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Greg Edmeades1, Jill Cairns2, Jeff Schussler3,
Amsal Tarakegne2, Stephen Mugo2,
Dan Makumbi2 and Luis Narro2
1 Consultant; 2 CIMMYT; 3 Pioneer Hi-Bred International
Acknowledgments
Project staff of WEMA, DTMA and IMAS
NARS in sub-Saharan Africa and the Andean zone
Colleagues from Pioneer Hi-Bred Int.
CIMMYT
Dedicated Post Docs, and field staff
Colleagues
2
What we’ll cover today
Introduction
Lessons from the past
Drought, Low N, acid soils
Guiding principles
Looking forward
Breeding approaches
Key components : agronomy, partnerships
Conclusions
3
Introduction
Population growth: 7 bn today, 9.1 bn by 2050
Limits on arable land area expansion Maize in more marginal environments
Increase of staple crop yield is slowing
Climate change
BUT we have:
•New tools
•Better genetic and physiological information
4
Environment is changing
Temperature: +1-1.5C by 2030; +2.5-3oC by 2050
Water: Rainfall, runoff increase; crops are drier
Probable increase in climatic extremes
Global dimming in Asia
N prices rise; soil acidification from N application
5
-- Maize areas will be hotter and drier, dimmer, and
subject to extreme weather
-- Opportunities in winter and in cool northern areas
Meanwhile, in temperate zones, plant
density has steadily risen
1986 1988 1990 1992 1994 1996 1998 2000 20025.0
5.5
6.0
6.5
7.0
Slope = 689 plants ha-1 yr-1
R2 =0.98**; 16 df
Source : Annual Corn Belt Farm Survey data
Year of farmer survey
Seed
s p
lan
ted
m-2
1920 1940 1960 1980 2000
5
10
15
20
Slope = 760 plants ha-1 yr-1
N=50; R2=0.35; P<.001
Year of release
Op
tim
um
den
sit
y
(pla
nts
m-2
)
Density tolerance = general tolerance to abiotic stresses 8
But why not select just for yield? Secondary traits and selection
Useful secondary traits (under stress) are
Correlated with yield under stress
High and stable heritability
Cheap, fast to measure
When used with yield in a selection index, heritability
of index rises
Index increased genetic gain by 14% under low N (Bänziger and Lafitte, 1997)
9
Lessons from the past: drought
Tropical: research started by CIMMYT in 1975
on a single population
Extended to 7 populations in 1985
Exported to Africa in 1996 and to Asia in 2000
Temperate: research began in mid 1960s led by
Pioneer and DeKalb
Amplified from 1997 onwards by all major companies
10
Tremendous increase in
interest in drought tolerance in maize in the last 40 years
Selection in tropical populations
Recurrent S1 or FS selection; 10% intensity, rain-free locations; 4 to 9 cycles; 6 populations
Heat and drought in Obregon, drought in Tlaltizapan
Three managed drought stress regimes: WW, IS and SS; 2 reps
Primary trait: Grain yield under stress, optimal
Secondary traits: ASI, EPP, staygreen, leaf rolling, tassel size
1988: DTP started from DT sources – improved, temperate, tropical, landraces, mixed color, open-ended
11
Gains per cycle under stress (drought;
low N) or unstressed environments.
N (popn)= 6; N (cycles)=2-9; N (env.) = 4-10
Grain yield ASI
kg ha-1 cycle-1 d cyc-1
Population Drought Unstressed Low N Drought
Maximum 288** 177** 233** -2.1**
Minimum 80** 38** 64 ns -0.3**
Mean 166 99 166 -1.0
Relative yield (%) 30 100 59 30
Source: Edmeades, 2006 12
Gains were maintained outside of
adaptation zone
2 4 6 80
2
4
6
8
La Posta Seq C6
La Posta Seq C0
Mean environment yield (t ha-1)
Va
rie
ty y
ield
(t
ha
-1)
14
Africa: experimental hybrids (4) vs. best private
company hybrids (checks)
23 randomly stressed locations, Eastern and southern Africa
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
0.0 2.0 4.0 6.0 8.0 10.0
Y ie ld o f the tr ia l (t/ha )
Yie
ld o
f th
r v
ari
ety
(t/
ha
)
Experimental Checks
Source: Banziger et al., 2006 15
Gains in yield in US hybrids Source: Schussler et al. 2011
16
Year of Hybrid Release
1930 1940 1950 1960 1970 1980 1990 2000 2010
Gra
in Y
ield
(t/
ha
)
2
4
6
8
10
12
14
16
18
y = 3.549 + 0.072x (r2 = 0.90): Drought
y = 8.269 + 0.092x (r2 = 0.85): Irrigated
y = 4.966 + 0.089x (r2 = 0.96): TPE
Irrigated, CA
Drought, CA
Target rainfed
environment
Flowering still a vulnerable growth stage GY vs. ASI in elite Corn Belt hybrids
126 elite hybrids, 2 water regimes, 2002
What we learned about drought
tolerance…..
