Cassava is generally grown by poor farmers living in marginal areas with adverse climatic and soil conditions. The crop is very suitable for these conditions because of its exceptional tolerance to drought and to acid, infertile soils. It is often grown on sloping land because of its minimal requirement for land preparation, and its ability to produce reasonably good yields on eroded and degraded soils, where other crops would fail. It has been shown (Quintiliano et al., 1961; Margolis and Campos Filho, 1981; Putthacharoen et al., 1998), however, that growing cassava on slopes can result in severe erosion, with high soil and nutrient losses. Thus cassava cultivation on slopes requires adequate cultural and soil conservation practices that minimize erosion (Howeler, 1994). Cassava is well adapted to poor or degraded soils because of its tolerance to low pH, high levels of exchangeable aluminium (Al) and low concentrations of phosphorus (P) in the soil solution. Studying the effect of pH on the growth of several crops grown in flowing nutrient solution, Islam et al. (1980) reported that cassava and ginger (Zingiber officinale) were more tolerant of low pH (< 4) than tomatoes (Lycopersicon esculentum), wheat (Triticum aestivum L.) or maize (Zea mays L.). Centro Internacional de Agricultura Tropical (CIAT; 1978) and Howeler (1991a) also reported that cassava and cowpeas (Vigna unguiculata) were more tolerant of acid soils with high levels of exchangeable Al, and were much less responsive to lime applications than common beans (Phaseolus vulgaris), rice (Oryza sativa), maize and sorghum (Sorghum vulgaris).

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Cassava mineral nutrition and fertilization

Cassava (Manihot esculenta Crantz) is an important source of food in the tropics. Phillips (1974) estimated that by 1980 it would provide 37% of the calories consumed in Africa, 11% in Latin America and 6% in the Far East forming the staple diet of 500 million people. Total world production in 1978 was estimated to be over 119 mill tonnes, mainly distributed among Africa, South America and Southeast Asia (FAO, 1979). Production figures for the major cassava producing countries of the world for the years 1976-1978 are shown in Table 1. Most of the world production of cassava is used for human consumption in tropical countries, the other main uses being for animal feed and the starch industry. The latter 2 markets, however, accounted for only 6.5% of the world production in 1974 (Anonymous, 1977). To an even greater extent than other tuberous crops, cassava is primarily a carbohydrate source containing little protein and as such is often considered as an inferior food. However, in much of the world where severe malnutrition and even starvation exists, the populations suffer not only from protein deficiency but also carbohydrate deficiency. The production of cassava products using traditional methods of preparation goes far to alleviate the problem: indeed it is significant that in areas where cassava is extensively grown, severe famines seldom occur. There are many descriptions of the traditional methods used to prepare foods from the cassava root but most are oriented to particular areas of the world. There is no study of the subject on a worldwide basis. The present paper reviews the literature, bringing together information from all the major cassava-producing areas in order to focus attention on the diversity of the processing techniques and the wide variety of cassava-based foods and beverages that are produced. Cassava leaves are also used as a food particularly in Africa and they are a good supplementary source of proteins and vitamins (Terra, 1964). As such their role in the diet is very different from that of the cassava root and they will not be discussed here. However, there is a need for further studies on the value of cassava leaves in the diet.

Traditional cassava-based foods: Survey of processing techniques

Occurrence of intervarietal or interspecific natural crosses has been reported for many crop plants in traditional farming systems, underlining the potential importance of this source of genetic exchange for the dynamics of genetic diversity of crop plants. In this study, we use microsatellite loci to investigate the role of volunteer seedlings (plants originating from unmanaged sexual reproduction) in the dynamics of genetic diversity of cassava (Manihot esculenta Crantz), a vegetatively propagated crop, in a traditional farming system in Guyana. A previous field study showed that farmers incorporate such plants into the germplasm for vegetative propagation, and that many of them are likely to be assigned by farmers to recognized varieties. Under strict vegetative propagation clonality of varieties is expected. The high proportion of polyclonal varieties observed suggests that incorporation of seedlings into the germplasm for propagation is a frequent event. The molecular variability assessed with microsatellite markers shows that there is high differentiation among heterozygous varieties, whereas populations of seedlings do not depart from the proportions expected under Hardy–Weinberg assumptions. Assignment of seedlings to a recognized variety on the basis of morphological similarity greatly increases genetic diversity within the variety. We argue that recombination and gene flow play a major role in the dynamics of genetic diversity of cassava in traditional farming systems. Documenting unmanaged sexual reproduction and its genetic consequences is a prerequisite for defining strategies of in situ conservation of crop plant genetic resources.

