Progress 10/01/03 to 09/30/08
Outputs
OUTPUTS: Technical information arising from the research was disseminated through professional journals and meetings, primarily involving the American Phytopathological Society. Farmers, crop consultants and other members of the agricultural community were exposed to research findings through cooperative extension publications & meetings, research farm tours, popular press including radio and print media and direct interaction with individuals. In these venues, the practical significance of the research to growers and sustainability of their farm operations was stressed. Information was also shared directly with undergraduate and graduate students in courses taught at South Dakota State University. PARTICIPANTS: Other than the principal investigator, this project involved technical support personnel and graduate students. This work provided training for one M.S. student who has subsequently gained a Ph.D. at another university Funding for most of the work came from commodity organizations in South Dakota, primarily the South Dakota Soybean Research & Promotion Council TARGET AUDIENCES: Target audiences for technical information include peer groups such as agronomists and other plant pathologists. Target audiences for applied information include farmers and crop consultants as well as the broader agricultural community. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
The most significant outcome of the research was to develop information regarding two major fungal diseases of soybeans: 1) Northern stem canker (NSC) of soybeans; caused by Diaporthe phaseolorum var. caulivora and 2) Phytophthora root & stem rot; caused by Phytopthora sojae. Significant outbreaks of a new or undescribed disease in South Dakota were investigated prior to the research period and led to the proposed research on NSC. The first major outcome of the research was to characterize epidemics of NSC in South Dakota and confirm the identity of the causal agent using molecular technology (PCR + restriction enzyme profiling of ITS regions of DNA). Molecular variabililty of the pathogen population was also analyzed. Based on these findings, it became urgent to understand the basis for epidemics of NSC and subsequent research was focused on greenhouse and field testing for resistance to NSC in soybean varieties and germplasm adapted for South Dakota. Some experiments on etiology and epidemiology were begun, but little progress was made due to lack of resources and lack of success in obtaining grant funding from outside sources. A wide variety of germplasm in maturity groups 0, I and II was tested over several years for resistance. Improvements in testing methods were also developed. Data on these field studies are included in each of the annual summaries. Despite extensive screening, no varieties with uniformly high levels of resistance were identified. In fact, the main result of the research was to point out the vulnerability of most soybeans to NSC. Observations on localized outbreaks of the disease were made and combined with screening experiments suggested that a large proportion of soybean germplasm could be susceptible to epidemics of NSC. Work on Phytophthora root & stem rot was also conducted. Most of this work consisted of assisting the SDSU soybean breeder in testing germplasm for resistance, primarily horizontal or partial resistance. Work was also conducted on race surveys to provide information relevant to deployment of specific resistance genes.
Publications
- No publications reported this period
|
Progress 01/01/07 to 12/31/07
Outputs
OUTPUTS: Completed replicated field trials on susceptibility of soybeans to Northern stem canker (NSC) caused by Diaporthe phaseolorum var. caulivora. Lines and varieties in maturity groups O, I and II in the Regional Uniform Soybean Trials were tested by the toothpick method. The collection included conventional line as well as Roundup Ready (glyphosate resistant) soybeans. These are the first data on susceptibility to NSC on a regional basis. Varieties and lines were rated on a scale of 0 (immune) to 10 (all plants killed). The mean for conventional entries was 5.0 (n=53) and the mean for Roundup Ready entries was 3.7 (n=59). The study identified some varieties with low reaction (0 or 1) that could possibly represent useful resistance. Further study will be required to confirm these findings. Completed a study on Phytophthora Root and Stem Rot (PRR) on the Phytophthora nursery in Brookings. The study compared incidence of PRR and yield on two varieties, one carrying the Rps-1k
resistance gene. Significant differences in PRR were seen between the two varieties, but most importantly we have finally been able to verify the buildup of Phytophthora races capable of defeating Rps1-k. This should allow us to test SDSU lines and varieties for Rps-1k under field conditions. Made additional collections of Phytophthora sojae isolates from fields in eastern South Dakota to contribute to the study of Rps-1k defeating races. Isolates have been established but are undergoing characterization for race I.D. and aggressiveness.
PARTICIPANTS: Thomas Chase was the principal investigator and is an Associate Professor of Plant Science at South Dakota State University. Undergraduate students involved in the research included Devin Boushek and Sonya Nelsen. The research was conducted as part of a regional project, the North Central Uniform Soybean Trials.
