The document outlines the significant maize diseases affecting Asia, highlights the impact of climate change on disease incidence, and discusses the progress made in breeding for disease resistance. It emphasizes the need for molecular breeding techniques and precision phenotyping to improve maize production and disease resistance in the face of future environmental challenges. Key diseases such as Fusarium and downy mildews are identified, and the importance of both conventional and molecular breeding strategies is noted for sustainable maize development.

1. Maize Diseases in Asia
Daniel Jeffers CIMMYT/China, Yunnan Academy of
Agricultural Sciences, Institute of Food Crops
Kunming, Yunnan, d.jeffers@cgiar.org

2. Outline
• The major diseases affecting maize in Asia
• Climate change and the possible effects on pathogen profiles and disease
incidence, especially in the tropical regions, concomitant with high
temperatures
• Progress through conventional breeding
• Possibilities to implement marker-assisted breeding for improving disease
resistance
• Precision phenotyping for disease response
• Conclusions and prospects

3. Background
• Approximately 52 million ha of maize in the Asian region with roughly 30
million of temperate maize in China
• The remaining 22 million ha is subtropical and tropical maize.
• Maize area in the region has increased by 13.2 % between 2006 and 2011
with 86% of the increase in area occurring in China with the displacement of
other crops including wheat, rice, and soybean (FAO Stat, USDA/FAS,
2011)
• Diseases cause roughly a 12% yield loss across the region, and to meet the
demand for maize seen across Asia, breeding for host resistance is a key
component of the germplasm improvement activities to reduce losses,
provide yield stability, and maintain grain quality.

4. Major diseases affecting maize in Asia
Fusarium verticillioides ear and stalk rot
Stenocarpella ear rot (Diploida)
Banded leaf and sheath blight
Phaeosphaeria leaf spot
Maize Mega environments
Turcicum leaf blight
Asperigillus ear ros
Maydis leaf blight
Downy mildews
SCMV/MDMV
Gray leaf spot
Common rust
Polysora rust
Ear rots
Temperate 4.0 3.0 5.0 2.5 3.5 5.0 2.5 2.5 1.5 2.5 4.0 2.5 3.5
Highlands 4.0 2.0 5.0 3.5 5.0 3.0 5.0 4.5 1.5 1.8 4.8 1.0 5.0
ST/Upper
2.5 1.5 4.0 3.0 5.0 3.0 5.0 3.5 1.5 2.0 4.0 1.0 4.5
wet MA
ST/Lower
2.0 1.5 1.5 2.0 2.0 3.0 2.5 3.0 1.5 2.0 3.5 1.5 3.0
wet MA
ST/Dry
mid- 3.5 3.0 2.0 4.0 3.0 4.0 2.5 2.0 4.0 2.5 2.5 1.5 3.0
altitudes
Wet
1.5 4.5 1.0 3.8 1.3 4.0 1.5 2.0 3.5 1.5 2.0 1.0 2.5
lowlands
Dry
3.5 5.0 2.0 5.0 1.8 5.0 1.5 2.0 4.8 2.0 2.0 1.0 3.5
lowlands
†Classification based on a 1-5 scale (1 = economically very important; 5 = not economically important); Source: Mahuku, 2011

5. 1 2 3
5 4
Systemic Downy Mildew Pathogens of Asia
Peronosclerospora spp.
1. Thai variant, sorghum downy mildew (P.
sorghi, proposed P . zeae)
2. Java downy mildew (P. maydis)
3. Philippine downy mildew (P. philippinensis)
4. Rajasthan downy mildew (P. heteropogoni)
5. Sorghum downy mildew (P. sorghi)

6. Downy Mildew focus for Asian regional activities due to
severe disease losses associated with infection.
Breeding for resistance to this group of
pathogens has been a major priority in
tropical and subtropical environments

7. Primary tropical foliar
diseases favored by
warmer temperatures
polysora rust maydis leaf blight
(Puccinia polysora) (Bipolaris maydis)
Primary
subtropical and
temperate foliar
diseases favored
by cooler
temperatures
Common rust Gray leaf spot Turcicum leaf blight
(Puccinia sorghi) (Cercospora zea-maydis) (Exserohilum turcicum)

8. Banded leaf and sheath blight
(Rhizoctonia solani AG1-IA ) predominant
Primarily tropical and subtropical disease favored by warm humid conditions

9. Fusarium graminearum ear rot Stenocarpella maydis ear rot
Favored by cooler
temperatures
Fusarium verticillioides ear rot
Major ear rots in
the Asian region Important not only for direct losses, but
as well for the mycotoxins they produce
including aflatoxins, fumonisins,
Favored by warmer deoxynivalenol, zearalenone, and
temperatures diplosporin that make the grain unfit and
potentially lethal for human or animal
Aspergillus flavus ear rot consumption

