A DISSERTATION SUBMITTED IN PARTIAL FULFILMENT OF THE
REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN
MOLECULAR BIOLOGY AND BIOTECHNOLOGY OF SOKOINE
UNIVERSITY OF AGRICULTURE. MOROGORO, TANZANIA. 2017
Begomoviruses are whitefly-transmitted viruses belonging to the family Geminiviridae
presenting most devastating threat to food security. This study was initiated to asses
cassava mosaic disease (CMD) severity and genetic diversity of DNA-B component of
East African cassava mosaic viruses (CMD) that infect cassava plants from main cassava
growing regions in Tanzania. The study involved field survey, rolling cycle amplification
(RCA) followed by next generation sequencing (NGS). The symptoms of CMD severity
in the areas where samples were collected ranged from moderate (2.82) to high (3.95)
using a 1-5 (CMD symptoms severity score scale). Nucleotide sequence identity of 39
isolates identified in this study and that of 32 sequences retrieved from database ranged
from 30% to 100%. Current study has reported the presence of EACMMV-Malawi
(Accession number JX658684) from isolate TZ_KIB1 shared 98% nts identity and 93%
to 98% nt identity with other isolates that were found in the same cluster (branch) with
2753 nts sequence length. Moreover, the presence of four isolates TZ_MBE, TZ_SUM,
TZ_KIR and TZ_KAS from southern zone has also been described, shared 97% to 100%
nts identity with EACMCV-TZ1 (Accession number AF112355) and 100% nts identity
with other isolates from the study. Also, African Cassava Mosaic Virus (ACMV) from
isolate TZ_TAR1 with 100% nucleotides (nts) identity to ACMV [(Nigeria /Ogo)
Accession Number AJ427911] and 2718 nts sequence length from lake zone of Tanzania
has been identified. Moreover, in this study isolates TZ_TAR3, TZ_ROR1, TZ_MIS,
TZ_HAN and TZ_KIB1 showed recombination associated within themselves as well as
with other isolates identified in the previous studies. In conclusion, the current study
showed a greater genetic diversity of begomoviruses DNA-B being more diverse than
previously thought that could be linked to geographical area and high rate of
recombination.