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Fwd: PRO/PL> Sudden death syndrome, soybean - USA (KY)

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  • Gloria Baikauskas
    ProMED-mail wrote:Date: Thu, 11 Aug 2005 15:37:59 -0400 (EDT) To: From: ProMED-mail
    Message 1 of 1 , Aug 11, 2005
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      ProMED-mail <promed@...> wrote:Date: Thu, 11 Aug 2005 15:37:59 -0400 (EDT)
      To: <promed-plant@...>
      From: ProMED-mail <promed@...>
      Subject: PRO/PL> Sudden death syndrome, soybean - USA (KY)


      SUDDEN DEATH SYNDROME, SOYBEAN - USA (KENTUCKY)
      ***********************************************
      A ProMED-mail post

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      International Society for Infectious Diseases


      Date:10 Aug 2005
      From: ProMED-mail

      Source: StopSoybeanRust.com, 9 Aug 2005 [edited]


      Kentucky soybean update: Rust, no. Sudden death syndrome: yes
      -------------------------------------------------------------
      As of August 3005, there is no confirmed soybean rust anywhere near Kentucky.

      However, according to Donald Hershman, Plant Pathologist, University
      of Kentucky Plant Disease Diagnostic Lab at Princeton has received
      numerous samples of soybean sudden death syndrome (SDS). Hershman
      reports that SDS is developing rapidly in some fields in southern
      Illinois, suggesting that SDS may be a significant player this year.

      By way of background, SDS is a root disease caused by the fungal
      pathogen _Fusarium solani_) f.sp. _glycines_. Roots of plants are
      infected and become diseased during the vegetative stages of plant
      development. Then, typically as plants enter the pod development
      stages, foliar symptoms are expressed as a result of foliar
      sensitivity to one or more plant toxins produced by the fungus in
      diseased root tissue.

      In extreme cases, plants can die prematurely, with yields being
      dramatically impacted. In some years (such as 2004), plants will show
      symptoms early and later recover, with no impact on crop yield. In
      most years the response is somewhere in the middle of these 2
      extremes.

      SDS is characterized by a rotting of the primary and secondary root
      system and a subtle brown discoloration of the stem tissue
      immediately inside the green exterior. Leaf symptoms that start as
      yellow spots and blotches between the veins of upper leaves
      (usually), leading to large areas of brown tissue between the veins,
      and eventual defoliation of the leaflets, but not the petioles.

      Abortion of flowers and young pods is common. Symptoms usually
      develop first in hot spots in fields of varying shapes and sizes.
      Entire fields may eventually become involved in severe instances, but
      even then, there are typically areas in fields where the disease is
      more severe than in others.

      At this time, there is nothing that can be done to make the disease
      less or more serious. The die is cast, as it were. SDS is in a race
      against time with the crop. If the crop reaches the R5-R6 stage
      before the disease is severe, then the yield prognosis will be
      excellent. Serious disease prior to the R5 stage, however, can result
      in substantial yield reductions. Typically the earlier the onset of
      serious SDS, the greater the impact will be on crop yield.

      Hershman was surprised to see so much SDS, considering the
      predominately dry conditions we had in June and July. He recalled the
      cool conditions that lingered in April and early May, and the fact
      that many growers planted earlier than normal in an attempt to escape
      soybean rust. Both the cooler soils and early planting dates may have
      resulted in more root infection by the SDS pathogen than is "normal".
      Then, the later season moisture stress conditions probably encouraged
      foliar symptom expression of SDS.

      He said that there is nothing one can do now to ameliorate the
      effects of SDS; the disease will have to run its course. However, the
      disease can be drastically reduced next season by planting a
      resistant variety coupled with avoiding late-April and early-May
      planting dates.

      [Byline: Donald Hershman]

      --
      ProMED-mail



      [Initially, the cause of SDS was elusive, with mechanical, cultural,
      environmental and biological factors all considered possible. Early
      studies involving soil fumigation indicated that the origin was
      biological. Subsequent work in Arkansas and Mississippi proved that
      SDS is caused by a strain of the common soil fungus _Fusarium solani_
      (FS-A). This result has been confirmed by work in Indiana and
      Missouri and is now generally accepted. Although FS-A is the primary
      organism associated with SDS, other pathogens may also be involved in
      disease development. The most studied of these is the soybean cyst
      nematode (SCN). Mississippi researchers found that while SCN is not
      required for severe SDS to occur, SCN at sufficient levels
      exacerbates foliar symptoms, leading to early and severe SDS. This
      finding is important, since the disease's timing and severity,
      relative to soybean development, determines how severely the yields
      are reduced. In addition to SCN, other soybean pathogens (foliar and
      root/stem infecting) are being studied for their potential role in
      SDS development. Preliminary data suggest that any stress factor
      (biological, mechanical or environmental) may magnify SDS symptom
      expression and cause SDS-affected plants to deteriorate earlier and
      die prematurely.

      Other conditions that affect SDS severity are planting date and
      nematode injury. Early planted soybeans generally suffer more injury
      than those planted later. The positive correlation between soybean
      cyst nematode injury and SDS severity was noted by some of the first
      researchers to study the disease. While the presence of _H. glycines_
      tends to exacerbate problems with SDS, it is not required for
      successful establishment of _F. solani_ f. sp. _glycines_ in its host.

      The best way to avoid SDS in future cropping is to avoid early
      planting, plant early to mid-season varieties, and plant varieties in
      SDS-prone fields which are not highly susceptible to SDS. True
      resistance to SDS is not yet available. However, avoiding planting
      highly susceptible varieties will usually help by delaying disease
      onset until the later stages of crop development as discussed above.

      Links:




      - Mod.DH]

      [see also:
      2004
      ----
      Sudden death syndrome, soybean - Argentina 20040824.2357
      2003
      ----
      Sudden death syndrome, soybean - USA (MN) 20030328.0776
      Sudden death syndrome, soybean - Argentina 20030412.0886
      2002
      ----
      Sudden death syndrome, soybean - USA (DE & MD) 20020710.4721
      Heterodera glycines, soybean - Europe: alert 20020802.4914
      2000
      ----
      Soybean crop deaths - USA (Midwest) 20000827.1431
      Soybean Fusarium infection, improved detection 20000920.1622]
      ......................................dh/pg/jw
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