Evaluation and comparison of domestic chestnut (Castanea sativa Mill.) populations in Slovenia
Anita Solar1, Andrej Podjavorsek2, Gregor Osterc1, Franci Stampar1
1 University of Ljubljana, Biotechnical Faculty, Agronomy Dept, Jamnikarjeva 101, Ljubljana,
2 Secondary School of Agriculture Maribor, Vrbanska 30, Maribor, Slovenia anita.solar@email.si
Abstract
171 genotypes of Castanea sativaMill. from three Slovenian regions were analyzed. The weight of individual nuts was the most variable trait (10.6 ± 8 g). The number of nuts per kilo varied from 54 to 286. The largest nuts were found in the Mediterranean region, where they exhibited character- istics of the marron. There were also some isolated trees among the continental subpopulations with large nuts displaying marron characteristics. No great differences in flavor were found between the continental and the Mediterranean genotypes. Cluster analysis revealed relatively large genetic differentiation between continental and Mediterranean genotypes, but genetic similarity within the continental subpopulations. The continental genotypes fell into six clusters, and the Mediterranean genotypes into one cluster. With RAPD-PCR, 97 polymorphic DNA fragments out of 117 cumulatively amplified fragments were detected. The chestnut genotypes were divided into one “Mediterranean” and four “continental” clusters. Differentiation according to pomological traits was weak in the RAPDs analysis.
Keywords: Sweet chestnut, genetic variability, pomological traits, RAPD analysis
1 Introduction
Sweet chestnut (Castanea sativaMill.) is widespread in Slovenia. It grows all over the country except in the cold climatic conditions in the Alps (north and north-west part of Slovenia) and also in the Dinar part on limestone and dolomite (JURCet al.1994). Chestnut fruit was important in the past, particularly in north-eastern Slovenia, where, in the words of a well- known local proverb, people harvested wheat and potato from a chestnut tree. They used to exchange one measure of chestnut nuts for a measure of wheat or two measures of potato (DEBEVC1981). Chestnut fruit was also highly valued in the south-west in the Gorica region, where domestic chestnut as well as quality marron was grown (SOLAR1996). From there it was exported to Slovene cities and sold at attractive prices.
The Slovenian chestnut populations are mainly natural. In some smaller areas where chestnut fruit is economically important, the populations are mixed with combinations of natural and artificially created stands with newly introduced cultivars. Today there is con - siderable demand for new chestnut plantations. However, the quality of the plant material is often poor.
In order to determine the breeding value of our chestnut germplasm, we started to inves- tigate different domestic populations. Ten years ago, we began selecting autochthonous, genetically variable genotypes in order to choose the best and best-adapted genotypes for further clonal propagation and for planting in new orchards (PERIC 1990, SIBAV and KODRIC1993, STAMPARet al.1993, SOLARet al.1999, PODJAVORSEKet al.1999).
2 Materials and methods
Three chestnut populations were chosen in the main chestnut-growing regions of Slovenia: A (east), B (central) and C (south-west, Mediterranean). Continental climatic conditions are charac- teristic of the regions A and B, while the climate in the region C is more Mediterranean.
After the in situ exclusion of trees infected with Cryphonectria parasiticaand trees with low vigour, 25 nuts from 171 genotypes (93 from region A, 51 from B and 27 from C) were analyzed according to the UPOV (1989) during three successive years. The length, width, thickness and weight of the nuts, and the length and width of hilum were measured. The number of nuts per kg were counted and the embryony, pellicle penetration, cavity, shape and colour of the nuts were estimated. The taste of the cooked nuts was evaluated by three tasters. The genetic similarity of the genotypes was determined using cluster analysis. A dendrogram was constructed based on similarity by applying UPGMA in the statistical programming package STATISTICA for Windows (1994).
46 genotypes (19 trees from region A, 17 from region B and 10 from region C) already analyzed for pomological traits were included in the RAPD analysis. Genomic DNA was isolated from young leaves. Dneasy Plant Mini Kit (Qiagen) was applied in the process of isolation.
