Interactions among leafhopper Vector populations, maize streak virus disease, Agro - environmnets and soil fertility in Kenya

A study undertaken in thirteen locations in the west Kenya´s high potential areas ranked maize streak virus disease (MSV) as the most widespread crop disease (DFID, 2000). The disease is transmitted by a leafhopper of the genus Cicadulina. Reports indicate that there are over six important species distributed in different regions of the country. However, scanty information is available on insect biotype and virus strain presence across regions, seasons and on crop hosts (Okoth et al., 1987; Odhiambo et al., 2000). Rose (1972) reported that long - flying biotypes of C. mbila are important in terms of survival and dispersal of the species during dry seasons. This proposed work intends to answer the question of whether agro-environmental factors and soil nutrient levels have any effect on plant health and MSV symptom expression in Kenya. The methodology for conducting the research will include surveys using stratified sampling procedures in the designated sites in Nyanza, Western Central and coast provinces. Survey protocols will be elaborated in such a way that the habitat, pest and soil type data can be subjected to multivariate analysis. Using standard protocols, DNA will be extracted from the insects / virus and amplified using the commercially available oligonucleotide primers. The amplified DNA will be analysed by agarose gel ectrophoresis and the level of heterogeneity assessed using standard computer software packages. The DNA methods will allow further characterization of the Cicadulina spp and the MSV to biotype / strain level (Gozlan et al., 1997; Kimani-Njogu et al., 1998). This technique will also indicate presence or absence of Cicadulina spp. biotypes in Kenya and confirm whether virus strains are region specific in the country. The information obtained from above studies will be used to provide further evidence and guidelines for identifying the test insect to be used in the laboratory bioassays. The first objective will be the manipulation of time of nitrogen application at different crop development stages in order to determine the effect of fertilizer on disease incidence. Secondly, comparative tests of combination levels of inorganic and organic fertilizers on infection and expression of the MSV disease will be done. Data from the laboratory bioassays and from the field studies will be compared using repeated measures analysis using the SAS procedure. Finally, clearly identified taxonomic status of the vector and the virus strain will be invaluable to the on-going maize breeding program to identify resistant varieties.