Native starch evaluation and genetic distance analysis using AFLP of elite cassava (Manihot esculenta Crantz) genotypes from Malawi
English:The starchy tuberous roots of cassava (Manihot esculenta Crantz) provide more than half of the calories consumed by more than 800 million people in the South America, Asia and Africa. Cassava is a staple for more than 30 % of the Malawi population, while in the rest of the country it is grown for food security, as a snack, and a cash crop. A prerequisite for any genetic improvement programme of cassava is knowledge of the extent of genetic variation present between cultivars and genetic distances between them, and between cassava and closely related species with which hybrids could be produced. This can be achieved through characterisation of germplasm either using morphological, biochemical or DNA markers. Industries that use starch in Malawi have not been willing to use cassava starch because the powder sold by some suppliers as 'cassava starch' was inferior. This study was therefore initiated with the following objectives: (1) To determine the genetic distances/relatedness of commercial Malawi cassava varieties and promising clones using AFLP and morphology descriptors; (2) To evaluate the Malawi commercial cassava varieties and promising clones for starch extraction and quality; (3) To assess the feasibility of using native cassava starch in the industrial sector in Malawi; and (4) To evaluate the commercial cassava varieties in Malawi and promising clones for dry matter content.Trials with 20 cassava genotypes were planted at Chitedze and Makoka in Malawi in November 2000, and were harvested in December 2001. Morphological characterisation was done during plant growth and at harvest. The quality parameters included: protein, moisture and ash content, pH and whiteness. Feasibility studies in the use of cassava starch in the pharmaceutical, textile, battery making and packaging industries started in December 2001. 106 The results show that all the cassava genotypes produced starch containing no detectable protein, similar to the starch used in the pharmaceutical industry. The moisture content ranged from 11.85 to 13.65 %, which is lower than the recommended maximum of 14 %. The recommended maximum ofO.5 % for ash was much higher than the values of cassava starch, which ranged from 0.10 to 0.20 %. The recommended pH for starch is between 4.5 and 7.0, and cassava starch was within these limits, ranging from 5.0 to 5.9. The cassava starch was as white as the corn starch currently being used. Trials have shown that cassava starch can successfully be used in the making of tablets, batteries, packaging material and textile manufacture. Thus, native cassava starch is suitable for use in various industries. This study has also dispelled fears that cassava starch is of low quality and that it is not effective in some industries. Hence, the ideal quality of starch was confirmed in this study. What is required is strict quality control for cassava starch so that industry receives what they pay for. MBS needs to develop national standards for starch, which will help in the enforcement of the quality control for any starch produced in Malawi. This task will be facilitated by the recommendations made in this thesis. Additive main effects and multiplicative interaction (AMMI) was strongly correlated with other stability parameters like Wi-ecovalence, stability variance - no covariate and cultivar superiority measure. AMMI is therefore recommended for use in the stability analysis of starch quality parameters since it provides additional information on the allocation of unstable genotypes into their appropriate environments. This study has demonstrated that genotype has a greater influence on root dry matter than the environment. This agrees with the hypothesis that one or a few major genes control root dry matter in cassava. This study has also revealed that the genetic distances for the local cultivars, locally bred clones and introduced genotypes are equally divergent. This is supported by the distribution of the genotypes in different clusters despite their origin Genetic distances determined by morphological characterisation correlates to similar values using AFLP fingerprinting (r=0.98). It is however, a prerequisite that morphological characterisation be based on constant traits, and the conversion of the morphologic data into binary characters needs careful consideration to meaningful results.
