plant Biology, Michigan State University, East Lansing, MI 48824; (2) Department of Plant Pathology, Michigan State University, East Lansing, MI 48824. Publication no. P-2004-0037-NCA.
Fusarium graminearum is the causal agent of head blight and rot diseases of many crop plants. Inoculum production is an important step in the disease cycle. A functional genomics approach was adopted to identify genes that are important to inoculum development in F. graminearum. A unigene cDNA microarray representing ~2000 genes was produced from cDNA libraries of maturing perithecia, carbon-starved mycelia, and nitrogen starved mycelia. A dye-swap experiment was performed to compare the expression profiles in mature non-differentiated hyphae and hyphae induced to form perithecia. Statistic data analysis was done using R. The differential gene expression and a validation of the quality and reproducibility of the array will be presented.
Effect of temperature on the reaction of soybean to Tobacco streak virus. P. F. RABEDEAUX and C. R. Grau. Dept. of Plant Pathology, University of Wisconsin-Madison, Madison, WI 53706. Publication no. P-2004-0038-NCA.
Tobacco streak virus (TSV) is one of four viruses currently threatening soybean production in the North Central region of the United States. Host resistance to TSV is a desirable control strategy to reduce disease potential, but complete resistance to TSV has not been identified in soybean. Previous studies suggest that different soybean lines react differently to TSV and that temperature plays a major role in symptom development. The goal of this study was to quantify the effect of temperature on the TSV-soybean system. After inoculation of six soybean lines with TSV isolate C, plants were incubated at one of three temperatures: 18°C, 24°C and 30°C for 14-16 days. Significant differences were observed in area under the disease progress curve (AUDPC) across temperatures (P = 0.0008) and among soybean lines (P < 0.0001). Northrup King Brand S19-90 had the lowest AUDPC at 18°C and 24°C, while Colfax had the highest AUDPC at all three temperatures. Significant temperature by soybean line interactions were also observed, suggesting that evaluating soybean germplasm for resistance to TSV requires strict control of air temperature.
Carrot susceptibility to Alternaria and Cercospora foliar blights - An important component in disease management programs for growers. P. M. ROGERS and W. R. Stevenson. Dept. of Plant Pathology, University of Wisconsin, Madison, WI 53706. Publication no. P-2004-0039-NCA.
Carrot foliar blights caused by Alternaria dauci and Cercospora carotae lead to significant and recurrent yield reductions wherever carrots are grown. A 2001 survey of carrot producers in Wisconsin emphasized grower reliance upon repeated fungicide applications to manage foliar disease outbreaks and maintain yields. Field trials evaluating disease resistance among 40 cultivars and breeding lines were conducted in Wisconsin at 2 locations in 2001 and 2002. Disease severity was rated weekly on each plot entry using a 0-11 Horsfall-Barratt scale. Entries were observed in susceptible, tolerant and resistant categories. While significant differences were observed in disease response among plot entries, more than 60 percent were susceptible to both pathogens. Among materials evaluated, Bolero, Carson and Sirocco represented enhanced levels of disease resistance, while Fontana, Gold King and Lucky B were susceptible. Field resistance to foliar diseases will benefit carrot producers by minimizing chemical applications and grower costs, while maintaining equivalent carrot yield and quality.
Tracking changes in sensitivity of Alternaria solani to azoxystrobin in WI. N. ROSENZWEIG and W. R. Stevenson. Dept. of Plant Pathology, Univ. of Wisconsin, Madison, WI 53706. Publication no. P-2004-0040-NCA.
A new fungicide chemistry, azoxystrobin (AZ) (Quadris) entered the U.S. marketplace in 1999 and provided outstanding control of potato early blight. Initially in 1997, disease progress curves (DPC) for field plot treatments with AZ resembled flat lines. Now that growers have used Quadris for the past four and in some cases, five years, the level of early blight control appears to be declining. Over the past four growing seasons (1999-2002) the DPC’s in field trials treated with AZ (3 sprays)/chlorothalonil (CH) (6 sprays) were progressively similar to the S-shaped curves seen with programs using only CH. During 2002, fungicide programs totaling 10 sprays tested alternations of AZ (1-6 sprays) and CH (4-9 sprays). Variability of isolate in-vitro sensitivity to AZ (ED(50)) was lowest in plots treated with alternating AZ (3 sprays) and CH (5 sprays) (P = 0.05), but provided similar efficacy and S-shaped DPC’s to other tested alternations.
Effect of temperature and photoperiod on phenolic deposition in potato cvs. susceptible and resistant to Phytophthora infestans. O. A. Rubio (1,2), W. Kirk (2), D. Douches (3), R. Hammerschmidt (2), and A. da Rocha (2). (1) INIFAP Mexico; (2) Dept. Plant Pathology; (3) Dept. Crop and Soil, Michigan State University, East Lansing, MI 48824. Publication no. P-2004-0041-NCA.
