Agriculture Reference
In-Depth Information
All parts of the yam-bean plant, except the tubers, contain rotenone and various
other rotenoids. These toxic compounds are usually at low concentrations in young
plants and plant parts, and thus young or immature plant parts are used for food.
However, toxic levels in mature leaves, stems, pods, and seeds prevent their use by
either humans or animals. Because of trimming and harvesting when the plant parts
are young and because local populations are aware of the toxicity problems, cases of
toxicity are rare. Rotenone can be isolated from seeds, making them valuable as a
source of this chemical.
5.8.3 Tannia
Tannia is related to cocoyam, also called taro, being from the same Araceae family.
Because of this, it is sometimes called the new cocoyam, although this name can
cause confusion. Tannia originated in northern South America but has spread to
other parts of the world, notably Africa. Where grown, it is a staple of subsistence
farmers. The tuber contains both calcium oxalate (calcium oxalate is a common form
of kidney stone) and saponins, which can be both toxic and digestive irritants. For
these reasons it is roasted or otherwise cooked to remove some or all these components
before eating.
Tannia is grown from corms planted in well-prepared soils, that is, plowed and har-
rowed. Weeding is important for good yields. After between 10 and 12 months the
plants die back and the corms are dug and harvested. Corms can be washed, disinfected,
and subsequently stored in cold rooms.
5.9
GENETICALLY MODIFIED ROOT CROPS
As with most crops, those grown as major crops in developed countries have gotten the
most investigation, in terms of genetic engineering, to produce genetically modified
crops. With root crops the potato has had by far the most number of genetically modi-
fied varieties developed. As with most genetically modified crops, the first concern has
been development of crops resistant to pest, primarily insects and microorganisms. This
is particularly true for potatoes. However, potatoes genetically engineered to be herbi-
cide resistant and higher in protein have also been developed.
Interestingly enough, although genetically engineered potatoes have been devel-
oped and released to the farming community, they have subsequently been withdrawn
because of concerns over their safety, particularly in relationship to processed potato
products. There has been some considerable controversy over the safety of potatoes
genetically engineered to have more protein. Another interesting development is
genetically engineered potatoes designed to be a source of starch for paper making.
The genetic modification of sweet potatoes has made little progress, and even less
genetic engineering has been done on yams and taro. In the case of taro, in addition to
consumption concerns, there are religious concerns since taro is a religious symbol in
some Pacific island nations and the state of Hawaii.
Additional information about genetically modified crops is given in Chapter 11.
