Maize Diseases in AsiaDaniel Jeffers CIMMYT/China, Yunnan Academy ofAgricultural Sciences, Institute of Food CropsKunming, Yunnan, firstname.lastname@example.org
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
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.
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
Banded leaf and sheath blight (Rhizoctonia solani AG1-IA ) predominantPrimarily tropical and subtropical disease favored by warm humid conditions
Fusarium graminearum ear rot Stenocarpella maydis ear rot Favored by cooler temperatures Fusarium verticillioides ear rotMajor ear rots inthe 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
Post flowering stalk rots (PFSR) most prevalent in theregionFusarium 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
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 primarilya problem of the temperate China and a related virus, MRDV in Iran
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.
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.
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.
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.
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.
Production of fungal cultures inthe lab for use in performingartificial inoculations in the field.Pathogen isolates should beprescreened to use the mostvirulent isolates in fieldevaluations.
Precision phenotyping• New techniques including metabalomics, and proteonomcis may be needed to work with some complex traits like ear rot resistance.
Seed based defense mechanisms implicated in resistanceto ear rotsFusarium ear rot Aspergillus ear rot Cuticular WaxesPericarp thickness Β-1,3 gluconaseCuticular waxes 14kDa trypsin inhibitorAmylase inhibitor Pathogenesis-related proteinsPathogenesis-related (PR10)proteins (PR) Ribosome inactivating protein (RIP) Zeamatin Aldose Reductase (ALD) Glyoxalase I (GLXI) Anionic peroxidaseGibberella ear rot Peroxiredoxin 1 (PER 1) Water stress inducible protein4-ABOA (WSI)Diferuloylputrescine 16.9/17.2 kDa Small heat shockE-ferulic acid proteinDehydrodimers of ferulic acid Globulin I and IIGuanylyl cyclase like protein Late embryogenesis abundant(ZmGC1) protein (LEAIII) Cupin domain containing protein (Zmcup)
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
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.