 Soybean
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Black Root Rot in Soybeans
June 18, 2009
(4 minutes: 9 seconds)
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(4 minutes: 9 seconds)
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Audio/Video Script:
Scott Monfort
Extension Plant Pathologist
[Title Slide – Black Root Rot in Soybeans, Dr. Scott Monfort, Extension Plant
Pathologist, Number 4 - June 18, 2009, Your Arkansas Soybean Podcast, University of Arkansas Division of Agriculture, Arkansas Soybean Promotion Board]
[Scott Monfort in a soybean field] Hi, I’m Scott Monfort, Extension Plant
Pathologist for the University of Arkansas Division of Agriculture. Today, I
want to take a moment and talk to you a little bit about an emerging problem
that we’re seeing in soybeans. It’s called black root rot and it’s presenting
itself in these soybean acres that were once produced in cotton.
[Slide – Black Root Rot; Caused by fungus called Thielaviopsis basicol;
Primarily affects cotton in Arkansas; Affects root system; Develops during
cool, wet conditions early plant growth stages; Soil-borne fungus common to
Arkansas. Picture of soybean pods. ] Traditionally, black root rot, caused by
the fungus Thielaviopsis basicola [picture of fungus], has been a disease
primarily affecting cotton in Arkansas. [Pictures of plants showing black root
rot, some heavily damaged and some with minimal damage] Black root rot affects
the plant’s root system - infecting root tissue which can lead to seedling death
in severe cases. [Picture of a soybean field] Environmental conditions that
encourage the development of the disease are cool, wet conditions during early
plant growth stages. Black root rot is a soil-borne fungus that is indigenous to
Arkansas soils. [Slide – Black Root Rot; Caused by fungus called
Thielaviopsis basicol; Primarily affects cotton in Arkansas; Affects root
system; Develops during cool, wet conditions early plant growth stages;
Soil-borne fungus common to Arkansas. Picture of soybean pods. ]
[Pictures of a soybean fields] Due to a combination of cool, wet weather and
recent shifts in acreage from cotton to soybeans in the last two years, black
root rot is becoming an issue for soybean growers. [Slide – 2008 Field
Observations; Picture of fields and plants; Field in Phillips County with
seedling death and stunted plants; Estimated 35% of field affected.] In 2008,
suspect plants were examined in an east central Arkansas soybean field. Initial
disease symptoms were similar to those found on cotton infected with black root
rot. Disease incidence was estimated at 35% of the field. [Slide showing image
of Phillips County Field with Black Root Rot Infection in 2008. Image shows
disease impacted areas where plant vigor is poor.] A classified image of the
affected field helps illustrate the impacted areas shown in dark reddish brown
color. To confirm the diagnosis of black root rot on these soybean plants,
pathogenicity tests were conducted.
[Slide – Diagnosing Black Root Rot; 1. Examine the root system for presence
of blackened, deformed roots. 2. Plate infected roots on specialized media
specific to Thielaviopsis basicol Picture of soybean pods.] The best way
to distinguish this disease is to examine the root system of the plant. [Picture
of roots with signs of black root rot.] The primary diagnostic characteristic of
black root rot is blackened, deformed roots. [Pictures of plants showing
infected root comparisons of black root rot, some heavily damaged and some with
minimal damage] The blackened roots are the result of fungus infection and
colonization of cortical tissue [Picture of roots with blackened root rot] which
eventually leads to root necrosis. [Pictures of roots being tested in a petri
dishes] Confirmation of the fungus can be achieved from plating out infected
roots on specialized media specific to Thielaviopsis basicola. [Pictures
of Thielaviopsis basicola fungus groing from infected root system in a
petri dish] A positive result will show growth of the fungus out of the infected
root tissue as dark-colored round colonies on the media.
[Slide – Above Ground Disease Symptoms; Seen within first four weeks of
growing season; Can look similar to other issues like: Soil compaction problems,
Nutrient deficiencies, and Plant stress issues, i.e. drought stress; Suspect
plants require diagnostic confirmation in a lab. Picture of soybean pods.]
Symptoms of black root rot can also be observed above ground within the first
four weeks of the growing season. However, they can appear similar to symptoms
of other plant health issues like soil compaction problems, nutrient
deficiencies, or general plant stresses.
[Scott Monfort in a soybean field] Three typical above-ground symptoms that
we observe with black root rot are, one, severe stunting. We also see stacking
of the nodes, and the third symptom that we see a lot in this situation is
chlorotic spots that form along the veins of the leaves.
[Slide –2009 Research on Black Root Rot; Greenhouse studies and field trials;
Goals, to understand potential of disease on soybeans, and to generate possible
control recommendations. Picture of soybean pods.] Research trials have
continued in 2009 in field and greenhouse settings to understand the potential
of this disease on soybeans and to generate possible control recommendations.
[Slide –2009 Research on Black Root Rot; Will evaluate – Soybean varieties for
disease resistance and seed treatments for potential control. Picture of soybean
pods.] These research trials will evaluate varieties for potential resistance as
well as seed treatments for potential control. [Slide – Bar chart showing black
root rot green house test results in 2008.] So far, greenhouse trials have shown
black root rot to have a significant impact on soybean seedling survival – 38
out of 100 plants survived in infested soil compared to 71 out of 100 plants in
non-infested soil. [Slide – Black Root Rot Green House Test, 2008 showing
pictures of petri dishes with test results; Fungus does not grow out of
non-infected roots; Thielaviopsis basicola grows out of infected roots on
specialized media.] All surviving plants grown in infested soil were found
positive with black root rot.
[Slide –Black Root Rot Impact on Soybeans; Very few control options known;
Could have yield-limited potential but no studies confirm yield loss; On-going
research to learn more about disease. Picture of soybean pods.] Currently, very
few control options are known to prevent development and spread of this disease
in soybeans. Black root rot could have yield-limiting potential, however, no
studies have confirmed yield loss in soybeans to date.
[Slide –Think you have Black Root Rot? Contact your local county agent for
referral to a state extension plant pathologist. Picture of soybean pods.] If
you think you may have symptoms of black root rot, contact your local county
agent for referral to a state extension plant pathologist.
Announcer
[Narrator] Your Arkansas Soybean Podcast is a production of the University of Arkansas Division of Agriculture and was funded in part by the Arkansas Soybean Promotion Board. For more information on soybean farming in Arkansas contact your local county Extension Office. [Title slide - For more information contact your local county Extension office. Your Arkansas Soybean Podcast, University of Arkansas Division of Agriculture, Arkansas Soybean Promotion Board]
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