PEST MANAGEMENT: DISEASES
Rice Genotype Response to Fungicide
and Insecticide Seed Treatments
C.S. Rothrock, S.A. Winters, and R.L. Sealy
ABSTRACT
Stand establishment problems occur frequently in Arkansas rice fields and are
commonly associated with cool soil temperatures (early planting) and saturated soils. In
2011, seven trials at three locations examined the efficacy of seed treatment chemistries
and genotypes in improving stand establishment. The study included seven genotypes
which differed in their cold tolerance and resistance to seedling disease caused by
Pythium spp. The seed from each genotype received no treatment or the seed treatments Allegiance (metalaxyl), Allegiance + Cruiser (thiamethoxam), or Allegiance +
Cruiser + Dynasty (azoxystrobin). The plant stand for Kaybonnet was increased by
seed treatments for each of the five trials having a response. The cultivar Templeton
and two genotypes (PI560243 and RU0701124) which have previously shown some
Pythium spp. resistance responded to fungicides with increased plant stands in one of
the five trials. The genotypes PI560247, PI560281, and STG05F5-03-088, which have
demonstrated some resistance to Pythium spp., did not respond to fungicide seed treatment. The fungicide Allegiance provided similar control to the combination fungicide
treatments Allegiance + Cruiser and Allegiance + Cruiser + Dynasty. The fungicide
metalaxyl has activity only against oomycetes indicating that Pythium spp. are the primary seedling pathogens causing stand losses of rice in Arkansas. Stand improvement
from fungicides was greater for earlier planting dates compared to the final planting
date for a location. Root scanning data demonstrated that for the susceptible cultivar,
Kaybonnet, Allegiance was effective in improving root growth and development compared to no seed treatment. The research demonstrates that fungicide seed treatments
or Pythium-resistant cultivars improve rice stand establishment.
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AAES Research Series 600
INTRODUCTION
Pythium spp. are the most common seedling disease pathogens isolated from
rice in producers’ fields in Arkansas. These pathogens can cause seed rot and death of
seedlings before or after emergence and may reduce vigor of surviving seedlings. P.
arrhenomanes and P. irregulare are the most important Pythium seedling pathogens on
rice (Cother and Gilbert, 1993; Eberle et al., 2008). Seed treatment fungicides, including metalaxyl and mefenoxam, that have activity against this group of pathogens are
effective in increasing stands under cool soil temperatures and wet soils which favor
Pythium seed and root rot. Research funded by the Rice Research and Promotion Board
also has identified cold-tolerant Pythium-resistant rice genotypes that hold the promise
for more reliable stand establishment for marginal planting environments in Arkansas
rice fields (Rothrock et al., 2006, 2010).
This research examined the value of fungicide and insecticide seed treatments
and genotypes on stand establishment and seedling root development over a range of
planting environments.
PROCEDURES
Seven trials were conducted at three locations in Arkansas in 2011. Planting dates
ranged from 21 March to 11 May. The trial locations were Pine Tree Branch Experiment
Station (Colt), Northeast Research and Extension Center (Keiser), and Rice Research
and Extension Center (Stuttgart) representing the White River, Delta, and Grand Prairie
ecosystems, respectively. The trials evaluated seven genotypes (Kaybonnet, PI560243,
PI560247, PI560281, RU0701124, STG05F5-03-088, and Templeton) which differed
in their resistance to seedling disease caused by Pythium spp. Each genotype had no
seed treatment or the seed treatments Allegiance (metalaxyl), Allegiance + Cruiser
(thiamethoxam), or Allegiance + Cruiser + Dynasty (azoxystrobin). Each test was a
split-plot design with genotype as the main plot and fungicide treatment as the subplot.
Stand counts for each plot were the mean of three 1-m row counts. Analyses included
stand and relative stand between the seed treatment and non-treated seed treatment.
