2000 Potomac Division Meeting Abstracts
March 22-24, 2000 - Newark, Deleware

Posted online April 19, 2000

Etiology and epidemiology of Trichoderma green mold in association with the cultivated mushroom, Agaricus bisporus. M.G. ANDERSON, D. M. Beyer, and P. J. Wuest. The Pennsylvania State University, 210 Buckhout Lab, University Park, PA 16802. Publication no. P-2000-0001-PTA.

Hybrid white, hybrid off-white, and brown strains of Agaricus bisporus were compared for resistance to green mold caused by Trichoderma harzianum biotype 4 (Th4). Seven spawn strains were assessed for total weight of mushrooms (g) with or without the addition of a 1 × 10(^7) spore suspension Th4 added at spawning. The study was conducted in a series of seven bag crops at the Mushroom Research Center (Pennsylvania State University) to reproduce commercial growing conditions. Significant differences were detected among hybrid mushroom strains in response to Th4 infestation. The hybrid white strain was the most susceptible to green mold, sustaining a mean yield loss of 96%. Hybrid off-white strains exhibited intermediate susceptibility with yield losses of 56-73%. Brown strains were highly resistant to green mold, with yield losses of 8-14%. Excessive spawn handling did not have a significant impact on development of green mold. From these findings we propose a continuum of spawn strain resistance, and suggest the use of brown strains to manage green mold outbreaks, particularly where benomyl resistance is a threat.

Characterization of cDNA clones differentially expressed in soybean severe stunt virus-infected soybean. M. D. V. R. BASNAYAKE (1), J. Burnside (2) and T. A. Evans (1). (1) Department of Plant and Soil Sciences, (2) Department of Animal and Food Sciences, University of Delaware, Newark, DE 19717. Publication no. P-2000-0002-PTA.

Soybean severe stunt is a soilborne disease caused by the soybean severe stunt virus (SSSV) affecting soybeans (Glycine max L.) in Delaware. Affected plants are severely stunted and necrotic. The goal of this research was to analyze changes in gene expression in soybean leaf cells during virus infection and to generate an expressed sequence catalogue. A cDNA library was developed from total poly (A) RNA from SSSV-infected soybean leaf tissue and analyzed by differential hybridization. High-density DNA array technology was utilized to monitor patterns of gene expression during the early stages of SSSV infection in the susceptible soybean cultivar, Essex. One hundred and fifty one sequences showed significant database matches while 94 had no matches. Thiol protease and photosystem I P700 chlorophyll A protein sequence expression was up regulated in infection and geranylgeranyl hydrogenase, and a water stress induced tonoplast intrinsic protein were down regulated.

Teliospore escape-proof containers for karnal bunt field studies. M. R. BONDE (1), S. E. Nester (1), G. L. Peterson (1), and M. Babadoost (2). (1) USDA-ARS, FDWSRU, Fort Detrick, MD 21702, and (2) Dept. Crop Sciences, Univ. Ill. Urbana, IL 61801. Publication no. P-2000-0003-PTA.

To study environmental effects on Tilletia indica survival, escape-proof containers were developed as a modification of Babadoost & Mathre (Phytopath. 89:S4) that allow teliospores to be buried in field plots without danger of escape. The 2-ft. long containers are constructed from 2-in. diam. PVC pipe with a series of screens at the ends to allow soil within the containers to contact the outside environment. Moisture can move through the soil within the pipes, entering at the top and exiting at the bottom. Stainless steel 20-um pore size screens at each end prevent possibility of teliospore escape, coarser screens entry of insects, and PVC grates protect against breakage. As another precaution, all infested soil is contained in sealed bags (20-um pore size) within a column of non-infested soil. The containers are constructed in two section. Plugs at each end covering the outside of the screens allow the pipes to be loaded with the pathogen and soil within a BL-3 containment laboratory. Pipes are then sealed and thoroughly washed before placement in the field.

Determination of the race profile of Phytophthora phaseoli, causal agent of lima bean downy mildew, on Delmarva. C. R. DAVIDSON, R. B. Carroll, M. Sedegui, and T. A. Evans. Department of Plant and Soil Sciences, University of Delaware, Newark, DE 19717-1303. Publication no. P-2000-0004-PTA.

