Effect of fungicide seed treatments on Fusarium virguliforme and development of sudden death syndrome in soybean
Sudden death syndrome (SDS) is a soilborne disease responsible for causing significant yield reductions across soybean-producing states. Recent research indicates that infection of the soybean radicle early in the season by Fusarium virguliforme (Fv), the SDS pathogen, is critical for disease development. This suggests fungicide seed treatments could be effective in limiting early infection possibly resulting in disease control. Field, greenhouse, and laboratory studies were conducted to evaluate eight fungicides in multiple seed treatment combinations for effects on Fv infection and SDS development. Seed treatments were applied to cultivars that were moderately resistant and moderately susceptible to SDS. Field studies were conducted at two locations: in 2008, the Valmeyer, IL location was naturally infested with Fv, and in 2008 and 2009 the Urbana, IL location had a natural Fv infestation and soil was augmented with sterilized grain sorghum colonized by Fv. Similarly, the greenhouse study was inoculated with sterilized, Fv infested grain sorghum to evaluate the same seed treatments on moderately resistant and moderately susceptible cultivars. The rolled-paper towel laboratory assay tested the individual fungicides in the growth chamber using a Fv macroconidial suspension to inoculate treated seed and assess effects on seed germination, plant length, lesion size, and disease severity. Fv DNA concentrations in soybean roots were measured using quantitative polymerase chain reaction (qPCR) in early vegetative stage roots. Soybean roots from the field were collected at three timings for digital scanning and analysis with root analysis software to measure root disease symptoms. Roots were scanned and analyzed at the completion of the greenhouse trial. SDS foliar symptoms were rated several times throughout plant growth and the area under disease progress curve (AUDPC) was calculated. Harvest data were collected for the field study. In the field, seed treatments had no effect on Fv DNA concentrations in roots. Seed treatments had very little effect on roots analyzed from the field. Most seed treatments did significantly decrease SDS foliar symptoms at the Valmeyer field study compared to the control, but no differences in foliar symptoms were observed for the Urbana field studies. Yield was unaffected by seed treatments. In the greenhouse, Fv DNA concentrations were reduced by a treatment combining mefenoxam + thiophanate-methyl + azoxystrobin + B. pumilus + prothioconazole + fludioxonil compared to the non-treated control; however, the reduction in Fv DNA did not improve root growth or decrease SDS foliar symptoms compared to the non-treated control. The Fv DNA concentrations in roots did not significantly correlate to SDS foliar symptoms in the field; however, a significant positive correlation was found in the greenhouse between Fv DNA and SDS foliar symptoms. Several seed treatments decreased lesion length and disease severity compared to the non-treated inoculated control in the rolled-towel laboratory assay, but the biological seed treatment, B. pumilus, significantly decreased seed germination and plant length while increasing lesion length and SDS severity compared to the non-treated inoculated control. In conclusion, none of the seed treatments evaluated proved to have consistent effects on Fv or SDS.
Fusarium virguliforme, Fusarium, seed treament, Sudden Death Syndrome (SDS), Fungicide, Soybean, root rot, Fusarium solani f. sp. glycines
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign