Evaluation of new expressed simple sequence repeat markers for genetic studies and identification of cassava brown streak disease resistance
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Date
2010
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Publisher
Sokoine University of Agriculture
Abstract
Evaluation for effectiveness of new expressed simple sequence repeat (ESSR) marker is
an important component in the genetic improvement of cassava crop for agricultural
development. ESSRs are often the markers of choice for genetic studies and identification
of CBSD resistance. This study was aimed at: (i) Determining the optimum PCR
conditions on annealing temperature and MgCh concentrations, ii) Identifying
polymorphic loci for ESSR markers for genetic studies of cassava (iii) Identifying
polymorphic loci of ESSR markers linked to CBSD. PCR amplification of each ESSR
locus was optimized for annealing temperature and MgCh concentration. Variation at each
ESSR locus was assessed in 24 cassava genotypes from 11 different countries all over the
world. Successful amplification was achieved from a total of 68 primer pairs of which 53
showed polymorphism within the diversity of cassava genotypes panel. A total of 231
alleles were observed with an average of 4.35 alleles per marker and a range of 2 to 11
alleles. The PIC values measured by the frequency of alleles ranged from 0.173 to 0.844
with average allele frequency of 4.91. Fourteen (14) primer pairs were polymorphic to
identification of genotype linked to CBSD resistance total of 63 alleles with average of 4.5
alleles per locus. These markers will be useful for application in genetic conservation and
plant breeding. The genetic diversity observed by dendrogram revealed four major clusters
and one sub clusters, varieties most closely related were Per 458 and Mex 55 (D=0.1732),
TME 1389, and TME 1368 (D=0.1982), Mkita and Kalolo (D=0.3981) followed by
Pesangani and Kigoma (0.4912) while distantly related genotype were these varieties BRA
990 and Mcx 55 (0.7089). Albert and Mkita (0.6036), BRA255 and Cubl (0.6054), TME
230 and TME 539 (D=0.59I4), and Namikonga and Albert (0.5139).
Description
Dissertation
Keywords
Genetic studies, Expressed simple sequence repeat (ESSR), Cassava crop, Cassava brown streak disease resistance