With the development of a new race of P. phaseoli and a lack of resistant cultivars, epiphytotics could lead to devastation of Delmarva’s lima bean industry. Rapid and accurate identification of new races is essential for effective disease control. A new race of P. phaseoli was implicated in recent disease outbreaks on previously resistant cultivars. To confirm this, isolates of the pathogen were collected from infected plants in the region. Race identification was determined by inoculating cultivar differentials with selected isolates and by allozyme analysis for the glucose-6-phosphate isomerase (Gpi) and peptidase (Pep) alleles. Some of the isolates were different than race D according to cultivar differentials. Single spore isolates of races C, D and E were tested on cultivar differentials to insure pure race cultures. Results showed that both races D and E were pure while race C was not. Differences between the single spore isolates were visualized by allozyme analysis. Using Gpi and Pep overlays of allozyme analysis, gels exhibited no difference in banding patterns between the races. The use of cultivar differentials proves that a new race, designated as E, of P. phaseoli now exists in the Delmarva region but further studies using DNA fingerprinting are required to determine the genetic differences between the races.

Fungicide evaluation for control of downy mildew of baby lima bean. JENNIFER D. DOMINIAK, R. P. Mulrooney, and T. A. Evans. Department of Plant and Soil Sciences, University of Delaware, Newark, DE 19717-1303. Publication no. P-2000-0005-PTA.

Fungicides were evaluated for efficacy to control downy mildew of baby lima bean caused by Phytophthora phaseoli Thaxter. The test was performed near Georgetown, DE and design was a randomized complete block with four replications. Four fungicide applications were made beginning at flower initiation, and plots were harvested Oct. 4-5, 1999. ‘Early Thorogreen’ baby lima bean were inoculated twice with a sporangial suspension of race E and plants were fogged nightly. Disease severity was high in all treatments except mefanoxam plus 60% copper hydroxide (CH) which had only 9.5% plants infected. In all other treatments, the percentage of infected plants was greater than 50%. Treatments that yielded well include azoxystrobin at 0.67 L/ha alternated weekly with 53.8% CH at 2.24 kg/ha, 53.8% CH at 1.12 and 2.24 kg/ha, zoxamide at 0.28 kg/ha, and mefanoxam plus 60% CH at 2.24 kg/ha. Phytotoxicity was correlated with products containing copper, but did not appear to affect yield with some treatments. Chlorothalonil at 2.02 kg/ha was evaluated post-infection, but yield was not statistically different from the control. Azoxystrobin at 1.13 L/ha and 53.8% CH at 2.24 kg/ha were also tested post-infection and were ineffective at reducing infection.

The search for resistance to race E of Phytophthora phaseoli, the causal agent of downy mildew of lima bean. T. A. EVANS and D. P. Whittington. Dept. of Plant and Soil Sciences, University of Delaware, Newark DE 19717. Publication no. P-2000-0006-PTA.

Lima bean (Phaseolus lunatus) is the cornerstone of the vegetable processing industry on Delamarva with 10,000-15,000 acres valued at $3.4 million grown yearly. In 1995 a new variant, race E, of the pathogen was detected and was widespread by 1999 with losses of 20-25% estimated for some fields. As no efficacious fungicide was labeled on lima bean to control the disease, a search for resistance began. Three strategies were employed to find or develop resistance: 1) screen cultivars for resistance, 2) select resistant variants from a heterogeneous cultivar demonstrating some level of tolerance in the field, 3) screen new genotypes developed through private breeding efforts for resistance in the field. Of the 12 commonly planted baby lima bean cultivars evaluated, only C-Elite and 184-85 where rated as resistant to race E. When 3,000 seedlings of ‘Eastland’ were screened in the greenhouse, 31 were resistant. In field evaluations, 5 of 31 lines were both resistant and horticulturally acceptable. In field evaluations of elite breeding lines, 8 of 15 were resistant to race E.

Natural infection of soybean with a soybean dwarf-like virus in Virginia. A. FAYAD, S. A. Tolin, and M. Baldwin. Dept. Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061. Publication no. P-2000-0007-PTA.

