“This first generation of hybrids is based on chance finds in available germplasm. The second generation will come from the inbred lines that we are developing,” said B.M. Prasanna, director of the CIMMYT Global Maize Program and now also MAIZE CRP. “We are also incorporating resistance into as many as 25 commercial lines using genetic marker-assisted backcrossing.”
New options on the maize seed market offer an immediate opportunity for farmers to control the impact of MLN in their fields, but a long-term strategy is still needed to secure the crop’s future.
The difference between MLN tolerance and susceptibility is profound
“This was good as an emergency response, because we needed to react. But in the long run we need to develop diverse sources of material with greater resistance to MLN,” said Mezzalama. The targeted search for sources of MCMV resistance in the genebank aims to ensure a diverse supply of fully MLN-resistant hybrids for the future.
Earlier, studies had found that seed transmission did not play a role in the spread of MCMV in the US, but the experience in Kenya suggests otherwise. “The fact that it is transmitted by seed makes control more difficult. This poses a big challenge to seed processors, and phytosanitary services in the region,” Mezzalama.
Breaking the disease transmission cycle in the field is also important. In the affected area of Kenya, maize is grown continuously throughout the year, meaning that insect vectors can carry the viruses from crop to crop, season to season. “Many weeds are also susceptible to MCMV, and even sugarcane and millet can host the virus. Planting non-host crops will help reduce the inoculum reservoir,” said Mezzalama.
MAIZE CRP is funding a project with the International Centre of Insect Physiology and Ecology (ICIPE) to further investigate insect vector dynamics through its competitive grants initiative (CGI). CGI funds have also been granted to the Federal University of Nigeria to help prevent the spread of MLN elsewhere in Africa, with support from the International Institute for Tropical Agriculture (IITA). Plans are afoot to set up an MLN quarantine facility at Harare, Zimbabwe.
MLN poses an existential threat to maize food systems but, with the right resources, plant pathologists and breeders are well-equipped to face such challenges.
We often cannot predict disease outbreaks, but we have to react quickly when such crises arise, as was also recently the case of wheat stem rust - Monica Mezzalama
The international partnership to develop a comprehensive response to MLN continues to make progress on all fronts. The next phase will build capacities in sub-Saharan Africa by creating a transnational ‘community of practice’ among phytosanitary agencies and giving the commercial seed sector, especially small-to-medium size companies, access to MLN diagnosis and the ability to produce clean seed for farmers.