Unmanaged sexual reproduction and the dynamics of genetic diversity of a vegetatively propagated crop plant, cassava (Manihot esculenta Crantz), in a traditional farming system

Studies of Manihot esculenta Crantz and Related Species

Nine cassava cultivars IAC 12, IAC 13, IAC 14, Fecula Branca, Espeto, Branca-de-Santa Catarina, Fibra, Verdinha and Mico were evaluated for roots and branches productivity, dry matter contents and bacterium resistance. The trials were carried out during the years of 1994/95, 1995/96 and 1996/97, in Araruna, Northwest Region of Parana State, Brazil. The treatments were arranged in a randomized complete block design with four replicates. In the joint analyses, the cultivar vs. year interaction effect was significant (P < 0,05) for all the characteristics evaluated. In spite of that, it was possible to conclude that IAC 14 and Fecula Branca had the highest branch yield and root yield, respectively. The cultivars IAC 14, Fecula Branca, IAC 13 and IAC 12 presented the highest root dry matter contents. Mico, IAC 14 and Fecula Branca showed the highest bacterium resistance.

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Avaliação de cultivares de mandioca na Região Noroeste do Paraná

The cassava plant (Manihot utilissima Pohl) is native in Brazil and was already used by the indians as a main source of food before the arrival of the Europeans. Wild species of Manihot are found in several parts of Brazil and in other South American countries. Cassava roots are one of the chief sources of carbohydrates for a large part of the Brazilian population. It is also widely used to feed animals. In parts of Brazil they are used as raw material for the starch industry. In 1946 there were about 900 000 hectares of cassava planted in Brazil. In the State of Sao Paulo little attention had been given to the agricultural problems of the cassava crop prior to 1935. At this time an extensive series of field trials was started by the Instituto Agronomico, Campinas, to obtain information on the various problems of this crop. Since then a large amount of data has been obtained, and the present paper is a summary of the work that has been carried out. Over 600 varieties were collected from several parts nf Brazil to be used as basic material for selection or synthesis of high yielding and disease resistant types. Extensive field tests have shown that the highest yielding and most resistant varieties were: "Branca de Santa Catarina", "Preta", "Cafelha", "Brava de Itu", and "Itu". They are more suitable for industrial purposes than the common variety known as "Vassourinha". The variety "Guaxupe" was found to be the best for human consumption and as a forage. In experiments on methods of planting, the use of cuttings 50 cm long stuck in the soil in a vertical or slanting position, leaving about 35 cm above ground, gave better results than cuttings 15 cm long, placed in a horizontal position in furrows as it is usually done by the farmers. Fertilizer experiments showed that, as a rule, phosphates gave the highest increase in yield. Nitrogen or potassium, either alone or together, had no effect on yield. When one or both of these elements were added to phosphates the yields were better than with phosphates alone. The period from May to August is the regular cassava harvesting time in the State of Sao Paulo. Experimental plantings made during these months gave higher yields than those made in October, the usual time of planting. Furthermore, when the planting is made soon after harvest the losses of cutting that occur during a long storage are avoided. In field test cuttings 20 to 25 cm long, planted in furrows, secured better stands and higher root production than were obtained with shorter cuttings. Data from field trials indicated that a spacing ranging between 0,80 x 0,40 cm and 1,00 x 0,60, according to soil fertility, is more advantageous than the spacing of 1,20 x 0,60 cm as it is usually adopted. Test on depth of planting were made with 15 cm long cuttings planted in furrows 5, 10 and 15 cm deep, and subsequently covered. The plants grown from cuttings planted 15 cm deep produced less and were more difficult to be dug out. Planting at 5 cm depth is also inadvisable because the plants may be easily uprooted by erosion or strong winds. Planting at 10 cm depth is to be recommended. Studies on cassava bacterial wilt caused by Xanthomonas manihoti (Arthaud-Ber-thet) Burk, revealed that several common varieties and clones derived from seedlings show more resistance than the usually cultivated types. Cuttings of the resistant types were released to the growers and are now being widely used. A virus disease of the witches broom type, present in some localities, caused severe losses in cassava plantings made with the variety "Vassourinha". Tests carried out in infested areas showed that the variety "Brava da Ponte" is highly resistant to the disease, and the varieties "Preta" and "Holandi do Itagua" show a fair degree of resistance.

