Browsing by Author "January, Bonaventure"

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Relationship between insect vectors abundance and occurrence of rice yellow mottle virus in farmers’ fields in Kilombero district
(Sokoine University of Agriculture, 2012) January, Bonaventure
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.
Temporal abundance and distribution of rice yellow mottle virus vectors in farmers’ fields in Morogoro, Tanzania
(2017-08) January, Bonaventure; Rwegasira, Gration M
ice 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 Morogoro, the virus is increasingly becoming a serious problem to rice production. The part of the field and developmental stage of rice at which RYMV vectors are predominantly abundant were not known since the need for the study. The assessment of population abundance of RYMV insect vectors were conducted in the three divisions of Mngeta, Ifakara and Mang’ula of Kilombero district, in Morogoro Tanzania using sweep net in 4 m 2 quadrats. Results revealed the highest abundance of two RYMV vectors, Oxya hyla Serville, 1831 and Chaetocnema sp, on the border parts of the rice fields rather than in the middle parts. The study established that the density of RYMV vectors was dependent on crop growth stages where the number of vectors increased with increase in crop age and it is concluded that the two insects are the main vectors of RYMV in the study area.