1. The Effect of Increased Soil Fertility on Seedling
Disease Development of Soybean in Ohio
Meredith Eyre1, Steve Culman2, Anne Dorrance1
INTRODUCTION
Soil fertility may affect the development of soybean
diseases, including seedling disease caused by soil
borne oomycete pathogens. Fertility
recommendations for soybean in Ohio are over 20
years old and one proposed scenario is that more
phosphorus and potassium may be required to
support the increase in yields that has occurred over
the past 2 decades. Though increased fertility levels
have the potential to enhance crop productivity and
profitability, secondary effects on pathogens may
prove detrimental to overall plant health (Datnoff et
al., 2007). Several studies have documented an
increase in seedling disease incidence or severity in
response to increased fertility levels (Canaday and
Schmitthenner, 2010; Dirks et al., 1980; Pacumbaba
et al., 1997). Therefore, the objective of this study
was to evaluate the impact of higher rates of P, K, and
P+K on seedling diseases caused by oomycetes in
both field and greenhouse trials.
Figure 2 A and B. The 2015 Van Wert site received a record 37.4 cm rain in
June. Wet conditions were especially conducive to water molds.
METHODS
DISCUSSION
In field studies, no significant differences in stand nor yield
occurred at any of the 5 sites over 2 years. However, a
significantly higher number of damped-off plants in plots
treated with K occurred at one location (p= 0.041). In the
survey, a trend occurred in that the phosphorus, potassium,
and phosphorus plus potassium treatments seemed to
increase the number of oomycete isolates recovered,
suggesting an increase in seedling disease. A wide diversity
representing 16 species of Pythium and Phytophthora were
collectively recovered from both fields. Lower root and plant
weights occurred in plants which received fertility treatments
in 2 of 3 greenhouse trials as compared with the nontreated
control. However, high disease pressure and variable
greenhouse conditions likely complicated results.
References
1 Canaday C, Schmitthenner A, 2010. Effects of chloride and ammonium salts on the incidence of Phytophthora root
and stem rot of soybean. Plant Disease 94, 758-765.
2 Datnoff, LE, Elmer, WH, Huber, DM, 2007. Mineral nutrition and plant disease. St. Paul Minnesota, USA: APS Press.
3 Dirks V, Anderson T, Bolton E, 1980. Effect offertilizer and drain location on incidence ofPhytophthora rot in soybeans. Canadian
Journal ofPlant Pathology 2, 179-183.
4 Pacumbaba R, Brown G, Pacumbaba Jr R, 1997. Effect of fertilizers and rates of application on incidence of soybean
diseases in northern Alabama. Plant Disease 81, 1459-1460.
Acknowledgements
I would like to thank the OSU Soybean Pathology team for assistance with field and lab
work. Funding for this project was provided by the Ohio Soybean Council. Research
support provided by state and federal funds appropriated to The Ohio State University,
Ohio Agricultural Research and Development Center.
Seedling Disease
1. Soybean Pathology Lab (The Ohio State University)
2. Soil Fertility Lab (The Ohio State University)
OARDC, 1680 Madison Ave., Wooster, Ohio 44691
The Ohio State University / Department of Plant Pathology
Figure 1. Symptoms of Pythium and Phytophthora infection may include
lesions on the root, stem, or hypocotyls resulting in damping-off or reduced
stand.
RESULTS
Field Studies
Defiance
(2014)
Defiance
(2015)
Van Wert
(2014)
Van Wert
(2015)
Waynea
(2015)
Early stand emergence 0.930 0.357 0.876 0.236 0.229
Final stand emergence 0.189 0.634 0.559 0.772 0.078
Yield 0.183 0.967 0.486 0.679 0.680
aThe Wayne field site was decimated by a seedcorn maggot infestation.
Figure 3. The number of seedlings with damping-off symptoms differed
significantly between additional phosphorus, potassium, phosphorus and
potassium, and control treatments at Van Wert in 2015 (p= 0.041, LSD (0.05)=
27.4). Error bars represent standard deviation for each treatment.
