Agriculture Reference
In-Depth Information
Peru, and potato, cassava, and sweet potato in Peru and
western South America. Sunflower (
Helianthus
)isthe
only major crop species with a centre of origin in North
America and indeed most other crops grown in the USA
and Canada evolved from other continents. Rice, soy-
bean, sugarcane (
Gramineae andropogoneae
), and the
major fruit species (orange, apple and banana) were all
first domesticated in China and the Asian continent a
few millennia
BC
. Examination of archeological remains
show that the dates of crop domestication in Africa were
later; yet sorghum, oil palm, and coffee are major world
crops that have their centre of origin in this continent.
Similarly, cabbage and a few other vegetable crops have
their centre of origin in Europe. Given more research,
it may be found that many more of today's crops were
domesticated at earlier periods.
Several crops of importance have been domesticated
relatively recently. Sugar beet was not grown commer-
cially in Europe until the 18th century, while rubber,
date palm and coconut palms were not domesticated
until the end of the 19th century. The forage grasses,
clovers, and oilseed rape (
Brassica napus
L. or
B. rapa
L.)
also are recently domesticated crops, although some
researchers would argue that these crops have yet to
make the transition necessary to be classified as truly
domesticated. New crops are still being recognized
today. The advent of bioenergy crops has identified the
oilseed crop camelina (
Camelina
spp.), and the biomass
crop switchgrass (
Panicum virgatum
) as potential new
crops species which have yet to be grown in large scale
commercialization.
A high proportion of today's major crops come
from a very small sub-sample of possible plant species
(Figure 1.1). It has been estimated that all the crop
species grown today come from 38 families and 91 gen-
era. Therefore, the source of our present day crops
are more diverse than we have shown, although they
still only represent a fraction of the total families and
genera which have been estimated to exist within the
angiosperms as a whole. Also, it should be noted that the
sources of origin of these crops are spread over Europe,
the Near East, Asia, Africa and America.
At some time in the past, each of our present day crop
species must have originated in one, or more, specific
regions of the world. Originally it was thought that
there were only 12 major centres of origin including
the Near East, Mediterranean, Afghanistan, the Pacific
Rim, China, Peru, Chile, Brazil/Paraguay and the USA.
More recent research has altered this original view and
it is now apparent that:
Crops evolved in all regions of the world where
farming was practiced.
•
•
The centre of origin of any specific crop is not usually
a clearly defined geographic region. Today's major
crops are more likely to have evolved over large areas.
•
Early farmers and nomadic travellers would have been
responsible for widening the region where early crops
have been found and added confusion concerning the
true centres of origin.
•
Regions of greatest crop productivity are rarely related
to the crop's centre of origin.
Overall therefore, domesticated crops have origi-
nated from at least four of the six world continents
(America, Europe, Africa and Asia). Australian abo-
rigines remained hunter-gatherers and did not become
farmers, and indeed farming in Australia is a rela-
tively new activity started after western settlers arrived
there. No surprisingly therefore few of today's major
agricultural crops originated in Australia; however, a
recently domesticated crop (Macadamia nuts) does have
its origin in this continent.
NATURAL AND HUMAN SELECTION
All domesticated crops have been developed from
wild, “weedy” ancestors. Early farmers modified weed
species into modern-day crops through a process
of genetic manipulation and selection. As a result
these crop species have been sufficiently altered such
that they can be considered to be domesticated.
A definition of domestication has been given by
Professor N.W. Simmonds as follows: “
a plant popula-
tion has been domesticated when it has been substantially
altered from the wild state and certainly when it has been
so altered to be unable to survive in the wild
”. The first
part of this definition can certainly be readily accepted
for almost all modern-day agricultural crops, although
we still propagate many crops (e.g. date palm) where
the crop species are modified only slightly from ancient
ancestors. It is not always possible to relate domestica-
tion with a lack of potential to survive in non-cultivated
