Post on 11-Apr-2017
Breeding for disease resistance in Maize
Stephen Mugo, George Mahuku, Dan Makumbi and C. Magorokosho, Suresh L.M.
Presentation made to the New Maize Breeder’s Training Course, Lusaka, Zambia, 17 August – 4 Sept, 2015
Maize Diseases Maize production in sub-Saharan Africa is affected
by a wide array of diseases Environmental conditions prevalent in the different
agro-ecological zones are conducive to the growth and spread of pathogens
Different disease complexes affect maize production in the lowlands and mid-high altitudes
Diseases often reduce production and cause up to 100% yield loss under severe epidemics depending on environmental conditions
Need to manage disease in maize
• Prevent economic losses– Reduced yields– Increased production
costs– Poor quality grain
• Reduce or eliminate the risks associated with presence of a disease
• Guarantee food security
Constraints Lowlands Mid-altitude-highlands Foliar diseases (reduce photosynthetic area) Gray leaf spot (Cercospora zeae-maydis) x Northern corn leaf blight (Exserohilum turcicum) x Southern corn leaf blight (Bipolaris maydis) x Common rust (Puccinia sorghi) x Southern rust (Puccinia polysora) x Downy mildew (Peronosclerospora sorghi) x Maize streak virus disease x x Ear rots (reduce quality of maize grain) Diplodia ear rot (Stenocarpella maydis) x Aspergillus ear rot (Aspergillus flavus) x x Fusarium ear rots (Fusarium moniliforme) x x Stalk rots (cause premature death of plants) Diplodia stalk rot (Diplodis maydis) x Fusarium ear rots (Fusarium moniliforme) x x Charcoal rot (Macrophomina phaseoli) x x =prevalent in the zone
Major maize diseases that significantly reduce maize production in different ecological zones in SSA
NCLB RustSCLB
GLS FV AF
MSV
Focus Diseases
A field heavily infected with GLS
A field heavily infected with NCLB –Kakamega, Kenya
Objective• Identify superior disease resistant germplasm for
incorporation into breeding programs • Collect good disease phenotypic data• Use association mapping approaches to understand
the organization of disease resistance genes in the maize genome
• Develop markers for marker assisted selection breeding
Research Strategy
• High precision multi-location phenotyping:– identify good sources of resistance for use as donors– Validate stability of resistance genes
• Association mapping studies– Leverage the DTMA AM set to identify chromosomal regions
involved in disease resistance – Organization of disease resistance genes on maize genome
• Fine mapping pipeline to develop functional markers– DH lines– F2.3, BC1, BC2, BC3 populations
Breeding for resistance to diseases Use of disease resistant cultivars is the most valuable and
practical means to control diseases It is also inexpensive, effective, and simple to apply over a
wide area in a target production zone
Requirements for development of disease resistant maize cultivars
1. Diverse germplasm2. Screening tools3. Test locations with consistently high disease pressure
Resistance is available for most of the economically important diseases in maize
Resistance is controlled mainly by One or a few genes (monogenic or oligogenic) Many genes (polygenic)
With additive and dominance effects
1.Vertical resistanceComplete resistance of a host to a specific race of a pathogenThe host plant exhibit hypersensitive reaction that prevents
the establishment and multiplication of the pathogenControlled by one (monogenic) or a few (oligoginic) genesPlants show distinct resistant and susceptible categories
Selection is thus easy in segregation populationsTransfer from source to other germplasm is also easy It is less durableHas been used to control very few disease in maize
Types of resistance
2. Horizontal resistanceEffect of resistance on the survival and reproduction of he
pathogen is less completeProvides less selection pressure on the pathogen
It retards the infection process and slows down the spread of the disease
Controlled by many genes (polygenic) each with small effect Resistance shows continuous variationIt is more durable and stable due to the buffering effect of
polygenesHas been used for controlling most diseases in maize
The two types of resistance can co-exist
Types of resistance
Factors affecting disease occurrence
* Climate change impacts the host, agent (pathogen) and environment
Environment (favorable)
Pathogen (virulent)
Host (Susceptible)
Man
•Temperature•Relative humidity•Rainfall•Dew•Solar radiation
Mechanisms for disease resistance1. Resistance to pathogen establishment•Immunity
– Prevent pathogen from establishing itself due to innate structural or functional properties of the host
•Hypersensitivity – Prevents pathogen survival and reproduction due to rapid
death of the host plant cells2. Resistance to an established pathogen
– Restricts the ability of the pathogen to spread and reproduce after becoming established in a host
3. Tolerance– The plant exhibits severe disease symptoms without a
serious loss in yield
Availability of diverse germplasm for screening as sources of resistance
• Sufficient genetic variation exists for most of the diseases in maize• Locally adapted or introduced maize germplasm• Old varieties and breeding stocks• Landrace collections
• Resistance alleles in these genetic resources can occur at low or high frequencies
• Resistance genes occurring at low frequencies can be gradually increased
• Genes at high frequency are easy to transfer
Based on reliable identification of good sources of resistance
This can be done through: Development of standardized, highly efficient inoculation techniques and
disease rating systems for major maize diseases that include: Fusarium ear rot (FSR); Fusarium stalk rot (FSR); Gray
leaf spot (GLS); Tar spot complex (TSC); and Turcicum leaf blight (TLB)
Establishment of misting systems at key and crucial sites to create microclimatic conditions suitable for disease development.
