Biology of Cicadulina leafhoppers and epidemiology of maize streak virus disease in West Africa

Abstract

Studies have been conducted in Nigeria on biology of Cicadulina leafhopper vectors of maize streak virus (MSV), the role of indigenous grasses as reservoirs of virus and vectors, and on incidence and severity of MSV in relation to maize varietal susceptibility/resistance levels. Cicadulina populations peak before rains end in the savanna and after the rains in the forest zone. The proportion of viruliferous leafhoppers increases as the season progresses. C. mbila is the predominant vector species; four other species are less common. Off-season survival of MSV and vectors occurs in riverine areas in grasses and in areas with hydromorphic soils where maize is grown during the dry season. However, streak found in many grasses in Nigeria is not readily transmissible to susceptible field maize. Weeds most likely to perpetuate an epidemiologically-competent MSV maize strain are Axonopus compressus (an introduced perennial), Brachiaria lata and Setaria barbata (indigenous annuals). MSV epidemics occur only in years when weather conditions allow vector survival and build-up, and where maize-competent strains are present in grass hosts. MSV disease reduces maize yield, but varieties differ in incidence and severity of disease, and yield loss. Resistant varieties exhibit tolerance—good yield performance when diseased—and lower disease incidence. Low disease incidence is partly due to insect resistance and potential for disease spread is lower on varieties exhibiting this character.

Keywords:

• disease resistance
• geminivirus
• maize
• virus vectors
• Zea mays