Читать книгу Principles of Plant Genetics and Breeding - George Acquaah - Страница 21

Food is the most basic of human needs. Plants are the primary producers in the ecosystem (a community of living organisms including all the nonliving factors in the environment). Without them, life on earth for higher organisms would be impossible. Most of the crops that feed the world are cereals (Table 1.1). Plant breeding is needed to enhance the value of food crops, by improving their yield and the nutritional quality of their products, for healthy living of humans. Certain plant foods are deficient in certain essential nutrients to the extent that where these foods constitute the bulk of a staple diet, diseases associated with nutritional deficiency are often common. Cereals tend to be low in lysine and threonine, while legumes tend to be low in cysteine and methionine (both sulfur‐containing amino acids). Breeding is needed to augment the nutritional quality of food crops. Rice, a major world food, lacks pro‐vitamin A (the precursor of vitamin A). The Golden Rice project currently underway at the International Rice Research Institute (IRRI) in Philippines and other parts of the world, is geared toward developing, for the first time ever, a rice cultivar with the capacity to produce pro‐vitamin A (Golden rice 2, with a 20‐fold increase in pro‐vitamin A, has been developed by Syngenta's Jealott's Hill International Research Centre in Berkshire, UK). An estimated 800 million people in the world, including 200 million children, suffer chronic undernutrition, with its attendant health issues. Malnutrition is especially prevalent in developing countries.

Table 1.1 Twenty‐five major food crops of the world.

Source: Extracted from Harlan (1976). The ranking is according to total tonnage produced annually.

1	Wheat
2	Rice
3	Corn
4	Potato
5	Barley
6	Sweet potato
7	Cassava
8	Grapes
9	Soybean
10	Oats
11	Sorghum
12	Sugarcane
13	Millets
14	Banana
15	Tomato
16	Sugar beet
17	Rye
18	Oranges
19	Coconut
20	Cottonseed oil
21	Apples
22	Yam
23	Peanut
24	Watermelon
25	Cabbage

Breeding is also needed to make some plant products more digestible and safer to eat by reducing their toxic components and improving their texture and other qualities. High lignin content of plant material reduces its value for animal feed. Toxic substances occur in major food crops, such as alkaloids in yam, cyanogenic glucosides in cassava, trypsin inhibitors in pulses, and steroidal alkaloids in potatoes. Forage breeders are interested, among other things, in improving feed quality (high digestibility, high nutritional profile) for livestock.