Principles of Plant Genetics and Breeding

20 CHAPTER 2
antiquity is established by archeological evidence. It is
from these centers that the crops diffused to their geographically
less restricted corresponding non-centers.
Other scientists including C. D. Darlington and I. H.
Burkill suggested that some variability could be
attributed to shifts in civilizations that brought about
migrations of crops, changes in selection pressure, and
opportunities for recombination.
Vavilov made other unique observations from his
plant explorations. He found that the maximum amount
of variability and the maximum concentration of
dominant genes for crops occurred at the center and
decreased toward the periphery of the cluster of diversity.
Also, he discovered there were parallelisms (common
features) in variability among related species and
genera. For example, various cotton species, Gossypium
hirsute and G. barbadense, have similar pubescence, fiber
color, type of branching, color of stem, and other features.
Vavilov called this the law of homologous series
in heritable variation (or parallel variation). In other
words, species and genera that are genetically closely
related are usually characterized by a similar series of
heritable variations such that it is possible to predict
what parallel forms would occur in one species or genera,
from observing the series of forms in another related
species. The breeding implication is that if a desirable
gene is found in one species, it likely would occur in
another related species. Through comparative genomic
studies, the mapping of molecular markers has revealed
significant homology regarding the chromosomal location
of DNA markers among species of the Poaceae
family (specifically, rice, corn, sorghum, barley, wheat),
a condition called synteny, the existence of highly conserved
genetic regions of the chromosome.
Industry highlights
Introduction and adaptation of new crops
Jaime Prohens, Adrián Rodríguez-Burruezo, and Fernando Nuez
Instituto para la Conservación y Mejora de la Agrodiversidad Valenciana, Universidad Politécnica de Valencia, 46022 Valencia,
Spain
The greatest service which can be rendered any country is to add a useful plant to its culture.
Thomas Jefferson (c. 1800; Figure 1)
Since the domestication of the first crops, societies that practice agriculture have been attracted to new crops because they
present opportunities for improving crop production and food supply. In fact, most of the relevant crops grown in a particular
region are usually native to other regions. Thus, any cultivated species grown in an area different to its center of origin
was, at one time, a new crop. Just to cite a few examples, soybean, wheat, rice, beans, tomato, or citrus, which are important
crops in Europe and USA are not native to these regions.
Diversification of crop production through the introduction of new crops is desirable for several reasons. New crops
represent an alternative to growers and markets with produces that have a high value and for which usually there is no
overproduction. They also may contribute to a sustainable horticulture because an increase in diversity reduces the problems
caused by pests and diseases caused by monocrop and allows a higher efficiency in the use of production factors. A
greater diversity of crops also favors the stability of production and growers’ incomes because the cultivation of a higher
number of species decreases risks against unpredictable environmental and market changes. Finally, new crops contribute
in improving ethnobotanical knowledge, which is a substantial part of folk culture.
Historically, the introduction of new crops has taken place thanks to the movement of plant material through trade
routes or by contacts among cultures. The discovery of America was one of the most important events in the adaptation of
new crops, which resulted in an enormous exchange of species between the Old World and the New World. Nowadays
it is estimated that 40% of economically relevant crops originated in America, and it is difficult to imagine the present
Old World’s culture and gastronomy without many American-originated crops. For example, corn, sunflower, potato,
tobacco, peanut, cocoa, beans, squash, pumpkin and gourds, tomato, capsicum pepper, and many others originated in
the New World and all of them were “new crops” in the Old World a few centuries ago. On the other hand, many Old
World crops adapted well in America and this continent has become the main producing area for some of them, e.g.
soybean (from China), coffee (from Africa and Arabia), or banana (from South East Asia).
A great effort in the attempt to adapt foreign species took place during the 18th and 19th centuries. There were several
outstanding stories in this endeavor, such as the establishment of rubber plantations in South East Asia, after seeds and
plants were smuggled from Amazon plantations; the expeditions in search of breadfruit, which is native to Polynesia and