GEM Germplasm – Unlocking Maize Diversity for Improving Host Plant Resistance
against West Corn Rootworm and Other Biotic Stresses
Principle Investigator:
Martin Bohn
Associate Professor for Maize Breeding and Genetics
University of Illinois, Urbana, Illinois
PROJECT DESCRIPTION
The Western corn rootworm (WCR) is a serious pest of maize in the U.S. and of
growing importance in Europe (Gray et al. 2009. Ann. Rev. Entomol. 53:303-321). Soil
insecticides, the use of transgenic maize hybrids producing a Bt toxin, and the rotation of
maize with other crops are successfully used to manage WCR populations. However, the
occurrence of WCR populations resistant to insecticides and adapted to cultural practices
raises the question of how sustainable transgenic control measures against WCR are.
Recent reports by Meihls et al. (2008. PNAS 105:19177-19182) and Lefko et al. (2008. J.
Appl. Entomol. 132:189-204) demonstrated the development of Bt toxin resistant WCR
populations under greenhouse conditions. The authors concluded that selection for Bt
resistance in WCR populations will be rapid if resistant WCR beetles do not have the
chance to mate with individuals unexposed to the Bt toxin. Therefore, pest management
systems integrating well designed refuges and multigenic host plant resistance will play an
important role in effectively managing WCR populations. A major roadblock towards
improved resistance to biotic stresses of maize is the apparent lack of genetic variation for
these traits in the Midwestern maize pools. This lack of diversity is in stark contrast to the
diversity available for improving other quantitative and agronomically important traits, like
grain yield, early maturity, or grain composition and emphasizes the need for broadening
the genetic basis of the Midwestern maize pools using exotic maize germplasm. The
overall goal of this project is the development of maize cultivars, i.e., inbreds and
populations, adapted to the U.S. Corn Belt, with improved host plant resistance against
WCR, ECB, and Fusarium by broadening the genetic basis for these characteristics using
exotic maize germplasm.
PROJECT ACTIVITIES
In order to ensure high WCR population densities in all fields used for germplasm
screening and evaluation in 2010 at the Crop Sciences Research and Education Center of
the University of Illinois at Urbana-Champaign, we employ a trap crop strategy. In 2009,
all fields for 2010 were planted with a corn-pumpkin mix in late June. This ensured that at
the end of the growing season WCR beetles preferentially laid their eggs in these fields. To
account for the spatial variation of egg laying, we used three replications in our field trials,
duplicated the WCR screening nursery, and grew rows of susceptible and resistant checks
in regular distances throughout the trap crop field.
1
Germplasm Development
A WCR nursery was established. It comprised of new GEM genotypes, segregating
F2 population derived from crosses between GEM-based inbreds with improved WCR
resistance (N=10 populations), and genotypes in different selfing generations (N=684,
derived from 4 GEM base populations). All germplasm in this nursery was exposed to high
WCR pressure. Genotypes with adequate WCR resistance were selfed.
In a protected nursery, S1 families of Cycle 0 of the Illinois WCR Synthetic selected
for their increased levels of WCR resistance in 2009 were recombined. New GEM
germplasm-derived inbreds with improved biotic stress resistance were crossed to form 10
new base populations. In addition, for the first time we applied double haploid (DH)
technology to developed double haploids from second cycle crosses selected for their
performance in the 2009.
Germplasm Evaluation
A set of 50 S4 inbreds was testcrossed to one tester and a set of 12 newly selected S6
lines were crossed with three testers. The testcrosses were produced as an in-kind
contribution by Pioneer Hibred in the summer season of 2009. All testcrosses were
evaluated for their level of WCR and ECB resistance as well as for their agronomic
performance in separated field experiments in the summer season of 2010. The
measurement of fumonisin concentration in grain obtained from the ECB trials is
underway.
In our Analysis of Variance, we defined inbred families as inbreds derived from the
same GEM source population. Within each inbred family different lineages were defined
by their pedigree relationships. Trait differences between inbred families and between
lineages within each inbred family were tested for significance using appropriate models.