Phenolic compounds (PC) that accumulate in cell walls of potato leaves infected by Phytophthora infestans (Pi) may contribute to resistance. PC deposition was measured before and after inoculation with Pi in 5 cvs. with different resistance levels. Plants were grown in chambers at 16 and 24ºC and 12/12 and 16/8 h photoperiod. Concentration of PC in cells on the leaf surface prior to inoculation was analyzed under UV light. Two days after inoculation with Pi, leaf discs were collected and lesion number recorded. PC deposition was classified by its location in the cells. PC concentration was highest at 16ºC and 16/8 h. Concentration of PC was different among the 5 cvs., but there was no correlation with disease resistance. All cultivars showed four different types of phenolics deposition. Concentration of PC in leaf surface cells prior to inoculation and deposition of PC in the infected cells are resistance components that do not fully explain resistance to Pi in potato leaves.
Disease control improves winter survival of summer red raspberry plants. A. M. C. SCHILDER, J. M. Gillett, and R. W. Sysak. Department of Plant Pathology, Michigan State University, East Lansing, MI 48824. Publication no. P-2004-0042-NCA.
In 2002 and 2003, beneficial effects of fungicide programs were observed on winter survival of ‘Tulameen’ summer red raspberries in a small plot trial in a commercial planting in South Lyon, MI. In 2001 and 2002, fungicides were applied with a CO(2) sprayer to 3-m sections of row and were replicated four times. Five sprays were applied at 7- to 13-day intervals from pre-bloom until harvest in both years. Several fungicides were tested in 2001: Captan (captan) + Benlate (benomyl), Abound (azoxystrobin), Nova (myclobutanil), and Pristine (pyraclostrobin + boscalid). In 2002, programs included Captan alternated with Nova or Abound, and compost tea. Untreated plots served as the control. Plots were visually assessed for foliar and cane diseases after harvest. Survival of fruiting canes was evaluated in the spring of 2002 and 2003. Leaf spot, cane anthracnose, and spur blight/cane blight were significantly reduced by all treatments. Significantly greater numbers of canes survived the winter in treated plots compared to the control. Programs containing Abound, Pristine and Nova were most effective.
Characterization of Ophiomyia simplex L. activity in commercial asparagus fields and its association with Fusarium crown and root rot. J. K. TUELL (1), M. K. Hausbeck (1), and B. Bishop (2). (1) Dept. of Plant Pathology; (2) Dept. of Entomology, Michigan State University, East Lansing, MI 48824. Publication no. P-2004-0043-NCA.
Fusarium oxysporum f. sp. asparagi and F. proliferatum have been implicated in asparagus decline, and pathogenic strains have been associated with O. simplex in MA. Commercial fields were monitored in 2001, 2002 for miner activity via weekly trapping of adults, stem damage, and puparia counts. Puparia and mined tissue were cultured. A bivoltine trend was seen in all fields with the highest numbers of adults trapped in early to mid-Aug. Mining damage was greatest in 1-year-old fields in early season with Fusarium sporulating on up to 30% of mined stems. There was no difference in the number of puparia collected per stem, but more adults had emerged during the growing season in 1-year-old fields, while in older fields more puparia were intact for overwintering. Pupae from mines had 15% F. proliferatum and 3% F. oxysporum (above ground); 11% and 17% (below ground); and stem tissue had 44% and 4% (above ground). Sporulation of Fusarium on mines may boost inoculum spread and young fields may have prolonged exposure to infection due to mining damage.
Sources of resistance to anthracnose in common bean Phaseolus vulgaris L. from Parana, Brazil. P. S. VIDIGAL-FILHO* (1), M. C. Gonçalves-Vidigal* (1), J. D. Kelly (2), and W. W. Kirk (3). (1) Maringá State University, PR, Brazil, 87020-900; (2,3) Dept. of Crop & Soil Science and Plant Pathology, Michigan State University, EL, 48823. Publication no. P-2004-0044-NCA.
Twenty-six cultivars of common bean from Paraná State, Brazil, were evaluated with Andean (7, 19, and 55) and Mesoamerican (9, 31, 65, 69, 73, 81, 89 95, and 453) races of Colletotrichum lindemuthianum. Seedlings from each cultivar were spray-inoculated with a suspension of 1.2 × 10(^6) conidia mL(^–1), in growth chamber and greenhouse experiments. Eight days after inoculation the plants were evaluated using a 1 to 9 scale. The resistance index ranged from 8 to 92%. Most of the cultivars (92%) were resistant to race 31. In addition, 60% of the cultivars showed resistance to races 9, 19, 55, 81, and 453, and 40% exhibited resistance to races 69, 73, 89, and 95. The most resistant cultivars were Carioca Pintado 2, Carioca Pintado 1 and Jalo Vermelho, and the most susceptible cultivars were Bolinha and Jalo Pardo which showed resistance only to race 31. These results indicate that the common bean cultivars evaluated have genes that could be useful in breeding programs for resistance to C. lindemuthianum.
