Update:
Sudden death syndrome (Fusarium virguiliforme) is an important disease that affects soybean yields across the United States every year. The pathogen survives in the soil where it starts infection on soybean roots as root rot. After root colonization, F.v. produces a toxin that spreads throughout the plant that kills the vascular system, which in turn, cuts off the plants' water supply. Because SDS impacts soybean yields, it is important to understand how the disease is spread to understand how to control it. Natural resistance to both the toxin and root phases of the pathogen differs among varieties of soybeans.
Objective 1. Screen adapted Kansas germplasm, sequenced plant introductions, and KSVT entries for SDS resistance using three high-throughput methods.
SDS
This objective has been the primary effort area of the KSC-funded work and was a continuation from the 2019-2020 project and overlaps with the final report for last year’s project. For SDS, germplasm has been screened using three methods: (i) culture extract/toxin assay method, (ii) rolled-towel method, and (iii) layer-cake method. Additionally, a subset of 20 lines from Dr. Schapaugh’s program, which have undergone cut-stem assay screening, rolled towel, and layer cake screening were screened in the field (Rossville, Kansas) for SDS reaction and AUDPC (area under the disease progress curve) in 2019. However, due to COVID-19, University-mandated constraints prevented repeating the field experiment in 2020. Due to seed limitations we were not able to repeat this field study this year. Therefore, we will have to increase seed and repeat next season.
The toxin assay has been completed for both the Kansas Soybean Variety Trial (KSVT) and the entries from Dr. Schapaugh's program (KS# breeding entries). During 20-21 some of these lines will be retested. The rolled-towel assay has been completed for the KSVT and a subset KS# breeding entries. The layer-cake screening has been completed for a subset of the KSVT and KS# breeding entries. Example data is available in table form in the attached PDF. The KSVT was not screened in the field for SDS. The SDS assays described above is nearly complete and a manuscript is in progress for submission to Plant Health Progress.
As previously mentioned, the simple rolled-towel pathogenicity assay has the potential to predict SDS field severity for soybean genotypes. In other words, entries that are rated as resistant in the rolled-towel assay are rated resistant in the field a larger proportion of the time, compared to the toxin (cut-stem) and layer-cake assay. The ultimate dependability of this association will be something that will continue to be worked out during future projects.
Objective 2. Examine the effect of seed treatment fungicides on F. virguiliforme colonization of seedlings and colonization by other pathogenic Fusarium spp.
Active ingredients including azoxystrobin and fludioxonil are being tested against soybean root-associated Fusarium spp. See Figure 5 for examples of EC50 data obtained from testing azoxystrobin, picoxystrobin, and pyraclostrobin on the commonly used Mont-1 isolate of F. virguliforme. Further, these active ingredients have been tested against a few isolates of F. proliferatum from soybean seedlings. See Figure 5 for an example of EC50 data from F. proliferatum for azoxystrobin. Testing of trifloxystrobin will continue in the next proposal year.
Objective 3. Determine pathogenic variability of F. virguiliforme isolates from multiple Kansas fields.
F. virguliforme isolates are being collected from soil, soybean residue, and symptomatic plants throughout the affected soybean production areas of Kansas as possible. See Figure 6 for examples of soil isolation plates used to isolate F. virguliforme from Kansas soils. Other root-associated Fusarium spp. were isolated from asymptomatic and symptomatic plants with emphasis on Fusarium proliferatum. Strains are isolated into pure culture and single-spored for long-term storage. See the 20-21 proposal for more detail.
Sample collection locations for strains of F. virguiliforme include Manhattan, Rossville, Silver Lake, Belleville, Scandia, and Columbus, KS. Locations from additional fields in various Kansas counties were added later in the project. Also, we have initiated a collaboration with Plant Disease Diagnostic Lab at K-State to obtain additional samples for isolate collection from those that come in from around the state, further widening our collection scope. Isolate collection will continued past the end of the current project period as it is important to capture pathogen variability in the state.
View uploaded report 