Mapping of single nucleotide polymorphism markers for tolerance to cassava brown streak disease of mkombozi x tms 4(2)1425 population
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Date
2014
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Publisher
Sokoine University of Agricuture
Abstract
Cassava Brown Streak Disease (CBSD) is a viral disease that impacts cassava tuberous
root quantity and quality by causing a brown, dry, corky necrosis within the starch
bearing tissues. Tire efficient way to control this disease is the use of resistant cassava
varieties. This study was carried out to genotype the mapping population of Mkombozi x
TMS 4(2)1425 and develop a single nucleotide polymorphic (SNP) genetic linkage map.
Before SNP genotyping was done, the study to determine the integrity of 325 Fl
individuals using ten polymorphic simple sequence repeat (SSR) markers to eliminate
unknown parental combinations was done. SSR data revealed 158 true crosses, 135 off-
types or admixtures, 31 selfs and one genotype (MT 210) was rejected due to many
missing data. SNP genotyping was carried out using a reduced representation genotyping-
by-sequencing approach at the University of Berkeley. Genetic linkage analysis was
performed using Join Map software, version 4.1, Linkage analysis resulted in a total of
1136 SNP markers spanning 3207.9 cM assigned into 18 linkage groups (LGs) of the
integrated linkage map. The average marker spacing of 3.4 cM that ranged from 1.3 cM
to 10.1 cM was observed from this population. The total of 802 SNP markers were
distributed on 19 LGs of female parent (Mkombozi) spanning 2848 cM with an average
marker spacing of 3.7 cM ranging from 1.7 to 6.2 cM. On the male parent (TMS
4(2)1425), 593 SNP markers were distributed on 18 linkage groups spanning 2482.8 cM
with average marker spacing of 5.2 cM ranging from 1.9 cM to 12.6 cM. The genetic
linkage map developed in this study will be used for the identification of molecular
markers and quantitative trait loci (QTLs) associated with CBSD tolerance in Mkombozi.
The molecular markers and QTLs identified provide useful materials to breed and select
CBSD resistance cassava varieties through marker-assisted selection (MAS).
Description
Dissertation
Keywords
Single nucleotide polymorphism, Cassava brown streak disease, Cassava tuberous root quantity, Mkombozi x tms 4(2)1425