PhD Theses

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Browsing PhD Theses by Subject "Agricultural pest"

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    The Role of the Whitefly (Bemisia Tabaci Gennadius) in the Transmission and Spread of Cassava Brown Streak and Cassava Mosic Viruses in the Field and Semi Field Conditions.
    (University of Dar es Salaam, 2015) Jeremiah, Simon Cephas
    Cassava brown streak disease (CBSD) and Cassava mosaic disease (CMD) are the major biotic stresses in cassava-growing areas in East and Central Africa, causing yield and quality losses on tubers. No transmission experiments conducted before 2004 were successful on transmission of Cassava brown streak viruses (CBSVs). A series of experiments were conducted at Kibaha sugarcane research, Ukerewe Island in Tanzania, Namulonge research institute in Uganda and NRI in the United Kingdom. The objectives were to investigate the field spread of cassava brown streak viruses (CBSVs), causing cassava brown streak disease (CBSD). To determine associations between spatial distributions of B. tabaci and CBSD in farmers' fields. To quantify relationships between climatic factors, whitefly abundance and CBSD symptom expression in field and under screen house conditions. Also, to establish the transmission characteristics of CBSVs and determine the transmission efficiency of B. tabaci as the vector of CBSVs. The results reported that viruses are acquired by whiteflies at a short period of only 5 minutes and retained in the insect body for not than 24 hours. Surveys conducted in Tanzania (20092011) showed positive relationships between CBSD and whitefly population in the field (2009, 12=0.89; 2010, 12=0.80; 2011, 12 =0.98) for Coastal lowland. Similarly, positive correlations between CBSD and whitefly abundance in the Lake zone in 2009 (r2=0.92) and 2010 (12=0.85). Consequently, these findings suggest more work on whitefly control strategy to reduce the disease spread, and more studies on B. tabaci/CBSV/ Cassava pathosystem. Addition of NPK increased disease symptoms' expression than it was observed in other plots without fertilizers, hence more symptoms are expressed in