Table 1. P-values from Analysis of Variance (ANOVA) for stand and yield from a field
study that evaluated the addition of phosphorus, potassium, and phosphorus plus
potassium at 5 locations in Ohio with a history of seedling disease.
Survey of symptomatic seedlings
Greenhouse Studies
Figure 5. In a field study that evaluated the addition of phosphorus, potassium, and phosphorus plus
potassium, isolates were recovered from soybean roots collected at the VC growth stage from a
survey conducted in Defiance and Van Wert Co. in 2015. All recovered isolates were observed at 100
to 400x and samples containing oospores were characterized as oomycetes. Although identification
through BLAST analysis of the ITS region was attempted for all oomycetes, only a subset were
successfully sequenced and subsequently identified as Pythium or Phytophthora. The number of
Pythium and Phytophthora species recovered from each treatment is also included.
Figure 4. Pythium and Phytophthora species were recovered from soybean roots collected at the VC
growth stage from Defiance and Van Wert in 2015. Fields were treated with phosphorus, potassium,
and phosphorus plus potassium in a study to determine the fertility effect on the frequency and
diversity of oomycete species recovered.
Figure 6. Greenhouse experiments designed to replicate field studies were conducted
with infested field soil.
• Five field sites in Ohio with a history of seedling disease:
Defiance Co. (2014), Defiance Co. (2015), Van Wert Co. (2014),
Van Wert Co. (2015), Wayne Co. (2015).
• Treatments applied at planting included:
• Phosphorus: 100 lb/a of P2O5 (applied as DAP)
• Potassium: 100 lb/a of K2O (applied as potash)
• Phosphorus + potassium: 100 lb/a of P2O5 +100 lb/a K2O
• Nontreated control
• Treatments were arranged in a randomized complete block
design with six replicates at each site. Untreated seed of one
susceptible cultivar was used throughout the study.
• Early stand, final stand, and yield data were collected and
analyzed.
• In an intensive survey of Defiance and Van Wert fields in 2015,
isolates were recovered from the roots of symptomatic
seedlings at the VC growth stage and identified through ITS
sequencing and BLAST analysis.
• Greenhouse assays replicated field experiments with infested
field soil. Soil from Defiance and Van Wert were used in 3
separate trials.
Field Studies
Survey of symptomatic seedlings
Greenhouse Studies
b
a
b
b
0
20
40
60
80
100
120
140
P K PK none
Plantsaffectedbydampingoff(plants/30'row)
Number of Seedlings Affected by Damping-off
at Van Wert in 2015
Table 2. P-values from Analysis of Variance (ANOVA) for stand, root ratings, and plant weights
from a greenhouse study that evaluated the addition of phosphorus, potassium, and
phosphorus plus potassium to field soil collected from Defiance (Def) and Van Wert (VW), each
with a history of seedling disease. Three trials were conducted with soil from each field.
Figure 7. A) In greenhouse assays, seedling
disease was observed in all treatments
except the steamed soil control, which was
not included in the ANOVA. B) Definitive
oospores were observed and oomycete
isolates were recovered from the roots of
seedlings.
A
B
0
5
10
15
20
25
30
P K P/K None
NumberofIsolates
Oomycete Isolates Recovered
from Van Wert
0
5
10
15
20
25
30
P K P/K None
Numberofisolates
Oomycete Isolates Recovered
from Defiance
0
2
4
6
8
10
12
14
Isolates
Oomycete Isolate Identification by Field
Defiance
Van Wert
0
2
4
6
8
10
12
14
Isolates
Isolate Identification by Treatment
none
PK
K
P
Variable VW 1 VW 2 VW 3 Def 1 Def 2 Def 3
Stand 0.111 0.054 0.791 0.625 0.254 0.069
Root rot rating 0.092 0.045 0.778 0.403 0.111 0.320
Root weight 0.120 0.028 0.703 0.100 0.112 0.002
Root weight/stand 0.578 0.625 0.193 0.014 0.219 0.779
Plant weight 0.124 0.056 0.466 0.362 0.110 0.002
Plant weight/stand 0.571 0.371 0.376 0.019 0.361 0.363
A
B