An international collaboration of scientists is developing germplasm screening to identify disease resistance in corn, and training programs for East African scientists to manage maize lethal necrosis in East Africa.
Maize is the staple food crop for subsistence farmers in East Africa. An alarming threat to food security emerged when a new, unidentified disease was first discovered in the southern Rift Valley of Kenya, causing 40-100% crop losses, and spread to other maize growing areas in the country. Plants developed small cobs with poor or no grain set; plants frequently died before maturity. The disease has now spread to neighboring countries in East Africa. Working with with Kenya Agricultural Research Institute and the International Maize and Wheat Improvement Center in Mexico, USDA and Ohio State scientists are training local scientists and and screening germplasm to identify genetic resistance and management approaches for the disease.
A systematic process was used to identify the pathogen(s) causing the death of maize plants. Diseased plants exhibited leaf mottling and other symptoms characteristic of viruses; all diseased plants had similar symptoms. Insect disease vectors, specifically aphids, leafhoppers and thrips, were surveyed. Thrips populations were found to be high in diseased fields. The disease symptoms and presence of thrips suggested the problem could be associated with Maize chlorotic mottle virus. Tests were positive for this virus, however, the observed symptoms were more severe than commonly seen with the virus. Using serological (antibody-based assays) and genome sequencing tools, USDA ARS and OARDC scientists identified Maize chlorotic mottle virus and another virus, Sugarcane mosaic virus, in diseased maize. Together, the two viruses form a disease complex, Maize lethal necrosis, which was determined to be the cause of the crop losses. Using diverse germplasm resources, screens for resistance to control MLN have commenced. Visits by USDA-ARS scientists have facilitated development of germplasm screening resources in East Africa and experiments in the US.
The first report of the co-infection of the two viruses - Maize chlorotic mottle virus and Sugarcane mosaic virus - associated with maize lethal necrosis in Kenya resulted from work at OARDC through international collaborations. Commercial and easy-to-use diagnostics can now be used to rapidly confirm the presence of maize lethal necrosis, allowing farmers to make critical decisions on whether to destroy crops. Identification of the two viruses associated with maize lethal necrosis allowed collaborators to develop a centralized screening facility so that maize breeders can effectively test new lines and hybrids for resistance to this devastating disease. Germplasm screening to identify resistance has commenced, and collaborations are established to train East African scientists in the expertise required to manage the disease outbreak. This is critical because the rapid development of disease-resistant varieties of maize has now been established as a priority for Kenyan agriculture, as no chemical treatment options exist for virus diseases. The collaboration between international scientists and organizations is an excellent example of how resources and expertise can come together to address disease threats to food security.
M. Redinbaugh, USDA ARS and OARDC; Oklahoma State, Kenya Agricultural Research Institute; and Mexico's International Maize and Wheat Improvement Center (CIMMYT)