Cassava has been neglected and considered as a primitive crop, food for the poor and a crop with poor nutritional value for a long time. Cassava provides more dietary energy per unit area than any staple crop. Population increase, multiplicity of cassava uses, unusual climatic variations and prospects of global warming highlight advantages of possible uses of this hardy drought tolerant crop. Policy makers realised the importance of cassava and are encouraging its promotion through research, production and utilisation. Since the crop has lagged behind for a long time, there exist knowledge gaps in many areas.
Commercialisation of cassava, and biotic and abiotic factors encourage genetic erosion.
Management and use of germplasm in production and breeding programmes need knowledge of
genetic diversity. Hence, there existed a need to collect, characterise, evaluate, conserve and use Malawian cassava germplasm. Indigenous knowledge revealed wide genetic diversity because farmers reported a wide range of quantitative and quality attributes, which they preferred or disliked in existing Malawian cassava germplasm. Morphological markers failed to uniquely distinguish all analysed accessions. Manyokola5 and Mbundumali1, Gomani1 and 2, and Matuvi and Depwete were morphologically identical. However, morphological markers revealed high levels of genetic diversity with Dice genetic similarity (GS) ranging between 0.083-1.000. The most distant accessions were Beatrice (local cultivar) and Yizaso (CH92/112; locally screened). AFLP characterisation using cluster analysis indicated narrow genetic diversity with a GS range between 0.778-0.946 and uniquely differentiated all analysed accessions. The closest accessions were Mabundumali1 and Manyokola5 (GS=0.946), and Gomani1 and 2 (GS=0.938). PCA analysis for AFLP markers revealed that PCA axis 1 displayed narrow genetic diversity but PCA axes 2 and 3 displayed wide genetic diversity. AFLP analysis of cassava germplasm grouped accessions according to pedigree and geographical origins. Morphological and AFLP markers were not similar but significantly correlated, indicating the need to use both markers in characterisation of cassava
germplasm. Screening of AFLP primers revealed that M-CAA/E-ACA, M-CAA/E-AAC, M-CAT/E-ACA,
M-CAT/E-AAC, M-CTT/E-ACT and M-CTT/E-ACC were convenient and efficient in analysing
cassava. Further analysis indicated that a combination of four primer pairs was more cost and time efficient and gave similar resolution compared to a combination of six primer pairs, the best being M-CAA/E-ACA+M-CAA/E-AAC+M-CTT/E-ACT+M-CTT/E-ACC. Evaluation of genotypes for starch extraction was done just before or at onset of the rainy season
(October-November), within the rainy season (January) and towards the end of the rainy season (March-April). Results indicated that the best genotypes were Mkondezi, Silira, Mbundumali and CH92/082. Starch extraction done just before or at onset of the rainy season gave the highest starch extraction rates compared to the middle of the rainy season. Apart from high recovery of starch in October-November, it is convenient for drying starch using open-air method and releases land for other crops in the following rainy season. Makoka was the best site for growing cassava for starch extraction. Starch extraction rate on fresh root weight basis had a direct relationship with starch yield as opposed to starch extraction on dry root weight basis. Cassava starch from different genotypes were characterised for physical and functional properties. Results indicated that Silira, 81/00015, Mbundumali and Sauti were easily dextrinised and 80% solubility was achieved within 60min of dextrinisation at 100 o C after acidification with 0.1M HCl. Pyrodextrin from Mkondezi variety after dextrinisation for 40min turned out to be similar in functional properties to amylmaize starch. Cassava starches had lower gelatinisation temperatures desired for hot-setting adhesives since less heating is required to gelatinise cassava starch, which leads to energy saving. Functional properties of 83350 native starch was different from the rest of the genotypes but was very close to amylmaize starch as revealed by DSC.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-07042006-090839 |
| Date | 04 July 2006 |
| Creators | Benesi, Ibrahim Robeni Matete |
| Contributors | Dr Nzola M Mahungu, Prof MT Labuschagne, Dr L Herselman, Prof John K Saka |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-07042006-090839/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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