*Financial from Capes.
Soybean root necrosis in response to infestation levels of Fusarium solani f. sp. glycines. L. J. XING (1), J. B. Santini (2), and A. Westphal (1). (1) Dept. Botany & Plant Pathology; (2) Dept. Agronomy, Purdue University, West Lafayette, IN 47907. Publication no. P-2004-0045-NCA.
Sudden death syndrome of soybean (SDS) is a severe soil-borne problem in the Midwest. To identify pot assay conditions for screening biological or chemical control agents, soybean (cv. Williams 82) was grown in 120-ml plastic cones containing inoculum of Fusarium solani f. sp. glycines (S. Abney’s Francesville, IN isolate). In a 3-factor factorial experiment, five levels of infestation were established by adding sand-cornmeal media (SC) (at 5.8 × 10(^4) to 7.3 × 10(^6) macrospores/ml of soil) to autoclaved sand-soil mix (SS) (2:1). A 1:1 mix of SC and SS, and a non-amended SS were controls. Factors were: (A) infestation level, (B) watered from the bottom or from the top, and (C) transplanted 10-day-old seedlings, or direct-seeded. The experiments were arranged in randomized complete block design with 4 replications and conducted twice, at 25°C, 16-8-h day-night in a greenhouse or in a growth chamber. After 8 weeks, root necrosis was estimated visually on a scale of 0 to 100%. Root necrosis was always greater in infested soil than in the controls. Roots were more necrotic as inoculum levels increased (11,700 × 5(^I), I = 1 to 4); the stronger increase of root necrosis (RN) was in the top-watered greenhouse experiments (RN = 0.02 + 0.26 I). Greenhouse tests at low inoculum densities will be useful for testing disease-suppressing agents.
Genome plasticity in natural Erwinia carotovora subsp. carotovora isolates. M.-N. YAP and A. O. Charkowski. Dept. of Plant Pathology, Univ. Wisconsin, Madison, WI 53706. Publication no. P-2004-0046-NCA.
Genomic diversity of 62 Erwinia carotovora subsp. carotovora (Ecc) potato isolates representing at least 39 serotypes was assessed by pulsed-field gel electrophoresis analysis of I-CeuI-RFLP, which targets bacterial rRNA operons. Seven I-CeuI fragments and at least ten pulsotypes were identified with significant polymorphism in fragment sizes ranging from 200 kb to 400 kb. Homologous housekeeping genes flanking the enterobacterial rRNA operons and known Ecc virulence genes were mapped onto the I-CeuI fragments, allowing for comparison of physical maps to other enterobacterial pathogens. Intraspecies variation was also revealed by biological tests and allelic polymorphisms in two housekeeping genes, mdh and acnA. Among several less virulent Ecc strains, one failed to elicit HR in tobacco and was found to be absence in hrp genes. Overall, less virulent strains had unique chromosomal structures resulting from genomic rearrangement and deletion. These data indicate a particular pulsotype is possibly correlated with pathogenicity.
Incidence of Bean pod mottle virus and Alfalfa mosaic virus in Nebraska soybean fields. A. D. Ziems and L. J. Giesler. Dept. of Plant Pathology, University of Nebraska, Lincoln, NE 68583-0772. Publication no. P-2004-0047-NCA.
Soybean is produced on 4.7 million acres in Nebraska. Soybean viruses are an important production issue because they affect seed quality and yield. Bean pod mottle virus (BPMV) and Alfalfa mosaic virus (AMV) are known to occur in Nebraska, but incidence levels have not been reported. Surveys for BPMV and AMV were conducted in 2001 and 2002 with cooperation of the Nebraska Agricultural Statistical Services. In 2001, 94 fields representing 46 counties and, in 2002, 87 fields representing 49 counties were selected randomly. Twenty trifoliate leaves were randomly collected from each field. To determine virus incidence, each leaf was tested with ELISA. In both years, BPMV was the most prevalent with 51% of the fields testing positive in 2001 and 87% in 2002. AMV was detected in 40% and 26% of the fields in 2001 and 2002 respectfully. Within-field incidence ranged from 0-100% for BPMV and AMV. Both viruses were distributed throughout the soybean-producing region of Nebraska, but there was a county distribution difference between 2001 and 2002. As both AMV and BPMV are apparently common in Nebraska, there is a need to assess yield impact on soybean production.