Afrikaans: Die styselagtige tuberagtige wortels van cassava (Manihot esculenta Crantz) voorsien meer as helfte van die kalorië wat verbruik word deur meer as 800 miljoen mense in Soid Amerika, Asië en Afrika. Cassava is die stapevoedsel van meer as 30% van die Malawi populasie, terwyl dit in die res van die land verbou word vir voedsel sekuriteit, as 'n snoephappie en as 'n kontant gewas. 'n Voorwaarde vir enige program van genetiese verbetering van cassava is kennis van die hoeveelheid genetiese variasie wat teenwoordig is tussen cultivars en die genetiese afstande tussen hulle en met naby verwante spesies waarmee basters gemaak kan word. Dit kan bereik word deur die karakterisering van kiemplasma deur morfologiese, biochemiese of DNA merkers. Industrië wat stysel gebruik in Malawi is onwillig om cassava stysel te gebruik, omdat poeier wat deur handelaars in die naam van cassava stysel aan hulle voorsien is, misluk het. Hierdie studie is dus geïnisieer met die volgende doelwitte: (1) Om die genetiese afstande / verwantskappe van kommersiële cultivars en belowende klone van Malawi te bepaal met die gebruik van AFLP en morfologiese beskrywers; (2) Om die Malawi kommersiële cassava cultivars en belowende klone te evalueer vir hulle stysel ekstraksie en die kwaliteit van ongemodifiseerde stysel; (3) Om die bruikbaarheid van ongemodifiseerde stysel in die industriële sektor van Malawi te ondersoek; (4) Om die Malawi kommersiële cassava cultivars en belowende klone te evalueer vir droë material inhoud. Proewe met 20 cassava genotipes is geplant by Chitedze en Makoka in Malawi in November 2000, en is geoes in Desember 2001. Morfologiese karakterisering is gedoen tydens die groeiseisoen en met oestyd. Die kwaliteits parameters wat oorweeg is, was: proteïen, vog, as inhoud, pH en witheid. Lewensvatbaarheids studies vir die gebruik van cassava stysel in die farmaseutiese, tekstiel, battery en verpakkings industrië is begin in Desember 2001. Die resultate het getoon dat al die cassava genotipes stysel geproduseer het wat geen proteïen het nie, soortgelyk aan stysel wat gebruik word in die farmaseutiese bedryf. Die vog inhoud het gewissel van 11.85% tot 13.65% wat laer is as die voorgestelde maksimum van 14%. Die voorgestelde maksimum van 0.5% vir as was baie hoër as die waardes van 0.10% tot 0.2% wat gekry is vir die stysel. Die voorgestelde pH vir stysel is tussen 4.5 en 7.0, en die cassava stysel se waarde was binne hierdie perke, en het gewissel tussen 5.0 en 5.9. Die cassava stysel was net so wit soos mielie stysel wat tans gebruik word. Proewe het getoon dat cassava stysel suskesvol gebruik kan word vir die maak van tablette, die verdunning van medisyne, batterye en verpakkings materiaal. Dus is ongemodifiseerde stysel bruikbaar in verskeie industrië. Hierdie studie het vrese besweer dat cassava stysel van swak kwaliteit is en dat dit nie effektief in sekere industrië is nie. Daarom is die ideale eienskappe van cassava stysel bevestig in hierdie studie. Streng kontrole is nodig sodat industrië kry waarvoor hulle betaal. MBS moet nasionale standaarde vir styselontwikkel wat sal help met die toepassing van kwaliteits kontrole van enige stysel wat geproduseer word in Malawi. Dit behoort maklik te wees omdat hierdie studie die stysel standaarde hersien het. AMMI (additive main effects and multiplicative interaction) was sterk gekorreleer met ander stabiliteits parameters soos Wi-ekovalensie, stabiliteits variansie - geen kovariaat en cultivar superioriteits analise. AMMI word daarom aanbeveel vir die gebruik in stabiliteits analise van stysel kwaliteits parameters omdat dit addisionele informasie gee oor plasing van onstabiele genotipes in hulle regte omgewings. Daar is gedemonstreer in hierdie studie dat genotipiese invloed op wortel droë materiaal baie groter is as die omgewings invloed. Dit bevestig die hipotese dat een of 'n paar hoof gene droë materiaal in wortels beheer. Die studie het aangetoon dat genetiese diversiteit vir plaaslike cultivars, plaaslik geteelde klone en genotipes van buite ewe wyd is. Dit is aangetoon deur die verspreiding van genotipes in verskillende groeperings, ten spyte van hulle afkoms en deur werklike genetiese afstande. Die morfologiese karakterisering van die genotipes was sterk gekorreleer met die van die AFLP vingerafdrukke (r=0.9978) omdat morfologiese beskrywers gebasseer is op konstante (monogeniese) eienskappe. Dit is daarom belangrik dat morfologiese karakterisering gebasseer word op konstante eienskappe, en dat die omskakeling van morfologiese data na 'n binêre matriks effektief gedoen word soos beskryf in Hoofstuk 4, om sinvolle resultate te kry.