Maize lethal necrosis (MLN): Efforts toward containing the spread and impact of a devastating transboundary disease in sub-Saharan Africa

Abstract

Maize lethal necrosis (MLN), a complex viral disease, emerged as a serious threat to maize production and the livelihoods of smallholders in eastern Africa since 2011, primarily due to the introduction of maize chlorotic mottle virus (MCMV). The International Maize and Wheat Improvement Center (CIMMYT), in close partnership with national and international partners, implemented a multi-disciplinary and multi-institutional strategy to curb the spread of MLN in sub-Saharan Africa, and mitigate the impact of the disease. The strategy revolved around a) intensive germplasm screening and fast-tracked development and deployment of MLN-tolerant/resistant maize hybrids in Africa-adapted genetic backgrounds; b) optimizing the diagnostic protocols for MLN-causing viruses, especially MCMV, and capacity building of relevant public and private sector institutions on MLN diagnostics and management; c) MLN monitoring and surveillance across sub-Saharan Africa in collaboration with national plant protection organizations (NPPOs); d) partnership with the private seed sector for production and exchange of MLN pathogen-free commercial maize seed; and e) awareness creation among relevant stakeholders about MLN management, including engagement with policy makers. The review concludes by highlighting the need to keep continuous vigil against MLN-causing viruses, and preventing any further spread of the disease to the major maize-growing countries that have not yet reported MLN in sub-Saharan Africa.

Keywords: Africa; Breeding; Diagnostics; Maize chlorotic mottle virus; Maize lethal necrosis; Surveillance.

Fig. 1

(A) MLN-resistant inbred lines, CKDHL1705340 (left) and CKDHL1705309 (right), flanking an MLN-susceptible line, CML442; (B) MLN-resistant line, KS23-6 (left) versus an MLN-susceptible line, CML547 (right), 30 days after first artificial inoculation at the MLN Screening Facility, Naivasha (Kenya).

Fig. 2

Frequency distribution of maize lines (n = 5307) derived during 2014–2018 for MLN severity scores, based on evaluation under MLN artificial inoculation at Naivasha in Kenya.

Fig. 3

Responses of MLN-resistant versions vis-à-vis the recurrent parents (elite but MLN-susceptible lines) 30 days after first artificial inoculation at the MLN screening facility in Naivasha, Kenya. The MLN-resistant versions have qMLN_06.157 from KS23-6 (donor parent), transferred through marker-assisted backcrossing.

Fig. 4

Results of MLN surveys (based on MCMV immunostrip data, coupled with evaluation for MLN symptoms, if any) undertaken by NPPOs in eastern and southern Africa, in partnership with CIMMYT, in (A) 2017 versus (B) 2018 versus (C) 2019.