Principles of Plant Genetics and Breeding. George Acquaah
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.
1.4.2 Addressing food supply needs for a growing world population
In spite of a doubling of the world population in the last three decades, agricultural production rose at an adequate rate to meet world food needs. However, an additional 3 billion people will be added to the world population in the next three decades, requiring an expansion in world food supplies to meet the projected needs. The world population is estimated to reach 9 billion by 2050. Even though crop acreage in the US, for example, increased from 160 million acres (in 1926) to 225 acres (in 2015), arable land globally, including in the US, is on a steady decline due to a variety of factors, including the adverse impacts of climate change, surrendering of land to urban development, and salinization. Consequently, as the world population increases, there is a need for an agricultural production system that is apace with population growth but will be conducted on less land. Generally, it is estimated that about 40–60% of agricultural productivity is attributed to plant breeding efforts, through development of improved varieties. This calls for improved and high‐yielding cultivars to be developed by plant breeders. With the aid of plant breeding, the yields of major crops have dramatically changed over the years. Another major concern is the fact that most of the population growth will occur in developing countries where food needs are currently most serious, and where resources for feeding the people are already most severely strained, because of natural or human‐made disasters, or ineffective political systems.
1.4.3 Need to adapt plants to environmental stresses
The phenomenon of global climatic change that has been occurring over the years is partly responsible for modifying the crop production environment (e.g. some regions of the world are getting drier and others saltier). This means that new cultivars of crops need to be bred for new production environments. Whereas developed economies may be able to counter the effects of unseasonable weather by supplementing the production environment (e.g. by irrigating crops), poor countries are easily devastated by even brief episodes of adverse weather conditions. For example, development and use of drought‐resistant cultivars is beneficial to crop production in areas of marginal or erratic rainfall regimes. Breeders also need to develop new plant types that can resist various biotic (diseases and insect pests) and other abiotic (e.g. salt, drought, heat, cold) stresses in the production environment. Crop distribution can be expanded by adapting crops to new production environments (e.g. adapting tropical plants to temperate regions). Development of photoperiod insensitive crop cultivars would allow the expansion in production of previously photoperiod sensitive species.
1.4.4 Need to adapt crops to specific production systems
Breeders need to produce plant cultivars for different production systems to facilitate crop production and optimize crop productivity. For example, crop cultivars must be developed for rain‐fed or irrigated production, and for mechanized or non‐mechanized production. In the case of rice, separate sets of cultivars are needed for upland production and for paddy production. In organic production systems where pesticide use is highly restricted, producers need insect‐ and disease‐resistant cultivars in crop production.
1.4.5 Developing new horticultural plant varieties
The ornamental horticultural production industry thrives on the development of new varieties through plant breeding. Esthetics is of major importance to horticulture. Periodically, ornamental plant breeders release new varieties that exhibit new colors and other morphological features (e.g. height, size, shape). Also, breeders develop new varieties of vegetables and fruits with superior yield, nutritional qualities, adaptation, and general appeal.
1.4.6 Satisfying industrial and other end‐use requirements
Processed foods are a major item in the world food supply system. Quality requirements for fresh produce meant for the table are different from those used in the food processing industry. For example, there are table grapes and grapes bred for wine production. One of the reasons why the first genetically modified (GM) crop (produced by using genetic engineering tools to incorporate foreign DNA) approved for food, the “FlavrSavr™” tomato, did not succeed was because the product was marketed as a table or fresh tomato, when in fact