Progress 10/01/04 to 09/30/05
Outputs
4d Progress report. This report serves to document research conducted under a specific cooperative agreement between ARS and Dr. Jim Niehuis of the University of Wisconsin. Additional details of research can be found in the report for the parent project, 5348-21000-020-00D entitled, "Plant Germplasm Conservation and Research," and progress over the last year. Since first identified in Wisconsin in 2000, the soybean aphid virus complex has cost the snap bean industry millions of dollars in losses. Economic losses were greatest in 2000, 2001 and 2003 while losses in 2002 and 2004 were minimal. The viral disease complex can cause plant stunting, leaf mottling, pod deformities, severe yield losses and pod necrosis in snap beans. Late season production fields are particularly susceptible because of high aphid populations. Foliar sprays and seed treatments have proven ineffective and commercial cultivar evaluation trails indicate that resistance to the complex does not
exist in commercial germplasm; however, levels of tolerance has been observed. Thus, a genetic solution allowing the transfer of favorable genes to adapted cultivars is the best solution to the future security of the snap bean industry. Through extensive surveys of Wisconsin snap bean production areas in 2002 and 2003, cucumber mosaic virus (CMV) and alfalfa mosaic virus (AMV) were identified as important components in the complex. However, the role of clover yellow vein virus (CYVV) is not clearly understood and unidentified viruses, different strains of viruses and other agents may be involved. Materials and Methods Germplasm: In 2004, 423 PI Phaseolus vulgaris accessions were evaluated at Arlington, WI ARS in 2004. These 423 accessions represent the USDA core Phaseolus vulgaris collection. This core serves as a representative sample, with 95% probability of maintaining rare alleles, of the over 12,000 Phaseolus vulgaris accessions maintained in the reserve collection at the
Pullman, WA facility. In 2005, in collaboration with Drs. Walt Stevenson and Craig Grau, UW- Madison and Dr. Ben Lockhart, University of Minnesota. We will evaluate the 11 PI accessions that were visually symptomless and ELISA negative from the 423 PI accessions evaluated in 2004. These accessions will be evaluated at three locations including West Madison ARS and two commercial snap bean production fields near Markesan, WI and Randolf, WI. Experimental Design: 423 PI accessions were planted at Arlington, WI ARS using a replication within block design on July 14, 2004. Commercial cultivars were included in the trial as susceptible checks. Twelve days prior to planting the trial, mixed spreader rows consisting of a 50:50 (by weight) mix of soybean and the snap bean cultivar Hystyle were planted using a 4-row corn planter. The same day the trial was planted; expanding trifoliate leaves of Hystyle in the spreader rows throughout the trial were chosen at random and manually
inoculated with AMV and CMV. Composite samples of 10 expanding trifoliate leaves from each plot was harvested from 10 plants with virus-like symptoms for ELISA evaluation in Dr. Thomas Germans lab, UW-Madison. This sampling method was chosen because our research objective was to confirm tolerance, not quantify incidence. This experimental design will be repeated for the 2005 evaluations. 2004 Results Arlington, WI ARS trial: Visual evaluations of the 423 PI accessions and checks on August 9, September 15 and September 23 were positive for virus-like symptoms. Soybean aphids in low numbers were found in the field. Visual data taken September 15 and September 23 indicated a 90% or better infection level. However, composite leaf sample ELISA results indicated that although soybean aphids were detected in the trial and CMV and AMV were in the spreader rows, only about 15% of the accessions tested AMV or CMV positive. These results suggest that there maybe have been other viruses,
virus strains or agents involved in the virus complex in 2004. Preliminary data indicates that 11 PI accessions appeared visually symptomless and ELISA negative in both replications. In 2004, soybean aphid populations were low, migrations were late and in some snap bean production areas of Wisconsin, the soybean aphid and the viruses it transmits were never detected. Cool temperatures throughout the growing season probably influenced aphid numbers. Throughout the 2004 growing season, virus-like foliar symptoms were observed in some snap bean production areas. ELISA results indicated that some of these symptoms were associated with CMV, AMV, CYVV or a combination of these viruses. In other instances, the symptoms could not be associated with the presence of any of these viruses. In these cases, with the exception of virus-like foliar symptoms, the plants appeared healthy and no apparent loss in yield was observed. Large populations of other aphid species and insects were detected
in these areas and may have contributed to these virus-like symptoms. Summary of 2004 Results: Based on data from two replications at Arlington ARS in 2004, 11 Phaseolus vulgaris PI accessions were visually symptomless and ELISA negative. These accessions will be increased in the greenhouse this winter for further evaluation in 2005. The idea of using tolerant plants is being widely discussed. The use of tolerant materials (when no loss in yield or quality results) may be an accepted alternative until resistant cultivars can be identified; however, these plants could serve as virus reservoirs.
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