Characterisation of Malawian cassava germplasm for diversity, starch extraction and its native and modified properties
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Date
2005-11-30
Authors
Benesi, Ibrahim Robeni Matete
Journal Title
Journal ISSN
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Publisher
University of the Free State
Abstract
English: 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.
Afrikaans: Cassava is in die verlede verwaarloos en beskou as ‘n primitiewe gewas, kos vir arm mense en ‘n
gewas met swak voedingswaarde. Cassava verskaf meer voedingsenergie per eenheid area as enige ander stapelgewas. Populasie toename, veelvoudige gebruike, ongewone klimaatswisseling, en die moontlikheid van globale verwarming beklemtoon die voordele van hierdie geharde, droogte tolerante gewas. Beleidmakers het die belangrikheid van cassava besef en moedig nou navorsing, produksie en gebruik van cassava aan. Omdat navorsing op die gewas vir lank agterweë gebly het, is daar kennisgapings wat gevul moet word om dit effektief te produseer, prosesseer en gebruik. Kommersialisering van cassava, en biotiese en abiotiese faktore bevorder genetiese erosie. Bestuur en gebruik rakende kiemplasma in produksie en teelprogramme vereis kennis van genetiese diversiteit. Daarom bestaan daar ‘n behoefte aan versameling, karakterisering, evaluering, bewaring en gebruik van Malawiese kiemplasma. Inheemse kennis het wye genetiese diversiteit aangetoon, omdat boere ‘n wye spektrum in bestaande kwantitatiewe en kwalitatiewe eienskappe aangetoon het wat hulle in bestaande Malawiese cassava kiemplasma verkies of afkeur. Morfologiese merkers kon nie tussen al die inskrywings onderskei nie. Manyokola5 en Mbundumali1, Gomani1 en 2, en Matuvi en Depwete was morfologies identies. Tog het morfologiese merkers wye genetiese diversiteit aangetoon met die Dice genetiese similariteits (GS) spektrum van 0.083-1.000. Die genotipes met die grootste genetiese afstand was Beatrice (plaaslike cultivar) en Yizaso (CH92/112; plaaslik geëvalueer). AFLP karakterisering met groeperings analise het baie nou genetiese diversiteit aangedui met ‘n GS spektrum van 0.778-0.946, maar alle inskrywings kon gedifferensieer word. Die mees verwante inskrywings was Mabundumali1 en Manyokola5 (GS=0.946), en Gomani1 en 2 (GS=0.938), wat met die morfologiese karakterisering as duplikate geïdentifiseer is. PCA analise vir AFLP merkers het getoon dat die PCA as 1 min genetiese diversiteit wys, maar PCA asse 2 en 3 het wye genetiese diversiteit getoon. AFLP analise van cassava kiemplasma het die inskrywings volgens geografiese oorsprong gegroepeer, wat verwant was aan die stamboom van die inskrywings. Morfologiese en AFLP merkers was nie dieselfde nie, maar was tog betekenisvol gekorreleer. Dit is dus goed om beide merkersisteme karakterisering van cassava kiemplasma te gebruik in. Evaluering van AFLP voorvoerders het getoon dat M-CAA/E-ACA, M-CAA/E-AAC, MCAT/E-ACA, M-CAT/E-AAC, M-CTT/E-ACT en M-CTT/E-ACC cassava effektief analiseer. Verdere analise het getoon dat ‘n kombinasie van vier voorvoerders net so goed was as ‘n kombinasie van ses voorvoerders. Die beste voorvoerders was M-CAA/E-ACA+M-CAA/EAAC+M-CTT/E-ACT+M-CTT/E-ACC. Evaluasie van genotipes vir stysel ekstraksie is net voor die begin van die reënseisoen (Oktober-November), in die reënseisoen (Januarie) en naby die einde van die reënseisoen (Maart-April) gedoen. Resultate het getoon dat die beste genotipes Mkondezi, Silira, Mbundumali en CH92/082 was. Styselektraksies wat net voor die begin van die reënseisoen gedoen is het hoër ekstraksie persentasies gegee as in die middel van die reënseisoen. Behalwe dat die ekstraksies so hoog was tydens Oktober-November, is dit ook ‘n baie geskikte tyd om die stysel te droog met die opelug metode, en dit maak die lande ook beskikbaar vir ander gewasse in die opvolgende reënseisoen. Makoka was die beste area om cassava te verbou vir stysel ekstraksie. Cassava stysel van verskillende genotipes is vir fisiese en funksionele eienskappe gekarakteriseer. Resultate het gewys dat Silira, 81/00015, Mbundumali en Sauti maklik gedektriniseer is en 80% oplosbaarheid is binne 60 min van dekstrinisering gekry by 100oC na asidifisering met 0.1M HCl. Pirodekstrinering van Mkondezi vir 40min het baie dieselfde funksionele eienskappe gewys as die van amylmaize stysel. Gelvorming vind by laer temperature plaas in cassava stysel as ander stysel, wat voordelig is vir hitte geaktiveerde plakmiddels, omdat minder energie nodig is om gelvorming te induseer in die cassava stysel, wat tot energiebesparing lei. Funksionele eienskappe van 83350 natuurlike stysel was verskillend van die van die ander genotipes, maar dit was baie dieselfde as amylmaize stysel soos gesien met die DSC.
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Keywords
Dissertation (Ph.D (Plant Sciences: Plant Breeding))--University of the Free State, 2005, Cassava -- Germplasm resources -- Malawi, Plant breeding -- Malawi, Cassava -- Identification -- Malawi, Germplasm, Pyroconversion, Ethnobotany, Starch, Modification, Solubility