Identification of disease hot spot sites, known for consistent, uniform and reliable disease incidence and pressure.
Approach to minimizing production losses from diseases
Resistance screening methods • Field, greenhouse (screenhouse) and laboratory-based
screening techniques are available for the major diseases of maize
• Use established screening techniquesEffectiveCheapEasy to handle depending on available facilities and personnelHigh throughput for screening a large number of breeding
materials • Field screening of breeding nurseries at hot-spot locations
with consistently high disease pressure is also effective• Evaluate selected resistant genetic materials in one location
(greenhouse, laboratory) at multiple-locations to expose them to different populations (races) of the pathogen
Test entries are exposed to adequate and uniform disease pressure.
Guarantee greatest differentiation of genotypes.
Objective of disease evaluations
Rate of progress to develop stable and durable disease resistance or marker development depends on: the use of reliable screening techniques use of as wide a spectrum of the pathogen as possible and at an
appropriate disease pressure Take note that:
Low disease pressure Unreliable results that slow down rate of genetic gain
High or severe disease pressure Eliminate low level resistance inherent in adapted
germplasm and may drastically narrow the germplasm base
Disease screening methods
Two major groups:
1. Naturally occurring epidemics
2. Artificially created epidemics
Disease screening techniques
Naturally occurring epidemics Hot spots Use of a location known for its high level of infection for a
particular disease Used for a pathogen with a local concentration of alternate
hostsAdvantages Cheap and easy to manage Test materials are exposed to all pathogen racesDisadvantages Success depends on year– to– year consistent expression of
epiphytotics adequate and uniform natural infections can rarely be
achieved in most locations Disease might not be evenly distributed within the field
Naturally occurring epidemics Enhanced natural infections to ensure adequate
disease levels Manipulation of planting dates Create favorable environmental conditions (e.g.
irrigation, enhanced drought etc) Use of spreader rows & use susceptible checks every
few rows (e.g. every tenth row) Sufficient replications (minimum of three) Multiple locations
Naturally occurring epidemic of common rust Puccinia sorghi
Parameter Batan (2008)
Batan (2009)
Batan (2010)
Combined location
Entry Variance 0.92 0.69 1.28 0.45
Residual variance 0.39 0.31 0.17 0.28
Heritability 0.82 0.87 0.96 0.85
LSD -05 1.24 0.92 0.66 0.91
CV 22.53 25.50 12.12 20.40
Resistant Susceptible
Replications =3Number of entries = 300 genotypes
Good phenotyping data across locations – Common Rust (Puccinia sorghi)
Oxalis sp. – an alternative host for Puccinia sorghi
Artificially created epidemics Environmental conditions favorable for optimal
disease development rarely occur every year Great variation in the severity of the disease within a
location in a year Ensure adequate epidemic development Versatile - Can be done in laboratory, greenhouse
and field
Inoculum production in the maize pathology laboratory in CIMMYT. The inoculum is produced on colonized sorghum grain and used for artificial inoculations of leaf diseases of maize (TLB, MLB).
Inoculations done at the 6-8 leaf stage. Colonized sorghum seed serves as sources of inoculum for 7 weeks under field.
In the case of Fusarium ear rot -
Steps for preparing inoculum
Inoculating with Fusarium ear rot -
Silk channel inoculation technique Kernel puncher inoculation technique
Disease phenotyping hubs Harare Kakamega / Embu
Misting system Environment conditions that
inherently favors expression of plant diseases
Protocols Well developed and available
for many disease Issues
Lack of standardization Common checks Limits harmonization of data
from different organizations
Protocols for reliable disease phenotyping
Evaluation – Resistance vs. susceptible
Data loggers Inoculation technique
Fieldbook and fieldlog
Parameters for reliable disease phenotyping
Various degree of TLB infection on different genotypes of maize despite of using same inoculum, same inoculation and observation time. Therefore, it requires standardized disease rating scale.