Soybean plants showing yellowing and virus-like symptoms were noticed in border rows in the field as early as three weeks after planting and observed throughout the summer and fall of 1999 in Blacksburg, VA. Mechanical transmission tests failed to transmit a virus to soybean and other legume test plants. Plant height, branching, pod number, seeds per pod and seed weight were reduced compared to adjacent non-symptomatic plants. Initial observations and history of the field suggested that the causal agent might be the Luteovirus soybean dwarf (SbDV). In total protein extracts analyzed by SDS-PAGE, a 25 KDa protein was prominent. Electron microscopy revealed spherical particles of approximately 26.5 nm in size. Serological analyses of dot-blots of minipurified virus were positive to antisera against SbDV and a lentil luteovirus. We believe this to be the first report in the US of natural infection of soybeans with SbDV.

Transmission of Cylindrocladium parasiticum in peanut seed. D. L. GLENN, P. M. Phipps, and R. J. Stipes. Dept. Plant Pathol., Physiol. & Weed Sci., VPI&SU, Blacksburg, VA 24061. Publication no. P-2000-0008-PTA.

Higher-than-expected incidence of Cylindrocladium black rot (CBR) of peanut has occurred in some fields after pre-plant fumigation with metam sodium. Speckled seed, characteristic of infection by C. parasiticum, was collected from shelling plants and assessed for its role in disease spread. The fungus was isolated at frequencies of less than 1% from normal seed and at 4, 30, 6, 2, and 64% from speckled seed of lots A, B, C, D, and E, respectively. Speckled and normal seed treated with Vitavax PC were planted in fumigated field plots (two 9.1-m rows) in a randomized complete block design with four replications. CBR incidence in plots planted to normal and speckled seed averaged 8.8 and 22.3, respectively, for lot B and 6.5 and 40.3 for lot E. Planting speckled seed from lot E significantly reduced yield (3505 lb/A) as compared to planting normal seed (4613 lb/A). Differences in CBR incidence and yield among seed types were not significant for lots A, C, or D. This study has demonstrated that seed transmission of C. parasiticum has a significant role in disease spread. The effectiveness of various management practices is under study.

Sequence analysis of coat protein and 3' non-translated region from U.S. plum pox potyvirus samples. ERIN D. GOLEY (1), Laurene Levy (2), Vessela Mavrodieava (2), Vern D. Damsteegt (1) and Douglas G. Luster (1). (1) USDA, Agricultural Research Service, Foreign Disease-Weed Science Research Unit, Ft. Detrick, MD; (2) USDA, Animal and Plant Health Inspection Service, National Plant Germplasm Quarantine Center, Beltsville, MD. Publication no. P-2000-0009-PTA.

Plum pox potyvirus (PPV), the causal agent of Sharka disease of Prunus, inflicts severe crop losses in affected areas. Although widespread in Europe, plum pox was not reported in North America until September 1999, when infected trees were observed in plum and peach orchards in Adams County, Pennsylvania. In order to determine the identity and strain causing the outbreak, DNA sequencing of the 3' non-translated region (NTR) and the coat protein (CP) gene was performed on virus isolated from leaf and fruit samples collected from symptomatic peach and plum trees. The 3'NTR and CP gene were amplified by RT-PCR using flanking primers, cloned, and sequenced using the BigDye Terminator Kit (PEABI, Foster City, CA] on a PEABI 310 capillary instrument. Sequences were reverse-strand proofed, edited and aligned. The CP and 3'NTR sequences of Pennsylvania samples from different sources (peach vs plum, fruit vs leaf) were found to be 99.5 to 100% identical to each other. CP sequences of Pennsylvania samples were 99.0 to 99.2% similar to the CP from PPV-D strain 3.3 RB/GF-Mp15GF (GenBank af172348), confirming the causal agent to be a D strain of PPV. The DAG (asp-ala-gly) amino acid motif, a putative indicator of potyvirus aphid transmission, was predicted from nucleotide sequences at amino acids 11-13 of the CP in all Pennsylvania samples.

Alternatives to copper for bacterial disease control in staked tomatoes. A. S. GRAVES and S. A. Alexander. Eastern Shore AREC, Virginia Polytechnic Institute and State University, Painter, VA 23420. Publication no. P-2000-0010-PTA.