10. Post flowering stalk rots (PFSR) most prevalent in the
region
Fusarium graminearum stalk rot (Gibberella)
Fusarium stalk rot (F. verticillioides syn F. moniliforme)
Stenocarpella maydis stalk rot (syn. Diplodia)
Macrophomina stalk rot (M. phaseolina)
Late wilt or Cephalosporium stalk rot (C. maydis)
Both Marcrophomina stalk rot and Fusarium stalk rot can be favored by high temperatures

11. Sugarcane Mosaic Virus. Maize Dwarf Mosaic Virus Rice Black-Streaked Dwarf Virus (RBSDV)
(SCMV/MDMV)
SCMV/MDMV is found in tropical to temperate areas, while RBSDV is primarily
a problem of the temperate China and a related virus, MRDV in Iran

12. Climate Change and Potential Change in Pathogen Profiles
•Based on climate change models we can expect more extreme weather events
in the future, and some areas including South Asia elevated temperatures.
•Maize production will be effected and as well the pathogens of predominance
can change based on the environmental conditions that favor their development.
•It is difficult to predict where the changes will occur for foliar diseases, but stress
related diseases including many of the ear rots and stalk rots can be expected to
have a significant impact on maize production under these conditions. Most
notable could be the severity of Fusarium ear rot and Aspergillus ear rot,
Fusarium stalk rot, and Macrophomina stalk rot.
•Linking improved agronomic practices including conservation agriculture,
together with breeding activities for heat and drought stress, and selection for
resistance to the stress related ear and stalk rots, would combine a more
favorable environment with important yield stability and grain quality traits.

13. Progress for Improved Disease Resistance Through Conventional Breeding
• Most disease resistance found in maize is quantitative resistance, and is
oligogenic to polygenic. Few sources of qualitative resistance have been
effectively used for maize.
• Losses to many of the key diseases in the Asian region have been reduced
significantly due the effective use of conventional breeding activities, though
a good understanding of the basis of resistance often is lacking.
• Population improvement activities over several cycles of selection, has
significantly improved performance of the germplasm both for agronomic
traits as well as quantitative resistance to maize diseases.
• Resistance to the foliar diseases including maydis and turcicum leaf blights,
gray leaf spot, polysora and common rust, and downy mildew are all
diseases effectively controlled through conventional breeding, where under
disease pressure the susceptible genotypes could be eliminated before
recombining the germplasm.
• The diseases where less progress has been achieved are banded leaf and
sheath blight, post flowering stalk rots, ear rots, RBSDV in Central China
and MRDV in Iran.

14. P501C4 P42C9, P44C10 P45C10 QPM line recycling
S2 S7 S2 S7
TLB # Families Accum # Families Accum # Families Accum # Families Accum
(1-5) % % % %
1 4 0.8 1 2.9 1 0.2 0.0 0.0
1.5 194 37.9 11 35.3 15 3.0 16.0 16.7
2 210 78.0 12 70.6 124 26.0 40.0 58.3
2.5 92 95.6 5 85.3 198 62.7 32.0 91.7
3 16 98.7 5 100.0 124 85.7 6.0 97.9
3.5 7 100.0 0 . 55 95.9 2.0 100.0
4 0 . 0 . 21 99.8 0.0 .
4.5 0 . 0 . 0 99.8 0.0 .
5 0 . 0 1 100 0.0 .
total 523 34 539 96
mean 1.9 2.0 2.6 2.2
Evaluation on a disease scale of 1-5, 1= 0% infection, 5= 100% infection.
Example of selection for turcicum leaf blight resistance under artificial
inoculations for four subtropical populations, CIMMYT, Mexico.

15. Example of selection for resistance to sorghum downy mildew under artificial
inoculations. CIMMYT, Farm Suwan Thailand.
Material % Downy mildew
0-10 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 91-100
Population 103 115 44 12 8 2 1 0 0 0 0
Population 147 97 33 15 4 1 1 0 0 0 0
Population 100 EVs 77 12 0 1 0 0 0 0 0 0
Population 145 EVs 237 23 3 1 0 0 0 0 0 0
Population 300 EVs 94 8 0 0 0 0 0 0 0 0
Population 345 EVs 155 6 0 0 0 0 0 0 0 0
MDR-DMR TLY 2007 324 11 4 0 0 0 0 0 0 0
Susceptible check 0 0 0 0 0 0 0 0 0 1
Source: Vasal, 1999

16. Progress in Understanding Disease Resistance Through the Use of
Molecular Breeding Techniques in the Asian Region
• The use of molecular markers to study the inheritance of resistance
to disease has been used for many of the major maize diseases
found in Asia, and has provided insight for the basis of quantitative
resistance (Prasanna et al. 2010).
• There has been successful tagging, validation and the transfer of
resistance QTLs to susceptible genotypes in several studies, but
even more studies have not been able to reach this goal of putting
molecular assisted selection into an effective breeding program.
Many reasons can account for this including a limited capacity to
identify small effect QTLs, large genotype x environment
interactions, and not being able to fine map the resistance QTLs.

