MSc. Thesis
Rice yellow mottle virus (RYMV) endemic to Africa is spread within and between rice
fields by several species of Chrysomelid beetles and grasshoppers. In Tanzania and
particularly in Kilombero District, the virus is increasingly becoming a serious problem to
rice production. The relationships between the insect vectors and RYMV disease
incidence and severity were not fully known hence the need for this study. The assessment
of both disease incidence and severity of RYMV and population abundance of its insect’s
vectors were conducted in the three divisions of Mngeta, Ifakara and Mang’ula in
Kilombero District, Tanzania in 4m2 quadrat.
Insect sampling was conducted using
sweep net while RYMD incidence and severity were visually assessed in a 4 m 2 quadrat.
Results of the insect identification indicated the presence of two insect vectors of RYMV
i.e. (Chaetocnema spp. and O. hyla). The population densities of these RYMV vectors
were higher at the border parts of the rice fields than at the middle parts. On the other
hand, the incidence and severity of RYMV disease increased with the age of the crop.
Results of within field distribution also indicated a random distribution of RYMV-affected
plants in the rice fields in the agro ecosystem. The field studies of the virus–vector
relationship established that RYMV occurrence varied in space and time and crop
development stages. The partial correlation analysis showed a positive relationship
between insect vector’s population density and the incidence and severity of RYMVD.
The two insect species were tested for their ability to transmit RYMV and both were able
to transmit the virus from RYMV-infected plants to healthy rice seedlings suggesting their
potential contribution to RYMVD prevalence in the agro-ecosystem.
Ministry of Agriculture, Food Security and Cooperatives (MAFSC)