Evaluation of S4 Testcrosses - Yield differences between GEM inbred families were
highly significant (P<0.001). Testcrosses of inbreds derived from CUBA117:S1520 yielded
on average of 200bu/acre with individual inbred testcross yields ranging from 163 to
254bu/acre (Tab. 1). The lowest yielding inbreds were derived from population MIRT-C5Y
with an average testcross yield of 151 bu/acre (range: 128 - 171bu/acre). In contrast, the
commercial check hybrids yielded an average of 209 bu/acre (range: 176 – 243bu/acre).
Most CUBA117:S1520 derived inbreds as testcrosses yielded as much as the commercial
checks. Differences between lineages within each inbred family were not significant. The
testcrosses tasseled on average 65 days after planting, varying between 63 and 67 days after
planting. In comparison to commercial check hybrids, testcrosses of GEM derived inbreds
flowered about 2 days later and were about 10cm taller.
Feeding of the first ECB generation larvae was minor. Damage due to second
generation ECB larvae was significant (P<0.001) between testcrosses varying between 0.4
and 6.8 (Tab. 1). Inbred families derived from populations MIRT-C5Y (ECB=2.4) and
UR13085:N0204 (ECB=1.5) showed the lowest ECB damage ratings. All other inbred
2
families were not significantly different among each other. However, inbreds within inbred
groups showed significant variation for ECB damage ratings. For WCR larvae feeding all
GEM derived testcrosses were not significantly different from the susceptible check
B37×H84 and commercial check hybrids not carrying the WCR-Bt gene (Tab. 1).
Evaluation of S6 Testcrosses - For S6 testcrosses, grain yield means ranged from
144 to 232bu/acre with an average yield of 187bu/acre (Tab. 2). The testcrosses tasseled
between 64 and 67 days after planting. The anthesis silking interval varied between one and
two days. The ear and plant heights ranged from 77 to 113cm and 192 to 244cm,
respectively. For grain yield, flowering time, as well as ear and plant height differences
between inbred groups means and commercial hybrids were in most cases not significant
(Tab 2). However, significant within group variation was found for all traits. Differences
between heterotic pools were not significant for all agronomic traits. ECB damage ratings
were low for all tested materials, whereas all testcrosses showed high WCR damage.
SUPPLEMENTARY ACTIVITIES
We continued our efforts to identify regions in the maize genome involved in the
resistance to WCR larvae feeding. Among other materials GEM derived inbreds with
improved levels of WCR resistance are of key importance. We were already successful in
identifying QTL regions in the maize genome. This information was employed to select
DH lines from the used mapping populations to initiate the development of germplasm for
QTL fine-mapping in the winter nursery 2010/2011 and to combine QTL through marker
assisted breeding. In order to obtain further QTL information for WCR resistance in maize,
we also continued evaluating QTL mapping populations derived from GEM-independent
germplasm. These evaluations were conducted in collaboration with Dr. B. Hibbard and
Dr. S. Flint-Garcia, USDA-ARS, Columbia, Missouri, who developed this germplasm.
In the Urbana field trials WCR pressure is immense, which potentially prohibits the
identification of germplasm sources with moderate levels of resistance/tolerance. We are in
the process of establishing a greenhouse assay to preselect promising materials before field
testing. In addition, we envision that this assay will provide the means to investigate the
role potential QTL play in WCR resistance.
3
Table 1
Means for 50 maize hybrids developed from crosses between 50 S4 lines derived from
GEM breeding crosses and a tester evaluated for agronomic characteristics, and their
resistance to European corn borer and western corn rootworm larvae feeding in field
experiments conducted in Urbana, IL, in 2010.
