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

Winter buds were used and analyzed for 14 isozyme loci. Allelic frequencies were used to evaluate the
level of genetic variability and differentiation within and between populations. The results of these
analyses can be summarized as follows:
Castanea sativa is characterized by a very high degree of genetic differentiation across its range in
Europe and in Turkey.
The genetic variability and differentiation within area decreases in east-west direction. This seems to
support the general contention that Turkey is the area closest to centre of origin of the species, and has
maintained the highest level of gene diversity. Genetic variability probably dropped during the expansion
of the range due to genetic drift and because of relatively limited gene flow also due to human influence.
High degree of genetic, morphological and physiological differentiation was observed between
population from two areas of Turkey: Black Sea coast and Aegean coast. The level of differentiation is
so high that it is not possible to exclude some speciation phenomenon which, on the other hand, has been
also reported in other plant and animal species. Black Sea coast is in fact characterized by a large number
of endemic species.
Finally, from a closer inspection on Turkish populations, a possible introgression area, between the two
genetically distinct forms of Castanea sativa was detected in the North-Western part of Turkey.
The finding of this possible introgression area or hybrid zone, if confirmed, could be of great theoretical
and practical interest.
These areas offer a valuable experimental material for studies of characters and processes involved in
divergence and speciation and for the safeguard and development of genetic resources.
In fact new genotypes are created from the crossing and subsequent interactions of similar but distinct
genomes. The resulting progeny may show: phenotypic characteristics unlike either of the parents;
eenhanced physiological stability; selective advantage in novel habitats; capacity to exploit resources
unused by either parents.
Moreover, introgression can result in a transfer of genetic information across the usual species
boundaries. This may contribute to the maintenance of larger quantities of genetic variation; more rapid
response to selection.
For all these reasons, the identification and conservation of hybridization and introgression areas as well
as centres of origin are of great interest for forest species and particulary for chestnut.
References
Davis, P.H. 1965. Flora of Turkey. Edinburg: Edinburg University Press. Vol. 1, pp.1-25.
Elston, R.C. 1971. The estimation of admixture in racial hybrids. Ann. Human Genet. (London) 35: 9-
17.
Huntley, B. and Birks, H.J.B., 1983. An atlas of past and present pollen maps for Europe: 0-13000
years ago. Cambridge: Cambridge University Press.
Kosswig, C. 1965. Zoogeography of the Near East. Systematic Zoology 4: 50-73.