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Date: Mon 27 Aug 2007
Source: Cattle Network [edited]
<http://www.cattlenetwork.com/content.asp?contentid=155466>

Sudden death syndrome (SDS) has been found in many Nebraska soybean fields over the last two weeks. This disease was only first confirmed in the state in 2004. Calls and samples across the eastern half of Nebraska suggest the disease is widespread, but in most fields large areas are not affected.

Sudden death syndrome of soybean is caused by the fungus _Fusarium solani_ f. sp. _glycines_. This is a different fungus than the one that caused early season damping off problems associated with soybean stands. This year's weather with moisture in the early season and at the early reproductive stage has been conducive to SDS. It should be possible to see full symptom expression now.

Early planting favors SDS. With all the information on increasing yields with earlier planting, we expect to see more of this disease.
Soil compaction and high fertility levels also have been associated with increased levels of SDS.

The foliar symptoms start with interveinal necrosis and the spots coalesce to form brown streaks between the leaf veins with yellow margins. Leaves eventually drop with the petiole (leaf stem) remaining attached. The root system will have a deteriorated tap-root and lateral roots will only be evident in the upper soil profile. The root cortex is light-gray to brown and may extend up the stem.
Typically, plants can be pulled from the ground easily and will have a dark blue fungal growth on the roots. The blue color will not be evident in dry soil conditions.

At this time SDS appears to be widespread in Nebraska, but it can be effectively managed. If a large area of the field is affected, early planting should be avoided and resistant varieties used next year.
Thus far, seed treatment has not been shown to be effective.

[Byline: Source: Nebraska Ag Extension]

--
Communicated by:
J. Allan Dodds
Former ProMED-mail plant disease moderator <dodds@ucr.edu>

[SDS was 1st discovered in the USA (Arkansas) in 1972 and has now become widespread in soybean-growing regions in the United States, Argentina, and Brazil. Plants turn yellow and die quickly after pod set and symptoms often appear in patches in a field. Yield losses may be more than 80 percent, depending on variety and timing of infection. Appearance of SDS at early pod fill is reportedly more damaging than its appearance at a later stage of plant development.
Yield reduction is the result of reduced photosynthetic area, defoliation, flower and pod abortion, and reduced seed size.

_Fusarium virguliforme_ (previously _F. solani_ f. sp. _glycines_) has been described as the causal pathogen in North America and _F.
tucumaniae_ in South America. Phylogenetic evidence indicates the 2 SDS pathogens do not share a most recent common ancestor, but appear to have evolutionary origins in the southern hemisphere since they are deeply nested within a South American clade of the _F. solani_ species complex. The fungi cannot be isolated from tissue above the soil line. Foliar symptoms are thought to be the result of a fungus-produced plant toxin.

It is suggested that any stress factor (biological, mechanical, or
environmental) may magnify SDS symptom expression and cause SDS-affected plants to deteriorate earlier. In particular, Soybean cyst nematode (SCN), although not required for severe SDS to occur, is reported to exacerbate foliar symptoms and lead to early and severe SDS, if present at sufficient levels. Other soybean pathogens affecting leaves, roots, or stems are being studied for a potential role in SDS development.

Map of US states:
<http://www.census.gov/geo/www/us_regdiv.pdf>

Pictures
Photo collection of SDS symptoms:
<http://www.ent.iastate.edu/imagegal/plantpath/soybean/sds/>
_F. virguliforme_:
<http://nspcc.cropsci.uiuc.edu/images/SDSmacroconidia.jpg>

Links
Information on SDS:
<http://www.indianasoybeanboard.com/SuddenDeath.shtml>,
<http://www.plantpath.wisc.edu/soyhealth/mgmtsds.htm>  and <http://www.ca.uky.edu/agc/pubs/ppa/ppa37/ppa37.htm>
Publication on taxonomy of SDS causal pathogens:
<http://www.mycologia.org/cgi/content/full/95/4/660>
_F. virguliforme_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=489315>
_F. tucumaniae_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=489463>. 
- Mod.DHA]

[see also in the archive:
2005
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Sudden death syndrome, soybean - USA (KY) 20050811.2350
2004
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Sudden death syndrome, soybean - Argentina 20040824.2357
2003
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Sudden death syndrome, soybean - Argentina 20030412.0886 Sudden death syndrome, soybean - USA (MN) 20030328.0776
2002
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Sudden death syndrome, soybean - USA (DE & MD) 20020710.4721 2000
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Soybean Fusarium infection, improved detection 20000920.1622 Soybean crop deaths - USA (Midwest) 20000827.1431]

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