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1 Introduction: Crop Production and Crop Losses
The present human population of the world is 5.7 billion, increasing
at an annual rate of 1.6 %. According to the latest estimates, the
rate of population growth will decrease slowly during the next century,
and the world population is expected to stabilize at about 11.5 billion
shortly after the year 2100. Figure 1.1 shows the expected growth in
the nearer future.
Fig. 1.1. Estimates of population growth in developed and developing
countries (Data from World Bank, cited in )
The rapid population growth in general and the fact that most of the
population growth takes place in developing countries rises the
question how these additional people can be fed. Basically, there are
two different possibilities to increase food production: Enlarging crop
yields on already cultured land, or expanding the area of cultured land
on previously uncultured land.
Reviewing the development of crop production since 1965 reveals a
massive increase. Figure 1.2 shows the differences in production
between 1965 and 1988-90 (average of three year period) of the
eight most important food and cash crops. The production of rice,
wheat and maize, which are the most important crops for human
nutrition, doubled during the last 25 years. Figure 1.3 indicates that
most of the production increase was due to higher yields per area.
Higher yields per area were possible because of the introduction of
high-yielding varieties, improved cultivation techniques, fertilizer use
and chemical crop protection measures - a development which has
been termed "green revolution".
Fig. 1.2. Comparison of the world-wide annual production of the eight
principal food and cash crops in 1965 and 1988-90 (average of the three
Fig. 1.3. Influence of increased yields per area and increase of cultured
area. The data for potatoes is not shown. Potato yields per area have
increased by about 10%, but have been overcompensated by a reduction in area
grown, resulting in a 6% decrease in production. Calculated data in
Fig. 1.4. Dietary energy supply per capita in 130 developing countries
from 1961/63 to 1987/89. 2000kcal per person per day is the minimum FAO
requirement for dietary energy. Data from FAO cited in.
The intensification of crop production improved the level of food
consumption in most developing countries (figure 1.4) during the last
30 years despite a world population growth of 2.4 billion in the same
period. However, the intensification also led to a number of
disadvantageous side-effects like erosion, deterioration of soil quality,
salinization, and others. Every year, about 1 % of the cultured area
has to be replaced because of these reasons. Especially in developed
countries, the use of agrochemicals is a growing public concern. The
amount of crop protection products used has risen steadily during
the past 30 years (figure 1.5). Presently, more than 25 billion US$
per year are spent for herbicides, fungicides, insecticides, soil
disinfectants and growth regulators. In Western Europe, the most
crop protection products are used per area of arable land, followed
by the USA. Figure 1.6 shows the expenditure per area in these and
the other principal farming regions of the world.
Fig. 1.5. Estimated world-wide expenditures on crop protection measures
from 1960 to 1990 (in US$, adjusted for inflation for the year 1989)
Fig. 1.6. Calculated expenditures in 1990 on fungicides, insecticides
and herbicides per hectare of arable land in the principal farming regions
of the world.
As can be seen in figure 1.7, losses prevented by chemical crop
protection are about 27 % (weeds 16 %, animal pests 7 %, diseases
4 %) of attainable production in the eight principal food and cash
crops. Nevertheless, about 42 % of total production in these crops
are lost to weeds (13 %), animal pests (16 %) and pathogens (13 %),
representing a market value of about 244 billion US$ (1989). The
losses in the different crops are shown in figure 1.8.
Fig. 1.7. Estimate of the contribution made by world-wide crop protection
to the production of the eight principal food and cash crops, in the period
Fig. 1.8. Actual production (1988-90, annual average) and losses due to
pathogens, animal pests (including viruses) and weeds.
Despite the use of pesticides, not only the absolute amount of losses,
but also relative losses have increased by about 3 to 10 % in the past
30 years (only in coffee the relative losses were reduced by about
5 %). This is thought to be due to the higher susceptibility of the
high-yielding varieties, the development of resistance to chemical
pesticides in pest and pathogen populations, the use of fertilizers
which not only promote growth but also increase susceptibility, and
the extension of production into regions where the pressure from
pests, pathogens and weeds is higher. The losses have increased
predominantly in developing countries, where appropriate crop
protection measures often cannot be taken because of their high
price and/or lack of knowledge.
Plant genetic engineering may contribute substantially to the
development of new pest and disease resistant varieties by increasing
the speed of conventional breeding and by transferring useful genes
from various plants and other organisms into crops. In the following
chapters of this report, the principal methods used to achieve these
goals are described. The present state of the art of genetic
engineering for pest and disease resistance and applications in
development or already realized will be presented. A brief discussion
of safety issues raised and the regulatory framework for field releases
and market introduction complements the topic. As not only plants,
but also other organisms like bacteria or viruses are genetically
engineered in order to prevent crop losses, these approaches are al
so briefly described.