Disease evaluation
Rating scale 1-5 for common rust(single leaf-based)
1 2 3 4 5
Foliar disease
Diseases rating keys / scales
Evaluating ear rots
Multi-location Disease Phenotyping
Phenotyping Site MSV GLS Et Ear rots Ps PP BMHarare, Zimbabwe X X XMpongwe, Zambia XKakamega, Kenya X X XEmbu, Kenya X X XKibos, Kenya X XCatalina, Colombia X XEl Batan, Mexico X X XAgua Fria, Mexico X X X XSan Pedro , Mexico X
Acatic, Mexico X
= Natural condition; = Artificial condition
P = 0.0001
EM-KN BA-Mex1 BA-Mex2 SL-Mex
EM-KN 1
BA-Mex1 0.86 1
BA-Mex2 0.87 0.96 1
SL-Mex 0.99 0.99 0.98 1
Phenotypic correlations between sites for common rust
Parameter San Pedro Lagunillas (Nayarit)
Acatic (Jalisco)
Santa Catalina (Colombia)
Paraguacito (Colombia)
Entry Variance
0.80 0.6 0.99 0.80
Residual variance
0.25 0.15 0.36 0.11
Heritability 0.86 0.89 0.89 0.95LSD -05 1.13 0.76 0.98 0.55CV 22.60 14.14 19.84 9.61Replications =3Number of entries = 300 genotypes
Good phenotyping data across locations – Gray Leaf Spot (GLS)
Good phenotypic data across locations
GLS (6) MSV (3) E. Turcicum (12)
P. Sorghi (5)
Var (Entry) 0.27 0.209 0.188 0.492
Var(LocxEntry) 0.45 0.121 0.182 0.079Var(Resid) 0.22 0.795 0.269 0.320
Grand_Mean 2.66 2.780 2.605 2.153LSD_0.5 0.87 2.510 0.729 1.399
H 0.76 0.62 0.91 0.91#Sites 6 3 17 3
Combined Analysis Across Location: four adaptive diseases
Best - bet Sources of disease resistanceMean Disease rating (1-5)
Stock ID Pedigree GLS (6 loc) MSV (3 Loc) NCLB(12 loc) Rust (5)
DTMA-3 [(CML395/CML444)-B-4-1-3-1-B/CML395//DTPWC8F31-1-1-2-2]-5-1-2-2-BB 1.43 1.12 1.74 1.30
DTMA-10 CIMCALI8843/S9243-BB-#-B-5-1-BB-2-3-4 2.06 1.60 1.67 2.13DTMA-11 CIMCALI8843/S9243-BB-#-B-5-1-BB-4-1-3 1.74 1.41 1.41 1.26DTMA-12 CIMCALI8843/S9243-BB-#-B-5-1-BB-4-3-3 1.71 1.72 1.79 1.63DTMA-13 CIMCALI8843/S9243-BB-#-B-5-1-BB-4-3-4 1.93 1.60 1.70 1.38DTMA-17 [CML312/CML445//[TUXPSEQ]C1F2/P49-
SR]F2-45-3-2-1-BBB]-1-2-1-1-2-BBB-B 1.87 1.12 1.80 1.59DTMA-90 CML311/MBR C3 Bc F112-1-1-1-B-B-B-B-B 2.24 2.37 2.50 1.59
DTMA-146 [CML-384 X CML-176]F3-107-3-1-1-B-B-B 2.25 2.45 1.94 1.71DTMA-268 La Posta Sequia C7-F33-1-2-1-B-B 2.25 2.23 1.99 1.58DTMA-293 La Posta Seq C7-F153-1-1-1-2-B-B-B 2.50 2.35 2.33 2.43DTMA-40 [CML144/[CML144/CML395]F2-8sx]-1-2-3-
2-B*5 2.01 2.03 1.70 1.52DTMA-19 [CML312/CML445//[TUXPSEQ]C1F2/P49-
SR]F2-45-3-2-1-BBB]-1-2-1-1-1-BBB-B 2.20 1.61 1.77 1.23DTMA-26 P502SRC0-F2-54-2-3-1-B 1.71 1.60 1.76 1.51
Disease resistance in best-bet DT linesMean Disease rating (1-5)
Stock ID Pedigree GLS (6 loc) NCLB(12 loc)
MSV (3 Loc)
Rust (5)
DTMA238DTPYC9-F46-1-2-1-2-B-B-B-B 2.87 2.67 2.41 2.28
DTMA-261La Posta Sequia C7-F180-3-1-
1-1-B-B-B-B-B 2.02 2.38 2.73 1.98
DTMA-79
(A.T.Z.T.R.L.BA90 5-3-3P-1P-4P-2P-1-1-1-B x G9B C0
R.L.23-1P-2P-3-2P-3-2P-1P-B-B-B)-B-16TL-3-1-4-B-B-B
2.19 2.94 2.44 2.2
DTMA-176CLQ RCWQ103=
(CML150xCML254)-B-16-2-2-2-B-B-B-B-B
2.87 2.88 2.9 2.78
DTMA-233DTPYC9-F46-3-4-1-1-B-B-B-B-
B 2.46 2.97 2.39 1.38
DTMA-193CL-RCY015 2.16 - 2.93 2.36
DTMA-165S87P69Q(SIYF) 109-1-1-4-B 2.73 1.37 3.65 3.36
DTMA-217DTPWC9-F24-4-3-1-B-B-B-B-B 3.86 2.69 3.29 3.14
DTMA-62CLA44-B-B 3.74 3.17 3.45 4.59
Conclusions• A large number of inbred lines, open-pollinated
varieties, hybrids, and source population with resistance to the major diseases are available for use– As sources of alleles to breed maize for resistance to the
major diseases• Other disease for which artificial inoculations are
conducted / protocols available– Ear rots (Fusarium and Aspergillus), Stalk Rots, turcicum
blight, southern corn leaf blight, common rust.
Conclusions
Information on sources of disease resistance on CIMMYT website & available to collaborators
Establishing diseases phenotyping network comprised of different institutions and seed companies etc.
Build capacity of collaborators on use of harmonized disease evaluation protocols
Thank you for your interest!