Abstract:
Maize lethal necrosis (MLN) disease caused by a dual infection of maize with Maize
chlorotic mottle virus (MCMV) and any cereal potyvirus such as Sugarcane mosaic
virus (SCMV), Maize dwarf mosaic virus (MDMV) or Wheat streak mosaic virus
(WSMV) was first reported in Kenya in 2011 in Bomet County. This study was aimed at
determining the presence and genetic variability of MCMV and SCMV in cereal crops,
wild and domesticated grasses and the spatial distribution of alternative hosts in maize
production regions of Kenya. Leaf samples of maize, grasses and other cereal crops were
collected from fields in Nyamira, Bomet, Vihiga, Makueni and Machakos counties.
MCMV and (SCMV) were detected by DAS-ELISA and confirmed by RT-PCR. The
PCR products were sequenced in both directions. The resultant sequences were edited
and compared with sequences from the Genbank followed by phylogenetic analysis. The
distribution of wild grasses harbouring MCMV and SCMV in Kenya was predicted. Six
grass weeds tested positive for MCMV and SCMV namely; velvet crabgrass (Digitaria
velutina), couch grass (Digitaria abyssinica), star grass (Cynodon dactylon), kikuyu
grass (Pennisetum clandestinum) and signal grass (Brachiaria brizantha). Nut grass
(Cyperus rotundus tested positive for MCMV alone. Napier grass (Pennisetum
purpureum) tested positive for MCMV alone. Sugarcane (Saccharum officinarum L.),
finger millet (Eleusine coracana) and sorghum (Sorghum bicolor) tested positive for
both MCMV and SCMV. The MCMV isolates nucleotide sequences were 98-100%
similar and mostly related to the Kenya and Rwanda isolates (99-100%). SCMV isolates
were 93-100% and were most related to China isolate (93-99%). Wild grasses
vi
harbouring MCMV and SCMV are spread throughout maize growing regions in Kenya.
The results indicate that alternative hosts are important in the epidemiology of MLNcausing
viruses and their role should be considered in the development of integrated
management strategies for MLN.