Genotype
AR16026:N1210-19-1-2-1
AR16026:N1210-19-1-2-2
AR16026:N1210-19-1-4-1
AR16026:N1210-19-1-6-1
AR16026:N1210-19-2-5-1
AR16026:N1210-19-3-2-1
AR16026:N1210-19-3-3-1
AR16026:N1210-19-3-6-1
AR16026:N1210-19-3-7-1
AR16026:N1210-26-2-1-1
AR16026:N1210-26-2-2-1
AR16026:N1210-26-3-2-1
AR16026:N1210-26-3-5-1
AR16026:N1210-26-3-6-1
CUBA117:S1520-22-3-1-1
CUBA117:S1520-22-3-4-1
CUBA117:S1520-22-3-5-1
CUBA117:S1520-22-3-7-1
CUBA117:S1520-25-1-1-2
CUBA117:S1520-25-2-1-1
CUBA117:S1520-25-2-4-1
CUBA117:S1520-3-1-2-1
CUBA117:S1520-57-1-1-1
CUBA117:S1520-57-1-2-1
CUBA117:S1520-57-1-7-1
CUBA117:S1520-57-1-8-1
CUBA117:S1520-57-1-8-2
CUBA117:S1520-9-3-5-1
CUBA117:S1520-9-3-5-2
CUBA117:S1520-9-3-6-1
CUBA117:S1520-9-3-6-2
FS8A (S):S0907-1-1-2-1
FS8A (S):S0907-1-1-2-2
FS8A (S):S0907-1-1-4-1
FS8A (S):S0907-1-1-4-2
MIRT-C5Y-5-2-1-1
MIRT-C5Y-5-2-1-2
MIRT-C5Y-5-2-6-1
MIRT-C5Y-5-3-1-1
MIRT-C5Y-5-3-1-2
MIRT-C5Y-5-3-1-3
MIRT-C5Y-5-3-2-1
MIRT-C5Y-5-3-3-1
UR13085:N0204-4-2-3-1
YLD
bu/acre
145.4
189.2
188.3
140.0
183.0
134.8
146.6
194.8
172.5
193.2
159.3
191.6
193.5
173.2
190.7
194.8
201.1
197.9
191.3
163.3
183.8
217.9
188.3
219.1
179.6
212.8
214.7
212.5
254.1
203.4
202.2
199.2
207.1
163.9
186.7
170.9
157.7
159.5
154.6
147.4
130.8
150.0
128.4
183.2
MF
FF
------ days ----64.1
65.4
63.5
66.5
66.1
65.1
65.5
65.6
65.3
65.0
65.5
63.8
64.4
64.6
67.1
.
67.3
.
66.3
66.9
66.2
63.8
64.9
65.3
65.9
66.0
65.4
66.5
66.5
66.0
.
64.9
65.2
64.8
64.1
66.2
.
.
64.6
64.9
65.8
67.0
66.5
64.7
65.3
66.3
66.3
67.4
67.0
66.8
67.6
67.1
66.8
66.3
66.9
65.3
66.2
66.4
68.0
.
68.3
.
67.5
68.1
67.1
65.4
65.7
65.7
66.9
66.9
66.1
67.5
67.3
67.2
.
65.9
66.8
65.7
65.2
67.0
.
.
65.6
65.8
67.1
68.2
67.5
66.6
4
Traits1
EHT
PHT
------ cm ----88.3
89.2
117.7
94.1
97.3
91.2
82.2
90.6
88.9
92.3
107.1
90.9
105.1
97.3
100.2
100.9
111.9
116.0
100.1
113.8
117.3
101.3
112.6
107.0
114.9
107.6
110.6
113.1
113.9
103.1
121.2
119.1
101.7
112.5
110.1
116.3
120.1
110.9
112.9
100.1
97.1
100.1
90.0
99.2
204.1
199.9
204.0
217.2
235.8
193.9
214.3
194.0
198.5
205.3
228.2
204.4
232.4
230.6
251.9
270.9
247.9
251.8
228.0
234.4
230.0
228.0
221.3
230.0
243.3
237.8
236.2
248.8
248.8
232.3
244.5
248.3
210.1
237.4
222.6
233.1
242.6
230.9
230.1
219.7
218.8
209.6
196.7
216.0
ECBa
0-9
3.1
5.0
4.2
2.5
2.2
6.0
2.7
2.0
3.0
5.5
4.8
4.3
5.0
6.8
2.7
3.1