In 2011, the effects of fungicide seed treatment on seedling growth also were
examined for Kaybonnet, PI560281, RU0701124, and STG05F5-03-088. From the
second planting date at Stuttgart (7 April), 15 to 20 seedlings were dug from each plot
of selected genotypes. Rice seedlings were washed for 20 min in running tap water
and roots and coleoptiles were assessed for disease. Root systems of seedlings were
scanned using the WinRHIZO system (Regent Instruments Inc., Canada) for root length
and volume. In addition, the WinRHIZO software characterized the root architecture
including root tips and branching patterns; forks, links, link length, and altitude. Root
parameters were averaged for each plot and analyzed by GLM using SAS (SAS Institute, Cary, N.C.). Treatment means for sites having a significant F-test were separated
by using a protected LSD, P = 0.05.
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B.R. Wells Rice Research Studies 2011
RESULTS AND DISCUSSION
Minimal soil temperatures at 10 cm (4 in.) the first 3 days after planting for the
trials ranged from 11 °C to 21 °C (51 °F to 70 °F) with a mean temperature of 14 °C to
24 °C (58 °F to 75 °F). One or more seed treatments increased stands for one or more
genotypes for five of the seven trials (Table 1). The plant stand for Kaybonnet was
increased by fungicide seed treatments in each of the five trials having a response. The
cultivar Templeton and two genotypes (PI560243 and RU0701124) which have previously shown some Pythium spp. resistance responded to fungicides with increased plant
stands in one of the five trials. The genotypes PI560247, PI560281, and STG05F5-03088, which have also demonstrated some resistance to Pythium spp., did not respond
to fungicide seed treatments. The fungicide Allegiance provided similar control to the
combination fungicide treatments Allegiance + Cruiser and Allegiance + Cruiser +
Dynasty. When differences among seed treatments were found Allegiance + Cruiser +
Dynasty increased stands compared to Allegiance alone in two of eight comparisons
and in one of eight comparisons Allegiance increased stands compared to Allegiance
+ Cruiser + Dynasty. There was no response observed when Cruiser was added to Allegiance. The fungicide metalaxyl (Allegiance) has activity only against oomycetes
indicating that Pythium spp. are the primary seedling pathogens causing stand losses of
rice in Arkansas. In addition, the frequency of fungicide response suggests that seedling
diseases were common and reduced stands in 2011. Stand improvement from fungicides
was greater for earlier planting dates compared to the final planting date for a location.
Several genotypes did not have a response to fungicides suggesting greater resistance
to Pythium seed and root rot than currently grown cultivars.
Root scanning technology demonstrated that for the susceptible cultivar, Kaybonnet, Allegiance was effective in improving root development, while Allegiance had little
to no effect on root growth for Pythium resistant genotypes (Table 2). For example,
relative root length and volume and number of root branches, forks, were increased on
seedlings from Allegiance-treated seed compared to non-treated seed for Kaybonnet.
This difference was significant for root forks compared to the two genotypes considered
resistant which were close to 1 for the relative response. Root tips did not differ among
genotypes and seemed to be increased for seedlings from Allegiance-treated seed. When
root topology was examined, the relative number of links (individual root segments)
and altitude (the largest path length, link total, to the base of the plant) for Kaybonnet
were increased with Allegiance treatment compared to the other two genotypes, while
relative link length was decreased by Allegiance treatment for Kaybonnet, indicating
increased branching as indicated by number of root forks. This data suggest surviving
rice seedlings treated with Allegiance have improved root system health in addition to
seed treatment fungicides protecting the seed and emerging seedling.
SIGNIFICANCE OF FINDINGS
This research suggests seedling diseases are a common cause of stand establishment problems in Arkansas and fungicide seed treatment or Pythium-resistant cultivars
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AAES Research Series 600
hold the promise for more reliable stand establishment for rice. Fungicide seed treatments are an effective option for managing seedling diseases. In addition, this data
suggest surviving rice seedlings treated with Allegiance have improved root health
with a larger root system and increased root branching to explore more soil and allow
greater water and mineral absorption. Pythium-resistant genotypes were demonstrated
to be as effective as seed treatments in preventing seedling disease losses.