17. Opportunities for improving the capacity to use molecular
tools to develop molecular marker assisted breeding
• The development of association mapping through linkage disequilibrium
analysis and the use of SNP markers, has greatly improved the power to
dissect the inheritance of quantitative traits (Yan et al. 2011). This has the
capacity to arrive at the gene level due to the coverage of the genome.
• Nested association mapping, with multiple parents included in crosses, and
a common parent in all crosses, has also improved the capacity to
understand the inheritance of complex disease traits (Kump et al. 2011).
• High throughput genotyping platforms are currently available and when
linked with precision phenotyping in the field, can provide the information
needed to effectively use MAS in a breeding program for complex traits.
Current genotyping costs are dropping and will make this a method more
adapted for use in breeding programs. CIMMYT activities will push for the
use of high throughput genotyping in rapid cycle genomic selection, to
develop robust germplasm with added stability for biotic and abiotic stress
traits, in high yielding germplasm.
• The use of doubled haploids to speed up the breeding process will be an
integral part of these changes.

18. Precision phenotyping
• Precision phenotyping is essential to take full advantage of the new
molecular tools for the identification of complex quantitative traits,
and will facilitate the effective use of genome wide selection in our
breeding activities.
• This includes the use of an appropriate field design and statistical
analysis, providing optimal environmental conditions for disease
development, having virulent pathogens, and the capacity to record
the most appropriate phenotypic traits associated with resistance at
the optimum time.
• CIMMYT recognizes precision phenotyping is a limitation frequently
for working with complex biotic and abiotic stress traits, and globally
there will be activities to improve phenotyping within CIMMYT and
by our research partners, through regional training courses.

19. Production of fungal cultures in
the lab for use in performing
artificial inoculations in the field.
Pathogen isolates should be
prescreened to use the most
virulent isolates in field
evaluations.

20. Turcicum leaf blight Fusarium graminearum ear rot
F. verticillioides ear rot
Maydis leaf blight Aspergillus flavus ear rot
Artificial inoculations to characterize resistance attributes
of maize genotypes
Downy Mildew Sugarcane Mosaic Virus
Maize Dwarf Mosaic Virus

21. Precision phenotyping
• New techniques including metabalomics, and proteonomcis may be
needed to work with some complex traits like ear rot resistance.

22. Seed based defense mechanisms implicated in resistance
to ear rots
Fusarium ear rot Aspergillus ear rot
Cuticular Waxes
Pericarp thickness
Β-1,3 gluconase
Cuticular waxes
14kDa trypsin inhibitor
Amylase inhibitor
Pathogenesis-related proteins
Pathogenesis-related
(PR10)
proteins (PR)
Ribosome inactivating protein (RIP)
Zeamatin
Aldose Reductase (ALD)
Glyoxalase I (GLXI)
Anionic peroxidase
Gibberella ear rot Peroxiredoxin 1 (PER 1)
Water stress inducible protein
4-ABOA (WSI)
Diferuloylputrescine 16.9/17.2 kDa Small heat shock
E-ferulic acid protein
Dehydrodimers of ferulic acid Globulin I and II
Guanylyl cyclase like protein Late embryogenesis abundant
(ZmGC1) protein (LEAIII)
Cupin domain containing protein
(Zmcup)

23. Some of the Key Research Collaborative Activities for Improving our
Capacity to Develop Disease Resistant Germplasm for Use in Asia
CSISA I, CSISA II
IMIC-Asia
CCAFS
NSFC Project, “Genetic dissection and molecular
improvement of resistance to three major maize foliar
diseases in China based on joint linkage-association
mapping” led by Dr. Jianbing Yan, Huazhong Agricultural
University (HZAU), Yunnan Academy of Agricultural
Sciences (YAAS), Sichuan Agricultural University (SCAU)
and CIMMYT
DTMA Project, Africa
IMAS Project, Africa
MasAgro Project, Mexico

24. Conclusions
• Disease resistance breeding activities in the Asian region have provided
many useful products for adding yield stability and quality to Asian maize
production.
• Several diseases including banded leaf and sheath blight, ear rots, post
flowering stalk rots, RBDSV and MRDV still have not identified diverse
resistant sources as seen with many of the foliar blights, and downy mildew.
• To meet the great demands for the future, including a production
environment often less favorable due to climate change, new tools including
rapid cycle genomic selection will be needed to develop robust abiotic
stress tolerant, disease resistant high yielding germplasm.
• Networking will improve the capacity of all research groups in the region to
benefit from the new molecular tools, and deliver the best products to the
farmers.