There are concerns for potential adverse environmental effects from the use of copper bactericides on staked tomatoes on the Eastern Shore of Virginia. The use of the systemic acquired resistance (SAR) product Actigard is being evaluated as a copper alternative in the control of bacterial diseases. Copper tolerant/resistant strains of bacteria spot and bacteria speck pathogens have been found in grower fields. Treatments were established in a randomized complete block design with four replications, and applied on a seven-day schedule. Bacteria pathogens isolated from the study areas showed a mixture of resistant and sensitive strains. Actigard provided effective control of bacterial diseases as compared to the standard copper treatments. These findings suggest that Actigard can replace copper in the control of bacteria diseases in staked tomatoes, and also reduce the possibility of copper effects on sensitive estuary systems found on the Eastern Shore of Virginia.

The purification and partial characterization of myrobalan latent ringspot Nepovirus. T. JAYAWARDENA (1), A. L. Stone (2), O. P. Smith (1), V. D. Damsteegt (2). (1) Dept. Biology, Hood College, 401 Rosemont Ave., Frederick, MD 21701-8575; (2) USDA-ARS-FDWSRU, 1301 Ditto Ave., Fort Detrick, MD 21702-5023. Publication no. P-2000-0011-PTA.

Myrobalan latent ringspot is a disease caused by myrobalan latent ringspot virus (MLRV) that affects Prunus species in southwest France. Research on nepoviruses such as MLRV is significant to the mission of Prunus crops grown commercially. The purpose of our investigation included purification of the virus from infected host Chenopodium quinoa tissue and the demonstration of infectivity in healthy plants, quantification of the highly purified virus using a standard protein assay, and partial characterization of the virus using polyacrylamide gel electrophoresis (PAGE) and western-blot analysis. Results obtained from PAGE indicated a distinct polypeptide with a molecular weight consistent with that of 55 kDal which has been reported for other MLRV isolates. Additionally, western-blot analysis confirmed immunoreaction of the virus with antiserum provided by a laboratory in France. Future work regarding MLRV includes the development of an enzyme linked immunosorbent assay (ELISA) for direct detection of the virus.

Cloning and partial sequence analysis of complementary DNA that corresponds to the 5' portion of the RNA genome of the dwarfing strain of soybean dwarf luteovirus. S. KANOTRA (1), C. Bailey (1), O. P. Smith (1), and V. D. Damsteegt (2). (1) Department of Biology, Hood College, 401 Rosemont Ave., Frederick, MD 21701-8578; (2) USDA-ARS-FDWSRU, 1301 Ditto Avenue, Fort Detrick, MD 21702-25023. Publication no. P-2000-0012-PTA.

The RNA genome of the dwarfing (D) strain of soybean dwarf virus (SbDV) has an established size of 5.6 kilobases (kb). Prior studies conducted at the USDA-ARS have established that 4.8 kb of the genome, corresponding to central and 3' regions, has been cloned as cDNA. The purpose of our study was to employ rapid amplification of cDNA ends (RACE) procedures to clone cDNA that corresponds to the remaining 5' portion of the viral genome. Using two primers designed internal to the 5' end of a cDNA that corresponds to the central portion of the genome, 5' RACE was conducted using viral RNA as a template. Analysis of the RACE product by agarose gel electrophoresis indicated that a cDNA fragment of 800 bp was produced. This amplified product was cloned into E. coli using plasmid vector pCR2. 1 - TOPO. On the basis of mini-prep analysis, two independent clones were verified to contain the 800 bp insert and these inserts were partially sequenced. Based on the sequence information from these clones, which includes a 40 bp overlap with the central region, we conclude that a majority of the 5' portion of the viral genome has been successfully cloned.

Functional diversity of small soil bacteria. K. L. KINNEER, K. M. Heldreth-Fleming, D. G. Panaccione, and A. J. Sexstone. Division of Plant and Soil Sciences, West Virginia University, Morgantown, WV 26506. Publication no. P-2000-0013-PTA.

Carbon substrate utilization of large-celled (LC, >0.45 micron) and small-celled (SC, <0.45 micron) bacteria within A and B horizons of cultivated and forested Guernsey silt-loam soil was assessed using BIOLOG GN and GP microtitre plates. Without enrichment, A horizon SC exhibited limited substrate utilization compared with LC. B horizon SC failed to utilize any carbon substrates, which suggests that they may be physiologically inactive and/or metabolically distinct from those in A horizon soils. Following enrichment in several liquid dilution cultures, A horizon SC from highly dilute enrichments produced substrate utilization patterns distinct both from all other enrichments of LC and SC obtained in less dilute enrichments. At any given inoculum dilution, A horizon SC utilized a greater number of substrates than B horizon SC, which exhibited positive substrate utilization following enrichment. Amplified ribosomal DNA (ARDRA) analyses of SC dilution culture enrichments demonstrated distinct bacterial sub-populations from a single soil sample.

