Establishing an international sweet chestnut
(Castanea sativa Mill.) provenance test: preliminary steps
Werner D. Maurer1and Josefina Fernández-López2
1 SGD Sued, Forest Research Institute for Forest Ecology and Forestry of Rhineland-Palatinate, Dept. Forest Gene Resources and Plant Production, D-67705 Trippstadt-Schloss, Germany Werner.Maurer@wald-rlp.de
2 Centro de Investigacions Forestais e Ambientais de Lourizan, Apt. 127, E-36080 Pontevedra, Spain fina@inia.es
Abstract
Based on our experience gathered during the establishment of a regional provenance test for sweet chestnut (Castanea sativaMill.) in southwest Germany, conceptional considerations are presented for designing a provenance trial which should cover the whole distribution range of this tree species. This preliminary proposal includes the specification of the objectives of the test and the selection of the provenances. Definite decisions on these will depend on the responses to questionnaires sent to COST G4 members and some other European research institutions working on sweet chestnut in order to evaluate ways of making sampling material from suitable occur- rences of sweet chestnut available and/or establishing experimental plots.
Keywords: Castanea sativaMill., sweet chestnut, provenance test, conceptional considerations
1 Introduction
Sweet chestnut (Castanea sativaMill.) is a widespread tree species occurring primarily in the countries around the Mediterranean basin, including the Black Sea region and the western part of the Iberian Peninsula. At the northern margin of its distribution range north of the Alps, extensive occurrences are found mainly in wine-growing areas (e.g. in Germany particu larly along the Rhine and Moselle valleys). Sweet chestnut has long been cultivated and bred. Most probably agamic propagation in the form of grafting was the method used to establish sweet chestnut stands. It must be assumed that a vast loss in the genetic variability of the sweet chestnut gene pool has occurred over the centuries because, as a rule, just the phenotypes of highest quality and, consequently, only a few genotypes were propagated within each stand. Furthermore, as parasitic diseases spread, many stands were completely destroyed, especially those containing grafted trees (FINESCHI and MALTOVI 1991).
Ac cordingly, the present populations in western Europe must be assumed to be the result of a mixture of native populations with the descendants of cultivated, grafted varieties. The species’ existence per seis not endangered, but rather the integrity of the gene pool, so that measures for preserving the residual intraspecific genetic diversity are urgently required (FINESCHIand MALTOVI1991).
Besides its economic significance in nut production and supplying wood, nowadays the silvicultural and ecological properties of sweet chestnut have increasingly gained import - ance both in the fields of forestry and environmental protection (cf.Anonymus 1996, 1997, in print). Consequently, in order to obtain an insight into the current state of the extent of genetic diversity and the adaptation to differing environments (including both adaptability and adaptedness), more genetic studies based on gene markers (isozymes, DNA markers) as well as so-called provenance tests are urgently required for this tree species.
2 Provenance testing of sweet chestnut
According to ERIKSSON(1996, 1998), a very strong differentiation of adaptive traits can be assumed among tree populations growing under different ecological conditions. This varia - bility is characteristic of provenances and may be expressed by various traits on the genetic, morphological, phenotypic and phenological levels. An insight into the extent of variability can be obtained by submitting provenances to specific testing procedures (cf.KOENIG1986).
For sweet chestnut only one single provenance trial had been reported world-wide. The trial was established in the fall of 1991 in Rhineland-Palatinate (Germany) (MAURERand TABEL 1997) in four experimental plots with different environments, and it comprises 16 prov - enances of southwest German origin. Unfortunately, one of the plots had to be abandoned later because of the very high mortality rate throughout the provenances due to frost.
In an initial genetic study, four of these provenances (those farthest from each other) were analyzed by “Random Amplified Polymorphic DNA” (RAPD) and “Random Amplified Microsatellite Polymorphisms” (RAMPO) molecular gene markers to assess the genetic structuring of these populations. Due to the similarity indices obtained in both pro- cedures, these provenances did not differ very much from each other, thus indicating a very close relationship (SCHIFFERet al.in print).
A draft summary of the provenance test based on this initial work as well as on the general aspects for provenance testing discussed by EDWARDS(1956) and KLEINSCHMIT
(1971) was elaborated by the COST G4 Working Group 2 “Genetic Resources” and is presented below.
3 Objectives of the sweet chestnut provenance test
Since only little is known about the genetic, morphological, phenotypic, and phenological diversity of sweet chestnut, the main objective of the intended provenance test is to investi- gate the variability of adaptive traits (ERIKSSON1996, 1998). Thus the test is expected 1) to obtain evaluation fundamentals for regional adaptedness and/or adaptability towards
biotic (in particular resistance towards Phytophthoraspp. and/or Cryphonectria parasitica) and abiotic (drought, frost, soil and precipitation pH, etc.) stress factors;
2) to assess traits that are relevant in forestry such as growth, forking, crown and bole form in view of their effects on quality and mass production;
3) to supply supportive information for setting up scientifically sound provenance and culti- vation recommendations for silvicultural purposes (MAURERet al.2000);
4) to provide information essential in ensuring the preservation of current genetic diversity (VARELAund ERIKSSON1995).
