Principles of Plant Genetics and Breeding

Figure 1 Thomas Jefferson, third president of the USA, and a
great promoter of the introduction of new crops.
THE ART AND SCIENCE OF PLANT BREEDING 21
was going to be a food supply for slaves in the West
Indies (Figure 2), and was described in the famous
Bounty mutiny (brought to the cinema in the
famous film Mutiny on the Bounty); or the introduction
of cinchona in the colonies of Africa and India
from South America, due to the medicinal importance
of quinine, obtained from cinchona bark,
against malaria.
Throughout history, the introduction of new
crops has contributed to an increase in the diversity
of the plants cultivated; however, the trend during
the last century, associated with industrial agriculture,
has led to a reduction in the number of crops
grown. In this respect, although around 3,000
species are known to have been used as a source of
food by humans, at present only 11 species (wheat,
rice, corn, barley, sorghum, millet, potato, sweet
potato, yam, sugarcane, soybean) contribute more
than 75% of world human food supply. More
worryingly, 60% of the calories consumed in the
world are based in just three crops (rice, corn, wheat),
and the trend is towards a concentration of production
in fewer and fewer crops.
Among the huge number of domesticated species,
there are many little-known species that only have
local relevance or have been neglected that could
be very interesting as “new crops”. Although the
denomination “new crop” seems to be more appropriate
for recently domesticated plants, it usually
refers to exotic crops. Actually, most of these “new
crops” were domesticated thousands years ago,
although there are examples of recent domestication
(in the 19th and 20th centuries) such as several
berries belonging to the genus Rubus that are currently
being introduced and improved in Europe.
Not all crops have the same opportunities of
succeeding when introduced in a certain region.
Success will depend on several characteristics of
the new crop, like a satisfactory performance under the new agroclimatic conditions and an easy adaptation to the cultural
practices commonly used in the cultivation of the main crops of the new region. Growers will be attracted to a new crop if
it adapts well to the existing crop.
There are few cases of immediate success in the introduction of new crops. In this respect, many crops were introduced
into the Old World after the discovery of America, although their acceptance differed and some of them did not succeed at
first. For example, Capsicum pepper had an early acceptance and its cultivation was fully established a few years after
being introduced. At that time, hot peppers became an alternative to black pepper and that surely contributed to its fast
worldwide spread. On the contrary, tomato needed much more time before being fully accepted. It was brought into
Europe a few years after the discovery of America. However, although there was some consumption in Spain and Italy, the
rest of European countries rejected it (perhaps because of its red colored skin, usually an indication of toxicity in nature,
and also because many Old World Solanaceae are toxic) and it was just used as an ornamental until the 19th century.
Nowadays, scientific and technological advances can make the introduction of a new crop a much shorter process
than centuries ago because of our knowledge in genetics, breeding, biotechnology, plant physiology, pathology, and
other disciplines. Breeding for adaptation has been a research field that has had a tremendous impact in the success of the
introduction of new crops. For example, the selection and development of materials insensitive to the photoperiod has
allowed the introduction of wheat into tropical areas. Also, adapted materials resistant to colder or warmer conditions, or
shorter growing seasons, have been obtained in several crops by a gradual and long process of progressive adaptation. For
example, in corn – a tropical plant – the natural and artificial selection on genetically diverse populations has allowed its