Impact on snap bean of ambient ozone at Long Island, New York. M. T. McGrath. Dept. of Plant Pathology, LIHREC, Cornell Univ., Riverhead, NY 11901. Publication no. P-2000-0014-PTA.

Yield and foliar injury due to ozone were compared for 14 ozone-sensitive and ozone-tolerant snap bean cultivars and lines grown under field conditions. The lines have similar growth characteristics and yield in the absence of ozone. From July through September when beans were grown, ozone was 80 ppb for 76 hrs on 20 days in 1998 and for at least 140 hrs on 21 days in 1999 (monitoring equipment was not functional on 22 days). Typically these high concentrations occurred between 1200 and 2400. Average daily 12-hr mean for July through September was 47.4 ppb in 1998 and 50.9 ppb in 1999. Daily 12-hr mean was 50 ppb for 34 of 92 days in 1998 and 32 days in 1999. Pods were harvested when immature (for fresh-market consumption) from some plants and when mature from others. Tolerant beans produced 37% more pods per plant by weight and 47% more pods by number harvested for fresh market than sensitive beans in 1999. Tolerant beans produced 41% more pods per plant by number and 51% more seeds harvested at maturity than sensitive beans. These results document that ozone is high enough to significantly reduce growth and yield of sensitive plants in an important agricultural county in New York.

Algal switching among lichen symbioses. M. D. PIERCEY-NORMORE and P .T. DePriest. Department of Botany, National Museum of Natural History, Smithsonian Institution, Washington, D. C. 20560. Publication no. P-2000-0015-PTA.

Fungi of the lichen genus Cladonia form symbiotic relationships with green algae of the genus Trebouxia. We sequenced Internal Transcribed Spacers (ITS) of nuclear rDNA using algal and fungal specific primers for symbionts collected from three continents representing seven sections of Cladonia, Cladina, and related genera. Little variation was found among the ITS sequences, a pattern supported by mitochondrial large subunit gene sequences and RAPDs. When incongruence and randomization tests were performed on fungal and algal phylogenies there was no evidence for parallel cladogenisis or cospeciation. Algal switching, long distance dispersal, and strong fungal selection for the algal partner may explain the lack of evidence for cospeciation among these lichen symbionts.

Evaluation and characterization of bacterial isolates as seed treatments for the control of take-all in soft red winter wheat in Virginia. D. P. ROBERTS (1), E. L. Stromberg (2), G. H. Lacy (3), and J. S. Buyer. (1) Biocontrol of Plant Diseases Laboratory, USDA-ARS, Beltsville, MD, (2) Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, VA, and (3) Soil Microbial Systems Laboratory, USDA-ARS, Beltsville, MD. Publication no. P-2000-0016-PTA.

Take-all of wheat, caused by G. graminis var. tritici (Ggt), causes severe economic losses in Virginia. We describe a method to rapidly screen large numbers of diverse bacteria for suppression of Ggt under field conditions. Candidate bacterial strains were isolated from wheat roots and identified by FAME analysis. Seed treatments, containing candidate bacterial strains, were planted with a head row planter in randomized complete blocks of 150 treatments with four replications along with Ggt-infested, dead wheat seed. Rows were single 7-in wide and 4 ft long. The total above ground biomass from a one meter section of each row was collected with a sickle bar mower and weighed after the growing season. Disease control was observed with several bacterial seed treatments that was better than chemical controls as observed by superior biomass production.

History of plant pathology in Virginia: A 110-year chronology. P. M. SFORZA, C. W. Roane, and K. K. Hatzios. Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, VA 24061. Publication no. P-2000-0017-PTA.

The Virginia Agricultural Experiment Station (VAES) in Blacksburg was created by an act of the Virginia General Assembly in 1886. The study of plant diseases in Virginia began soon afterwards when William B. Alwood was appointed Vice-Director of VAES and Professor of Horticulture and Entomology in 1888. For over 110 years, the advancement of plant healthcare and service to Virginia’s farmers and citizens have continued to develop through public, private, and institutional efforts. In 1999, the Department of Plant Pathology, Physiology, and Weed Science at Virginia Tech celebrated 110 years of plant pathology in Virginia and the 50th anniversary of the department. A poster chronology of important events was constructed based on historical documents including "A History of Plant Pathology in Virginia (1888-1974)" written by C. W. Roane, "110 Years: 1889-1999" edited by K. K. Hatzios for the anniversary celebration, and other documents and photographs from the departmental archives.

