Progress in Identifying MLN Resistant Maize Germplasm George Mahuku, D. Makumbi, D. Bish, A. Wangai, Y. Beyene, S. Mugo, K. Semagn, and B.M. Prasanna Workshop to develop a strategic plan for Maize Lethal Necrosis disease for Eastern and Central Africa, Jacaranda Hotel, Nairobi, Kenya, 21-23 August, 2013.

What is Maize Lethal Necrosis MLN Potyvirus SCMV MDMV WSMV MCMV Individual infection with each virus can also cause disease Typically, infection with one virus results in milder symptoms than MLN but reaction depends on germplasm and viral strain.

Susceptible Germplasm Virus: Either individual or compound Susceptible Germplasm MLN Development Vectors: Presence of aphids and thrips, other insects Environment: Conditions favoring vectors and disease

Requirements to identifying MLN resistant germplasm Disease screening tools Diverse germplasm Test locations with consistently high biotic stresses pressure Standardized screening protocols

Resistance screening tools Use field, screen house and laboratory-based screening tools Established using artificial inoculation or infestation Standardized disease establishment and evaluation protocols Ability to handle large populations / germplasm (high throughput for large scale screening) Diagnosis of viruses Use hot-spot locations with consistently high disease, and pest pressure for screening Re-evaluate selected resistant materials in multiple-locations to expose them to different strains or biotypes

Screening maize germplasm for MLN: Artificial inoculation SCMV amplification MCMV amplification MCMV + SCMV amplification

Field inoculation and reaction of germplasm Variation for reaction to MLN disease as of 2, January 2012

Centralized MLN screening Facility 20 Ha being established in Naivasha for MLN screening Labs Greenhouses Field

Use of Disease Hot Spots Use hot-spot locations with consistently high disease, and pest pressure for screening Naivasha, Kenya Bomet, Kenya Babati, Tanzania Arusha, Tanzania Need to identify more sites in other countries

Diverse germplasm Sufficient genetic variation exists for most diseases, pests and parasitic plants in maize Locally adapted or introduced maize germplasm Landrace collections Old varieties and breeding stocks 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

Distribution of severity scores among 200 inbred lines

Reaction of selected hybrids to MLN disease Entry 1-17: elite experimental hybrids Entry 18: Susceptible tester Entry 20-22: Tolerant SC testers Entry 23-28: Commercial checks

Why develop standardized protocols? Harmonize data collection amongst sites Enable collaborators and partners to interpret and share data Support registration, regulation and release of varieties across borders Optimization time and resources devoted to screening Good phenotyping is key to identifying good markers and developing MLN resistant germplasm.

Conclusions There is genetic variation for response to MLN Extensive screening of germplasm may lead to identification of more sources of resistance Need to identify more sites and create a network of Screening Sites Develop standardized protocols and transfer to partners

Challenges Lack of knowledge on number of strains of different viruses Little or no knowledge on epidemiology of MLN in Africa Lack of guidelines on management of vectors Restrictions on movement of seed for research across countries Lack of dedicated greenhouse for inoculum generation and large farms for germplasm screening

Acknowledgement KARI Monsanto USDA Ohio State University Sunripe Farm, Naivasha Olerai Farm, Narok