Integration of Conservation Strategies of Plant Genetic ... - Genres

irrigation etc. reaching their ultimate level of control in greenhouse production. Biotic stresses are
met by chemical control combined with in time often temporary resistances and tolerances
obtained through breeding. The main objective changes from yield stability and sustainability to
maximizing bulk production. The latter has led to selection for uniformity within varieties as a
natural consequence. Maintaining genetic diversity within varieties and between crops is thus not
any more practised as part of the farming systems. Hence, modern agriculture doesn't contribute
to maintaining genetic diversity. Ex-situ conservation in such situations becomes not just desirable
but absolutely essential.
Geographical differentiation
A geographic distribution of modern and traditional agriculture will parallel the distribution of
relative importance of ex-situ and in-situ conservation strategies.
Developing countries
In most developing countries introduction of modern varieties and high in-put agriculture is
limited to a number of major crops and concentrated in limited areas with generally favourable
production environments. Modern plant breeding has successfully raised the genetic yield potential
of crops, mainly by increasing the amount of dry matter diverted to harvested product and less
through an increase of total biomass. The expression of a higher yield potential of modern
varieties compared with traditional landraces is generally based on a better utilization of external
inputs, notably fertilizers and irrigation for harvested product. In addition plantbreeding has been
effective in improving specific characteristics that have a high level of qualitative genetic control,
such as single gene controlled disease resistances. Breeding for the required tolerances of or
adaptation to complex and variable (in time and over small distances) environmental stress
situations without the use of costly compensating external inputs is extremely difficult and often
has a low cost/benefit ratio in terms of overall production increases. Also many minor crops often
do not justify in terms of realized improvements the high cost of institutional breeding
programmes.
Hence in these regions essentially two systems of crop improvement and seed production can be
recognized.
1 A Formal Institutional System linking ex-situ genebanks with institutional and private
industry breeding, seed production and ultimately distribution of improved varieties to
farmers. Such farmers thus benefit from genetic diversity in a linear model of transfer.
Modern improved varieties appear to have their main impact in the more favourable
production environments and generally require for full exploitation of improved yield
potential the use of external inputs such as fertilizers and additional control of both biotic
and a-biotic stress factors.
2 A Non-institutional Informal System, consisting of farmer households and communities
still growing landraces and integrating utilization and conservation of genetic diversity in
a dynamic system of crop improvement and seed production based on local knowledge
systems.
This system is responsible for maintaining a large source of still available genetic diversity