Gains: 100 kg/ha/yr in tropicals using MSEs and 70 kg/ha/yr in temperates using METs
Pioneer: 1 MSE site = 10 MET sites in the target area
Drought tolerance is at no cost to yield potential
Useful secondary traits: barrenness and ASI
Susceptibility at flowering is reduced by conventional selection using wide area testing
Temperate hybrids lack variation for functional staygreen under stress
**Guard against escapes: monitor flowering date
18
Heat tolerance Possible sources of drought and heat tolerance
Source: DTMA Association Mapping Panel (J. Cairns)
Drought tolerance does not automatically equate to heat tolerance
19
Lessons from the past: nitrogen
NUE research started in
temperate germplasm in
the 70s and 80s
Low N tolerance started
in CIMMYT in 1986
N depletion
Recurrent selection
20
Selection in tropical populations
Across 8328 BN: Recurrent FS selection; depleted low
N plot beside high N plot (200 kg N/ha) in Poza Rica
Primary trait: Grain yield under stress, optimal
Secondary traits: ASI, EPP, staygreen; monitor
anthesis
Pool 16 BNSEQ: S1’s evaluated under low N and
drought
21
Response of grain yield to recurrent
selection under low and high N (Source: Lafitte and Bänziger 1997, DDLTM: 485-489)
Low N High N0.0
2.5
5.0
7.5C0
C5
Gain 5.1%/cyc84 kg/ha/cycle*
Gain 2.4%/cyc120 kg/ha/cycle*
Evaluation environment
Gra
in y
ield
(to
n h
a-1
)
23
Effect of design and index selection on
predicted gains under low N
(Source: Bänziger and Lafitte (1997), DDLTM: 401-404)
RCBD Lattice Lat + index0.0
0.1
0.2
0.3RCBD
Lattice
Lat + index100%116%
137%
Options
Pre
dic
ted
sele
cti
on
resp
on
se (
t h
a-1
)
24
Leveraging other traits…. Proportion of gains in drought tolerance
captured under low N
0.3 0.4 0.5 0.6 0.7 0.80.2
0.4
0.6
0.8
1.0
Low High
N Stress level (1-GYloN/GYhiN)
Pro
po
rtio
n o
f D
RT
gain
scap
ture
d
25
Summary from past low N research
Gains of around 5% per year under low N possible in
“improved” germplasm at yields of 2 ton/ha
Key traits are GY, staygreen, kernels per ear, ASI
Strong correlation with drought tolerance under
moderate N stress
Soil uniformity and designs strongly affect gain
27
Lessons from the past: soil acidity
Acid soils (pH < 5.5) affect 3,950 M ha globally
As pH falls Al3+ ions damage roots; P less available
Screening: normal vs. 40-60% Al3+ saturation and
two levels of P (4 and 15 ppm)
Program commenced in the 1970s in Cali Colombia;
based on EMBRAPA research
Callose formation in roots related to injury from Al3+
28
Maize grain yield on acid soils CIMMYT 1975-2008
Narro, 2011
1975 1994 2000 2008
Under typical soil conditions: pH 4.7; Al3+ saturation = 60%
There has been remarkable progress
Principles emerging
Most maize populations have a low frequency of stress adaptive alleles, often with small effects
Increased stress tolerance possible at no cost to yield potential
Well-targeted managed stress environments efficiently accelerate gains for stress tolerance
Secondary traits point to key mechanisms--- but contribution will dissipate with selection
31
Looking forward….
