22
2 Genetic Resources: Status, Development, Losses, and Conservation
Each new breeding activity has the principle of narrowing the genetic base of the
source variety. On the other hand, incorporating new traits by introducing genes
broadens again the variety's genetic base. For instance, according to Tarp (1995),
today's genetic base of tomatoes is broader than 40 years ago. Another method in
assessing the genetic variation in one given crop is to monitor genetic
vulnerability. Genetic vulnerability is the genetic constitution of a crop, if it is
uniformly susceptible to a pest, pathogen or environmental hazard (NRC, 1972).
Genetic vulnerability is a consequence of decreasing genetic variation in a given
area, mainly through the widespread replacement of diverse varieties by
homogeneous modern varieties. Two factors determine the vulnerability: (I) the
relative areas devoted to each cultivar, and (2) the degree of uniformity
(relatedness) between cultivars. The uniformity in modern varieties is higher than
in landraces. Genetic vulnerability creates a potential for widespread crop losses
because of the increased susceptibility to pest, pathogen or environmental
hazards. The 1840s' pandemic oflate blight in potatoes (Phytophtora infestans) in
Ireland is a famous example of the danger of genetic uniformity. More examples
of genetic vulnerability in countries are given in Table 2.4. Genetic uniformity of
crops will increase in the future through the improvement and increased
application of biotechnology in agriculture.
The possibility of losing genetically coded information from farmers' fields is
increasing because of the threat of losing traditional varieties and crop species.
Therefore, the irreversible loss of genes, as well as the loss of gene complexes,
plant varieties, and crop species are feared.
Consequently, this threat is the major incentive for the increased conservation
activities of the last 30 years. As has been discussed in this section, a narrowing in
species diversity utilized for agriculture and a decline in crop varietal diversity
can be pointed out. Even though a significant drop in the landraces' share of all
agricultural varieties can be seen since the turn of the century (Fowler and
Mooney, 1990), the concentration of area among the top cultivars is lower at
present than it was at the summit of the Green Revolution period (Smale, 1996b).
Agrobiodiversity is not decreasing overall, but a decline of specific diversity at
specific places at a specific time can be seen - i.e.:
• varieties were always used and never conserved by farmers for the longterm
9 ;
• the utilization of agrobiodiversity - and thereby its steady change - was the
only method of conservation;
• the intra-species diversity may be reduced according to the number of different
varieties grown on farmers' fields due to the replacement of traditional
varieties by modern varieties; not all the genetic information of these old
varieties is lost, however.
9
Farmers usually carry out ex situ conservation only by storing seeds from one harvest to the
next season.
2 Genetic Resources: Status, Development, Losses, and Conservation
Each new breeding activity has the principle of narrowing the genetic base of the
source variety. On the other hand, incorporating new traits by introducing genes
broadens again the variety's genetic base. For instance, according to Tarp (1995),
today's genetic base of tomatoes is broader than 40 years ago. Another method in
assessing the genetic variation in one given crop is to monitor genetic
vulnerability. Genetic vulnerability is the genetic constitution of a crop, if it is
uniformly susceptible to a pest, pathogen or environmental hazard (NRC, 1972).
Genetic vulnerability is a consequence of decreasing genetic variation in a given
area, mainly through the widespread replacement of diverse varieties by
homogeneous modern varieties. Two factors determine the vulnerability: (I) the
relative areas devoted to each cultivar, and (2) the degree of uniformity
(relatedness) between cultivars. The uniformity in modern varieties is higher than
in landraces. Genetic vulnerability creates a potential for widespread crop losses
because of the increased susceptibility to pest, pathogen or environmental
hazards. The 1840s' pandemic oflate blight in potatoes (Phytophtora infestans) in
Ireland is a famous example of the danger of genetic uniformity. More examples
of genetic vulnerability in countries are given in Table 2.4. Genetic uniformity of
crops will increase in the future through the improvement and increased
application of biotechnology in agriculture.
The possibility of losing genetically coded information from farmers' fields is
increasing because of the threat of losing traditional varieties and crop species.
Therefore, the irreversible loss of genes, as well as the loss of gene complexes,
plant varieties, and crop species are feared.
Consequently, this threat is the major incentive for the increased conservation
activities of the last 30 years. As has been discussed in this section, a narrowing in
species diversity utilized for agriculture and a decline in crop varietal diversity
can be pointed out. Even though a significant drop in the landraces' share of all
agricultural varieties can be seen since the turn of the century (Fowler and
Mooney, 1990), the concentration of area among the top cultivars is lower at
present than it was at the summit of the Green Revolution period (Smale, 1996b).
Agrobiodiversity is not decreasing overall, but a decline of specific diversity at
specific places at a specific time can be seen - i.e.:
• varieties were always used and never conserved by farmers for the longterm
9 ;
• the utilization of agrobiodiversity - and thereby its steady change - was the
only method of conservation;
• the intra-species diversity may be reduced according to the number of different
varieties grown on farmers' fields due to the replacement of traditional
varieties by modern varieties; not all the genetic information of these old
varieties is lost, however.
9
Farmers usually carry out ex situ conservation only by storing seeds from one harvest to the
next season.