2.6
2.0
3.2
2.4
4.2
3.5
4.2
4.7
3.4
5.1
5.1
1.4
2.4
3.8
3.4
5.0
3.6
4.5
4.7
1.0
2.8
2.7
2.0
2.8
1.5
1.1
0.4
2.8
RDR
0-3
2.8
3.0
3.0
2.9
2.9
2.7
2.8
2.3
2.8
3.1
2.4
2.5
3.6
2.8
3.0
2.9
2.8
2.9
2.9
3.0
2.8
2.1
3.1
3.0
2.9
2.9
3.0
3.0
3.1
2.9
2.9
2.8
3.1
2.8
3.0
2.9
2.8
3.1
2.9
2.4
2.9
2.8
2.9
2.7
RSZ
RRG
------ 1-6 ----3.4
2.7
2.7
2.5
3.0
4.2
4.5
2.1
3.3
3.2
2.6
2.2
3.0
2.9
2.4
3.8
3.9
2.0
4.1
3.5
2.6
2.7
4.1
4.0
3.5
3.0
4.2
3.5
3.1
3.4
3.7
3.8
4.1
3.3
4.2
4.0
4.2
3.6
3.6
3.8
3.9
4.0
4.1
2.1
4.7
4.6
4.8
3.5
4.2
5.4
5.3
5.4
5.0
5.2
4.9
4.7
4.8
5.2
5.3
5.9
5.2
4.9
5.0
5.5
4.4
5.7
6.2
6.2
5.4
5.7
4.9
4.3
4.7
4.6
5.8
5.4
6.4
5.9
5.1
5.8
6.0
5.5
4.7
5.4
4.8
4.8
4.8
3.6
Genotype
YLD
bu/acre
MF
FF
------ days -----
Traits1
EHT
PHT
------ cm -----
ECBa
0-9
RDR
0-3
RSZ
RRG
------ 1-6 -----
UR13085:N0204-4-2-4-1
UR13085:N0204-4-2-6-1
UR13085:N0204-4-2-8-1
UR13085:N0204-4-2-8-2
UR13085:N0204-6-1-3-1
UR13085:N0204-6-2-1-1
180.5
186.6
195.4
240.0
154.1
199.4
63.8
64.8
64.0
64.1
65.7
65.2
66.0
66.5
65.3
66.0
66.3
66.4
100.2
101.4
97.0
82.3
92.6
106.6
212.9
209.6
208.0
220.8
220.5
240.1
0.7
2.2
3.6
2.7
1.1
1.6
2.8
2.8
3.0
3.5
2.4
2.9
3.7
4.1
3.9
4.0
2.1
3.1
6.0
5.8
5.8
5.5
4.9
4.4
B37xH84-ins.
B37xH84-sus.
Check1-Bt
Check1-Isoline
Check2-Bt
Check3-Bt
Check4-Bt
Check4-Isoline
72.7
82.9
209.3
236.8
197.1
243.4
131.9
176.2
65.3
64.3
64.2
64.1
62.6
63.2
63.6
64.6
65.7
66.1
66.1
65.7
64.1
64.3
64.3
65.9
62.0
71.5
90.8
92.0
94.8
88.0
83.1
103.4
195.0
189.5
219.2
211.7
212.8
201.0
218.0
219.1
.
4.4
2.6
2.0
6.2
5.8
3.2
4.7
0.3
1.9
0.0
1.5
0.2
0.1
0.0
2.8
1.5
3.7
1.8
2.3
1.2
0.9
1.1
3.9
7.0
6.3
5.6
5.1
5.2
5.1
5.7
5.0
LSD
C.V.
Repeatability (%)
Mean (Checks)
Mean (without Checks)
50.6
13.6
60.4
199.1
182.6
1.4
1.0
70.0
63.7
65.4
1.3
0.9
69.0
65.1
66.6
21.9
4.7
71.8
92.0
103.4
14.9
7.1
70.5
213.6
225.5
2.1
31.2
57.2
4.1
3.2
0.92
22.45
69.00
0.1
2.9
1.7
33.9
25.4
1.3
3.4
1.8
21.3
1
5.7
5.2
YLD, grain yield in bu/acre; MF, male flowering in days after planting; FF, female flowering in
days after planting; EHT, ear height in cm; PHT, plant height in cm; ECB, stalk damage rating,
0=no damage, 9=stalk breakage below ear; RDR, root damage rating, 0-3 node injury scale; RSZ,
root size, 1=large root system, 6=small root system; RRG, root re-growth, 1=intensive re-growth,
6= no regrowth).
