INTERACTIONS AMONG MAIZE STREAK VIRUS-DISEASE, LEAFHOPPER VECTOR POPULATIONS AND MAIZE CULTIVARS IN FOREST AND SAVANNA ZONES OF NIGERIA

Monthly plantings of three maize cultivars with differing resistance/s usceptibility to maize streak geminivirus (MSV) and samplings of Cicad ulina leafhopper vectors were made from December 1988 to April 1990 in the humid forest and from May to November 1989 in the Guinea savanna zones of Nigeria. High MSV disease incidences (43-56%) were recorded o n susceptible cultivar TZB-Gusau in late-season (July-October) plantin gs. Hybrid 8321-21 showed significantly lower MSV disease incidence an d severity than the other two cultivars, TZB-Gusau and 8329-15. Cicadu lina species population peaks (5.2-13.5 leafhoppers/m(2)) were observe d before the rains ended in savanna locations and after the end of the rains in the forest zone. Cicadulina mbila was the predominant specie s, whereas C. storeyi (syn. C. triangula), C. arachidis, C. similis an d C. ghaurii were less common. The proportion of viruliferous leafhopp ers increased as the season progressed, reaching maxima of 15-25% at t he end of the growing season. Interactions between disease incidence, Cicadulina populations, maize cultivars and rainfall are discussed.