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When cassava is harvested too early, it often leads to reduction in yield, while delayed harvest leads to development of woody and fibrous tuberous roots, and reduction in starch content. The optimum harvest time is not known. The objectives of this study were to determine the effect of genotype, location and season on starch extraction in order to find an optimum harvest regime for cassava, and to find the best parameter for monitoring starch levels in cassava tuberous roots. Results showed that genotypic effect was large for starch weight, starch extraction rate on fresh weight basis, and root dry matter content. This suggested that high starch weights could be realised by selection of suitable varieties for starch extraction. It was found that cassava harvesting and starch extractions should be done between October and November since the highest starch extraction rates were achieved during that period, and drying of the extracted starch using the open air method was fast and convenient. The results also suggested that starch levels can efficiently be monitored using starch extraction rate on fresh root weight basis. Starch content on fresh root basis and root dry matter content can also be used to determine the optimum time to harvest cassava for starch extraction but were inferior to starch extraction on fresh root weight basis.

Cassava is the second most important staple food crop in Sub-Saharan Africa and is also an important food and cash crop in Malawi. A prerequisite for any genetic improvement programme is knowledge of the extent of genetic variation present between cultivars and genetic distances between them. This can be achieved through characterisation of germplasm using morphological, biochemical or DNA markers. This study was done to determine the genetic relatedness of commercial Malawi cassava varieties and promising clones using AFLP DNA markers and morphological descriptors, and to compare these methods in characterising cassava genotypes. Trials with 16 cassava genotypes were planted at Chitedze and Makoka in Malawi. Morphological characterisation was done during plant growth and at harvest. This study revealed that the genetic distances for the local cultivars, locally bred clones and introduced genotypes were divergent. This is supported by the distribution of the genotypes in different clusters despite their o...

Cassava is an important food and cash crop in Malawi. It is also becoming increasingly important for industrial use. The aim of this study was to investigate the native starch quality of different Malawi cassava genotypes. Trials were conducted at Chitedze and Makoka in Malawi in the 2000/01 season. Apart from root dry matter and starch extraction, starch quality parameters considered included protein, moisture and ash contents, pH and whiteness. Various stability measures were used to deal with the problem of genotype × environment interaction. The results showed that all the cassava genotypes produced starch with no protein and with colour as white as required by the industry. Moisture and ash contents and pH fell within the industry-recommended ranges. This suggests that native cassava starch is suitable for use in various industries. Additive main effects and multiplicative interaction (AMMI) was strongly correlated with other measured stability parameters and is therefore recommended for stability analysis of starch quality parameters. Genotype had a larger influence than environment on root dry matter. This agrees with the hypothesis that one or a few major genes control root dry matter in cassava. Copyright © 2004 Society of Chemical Industry

Cassava ( Manihot esculenta Crantz) is the second most important staple food crop in sub-Saharan Africa, providing upto 285 calories per person per day. Cassava starch is a potentially important industrial material in Malawi. Industries hesitate to use cassava starch because the powder sold by some suppliers has been grossly inadequate. This study was conducted to evaluate native cassava starch qualities for different Malawi cassava genotypes, determine the appropriate stability parameter to deal with GxE for starch quality traits, and potential for use of cassava starch by the main industries in Malawi. Trials were conducted in Malawi to examine starch quality parameters, root dry mater and starch extraction. Based on the results, the moisture and ash content were much lower than the recommended allowable maximum. The pH for cassava starch was within the recommended range. Additive main effects and multiplicative interaction (AMMI) were strongly correlated with other stability parameters such as Wi-ecovalence and stability variance–no covariate. From the results, genotype has a greater influence on root dry matter than the environment. Native cassava starch can be used in the pharmaceutical, battery and packaging material making and textile industries in Malawi. Key Words: Ash, Malawi, Manihot esculenta, sub-Saharan Africa RESUME Le manioc ( Manihot esculenta Crantz) est la deuxieme plus importante plante d'aliment de base en Afrique sub-Saharienne, pourvoyant jusqu\'a 285 calories par personne par jour. L'amidon de manioc est un produit industriel potentiellement important en Malawi. Les industries hesitent d'utiliser l'amidon de manioc parce que la poudre vendue par certains fournisseurs a ete grossierement inadequate. Cette etude etait conduite pour evaluer les qualites d'amidon de manioc autochtone pour les differents genotypes de manioc de Malawi, determiner le parametre approprie de stabilite de GXE a traiter pour les traits de qualite d'amidon, et le potentiel d'usage d'amidon de manioc par les principales industries en Malawi. Les essais etaient conduits en Malawi pour examiner les parametres de qualite de l'amidon, la matiere seche de racine et l'extraction d'amidon. Base sur les resultats, les genotypes de manioc ont produit l'amidon mais pas de proteine. Les teneurs d'humidite et de cendre etaient tres basses que le maximum admissible recommande. Le pH d'amidon de manioc etait dans l'intervalle recommande. Les principaux effets additifs et multiplicatifs d'interaction etaient fortement correles avec les autres parametres de stabilite tels que Wi-ecovalence et variance- no covariante de stabilite. A partir des resultats, le genotype a une grande influence sur la matiere seche de racine que l'environnement. L'amidon de manioc autochtone peut etre utilise dans les industries pharmaceutiques, de batterie, dans les fabriques de materiel d'emballage et industries textiles en Malawi. Mots cles : Cendre, Malawi, Manihot esculenta, Afrique sub-Saharienne African Crop Science Journal Vol.12(3) 2004: 205-216

