CASCADE  
 

Securing gene conservation, adaptive and breeding potential of a model multipurpose tree species (Castanea sativa) in a changing environment

CASCADE is a multidisciplinary research project aimed to integrate information from several research fields to devise long-term optimised strategies for the conservation of chestnut genetic resources. European chestnut was chosen as a model multipurpose species, grown extensively for its fruit and timber and important not only for rural diversification, local economies and cultures, but also for its contribution to the landscape and environment. A multidisciplinary approach, covering areas such as ecology, ecophysiology, pathology, molecular genetics, population genetics, quantitative genetics, gene conservation, tree breeding, environmental economics and forest management, was applied for the development of long-term strategies combining conservation of evolutionary and adaptive potential, exploitation of breeding stocks and preservation of Mediterranean landscapes.

 

 

For genetic studies, 82 populations were selected from UK, France, Greece, Italy and Spain according to different domestication levels, i.e. major management regimes (naturalized stands, coppices, fruit orchards) and covering a broad range of xerothermic indices. A fairly large amount of genetic variation was found among populations and the effective number of alleles decreased from southern Europe toward north and west. Three main gene pools were detected: (a) the north-eastern Turkish pool, thought to be the likely centre of diffusion of the species; (b) a Greek gene pool, located in a region never investigated so far; (c) the Mediterranean Turkish gene pool, from where the European pools seems to derive. Therefore populations from these regions should be considered both as targets for conservation of genetic resources and sources of useful variation for breeding.

Within-stand dynamics of genetic diversity in chestnut stands investigated seems to show a fairly high level of outcoming gene flow, ensuring a number of incoming migrants per generation large enough to counterbalance loss of diversity by inbreeding and drift. Mating probability drops below 0.01 for distances larger than 2 km, and increases up to about 10% for distances closer than 300 meters, indicating that in the presence of some clustering of like-genotypes, a certain amount of inbreeding is expected. Indeed, a weak though significant spatial structure has been detected for naturalized stands and managed coppices, the correlation of genotypes being positive up to 35-45 meters.

In the investigation on variation of adaptive traits, growth rhythm traits such as bud flushing, drought tolerance, and juvenile growth have been considered to have adaptive significance.

Both the phytotron experiment and the field (provenance-progeny) trials have highlighted a fairly large genetic control for growth and phenology traits, as well as large population differentiation. The above evidences confirm that chestnut stands have large adaptive potential and functional genetic resources to be usefully exploited for breeding purposes. The established six field experiments provide a good starting point for continued studies of growth, phenology and stem form. Development of a saturated map and identification of QTLs for bud burst and drought tolerance was also a great achievement.

Significant variability in Phythophtora cambivora susceptibility was observed between populations.

A diffusion map of P. cambivora and the distribution of associated Phytophthora species was developed and the effect of site on Phytophthora distribution and diffusion potential was displayed.

Evaluation of Socio-Economic and Environmental Impact has highlighted several points that may have strong relevance for the conservation of genetic resources in Europe. Local communities (questionnaire respondents) make regular and wide use of chestnut food product and locally-sourced timber for furniture or beams, have high levels of visitation or other recreational use of local chestnut forests, and strongly support government investments for the restoration of Chestnut high forest (over 80% in France, over 60% in Italy). The analysis of the annual household willingness to pay (WTP) for initiatives to support chestnut cultivation has revealed a fairly large WTP for restoration of chestnut high forests.

Forest tree gene conservation methods should be dynamic so that species can benefit from natural or artificial selection and thereby adapt to their environmental conditions. The Multiple Population Breeding System (MPBS) is a method that fulfils the criterion for dynamic gene conservation by allowing for adaptation under changes in environment, while allowing breeders to respond swiftly to possible changes in the value of different characters. Based on this concept and the project results, separate MPBS gene conservation programmes are proposed for wood and nut production. Within the project, synthetic indices for different conservation values were developed: additive trait conservation values (ATCV), pathogen tolerance conservation values (PTCV), and marker trait conservation values (MTCV).

 

For more information about the CASCADE project, click here.

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