Survey of a farm in Henrico County, Virginia for reservoirs of barley yellow dwarf viruses using ELISA. P. M. SFORZA, S. A. Tolin, and E. L. Stromberg. Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, VA 24061. Publication no. P-2000-0018-PTA.

A survey was conducted to identify reservoirs and characterize the strains of barley yellow dwarf viruses (BYDVs) on the Aigner farm in Henrico Co., Virginia. Samples (n=270) were collected at 6-8 week intervals from Apr 99 through Jan 00. Host identity and location were recorded and samples were tested for the strains (PAV, MAV, SGV, RPV and RMV) of BYDVs using DAS-ELISA. Twenty-nine species of grasses, 22 of which are reported hosts of BYDVs, were found on the farm. Grasses that tested positive for BYDVs during the survey were tall fescue, Festuca arundinaceae (PAV, May 99; RPV, Jan 00), orchardgrass, Dactylis glomerata (MAV, May 99; RPV, Oct 99 and Jan 00), and volunteer wheat, Triticum aestivum (RPV, Jan 00). In cultivated wheat, a shift was observed in the predominant strain from PAV in 1999 to RPV in 2000. In Apr 99, 53% (8/15) of the samples from wheat planted in fall 98 tested positive for the PAV strain. However, for wheat planted in fall 99, only 21% (3/14) of the samples tested positive for barley yellow dwarf and only the RPV strain was found.

The name of the cucurbit powdery mildew: Podosphaera (sect. Sphaerotheca) xanthii (Castag.) U. Braun & N. Shish. comb. nov. NINA SHISHKOFF. Cornell Univ., Riverhead, NY 11901. Publication no. P-2000-0019-PTA.

The powdery mildew of cucurbits is well-known, but its name has been a source of confusion. In the U.S. it is commonly called Sphaerotheca fuliginea, a name now limited to mildews with hosts in the Scrophulariaceae. Europeans call it S. fusca, a name based on a lost type specimen. Because host range and morphological studies had indicated that S. fusca consisted of at least two distinct taxa, it became necessary to select a neotype in order that the name "S. fusca" be fixed to one morphological form. The specimen selected corresponded to the taxon found on dandelions and other composites, while the remainder corresponded to "S. xanthii" sensu Junell and included taxa on sunflower, verbena, and cucurbits. Because Sphaerotheca is now considered synonymous with Podosphaera, the cucurbit powdery mildew was named Podosphaera (sect. Sphaerotheca) xanthii.

Gray leaf spot: Cercospora zeae-maydis small subunit rRNA genes. V. K. STROMBERG (1), P. M. Sforza (1), J. M. J. Ward (2), G. A. Hammond (3), E. L. Stromberg (1), and G. H. Lacy (1). (1) Plant Pathol., Physiol., and Weed Sci., VPI&SU, Blacksburg, VA 24061; (2) CEDARA, Pietermaritzburg, KwaZulu-Natal, RSA; and (3) Biol., Radford Univ, Radford, VA 24142. Publication no. P-2000-0020-PTA.

Genotypes (T1 & T2) of Cercospora zeae-maydis (Czm) vary in their ITS regions suggesting that sibling species exist (Wang et al., Phytopathology 88: 1269, 1998). We extend analyses to the small subunit ribosomal RNA gene (ssrRNA). For resistance breeding programs, it is important to know which Czm populations cause disease in a given region. Leaves with lesions were collected, air-dried, and imported into Virginia (APHIS PPQ permit). Fungi grown on V8 agar from single-spores were hyphal-tipped, tested for contamination, grown on V8 broth, and extracted for DNA. PCR-amplified ssrRNA genes and ITS regions were sequenced and compared with Cercospora beticola and C. sorghi sequences. Analyses confirmed T1 and T2 Czm in Virginia, T2 Czm in South Africa, and T1 Czm in Wisconsin. Interspecific sequence comparisons support the hypothesis that species-level differences exist between T1 and T2 Czm strains.