ACKNOWLEDGMENTS
This research was conducted with the support of the Rice Research and Promotion
Board. The authors want to thank Eddie Castaneda, Shawn Clark, and Mike Duren for
helping to establish the trials.
LITERATURE CITED
Cother, E.J. and R.L. Gilbert. 1993. Comparative pathogenicity of Pythium species
associated with poor seedling establishment of rice in Southern Australia. Plant
Pathology 42:151-157.
Eberle, M.A., C.S. Rothrock, and R.D. Cartwright. 2008. Pythium species associated
with rice stand establishment problems in Arkansas. In: R.J. Norman, J.-F. Meullenet, and K.A.K. Moldenhauer (eds.). B.R. Wells Rice Research Studies 2007.
University of Arkansas Agricultural Experiment Station Research Series 560:5763. Fayetteville, Ark.
Rothrock, C.S., R.L. Sealy, J.W. Gibbons, and F.N. Lee. 2010. Developing cold-tolerant cultivars with seedling disease resistance to Pythium species: Evidence for
and nature of resistance in RU0701124. In: R.J. Norman and K.A.K. Moldenhauer (eds.). B.R. Wells Rice Research Studies 2009. University of Arkansas Agricultural Experiment Station Research Series 581:84-89. Fayetteville, Ark.
Rothrock, C.S., R.L. Sealy, F.N. Lee, J. Gibbons, and R.D. Cartwright. 2006. Relationship of cold-tolerance and Pythium resistance to rice stand establishment. In:
R.J. Norman, J.-F. Meullenet, and K.A.K. Moldenhauer (eds.). B.R. Wells Rice
Research Studies 2005. University of Arkansas Agricultural Experiment Station
Research Series 540:138-142. Fayetteville, Ark.
92
Kaybonnet
PI560243
PI560247
PI560281
RU0701124
Stuttgart (3/21/2011)
None
18.5 b
32.5 a
21.6 a
25.0 a
25.9 a
Allegiance
33.6 a
27.7 a
28.2 a
26.6 a
23.1 a
Allegiance + Cruiser
25.1 ab
30.2 a
29.6 a
27.8 a
26.7 a
Allegiance + Cruiser + 32.1 a
33.0 a
33.4 a
25.5 a
30.3 a
Dynasty
P-value
0.0223
0.3846
0.1247
0.9429
0.0837
Pine Tree (4/8/2011)
None
23.3 a
29.4 a
34.1 a
25.3 a
28.8 a
Allegiance
29.2 a
31.3 a
28.9 b
26.3 a
29.6 a
Allegiance + Cruiser
32.9 a
33.1 a
30.1 b
26.9 a
30.3 a
Allegiance + Cruiser + 38.5 a
36.1 a
31.5 ab
23.5 a
28.3 a
Dynasty
P-value
0.0614
0.4652
0.0295
0.1097
0.9445
Pine Tree (3/31/2011)
None
15.6 c
20.4 a
20.5 a
22.9 a
18.5 a
Allegiance
24.0 b
23.4 a
22.6 a
24.5 a
22.2 a
Allegiance + Cruiser
24.8 b
23.8 a
22.3 a
25.5 a
23.0 a
Allegiance + Cruiser + 28.5 a
26.9 a
23.4 a
21.5 a
23.1 a
Dynasty
P-value
<.0001
0.0751
0.7703
0.3422
0.1117
Pine Tree (3/21/2011)
None
7.6 b¶
15.2 a
12.6 a
17.1 a
11.5 b
Allegiance
19.8 a
16.6 a
15.2 a
17.6 a
17.9 a
Allegiance + Cruiser
17.7 a
15.2 a
16.3 a
15.2 a
15.4 a
Allegiance + Cruiser + 18.6 a
16.5 a
14.8 a
17.8 a
15.5 a
Dynasty
P-value
0.0001
0.6596
0.4378
0.6550
0.0032
Fungicide
0.1439
21.9 a
24.2 a
17.0 a
27.0 a
0.6227
24.8 a
28.9 a
27.7 a
29.0 a
0.3793
22.0 a
20.8 a
22.0 a
23.4 a
0.7101
14.3 a
15.2 a
15.2 a
16.5 a
STG05F5-03-088
Table 1. Efficacy of seed treatments on stand establishment (plants/m) for seven trials.
