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Title:Optimizing conditions for production of toxin culture filtrate of Fusarium virguliforme, comparing isolates causing sudden death syndrome, and the use of soy milk to culture soybean pathogens
Author(s):Xiang, Yiwen
Advisor(s):Hartman, Glen L.
Department / Program:Crop Sciences
Discipline:Crop Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):sudden death syndrome
Fusarium virguliforme
toxic culture filtrates
stem-cutting assay
soy dextrose agar
soy dextrose broth
Abstract:Cell-free toxic culture filtrates of Fusarium virguliforme, the causal fungus of soybean sudden death syndrome (SDS), have been shown to cause foliar symptoms on soybean stem-cuttings similar to whole plant inoculations based on root infections. Foliar disease severity ratings of stem-cuttings were higher (P < 0.001) when they were immersed in culture filtrates of the fungus grown in soybean dextrose broth (SDB) than in potato dextrose broth (PDB) and when the fungus was grown for 18 and 22 days compared to growth for 6, 10 and 14 days in SDB. Foliar disease ratings of stem-cuttings were higher (P < 0.001) when incubated at 30 °C than at 25, 20 or 15 °C and when incubated at 8, 12 and 16 hours photoperiods than at 4 hours. Significant (P < 0.001) differences in foliar severity ratings occurred among 14 soybean genotypes using the optimized conditions in the growth chamber. SDS also occurs in South America, where several other species such as F. tucumaniae, along with F. virguliforme, have been reported to cause this disease. After an initial evaluation, nine soybean genotypes from Argentina and the U.S. were selected based on different disease rating levels, and tested with two F. virguliforme isolates and two F. tucumaniae isolates using seedling assay with infested sorghum and stem-cutting assay with cell-free culture filtrates. The area under the disease progress curves (AUDPC) values and shoot dry weight from the seedling assay and the AUDPC values from the stem-cutting assay differed (P < 0.05) by genotype and isolate. AUDPC values from the seedling assay were significantly negatively correlated (r = -0.63 at P < 0.0001) with the shoot dry weight, and significantly positively correlated (r = 0.44 at P < 0.0001) with the AUDPC values from the stem-cutting assay. A comparison was made between soy milk medium and media traditionally used for soybean pathogen maintenance (potato dextrose medium or V8 juice medium) to determine if soy milk medium was as effective for the growth and reproduction of nine soybean pathogens. Cercospora sojina, Colletotrichum truncatum and F. virguliforme grew significantly (P < 0.05) faster on soy dextrose agar (SDA) than on traditional media. A significantly (P < 0.001) greater mass of sclerotia was produced by Sclerotinia sclerotiorum grown on SDA than on potato dextrose agar. When the eight pathogens were grown on SDB, all produced significantly (P < 0.001) greater masses of dry mycelia than when they were grown on potato dextrose broth or a vegetable (V8) broth.
Issue Date:2013-05-24
Rights Information:Copyright 2013 Yiwen Xiang
Date Available in IDEALS:2013-05-24
Date Deposited:2013-05

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