4 Selection of sweet chestnut provenances
The selection of sweet chestnut provenances is based on the information outlined in the map
“Geographic distribution and phytoclimatology of Castanea sativaMill.” (Fig.1). Regarding the geographic distribution and phytoclimatology of Castanea sativa,sweet chestnut popu - lations exist in both Mediterranean (IV) and Atlantic climates (VI), in par ticular where the climate types oceanic, Central European, and temperate-humid dominate. There is a north to south gradient in rainfall and temperature. The range of distribution may thus be sub - divided into three sections (Areas A, B and C) that are marked by thick lines in Figure 1.
Thus testing of the provenances should be performed both in the northern part (climate type VI) and in the southern part (climate type IV) of each area. First and foremost, phytoclimatological aspects should be considered. Then the extent to which some other criteria are already fulfilled can be examined.
Provenances to be tested should include:
– populations originating from different ecophysiological conditions (taking into consider- ation primarily the climate and then the soil);
– populations in which the two diseases Phytophthoraspp. and Cryphonectria parasiticaare present;
– populations threatened with extinction;
– highly polymorphic populations, i.e. the Turkish and Caucasian populations.
Because of the wide range of distribution, 30 populations should be included in the prov - enance trials.
To take into account the different climate conditions, about 10 provenances of sweet chest- nut populations present in the following geographic regions within the Areas A, B and C should be included in the provenance test (pop[s]., abbreviation used for population[s]):
Area A: Iberian Peninsula (Portugal and Spain): 3 pops. in the Mediterranean region, 2 pops. in the Atlantic region, and 1 pop. in the Canary Isles; West France: 2 pops., i.e. 1 in the north and the other in the south; the Netherlands and South England:
1 pop. each.
Area B: East France/Corsica: 1 pop. each; Italy/Sicily: 2 pops. in North Italy, 1 pop. each in South Italy and Sicily; Austria, Germany, Switzerland and Tunisia: 1 pop. each.
Area C: Greece/Crete: 1 pop. each; Turkey: 1 pop. in western Turkey and 2 pops. in eastern Turkey; Bulgaria/Romania, Bosnia-Herzegovina/Croatia, Hungary, Slovakia, Slovenia and South Ukraine: 1 pop. each.
Fig. 1. The proposed locations of the provenances to be included in the sweet chestnut provenance test (larger black dots) within the range of distribution of the sweet chestnut (smaller black dots). The thick lines form the boundaries between the Areas A, B and C. The other lines mark the geographic regions of different climatic types (IV, Mediterranean; VI, Atlantic; [VII, steppe]) (adapted from ALLUÉ
ANDRADE1990).
5 Efforts in promoting the sweet chestnut provenance test
Basic strategies for provenance testing are discussed in detail by EDWARDS(1956) and KLEINSCHMIT(1971). In short, the authors stress the importance of 1) sampling of the plant material to be tested; 2) cultivating seeds/seedlings uniformly; these give valuable infor - mation on germinative capacity, mortality rates and phenological behavior; 3) transfering the two- to three-year-old plantlets to the experimental plots and arranging them; 4) per- forming surveys, recording and evaluating the data material obtained.
For sweet chestnut the situation is rather special as there are three levels of domestication for this tree species due to its diverse use. Thus there are natural stands, grafted fruit orchards and managed coppices. This means that these types of sweet chestnut occurrences should be included in the test but treated separately when selecting appropriate sampling stands.
At present, however, the complete extent of the intended provenance test and the organ- ization required cannot be decided upon definitely. Although 13 out of 23 countries (mainly non-EU members) have indicated their willingness to participate in the test, responses from some countries with major sweet chestnut occurrences are unfortunately still missing.
Before the project can be promoted, answers to the following questions must be received:
1) Who will supply sampling material?
2) Where can the test plots be established?
3) How many test plots can be established and managed?
6 Concluding remarks
In this work theoretical considerations and practical measures are presented to be taken into account in a preliminary framework for a sweet chestnut provenance test. The test should include provenances from the whole distribution range of sweet chestnut. In this con- text the CASCADE project, “Securing gene conservation, adaptive and breeding potential of a model multipurpose tree species (Castanea sativa)in a dynamic environment”, recently started in five European countries, should contribute valuable information for starting this international provenance test in the near future.
Acknowledgement
The authors wish to express their thanks to all the organizers of the COST G4 Action
“Multidisciplinary Chestnut Research” in the European Commission in Brussels and on the local level in different European countries who made the meetings of the Working Group 2 “Genetic Resources” from 1997 to 2001 possible. These meetings served as a scientific platform to discuss the establishment of a sweet chestnut provenance test.
7 References
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Accepted 25.2.02
