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MLN Gene Editing Project

The Maize Lethal Necrosis (MLN) Gene Editing Project seeks to use gene editing to develop maize lines tolerant to MLN, a devastating maize disease. The disease first appeared in Kenya in 2011, and by 2013 it reduced maize yields across the country by an average of 22%, resulting in lost production worth $180 million and forcing many farmers to abandon planting maize. By 2014 it had spread to D.R. Congo, Ethiopia, Kenya, Rwanda, Tanzania and Uganda, with a high risk of spreading to other maize-growing areas. Since then, CIMMYT and partners have successfully prevented the spread to any other countries in Africa through extensive training in safe practices, diagnostics and management. However, most maize varieties currently planted in Africa are susceptible to the disease, posing a major threat to the food security and livelihoods of millions who grow and depend on maize for food and incomes.

CIMMYT and its partners have developed MLN-tolerant hybrids, but the process is resource-intensive and takes approximately 4-5 years. Gene editing technology can accelerate the process and reduce breeding time to 2-3 years, so CIMMYT can get improved varieties to smallholder farmers faster.

This project will use gene editing to make four MLN-susceptible lines tolerant to MLN. The four susceptible lines are the parents of two popular, stress-tolerant but MLN-susceptible hybrids developed and commercialized before 2011 in Kenya and Uganda. The edited, MLN-tolerant lines will be used to make MLN-tolerant versions of the hybrids, which will carry all the farmer-preferred agronomic traits and stress tolerance of the popular hybrids, with the added advantage of MLN tolerance.

The MLN-tolerant hybrids will be available for planting on approximately 40,000 hectares, benefiting about 20,000 farmers by 2025 in Kenya. CIMMYT will work in close collaboration with partners from the public and private sectors to prepare for deployment of the hybrids to maximize equitable access by smallholder farmers.

Gene editing as proposed for this project replicates natural mutations in maize that strengthen tolerance to MLN. Scientists apply gene editing to change the susceptible version of a gene or genetic elements in a maize line to a tolerant version. This process eliminates the transfer of many undesirable genes that typically accompany the desired ones in traditional cross-breeding and often compromise yield or other important traits.


  • Use gene editing to develop superior MLN-tolerant maize hybrids faster than conventional breeding techniques
  • Increase smallholder farmer access to superior MLN-tolerant maize hybrids, to increase maize yields and improve food security and livelihoods
  • Overcome current seed production challenges due to MLN susceptibility of parental lines
  • Provide seed companies with royalty-free improved MLN-tolerant varieties, to keep costs down for farmers

Related documents:

MLN Gene Editing project brief

MLN Gene Editing project: FAQs