TARGET AUDIENCES: Target audiences include soybean breeders, soybean pathologist, crop consultants, extension educators and soybean farmers.
Impacts
The research identified levels of susceptibility/resistance to a serious fungal disease of soybeans. This will allow breeders and growers to make informed judgements about which varieties to employ. Breeders will be able to utilize resistant lines in developing varieites for soybean growers. The overall impact would be to lessen potential economic loss from disease.
Publications
- Chase, T.E. and R.L. Geppert.. 2007. Susceptibility to Northern stem canker in South Dakota soybean varieties. Phytopathology 97:S20
|
Progress 01/01/06 to 12/31/06
Outputs
Testing for resistance to Northern stem canker (NSC) was completed on South Dakota adapted soybean varieties and lines entered in the South Dakota State University Crop Performance Testing (CPT) program over the past three years (2004, 2005, 2006). Entries were inoculated with the same representative Diaporthe phaseolorum var. caulivora (DPC) isolate in all three years. Maturity groups 0, I, and II were represented among the varieties in the test. A total of 103 varieties were tested in 2004 and 2005, but only 39 of the varieties were carried through to 2006 crop performance testing. Each of ten plants of each variety per plot were inoculated at or near flowering. Inoculations were made by inserting a DPC colonized toothpick at or near a node and sealing with petroleum jelly. Three replicates for each variety were set up in each year's test. Number of plants per plots killed by girdling stem lesions was recorded after a 4-6 week period following incoculation.
Classification of reactions was as follows: 0 plants killed = immune; 1-3 plants killed = moderately resistant; 4 or greater plants killed = susceptible. Mean score among all varieties for 2003 was 5.7; for 2004 the mean rating was 7.1 and for the 39 varieties in the 2006 test, the mean score was a 4.6. In all three years the mean rating fell within the susceptible category. These results thus demonstrate a high degree of susceptibility in currently or to be deployed soybean germplasm in South Dakota. In another experiment, resistance to Northern stem canker was tested in forage soybean varieties. Little resistance was noted among the forage varieties tested. A field study followed the progress of NSC in a field that had a disease incidence of ca. 50% in 2005. The field was split between conventional and conservation tillage plots and planted with known susceptible soybean varieties. Disease did not develop in any of the plots, probably due to droughty conditions during most of the
early to mid-season. Production of perithecia, however, was abundant on infected residue left on the soil surface in the conservation tillage plots. The long-term survival and infectivity of DPC inoculum and its role in the epidemiology of Northern stem canker remains open to further investigation.
Impacts
Outbreaks of Northern stem canker can be quite serious to soybean growers. Under conducive environmental conditions there could be a widespread regional impact on soybean production due to this high degee of susceptibliity. The results of this study should provide a stimulus to soybean breeders and seed companies to begin to develop varieties with resistance to Northern stem canker.
Publications
- No publications reported this period
|
Progress 01/01/05 to 12/31/05
Outputs
A second year of field screenings for susceptibility to Phytophthora sojae, cause of Phytophthora root and stem rot (PRR) were conducted in 2005. The pattern of resistance to the field population of P. sojae races indicates that races virulent on Rps-1k and Rps-1c, Rps-1a and other genes were not present in this field. A check variety purportedly carrying the Rps-1a gene was, however, susceptible. The differential response will be the subject of further studies. Study of non-girdling cankers at the soil line in mature soybean plants was also conducted. The preliminary data suggest that these cankers result from soilborne infection by fungi in the Diaporthe/Phomopis complex rather than late infection by P. sojae. A second year of replicated screenings for resistance to Diaporthe phaseolorum var. caulivora (DPC; cause of Northern stem canker) in South Dakota adapted soybean germplasm and commercial varieties was completed in 2005. Data are currently being evaluated but
show very similar results to the previous year, demonstrating a high degree of susceptibility to DPC among lines and varieties A collection of forage soybean lines was evaluated for differences in biomasss production and nutritional components. The lines tested showed differential incidence of infection by fungi in the Diaporthe/Phomopsis complex (presumably Diaporthe phaseolorum var. caulivora, causal pathogen of Northern Stem Canker. Forage soybean lines showed differences in the incidence of non-girdling cankers on stems. Stems were not girdled by lesions as is usually the case with South Dakota adapted soybean lines and varieties that are grown for grain. A study was initiated on a commercial soybean field near Brookings, SD that had a very high incidence (ca. 50%) of stem canker during the 2005 growing season. Distribution of disease within the field was remarkably uniform. Isolates were established from infected plants and will provide the basis for a study on population
variabilty of the pathogen within a field. The field history involved alfalfa and corn in the immediately preceding rotations. This raises questions regarding alternate hosts as well as the etiology and disease cycle of Diaporthe phaseolorum var. caulivora on soybean. Studies on inoculum survival and production within this field are planned for the 2006 growing season
Impacts
The research quantifies levels of resistance to Northen stem canker in soybean varieties and lines and also opens up avenues to better understand the factors responsible for severe and as yet unpredictable epidemics of Northern stem canker.