5
Table 2
Means for 36 maize hybrids developed from crosses between twelve S6 lines derived
from GEM breeding crosses and three testers evaluated for agronomic
characteristics, and their resistance to European corn borer and western corn
rootworm larvae feeding in field experiments conducted in Urbana, IL, in 2010.
Genotype
YLD
bu/acre
MF
FF
---- days ---
Traits
EHT
PHT
------ cm -----
ECB
1-9
RDR
0-3
RSZ
RRG
---- 1-6 ---
AR17056_16*SS1
AR17056_16*SS2
AR17056_16*SS3
AR17056_3*SS1
AR17056_3*SS2
AR17056_3*SS3
AR17056_4*SS1
AR17056_4*SS2
AR17056_4*SS3
216.3
179.0
.
215.2
.
164.0
143.5
230.1
220.4
65.5
63.8
.
65.7
.
65.5
63.7
63.3
65.6
66.2
64.3
.
66.8
.
66.8
65.6
64.5
66.4
86.9
85.3
.
91.4
.
98.7
91.4
89.5
100.2
202.7
191.8
.
212.7
.
225.6
215.9
210.7
224.0
3.4
3.1
.
.
.
1.1
4.3
4.7
2.8
2.9
3.0
3.0
3.0
3.0
3.0
2.7
3.0
2.8
5.1
5.0
4.6
4.3
4.0
4.8
3.5
3.9
3.4
4.8
5.5
4.9
5.1
4.7
5.3
3.9
5.6
4.2
DKXL212.N11a01-02-5-2-11-1-B*SS1
DKXL212.N11a01-02-5-2-11-1-B*SS2
DKXL212.N11a01-02-5-2-11-1-B*SS3
DKXL212.N11a01-05-1-2-1-B-B*SS1
DKXL212.N11a01-05-1-2-1-B-B*SS2
DKXL212.N11a01-05-1-2-1-B-B*SS3
DKXL212.N11a01-05-1-2-2-1-B-B*SS1
DKXL212.N11a01-05-1-2-2-1-B-B*SS2
DKXL212.N11a01-05-1-2-2-1-B-B*SS3
DKXL212.N11a01-06-1-3-1-B-B*SS1
DKXL212.N11a01-06-1-3-1-B-B*SS2
DKXL212.N11a01-06-1-3-1-B-B*SS3
DKXL212.N11a01-09-3-5-1-5-B*SS1
DKXL212.N11a01-09-3-5-1-5-B*SS2
DKXL212.N11a01-09-3-5-1-5-B*SS3
177.1
.
161.8
157.0
175.8
206.5
206.4
191.2
188.3
176.3
148.6
165.6
194.7
174.4
187.0
66.5
.
.
66.9
64.3
65.7
65.8
64.5
65.8
65.6
65.8
66.6
64.6
66.1
65.6
68.1
.
.
68.0
65.8
66.8
66.9
66.1
67.4
67.2
66.7
67.5
66.8
67.5
67.6
103.2
.
101.0
90.0
83.7
82.8
101.5
102.8
95.5
111.9
94.8
97.7
107.3
90.3
87.3
222.4
.
234.1
220.5
200.5
227.0
233.9
218.3
226.5
222.8
221.0
221.4
239.6
217.7
224.1
3.4
.
4.2
4.1
3.9
2.6
4.5
2.4
5.0
4.8
2.7
4.8
4.9
4.6
1.7
3.0
2.9
3.0
2.9
3.0
2.9
2.9
2.9
3.0
3.0
3.0
2.9
3.0
2.9
3.0
2.9
3.0
2.8
3.7
3.5
2.9
3.4
1.4
2.9
3.1
3.2
3.9
3.5
3.7
3.2
5.3
5.0
5.5
4.1
3.9
3.6
5.5
1.5
4.8
5.3
4.3
5.4
3.9
4.3
4.4
BR52060:S0210-143-001-B-B*NSS1
BR52060:S0210-143-001-B-B*NSS2
BR52060:S0210-143-001-B-B*NSS3
BR52060:S0210-147-001-B-B*NSS1
BR52060:S0210-147-001-B-B*NSS2
BR52060:S0210-147-001-B-B*NSS3
205.1
163.8
180.6
.
