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This article in CS

  1. Vol. 52 No. 5, p. 2215-2223
    Received: Sept 19, 2011

    * Corresponding author(s): lleandro@iastate.edu
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Screening Method for Distinguishing Soybean Resistance to Fusarium virguliforme in Resistant × Resistant Crosses

  1. Alexander S. Luckewa,
  2. Silvia R. Cianziob and
  3. Leonor F. Leandro *c
  1. a Dep. of Agronomy
    b Dep. of Agronomy
    c Dep. of Plant Pathology, Iowa State Univ., Ames, IA 50011


Current greenhouse screening methods for soybean [Glycine max (L.) Merr.] sudden death syndrome (SDS) are not sensitive enough to evaluate progeny of resistant × resistant crosses, which can possess resistance alleles at up to 12 quantitative trait loci (QTL). The objective of the study was to modify the current greenhouse screening method, the layer method, to increase its sensitivity in distinguishing SDS-resistant lines. Three experiments were conducted using infested sorghum [Sorghum bicolor (L.) Moench] as inoculum. In Exp. 1, five different inoculum densities (1:1, 1:5, 1:10, 1:15, and 1:20 inoculum:soil ratio) were compared, and the optimum density to distinguish genotypes was identified. In Exp. 2, the association between SDS field ratings and greenhouse severity scores was determined. In Exp. 3, the inoculum layer method was compared to the proposed modified mixed method. Inoculum ratios 1:15 and 1:20 showed the largest difference in SDS ratings between soybean genotypes. The best time to assess disease severity was 30 to 36 d after planting (DAP), with the highest correlation with field ratings at 36 DAP (r = 0.82, p < 0.05). The proposed modified method shifted the frequency distribution of SDS scores toward a normal curve. The findings indicate that the modified screening method using a 1:20 inoculum:soil ratio correlated well with field data and provided adequate screening of lines possessing up to 12 SDS resistant QTL without negatively impacting germination.

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