Phenotyping is way behind genotyping in cost per dp
Basics that matter
Uniform fields and uniform plant spacing, input application
The right experimental design and spatial analysis
Represents TPE in photoperiod and temperature
Plot management: Grouping by maturity and/or vigor level;
adequate borders
Measure only traits that improve repeatability
32
Soil electrical conductivity maps help
avoid some field variability Source: J. Cairns
Chiredzi, Zimbabwe
33
Africa: genetic correlations between target
environments and managed stresses
34
Selection
environment
Genetic correlation
Optimal 0.80
Managed drought 0.64
Low N 0.91
Target = random abiotic stress with yields < 3 t/ha
Southern Africa, 2001-9 (Weber et al. 2011)
Africa: breeding approaches: conventional
35
Preliminary gains: Stage 2 early topcross trials vs. SC403
Southern Africa (N=88) Source: A. Tarekegne
Looking forward: sources
Donors are being identified
CLWN 201 for low N tolerance (G Atlin, IMAS)
For heat and drought tolerance (J. Cairns, DTMA)
36
DTMA Pedigree GY (t ha-1)
91 CML311/MBR C3 Bc F12-2-2-2/CML312SR 0.63
238 DTPYC9-F46-1-2-1-2 / CML312SR 0.59
. La Posta Seq C7-F64-2-6-2-2/CML312SR 0.55
62 CLA44 /CML312SR 0.49
231 DTPYC9-F143-5-4-1-2/CML-312SR 0.46
44 CML412/CML312SR 0.19
Trial mean 0.24
Remote sensing:
The normalized difference vegetation index (NDVI)
Infrared thermometry and spectral reflectometer
NIRS
New secondary traits under evaluation
37
BIOMASS / NDVI
y = 79,802x - 8,6683
R2 = 0,8845
0,00
10,00
20,00
30,00
40,00
50,00
60,00
0,000 0,100 0,200 0,300 0,400 0,500 0,600 0,700 0,800 0,900
NDVI
SH
OO
T (
gr.
DW
)
Looking forward: genome wide
selection
Conventional + GWS: careful phenotyping and
genotyping by sequencing with 10-450K SNPs
GEBVs as accurate as phenotypic evaluation in a
single drought trial (with H = 0.2-0.4);
Calculated from several traits
Cull DH lines before crossing and testing (Semagn et
al. 2011)
38
Genome-wide predictions vs. field
performance in temperate germplasm Source: Schussler et al., 2011
39
Observed vs. predicted relative grain yield of hybrids under
severe flowering stress in Woodland, CA
r = 0.94***
Yield BLUPs for eight conventional
drought tolerant hybrids Source: Schussler et al., 2011
40
Drought
stress
No drought
stress
Optimum® AQUAmaxTM
(t/ha)
6.89 11.94
Leading checks (t/ha) 6.56 11.59
Difference (t/ha) 0.33 0.35
N 223 >1200
Improvement (%) 5.0 3.0
Sites in high plains of the US (NE, KS, CO, MO, TX) 2008-10
Transgenics
41
Drought: MON 87460
Commercial launch in the US in 2012
WEMA: Deploying MON87460 in sub-Saharan Africa
stacked with Bt --- 2018
Additive effect assumed
Low N:
Pioneer: actively screening genes and constructs
Commercial: US in 2017?
Royalty free in sub-Saharan Africa in 2020 ? with IMAS
Critical factors for impact
42
Agronomy
Yield potential, input use efficiency
Conservation tillage
Hybrid x management interactions increasingly important
Dissemination
Affordable seed for risky environments – private and public
Partnerships Public-Private: hybrids; IP protection, GM technologies
Policies to encourage private investment
Conclusions…. We could > double impact in stressed environments
when
Tools are integrated: Genome-wide selection, conventional selection, DH production, well-run METs
Proven sources of stress tolerance (including transgenes) are widely used
Stresses in MSEs are matched to the target environment
Repeatability of field trials such that Sd ≤ 0.2 t/ha
Agronomic practices exploit improved genetics
Seed systems, markets, & infrastructure function well
Partnerships: private-public
We have the tools. The game is ours to lose 43