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Aspectos agronômicos da cultura da mandioca (Manihot utilissima Pohl)

Quarenta clones de mandioca, oriundos de diversos cruzamentos intervarietais, foram avaliados quanto a producao de raizes e outras caracteristicas, em Campinas e Pindamonhangaba (SP), no periodo de 1981 a 1984. Originalmente, foram plantados quatro ensaios em Campinas e quatro em Pindamonhangaba, em blocos ao acaso com quatro repeticoes. Cada ensaio teve 13 tratamentos, dentre os quais tres testemunhas comuns. Os resultados obtidos permitiram a selecao de 13 clones mais promissores, que foram novamente testados com a instalacao de mais um experimento em cada localidade, utilizando a mesma metodologia. Embora nenhum clone se destacasse significativamente quanto a producao de raizes, em relacao as testemunhas SRT 59 - Branca de Santa Catarina, IAC 12-829 e IAC-Mantiqueira, o IAC 576-70, oriundo do cruzamento SRT 797 - Ouro do Vale x IAC 14-18, evidenciou uma serie de caracteristicas favoraveis como mandioca de mesa. Assim, novo experimento foi conduzido em 1983/84, em Campinas, comparando-o com outras variedades de mesa, tendo como testemunha a SRT 454 - Guaxupe. Os resultados obtidos neste trabalho permitem concluir que o clone IAC 576-70 apresenta uma serie de vantagens agronomicas e culinarias, em relacao as tradicionais variedades de mesa em cultivo, como arquitetura da parte aerea, maior produtividade, razoavel resistencia de campo a bacteriose, bom aspecto das raizes, bom tempo de cozimento e cor amarela da polpa.

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Competição de clones de mandioca selecionados para mesa e indústria

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Determinação da toxicidade da mandioca pelo paladar das raízes "In Natura"

Em Campinas, SP, nos anos agricolas de 1982/83, 1983/84 e 1984/85, avaliaram-se oito diferentes clones de mandioca (Manihot esculenta Crantz) selecionados para mesa quanto a produtividade de raizes e ramas, indice de colheita, cozimento culinario, teor de acido cianidrico e cor da polpa das raizes. Os experimentos, instalados no inicio das chuvas (setembro/outubro) e colhidos nove meses apos o plantio, foram conduzidos em blocos ao acaso com quatro repeticoes. Entre o material estudado, os clones IAC 59-210, de polpa branca (obtido por autofecundacao do cv. IAC Mantiqueira) e IAC 289-70, de polpa amarela (originario do cruzamento do cv. SRT 797 - Ouro do Vale, com o cv. SRT 1 - Vassourinha Paulista), mostraram, no conjunto de caracteres avaliados, o melhor comportamento, superando o 'IAC Jacana' e o 'IAC 14-18', utilizados como testemunhas. O clone IAC 289-70 destacou-se pela facilidade de cozimento culinario, baixa concentracao de HCN, alto indice de colheita, produtividade media de 18,7 t/ha e polpa amarela das raizes, indicando a presenca de pigmentos carotenoides. A caracteristica mais relevante do IAC 59-210 foi a maior produtividade media, 20,6 t/ha, em magnitude.

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Características agronômicas e culinárias de clones de mandioca

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Araken Soares Pereira

Papers

Aspectos agronômicos da cultura da mandioca (Manihot utilissima Pohl)

Competição de clones de mandioca selecionados para mesa e indústria

Determinação da toxicidade da mandioca pelo paladar das raízes "In Natura"

Características agronômicas e culinárias de clones de mandioca

Seleção de novos clones de mandioca para mesa, pela toxicidade e paladar de suas raízes «in natura»