Cassava ( Manihot esculenta Crantz) and sweetpotato ( Ipomoea batatas Lam) are important food and cash crops in Malawi. However, key information regarding varieties grown, sources of planting materials, post-harvest handling, utilisation and tuber yields is lacking. A study was, therefore, conducted to source this information. Farmers grow mostly local varieties of cassava with own gardens as the main source of planting materials. Several varieties of sweetpotato are grown with Kenya (SPN/O, bred in Tanzania) as the most popular. Sprouts from previous season\'s gardens are the main source of planting materials. Cassava and sweetpotato are grown for food and cash. However, in some area cassava stems are used for fuel wood. Most farmers do not store fresh cassava roots but process them into makaka, kanyakaska and kadonoska , or sell them fresh. Processing for sweetpotato is limited to boiling and roasting. Most farmers store sweetpotato, but this is constrained by the sweetpotato weevil damage and rotting. Root yield ranged from 13.1 to 31.4 t ha -1 for cassava, and 10.2 to 14.0 t ha -1 for sweetpotato. Except for Nkhata Bay, the yields of both crops were much lower than from research stations. Unavailability of acceptable improved varieties, high incidence of pests and diseases, and poor cultural practices are the main causes of low yields in the targeted areas. Key words : Ipomoea batatas, Manihot esculenta, planting materials, weevil RESUME Le manioc ( Manihot esculenta Crantz) et la patate douce ( Ipomoea batatas Lam) sont des importants aliments et plantes generatrices de ressources en Malawi. Cependant, l\'information cle concernant les varietes plantees, les sources de materiels de plantation, les manœuvres post-recoltes, l\'utilisation et les rendements de tubercules manque. Une etude etait alors conduite pour approvisionner cette information. Les fermiers cultivent souvent les varietes locales de manioc avec comme source principale de materiels de plantation leurs propres champs. Plusieurs varietes de patate douce sont cultivees au Kenya (SPN/O, conditionnee en Tanzanie) comme le plus populaire. Les germes des champs de saison precedente sont la source principale de materiels de plantation. Le manioc et patate douce sont cultives pour la nourriture et l\'argent. Cependant, dans certaines aires les tiges de manioc sont utilisees pour le bois de chauffe. La plus part des fermiers n\'entreposent pas les racines de manioc frais mais transforment les en makaka, kanyakaska et kadonoska, ou les vendent frais. La transformation de la patate douce est limitee a l\'ebullition et au rotissage. La plus part des fermiers entreposent la patate douce, mais ceci est gene par les degâts et les avaries des charancons. Les rendements de racines ont varies de 13.1 a 13.4 t ha -1 pour la patate douce. A l\'exception de laurier Nkhata, les rendements des toutes les deux cultures etaient plus bas que ceux des stations de recherche. La non disponibilite des varietes ameliorees acceptables, l\'incidence elevee des pestes et maladies, et les pauvres pratiques culturales sont les causes principales de faibles rendements dans les aires visees. Mots Cles: Ipomoea batatas, Manihot esculenta, materiels de plantation, charancon African Crop Science Journal Vol.12(3) 2004: 295-303