Conservation and Sustainable Use of the Biosphere - WBGU

Agrobiodiversity: functions and threats under global change D 3.4
77
Table D 3.4-1
Global overview of domestic animal breeds and numbers at
risk.
Source: Loftus and Scherf, 1993
Species Number of breeds Breeds at risk
Cattle 783 112
Sheep 863 101
Goat 313 32
Pig 263 53
Buffalo 62 1
Horse 357 81
Donkey 78 11
world’s calorie needs (energy).With an additional six
species (sorghum, millet, potato, sweet potato, soya,
sugar cane and sugar beet), 75 per cent of the world’s
calorie needs are covered (Fig. D 3.4-3). In addition
to these ‘main species’ there are numerous cultivated
plant species that are only of regional significance.
For example, tef (Eragrostis tef) is extremely important
in Ethiopia but only marginally so internationally
(Rehm 1989). Furthermore, there is the complex
of what are termed ‘minor species’, ‘neglected crops’
or ‘under-utilized crops’, which are adapted to special,
often extreme, sites and are of local or regional
significance for human sustenance. ‘Neglected crops’
are cultivated plants that have been neglected by
research and breeders, eg coriander (Diederichsen,
1996) or yam, whereas ‘under-utilized species’ are
those not used very much in agriculture, eg Lupinus
albus in the Mediterranean.
Vavilov initially considered the gene centres to be
identical to their centres of origin. The theory was
developed further by Harlan among others (1971)
who defined centres and non-centres in order to differentiate
the regions of origin from the regions with
‘secondary’ or later colonization by the species (Fig.
D 3.4-4). A gene centre can therefore, but according
to more recent findings need not, be different from
the region of origin of a species (Hammer, 1998;
Becker, 1993). For example, in Ethiopia there is a
broad spectrum of farmers’ varieties of barley but
not one single wild form (Zohary, 1970), so barley
cannot have been domesticated there (in actual fact
its region of origin is far away in the Middle East).
Gene centres were mainly defined for cultivars.They
were and still are important sources in the search for
genetic variability for these species and often the destination
for collecting trips and studies.
In the gene centre of maize (Zea mays L.) in Mexico
there are regions in which the original ancestor of
maize, teosinte, can still be found alongside maize.
Thus, introgression into maize material is possible,
followed by further evolution of maize (Miller et al,
1995). This type of introgression from genetic material
is only one of the possible ways in which cultivars
can continue to evolve. Other ways are for example
recombination, epistasis and mutation (Rasmusson
and Phillips, 1997).
Regions with high genetic variability of a species
are generally in areas in which, as a result of natural
geographic diversity, there is a tradition of smallscale
agriculture. Often these are isolated, diverse
Gene centres
The theory of the gene centres of cultivars was developed
by the Russian scientist Vavilov (1926). The
gene centre of a species is the region in which the
greatest genetic diversity within that species occurs.
Rice
26%
Wheat
23%
7,000
Cultivated
plant species
Maize 7%
Others
18%
Millet 4%
120
30
of local/regional
significance
90 % of worldwide
calorie consumption
Figure D 3.4-2
Estimated number of cultivated plant species (globally).
Source: FAO, 1996b
Potatoes 2%
Sweet potatoes
2%
Sugar
9%
Soya oil
3%
Other
plant
oils 6%
Figure D 3.4-3
The most important cultivated plant species in terms of world
food provision.
Source: FAO, 1996b