0.5342
continued
27.1 a
31.9 a
30.6 a
34.0 a
0.0983
28.7 a
28.1 a
29.4 a
32.5 a
0.0021
18.0 c
28.0 a
22.7 b
23.5 b
0.0984
15.9 a
16.5 a
15.3 a
20.4 a
Templeton
B.R. Wells Rice Research Studies 2011
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Kaybonnet
PI560243
PI560247
PI560281
RU0701124
0.5729
40.6 a
39.2 a
36.6 a
39.7 a
0.6074
30.0 a
28.9 a
31.9 a
33.0 a
STG05F5-03-088
¶
0.1482
27.3 a
26.6 a
32.8 a
29.0 a
0.3987
38.6 a
44.6 a
43.2 a
44.6 a
0.3014
35.1 a
31.9 a
36.4 a
36.5 a
Templeton
Seed treatments within a trial and genotype followed by the same letter are not significantly different, protected LSD (P = 0.05).
Keiser (5/11/2011)
None
18.3 b
19.8 b
23.1 a
21.6 a
24.4 a
22.5 a
Allegiance
28.0 a
20.5 b
27.9 a
24.3 a
24.8 a
22.8 a
Allegiance + Cruiser
32.1 a
21.3 b
25.4 a
24.8 a
27.8 a
26.6 a
Allegiance + Cruiser + 27.4 a
26.8 a
26.4 a
24.9 a
28.4 a
24.5 a
Dynasty
P-value
0.0017
0.0005
0.2853
0.4938
0.2638
0.2147
Stuttgart (4/29/2011)
None
31.9 a
34.3 a
40.8 a
33.9 a
Allegiance
40.8 a
39.6 a
37.2 a
35.1 a
Allegiance + Cruiser
37.3 a
37.1 a
39.0 a
37.8 a
Allegiance + Cruiser + 40.0 a
38.7 a
38.1 a
36.9 a
Dynasty
P-value
0.1965
0.4877
0.8269
0.6191
Stuttgart (4/7/2011)
None
22.0 b
31.8 a
25.8 a
30.0 a
27.3 a
Allegiance
32.4 a
31.9 a
27.4 a
30.4 a
28.4 a
Allegiance + Cruiser
35.5 a
31.0 a
28.0 a
32.2 a
33.2 a
Allegiance + Cruiser + 37.1 a
30.8 a
30.6 a
31.2 a
29.9 a
Dynasty
P-value
0.0009
0.9658 0.5967
0.9127
0.1808
Fungicide
Table 1. Continued.
AAES Research Series 600
1.64 a§
0.97 a
1.03 a
0.0928
Root length
1.30 a
0.78 a
0.94 a
0.1971
Root volume
2.17 a
0.96 b
1.03 b
0.0443 Root forks 1.36 a
1.21 a
1.22 a
0.5417
Root tips
2.05 a
0.98 a
1.03 a
0.0519
Number of links
1.51 a
0.93 b
0.97 b
0.0347
Altitude
Seedlings were dug on 12 May 2011 from the Stuttgart planting date study planted on 7 April 2011. Mean of ≥ 15 seedlings.
Genotypes within a column followed by the same letter are not significantly different, protected LSD (P = 0.05).
§
¶
Kaybonnet
PI 560281
RU0701124
P-value
Table 2. Effect of fungicide seed treatment on relative root development and
root architecture (Allegiance treated seed/non-treated seed) for selected rice genotypes¶.
0.60 b
1.05 a
0.98 a
0.0286
Link length
B.R. Wells Rice Research Studies 2011
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