Theses and Dissertations Collection

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Browsing Theses and Dissertations Collection by Author "Biswao, Yongolo Mary"

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    Effects of harvesting intervals and quality of planting materials on cassava brown streak disease and yield of cassava
    (Sokoine University of Agriculture, 2014) Biswao, Yongolo Mary
    Investigations were conducted at Kibaha Sugarcane Research Institute, Coast region, Tanzania to identify cassava brown streak viruses (CBSVs) and their variants by Real-Time Polymerase Chain Reaction (RT-PCR) and to assess the effect of time of cassava harvesting on quality and yield loss associated with cassava brown streak disease (CBSD) infection. This study was prompted by the reported reduction in yield of cassava in Tanzania caused by CBSD. Two field experiments were conducted where the first sought to evaluate the effect of CBSD on above ground yield components and root yield of CBSD-infected and CBSD-free planting materials of Kiroba cassava variety. The second experiment assessed the effect of harvesting time on yield and quality traits for virus-free planting materials of Kiroba and Mwari varieties. The viruses (CBSV and UCBSV) were identified using RT- PCR assays from 220 cassava leaf samples of both varieties. Results indicated that plants affected by CBSVs may or may not express symptoms of CBSD but only molecular (PCR) diagnosis can be used to confirm the presence of either or both of the causal viruses. Use of CBSD-infected planting materials of Kiroba decreased root weight by 24%. However, the symptoms of CBSD were delayed for the plants whose planting materials were free from virus. The highest incidence (24.3%) of root necrosis for Mwari was recorded at 14 months after planting (MAP) and at the highest level of CBSD incidence (5.2%). Kiroba had the highest incidence (22 to 26.8%) of root necrosis from 12 to 16 MAP at the lowest (0%) to the highest CBSD incidence (14.5%). The highest yield (8.8 t ha'1) for Mwari was recorded at 14 MAP, which dropped to 8.0 t ha'1 at 16 MAP. The highest yields (8.1 and 9.3 t ha'1) foriii Kiroba were recorded at 14 to 16 MAP. It was recommended that virus-free planting materials should be used in order to avoid spread of CBSVs and reduce the intensity of root necrosis. More studies should be conducted using similar planting materials in a non-isolated field and during the second growing season to ascertain the reproducibility of the findings of this study before the findings are recommended to farmers