Abstract:
The study aimed at determining the spatial and temporal spread of cassava brown streak disease (CBSD) in field grown cassava in Chambezi, coastal Tanzania and identifying the alternative hosts of Cassava brown streak virus viruses (CBSVs). In determining the spatial and temporal spread of CBSD three treatments were used in the study and a no disease plot served as a control. Data were collected on CBSD severity, incidence and whitefly counts and analysed using SPSS for analysis of variance. Graphs for the temporal disease spread were established to explain the temporal disease spread and examined. Based on the shapes suggest that CBSD progressively increased with time, limited effects of blocking and treatments on foliar and stem incidence of CBSD was observed. The effect of time was highly significant on foliar and stem incidence (P < 0.005). In addition, the effect of blocking, treatments and time (MAP) was highly significant on whitefly population (P < 0.005). The study has shown that susceptible CBSD cassava cultivars become infected though CBSVs infected cassava plant(s) planted in the farm. In determining the alternative hosts of CBSD leaf samples were collected from shrubs and herbs with-virus like symptoms in the Coast, Dar es Salaam and Tanga Regions. Detection of CBSVs was done where samples from Annona senegalensis Pers. tested positive to CBSV whereas UCBSV was detected in Solanum incanum L. Psorospermum febrifugum Spach.var tested positive for the two viruses (CBSV and UCBSV) suggesting coinfections. This new findings sheds light on the origin of this viruses that was first reported from East Africa at Amani in Tanga Region. It further suggests that cleaning of new stock from virus might not offer an effective solution to CBSD management in areas where alternative host plants are rampant.