SOVRAN® Fungicide - Update on performance and resistance management guidelines. G. G. THOMAS, H. L. Ypema, and T. E. Anderson. BASF Corporation, 26 Davis Drive, PO Box 13528, Research Triangle Park, NC 27709. Publication no. P-2000-0021-PTA.

Sovran® fungicide (a.i. kresoxim-methyl) is a strobilurin fungicide developed by BASF in the NAFTA-region. The first registrations for Sovran fungicide on pome fruits, grapes and pecans in the United States were issued in May 1999. Sovran fungicide received registration on apples in Canada in December 1999. Sovran fungicide will be available for the entire growing season in the year 2000. It will offer growers excellent activity against many important plant pathogenic fungi by virtue of its high intrinsic activity and favorable biokinetic properties. The active ingredient, kresoxim-methyl, adheres strongly to the leaf surface under various weather conditions. Laboratory, greenhouse and field studies have demonstrated that kresoxim-methyl diffuses laterally over the leaf surface and translaminarly from one leaf surface to the other. As a result kresoxim-methyl exhibits both Surface Systemic Activity™ and translaminar activity. Sovran fungicide combines a strong inhibitory action against spore germination, surface mycelia and sporulation with a long residual activity and excellent crop safety. The presentation focuses on the management of apple and grape diseases in the Northeastern United States, and new use guidelines for the year 2000 to prevent the development of resistance to strobilurin fungicides.

Genetic screen to identify Arabidopsis mutants which overcome a nitric oxide synthase inhibitor block of the hypersensitive response. CATHY KINGDON WORLEY, Laura E. Maliszewski, Josh Hubner, and Allan D. Shapiro. Plant and Soil Science Department, University of Delaware, Newark, DE 19717. Publication no. P-2000-0022-PTA.

12,751 EMS-mutagenized M2 Arabidopsis plants were screened for their ability to overcome a L-NNA (a nitric oxide synthase inhibitor) block of the hypersensitive response (HR) elicited by inoculation with Pseudomonas syringae pv. glycinea Race 5 carrying avrRpm1. In wild-type Columbia accession Arabidopsis, 85% of the leaves exhibited a HR one day post-inoculation with 1 × 10(^8) bacteria/ml, but only 20% of the leaves exhibited a HR if 200 micromolar L-NNA was included in the inoculum. L-NNA had no effect on bacteria viability. For the screen, 5 leaves per plant were inoculated with bacteria plus L-NNA, and plants which exhibited HRs on at least 80% of the leaves were kept as positives. 793 plants tested positive. We will test 15 M3 from each positive to verify phenotypes. 6 lines have been re-tested in the M3 generation thus far, and 1 re-tested as a valid mutant which appeared to be dominant. We expect to identify genes involved in nitric oxide signaling or parallel pathways which can bypass the requirement for nitric oxide in the plant pathogen defense response.

Reactive oxygen, NDR1 and NPR1 in Arabidopsis disease resistance signaling. CHU ZHANG and Allan D. Shapiro. Department of Plant and Soil Sciences, University of Delaware, Newark, DE. 19717. Publication no. P-2000-0023-PTA.

Mutants in the NDR1 gene are compromised in resistance to multiple strains of Pseudomonas syringae and Peronospora parasitica. ndr1 mutants are also affected in specific processes correlated with disease resistance in a pathogen strain-specific manner. Previous work has suggested that NDR1 acts downstream of the oxidative burst and upstream of induced salicylic acid (SA) biosynthesis. This model would predict that levels of reactive oxygen production seen early in the response to avirulent pathogen should not be affected by the ndr1 mutation. A burst of hydrogen peroxide production was seen between 2 and 5 hours post-inoculation with P. syringae pv. tomato DC3000 carrying avrB or avrRpt2. No significant differences were noted between ndr1-1 and the Columbia parental. We have made an ndr1-1/npr1-2 double mutant. The npr1 mutation was not found to have any affect on the hypersensitive response (HR) either in the single or the double mutant. As such we conclude that the signaling pathway downstream of npr1 and any feedback affected by the npr1 mutation do not contribute to the HR. Analysis of PR-1, PR-2 and PR-5 induction in single and double mutants in response to both virulent and avirulent P. syringae showed that cell death and SA make independent contributions to PR gene induction.