Soybean Variety Response to Taproot Decline (TRD)

Paul Price, Padgett, Guy B.

Originally published January 18, 2019

Taproot decline (TRD) of soybean, caused by Xylaria sp., usually is not noticed until pod fill when interveinal chlorosis and necrosis (Figure 1) become evident from the turn row. However, the disease may cause seed rot, seedling disease (Figure 2), and plant death (Figure 3) at any point the growing season. Infected seedlings and vegetative stage plants usually go unnoticed because they are quickly covered by rapidly growing neighboring plants. Infected plants will break at the soil line when pulled. Roots will appear black when excavated (Figure 4), and are usually in contact with blackened debris from the previous season. Reproductive structures of the pathogen known as “dead man’s fingers” may appear at the base of affected plants or on other debris during periods of high humidity producing spores that resemble powdered sugar (Figure 5). Disease distribution within the row usually will have a focal point of dead plants, surrounded by those with foliar symptoms, and neighboring healthy plants. These areas may overlap creating a clustered and streaky distribution within a given field. Fields in soybean for two years or more are at risk to taproot decline, and yield losses can be significant. For more information concerning taproot decline, please read the first report at the following link:

Many requests for a list of susceptible/resistant varieties have been received prompting the release of preliminary data. During the past two off-seasons in the greenhouse, we have challenged varieties from the 2016 Official Variety Trials against the pathogen, Xylaria sp. The process is briefly described hereafter. We used sterilized millet infested with the pathogen to infest growing medium. Inoculum was standardized using inoculum concentration experiments (data not shown). A total of 145 varieties were screened. During each “run”, 4 replications of 40 varieties (4 seed/4” pot, planted in a linear furrow) were either inoculated at planting or left non-inoculated then removed to flood-irrigated greenhouse tables for three weeks. Plant roots were harvested, dried to final moisture, and weighed. The experiment was repeated once, and paired t-tests (α=0.05) were used to compare inoculated (n=8) vs. non-inoculated (n=8) root weights for each variety. For simplicity, we present the results here as the percentage of root weight reduction.

Paired t-tests indicated that significant root weight reduction occurred at 48% and higher. Based on percent root weight reduction, varieties were divided into four categories: susceptible (>48%), moderately susceptible (36-48%), tolerant (24-36%), and resistant (<24%). Out of 145, 97 varieties were deemed susceptible with percent root weight reduction ranging from 48 to 85%. There were 25 moderately susceptible, 16 moderately resistant, and 7 resistant varieties. For brevity, we will not present the susceptible varieties in this report. A list of all varieties included in the screening can be found here. Resistant, tolerant, and moderately susceptible varieties with corresponding percent root weight reduction are in Tables 1, 2, & 3, respectively. Field confirmation of these results is ongoing. Preliminary data from inoculated field trials indicates that varieties deemed resistant in the greenhouse show no significant response. Varieties deemed susceptible in the greenhouse show significant responses to inoculum in the field.

Table 1. List of TRD-resistant varieties as determined by inoculation and response.

Variety% Root Weight Reduction
CZ 4818LL18.879462
5067 LL22.559704

Table 2. List of varieties moderately resistant to TRD as determined by inoculation and response.

Variety% Root Weight Reduction
Armor 55-R6825.253945
CZ 5375RY26.205598
4880 RR27.926596
CZ 5225LL28.605468
Go Soy IREANE30.762175
4995 RR30.883269
AG 48X731.611326
AG 46X634.502577
5625 RR235.190462

Table 3. List of varieties moderately susceptible to TRD as determined by inoculation and response.

Variety% Root Weight Reduction
CZ 4105LL36.631044
REV 57R2137.152585
CZ 4222LL37.789292
REV 51A5640.734935
4967 LL43.925284
Armor 46-D0844.015611
Armor 48-D2444.107678
Go Soy 5115LL44.470801
Armor 48-D8045.47956
REV 56R6345.566353
REV 49R9445.659963
Rev 49L4945.896947

In addition to variety selection, data from research trials, numerous observations, and other anecdotal accounts indicate that tillage and/or rotation will reduce TRD incidence and mortality. To date, there are no recommended seed treatments for taproot decline. Ongoing research indicates that a few fungicides applied in-furrow at planting may be effective on the pathogen. Taproot decline is soil/debris borne; therefore, avoiding spread via equipment is recommended. More research is needed to develop and further refine management strategies for taproot decline.

For more information on these topics or others, please contact your local extension agent, specialist, nearest research station, or visit or

 Interveinal chlorosis and necrosis

Figure 1. Interveinal chlorosis and necrosis.

 Taproot decline

Figure 2. Taproot decline of seedling.

dead plant

Figure 3. Plant death caused by taproot decline.

Blackened root

Figure 4. Blackened root diagnostic of taproot decline adjacent to infested debris.

roots with taproot decline.

Figure 5. “Dead man’s fingers” produced by Xylaria sp., causal agent of taproot decline.

9/5/2019 7:02:07 PM
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