Black Root Rot in Soybeans - June 18, 2009
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 growing 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.
[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]