Publications
- No publications reported this period
|
Progress 01/01/04 to 12/31/04
Outputs
A field trial for susceptibility/resistance to northern stem canker in soybean caused by Diaporthe phaseolorum var. caulivora (DPC) was conducted at the SDSU research farm in Brookings, South Dakota in the summer of 2004. Plants were grown in hill plots and ten plants per plot were inoculated with toothpicks containing a pure culture of the pathogen grown axenically on autoclaved toothpicks. The number of plants killed by DPC was determined for each plot. The study involved 323 commercial and public glyphosate resistant varieties and lines as well as fifty-eight conventional varieties entered in the South Dakota State University Crop Performance Testing (DPT) program.. Maturity groups 0, I, and II were represented among both conventional and glyphosate resistant varieties and were designated as C0, C1,C2 and RR0,RR1,RR2 respectively. Three complete replications were included in the study. Responses were recorded as resistant or immune if 0% of plants were killed;
mildly resistant if 10-30% plants were killed; and susceptible if if 40% or great plants were killed. The percentage of within each class for the glyphosate resistant were: RR0 (1/11/88 ), RR1 (0/10/90) and RR2 glyphosate resistant (0/14/86) respectively. For conventional varieties the distribution was as follows for C0 (0/75/25), CI (0/16/84), and CII (0/11/89). These results demonstrate that susceptibility to northern stem canker is widespread among varieties and lines adapted for use in South Dakota. An ancillary aspect of this experiment was to compare levels of seed-borne infection by DPC in seed harvested from inoculated plants killed by DPC vs. uninoculated control plants. Nineteen varieties were included in this study. Seed infection by DPC in control plants was ca. 0.95%. In contrast, seed from infected plants had a 5.4% level of seed-borne DPC infection. Studies are being conducted to determine if cultures of DPC isolated from seed are genetically identical to the strain
used to inoculate stems. A field test of resistance/tolerance to Phytophthora root & stem rot in the CPT soybean varieties was also conducted. The field contains a population of Phytophthora sojae races to which the Rps1-k gene is apparently still resistant.. Entries were planted in hill plots and and flooded soon after to enhance conditions for infection and disease progress. Each plot contained replicates of a variety as well as susceptible and resistant checks. This allowed mapping of relative disease intensity across the field. The experiment was planted in three replications. The number of plants missing in each hill (due to pre-emergence damping off) was recorded along with the number of symptomatic plants. Phytophthora sojae activity was present throughout the field at a variety of intensities as judged by the checks. No conclusions are presented, since data are still being studied and analyzed, but this experiment should provide a meaningful field test for the Rps-1k gene
under field conditions.
Impacts
These studies provide specific information on the resistance and susceptibility to two important diseases in soybean varieties and germplasm adapted for commercial production in South Dakota. This information will provide a starting point for efforts to identify and incorporate host resistance to northern stem canker and Phythophthora root and stem rot into new varieties and lines.
Publications
- Chase, T.E. and Geppert R. 2004. Frequency of susceptibility to northern stem canker in soybean varieties from maturity groups 0 through II. American Phytopathological Society. Publication no. P-2005-0006-NCA.
- Zhang, D. and Chase, T.C. 2004. Molecular and genetic variability of Diaporthe phaseolorum var. caulivora isolates from South Dakota. Phytopathology 94:S114
|
|