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This article in CS

  1. Vol. 48 No. 6, p. 2334-2342
    Received: Jan 4, 2008

    * Corresponding author(s): skumud@email.uky.edu
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Mechanisms Involved in Soybean Rust-Induced Yield Reduction

  1. S. Kumudini *a,
  2. C. V. Godoyb,
  3. J. E. Boardc,
  4. J. Omielana and
  5. M. Tollenaard
  1. a Dep. Plant and Soil Sciences, Univ. of Kentucky, Lexington, KY 40546
    b EMBRAPA (Empresa Brasileira de Agropecuaria)-Soja, Rodovia Carlos Joao Strass, Caixa Postal 231, Londrina, PR, Brazil
    c School of Plant, Soil, and Environmental Science, Louisiana State Univ., Baton Rouge, LA 70803
    d Dep. of Plant Agriculture, Crop Science Bldg., Univ. of Guelph, Guelph, ON, Canada, N1G 2W1. Published with the approval of the Director of the Kentucky Agric. Exp. Stn. as Paper no. 08-06-049. Research was financially supported, in part, by USDA-Risk Management Agency


Soybean rust (SBR; caused by Phakopsora pachyrhizi Syd. and P. Syd.) leads to premature leaf loss and yield reduction. The objectives of this study were to assess effects of SBR infection on soybean [Glycine max (L.) Merrill] yield and to identify causes for the yield reduction. Experiments were conducted in the 2005–2006 and 2006–2007 growing seasons at Londrina, Brazil. The five treatments were SBR infection beginning at either (i) the R2 or (ii) R5 growth stages; nondiseased defoliation treatments to mimic the leaf loss when SBR started at either (iii) the R2 or (iv) R5 growth stages; and (v) a disease-free, nondefoliated control. The control and defoliation treatments were protected against SBR by fungicide applications. Disease severity, lesion area, and leaf area were monitored from R2 to R7. Biomass and seed yield were measured at maturity. Mean SBR-induced yield reductions were 67% when infection started at R2 and 37% when infection started at R5. Leaf loss alone reduced yield significantly in only one year and only when defoliation treatments were begun at R2 (31% in 2005–2006). Soybean rust–induced yield loss was attributable to (i) premature leaf loss, (ii) reduction in canopy green leaf area due to SBR lesions, (iii) reduction in dry matter accumulation per unit absorbed radiation by the nonlesion green leaf area, and (iv) reduction in harvest index. The response of harvest index was attributable to reduced seed set and seed mass resulting likely from SBR-induced reductions in rate of dry matter accumulation.

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