Genetic polymorphism of cassava (Manihot Esculenta Crantz) landraces commonly grown by Ruvuma Region farmers using simple sequence repeat (SSR) markers
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Date
2008
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Publisher
Sokoine University of Agriculture
Abstract
The study aimed at investigating the morphological and genetic relationships of
cassava (Manihot esculenta Crantz) landraces grown in Ruvuma Region in
Tanzania. Thirty nine cassava landraces were collected from farmers’ fields in
August, 2006. Purposive sampling was used to select study villages. The cluster
analysis and similarity matrix was computed using morphological traits and Simple
Sequence Repeat (SSR) markers based on Jaccard’s coefficient following the
unweighted pair group method with arithmetic averages (UPGMA) method using
Sequential and Hierarchical Numeric option (SAHN) program of NTSY-pc. A set
of 13 SSR primers out of 20 that were screened generated 75 (84.3%) polymorphic
bands out of 89 amplified DNA bands. Morphological characterization, SSR allele
diversity and association mapping were performed using 22 morphological
characters and 13 selected SSR primers. The jaccard’s coefficient for morphological
traits and SSR markers varied from 0.53-0.91 and 0.33-0.88, respectively. The
result obtained showed that use of morphological traits and SSR markers readily
distinguished the 39 cassava landraces at 0.91 and 0.88 similarity coefficients,
respectively. The results, summarized on both dendrograms, showed narrow genetic
diversity among the cassava landraces. Further, the dendrogram showed inter and
intra-cluster variation among the landraces used providing scope for its
improvement through hybridization and selection.
In both methods used (i.e.
morphological and SSR techniques) no cassava duplicate was identified, the most
morphologically closely related cassava landraces were Sindani and Ndingtwaka
with similarity coefficient of 0.91. Similarly the most genetically closely relatediii
cassava landraces were Mama and Mahuhu that had jaccard coefficient similarity of
0.88.
The result from the two methods used in study indicated that only four
landraces (i.e. Pesangani, Chilabula, Mwaya and K.asindand') were found to be
unrelated both morphologically and genetically. Such findings indicate that these
four cassava landraces could be included in National Cassava Improvement
Programs (NCIP) in Tanzania.
Description
Dissertation
Keywords
Genetic, Ruvuma region, Manihot esculenta Crantz, Cassava genetic polymorphism