192.6
211.8
65.2
65.8
65.8
.
64.6
63.8
66.0
66.9
66.9
.
66.6
64.5
76.5
92.4
101.7
.
109.3
106.5
209.7
224.7
217.2
.
229.4
240.6
.
3.3
2.3
.
5.3
4.0
2.9
2.8
3.0
2.9
3.0
3.0
3.8
3.7
5.0
3.9
3.7
2.7
4.9
4.4
5.5
5.1
5.3
5.2
NEI9004:S2818-003-001-B-B-B*NSS1
NEI9004:S2818-003-001-B-B-B*NSS2
NEI9004:S2818-003-001-B-B-B*NSS3
NEI9004:S2818-025-001-B-B-B*NSS1
NEI9004:S2818-025-001-B-B-B*NSS2
NEI9004:S2818-025-001-B-B-B*NSS3
189.2
184.2
187.9
199.4
162.8
232.8
64.4
65.6
64.5
65.8
66.2
64.5
66.3
66.8
65.9
66.7
68.1
65.4
86.0
84.9
105.5
91.1
101.8
113.3
217.9
216.3
232.1
211.6
221.8
244.4
3.6
4.6
5.1
3.2
2.9
4.3
3.0
2.9
3.0
3.0
3.0
2.9
4.6
4.0
4.3
5.4
3.4
4.1
5.5
4.8
5.7
5.7
4.8
5.9
B37xH84-ins.
B37xH84-sus.
Check1-Bt
Check1-Isoline
Check2-Bt
Check3-Bt
74.7
91.4
227.3
220.3
199.5
235.5
65.9
64.5
63.7
63.4
63.5
63.8
67.2
67.2
64.5
65.0
64.7
64.5
79.4
95.0
85.8
92.7
78.8
93.5
186.1
199.0
203.3
209.3
183.4
194.9
.
4.6
2.7
0.6
3.3
5.4
0.2
3.0
0.0
1.1
0.2
0.0
2.9
5.6
1.6
2.7
1.7
1.4
6.1
5.7
5.9
5.5
6.3
5.5
6
Genotype
YLD
bu/acre
MF
FF
---- days ---
Traits
EHT
PHT
------ cm -----
ECB
1-9
RDR
0-3
RSZ
RRG
---- 1-6 ---
Check4-Bt
Check4-Isoline
192.7
238.3
63.0
64.1
64.6
65.1
87.1
96.1
214.9
235.8
2.9
3.1
0.4
2.9
1.2
3.2
5.2
5.3
LSD
C.V.
Repeatability (%)
Mean (Checks-Bt)
Mean (without Checks)
38.8
10.2
75.1
219.0
187.2
1.2
0.9
70.1
63.6
65.3
1.5
1.1
63.0
64.7
66.5
18.1
9.4
39.0
89.0
95.7
22.8
5.1
53.9
207.0
221.2
2.8
38.7
20.8
3.0
3.7
0.4
8.2
95.82
0.2
2.9
1.4
24.0
56.7
2.0
3.8
1.5
18.2
27.6
5.6
4.8
1
YLD, grain yield in bu/acre; MF, male flowering in days after planting; FF, female flowering in
days after planting; EHT, ear height in cm; PHT, plant height in cm; ECB, stalk damage rating,
0=no damage, 9=stalk breakage below ear; RDR, root damage rating, 0-3 node injury scale; RSZ,
root size, 1=large root system, 6=small root system; RRG, root re-growth, 1=intensive re-growth,
6= no regrowth).
2
The high repeatability is due to the use of two very different sets of materials in this experiment,
i.e., susceptible WCR testcrosses and commercial checks carrying the Bt gene active against
WCR.
7