Cultivation

Manioc (Manihot esculenta) is also known as cassava or yuca. Cultivation is found mainly in tropical regions. In 2006, 226 million tons of cassava were produced worldwide. Nigeria was the leading producer (about 38 million tons). Other important producing countries are, among others, Brazil, Indonesia, Thailand and the Republic of Congo.

Utilisation

For many millions of people manioc is the main food source.

Foodstuffs

Manioc is essentially produced for its starchy tuberous roots. These are processed to:

• pita bread, tapioca pudding, purée, sauces, soup, snacks (manioc chips)
• alcoholic drinks (Kaschiri) from manioc flour
• as forage

The most well-known commercial product is tapioca (agglutinated starch from the manioc tuberous roots in granulate form). The EU imports 3.6 million tons of tapioca yearly mainly from Thailand. It is used:

• almost exclusively in mixed feed
• also as a special starch in foodstuffs

The protein-containing leaves are also harvested and consumed as

• a cooked vegetable.

Manioc contains linamarin, which can be converted into cyanide through damage to the tuber. This has to be destroyed by strong heating otherwise chronic signs of poisoning can occur.

Renewable primary products:

• the starchy tubers can be used in the production of bioethanol.

Gene technology: aims of research and development

Quality traits

Modified composition of components

• Reduction in the content of linamarin in the manioc tubers and thus reduced formation of cyanide. Researchers in the USA have succeeded in developing manioc plants that have less than 1% linamarin in their tubers.

Enrichment with health-promoting ingredients, such as:

• increase in the normally low protein content of the manioc tuber, which also lack certain essential amino acids

• increased beta-carotene and vitamin E content

• increased zinc and iron content

Agronomic traits

Resistance against pathogens

• Virus resistance against manioc mosaic virus

• Fungal resiatance
  
  

• Bacterial resistance: Containment of infestations with bacterial blight (Xanthomonas) and thus improved storage ability: manioc tubers are extremely sensitive and rot within a few hours, so that they cannot be stored.

Resistance against pests

• Insect resistance against borers

Renewable primary products, energy crops

• Increased starch content for industrial uses

• Scientists are undertaking a genome analysis of manioc with the aim of optimising the plants for energy production.

Plant development

• Enlargement of tubers

The bio- and gene-technological research and development with manioc are still in their beginnings. In the meantime they are being increasingly conducted by networks of different institutes in Switzerland, Columbia, Nigeria and some international centres. Once further development stages are completed the first genetically modified varieties will probably be tested in some South American and African countries and then be distributed free to small farmers.

Field trials with GM manioc