Twenty-one primers were used for the amplification of DNA. The RAPD data comprised 97 polymorphic DNA fragments out of 117 cumulatively amplified fragments. They were evaluated with phenetical methods from the NTSYS-pc computer package. Jaccard’s and Dice’s coefficients of similarity were used to evaluate genetic relatedness. The correlation between both coefficients was compared with the Mantel test. The analyzed genotypes were divided into groups using UPGMA (PODJAVORSEK1999).
3 Results
3.1 Pomological analysis
The pomological traits are summarized in Table 1. The weight of the nuts varied from 3.5 g (subpop. B1) to 18.6 g (subpop. A2) and 18.5 g (pop. C). The largest nuts (14.3 g) originated from trees of the Mediterranean area, C, while in the continental populations A and B the nuts were smaller (11.0 g and 7.9 g). But there were some isolated genotypes with large nuts (15.2–18.6 g) in the continental subpopulations (2 in A3, 1 in A2and 1 in B1). The number of nuts per kg varied from 54 to 286. The dimensions of the hilum scar were the most hetero - geneous in the genotypes from region B. The nut shapes of the Mediterranean genotypes were the least variable, and most were transverse ellipsoid. In the regions A and B, the nuts varied in shape. Most were globose and transverse broad elliptic, but ovoid, broad ovoid and globose shapes could also be found. In these populations, the colour of pericarp varied from light brown, brown, dark brown, reddish brown to blackish brown at harvest time. The genotypes from region C bore fruit with more uniform pericarp colours, usually light brown or brown with darker stripes, characteristic of marron types (BOUNOUSet al.1993). These genotypes often displayed weak pellicle penetration. Only 4% of them had strong pen - etration. There were some genotypes of the continental subpopulations (1 from A1; 2 from B1; 3 from A3; and 1 from B2) which also had weak pellicle penetration. All Mediterranean genotypes were monoembryonic, while in the continental regions, 5% to 40% of the nuts from some genotypes were polyembryonic. In the monoembryonic nuts, the inner cavity was almost always present. Cooked Mediterranean genotype nuts were a little bit sweeter than the continental nuts.
The UPGMA dendrogram established seven principal clusters. Six of them were relatively homogenous, while the last one was much more heterogenous. Three clusters included only trees from region B with very small nuts. Two thirds of the genotypes from the cluster No. 4 came from the Mediterranean region C, with large nuts and low pellicle penetration. One third of the genotypes of the fourth cluster belonged to region A. They had large nuts and displayed at least one of the marron characteristics. The fifth group consisted mostly of genotypes from region A, with three outliers from region C and one from region B. All of them had medium-sized nuts and medium-to-strong pellicle penetration. The genotypes with small-to-medium-sized nuts from region B were mainly included in the sixth cluster together with two outliers from region C and three from subpopulation A1with similar nuts. The seventh cluster included 21 genotypes from region A, 10 genotypes from region B and three genotypes from region C.
Table 1. Mean and coefficient of variation (CV) for fruit traits of chestnut genotypes from different subpopulations in Slovenia. A: east, B: central, C: south-west.
Trait Subpopulation
A1 A2 A3 B1 B2 C
Height Mean (mm) 2.6 2.8 2.7 2.5 2.5 3.0
of fruit CV (%) 5.1 5.4 6.8 9.6 6.2 8.8
Width Mean (mm) 3.0 3.1 3.3 2.7 2.9 3.4
of fruit CV (%) 6.0 5.4 6.1 10.9 6.2 8.0
Thickness Mean (mm) 1.9 1.9 2.0 1.7 1.9 2.0
of fruit CV (%) 9.0 9.6 7.3 12.2 6.6 9.0
Weight Mean (g) 9.5 12.0 11.6 7.1 8.7 14.3
of fruit CV (%) 16.5 17.3 16.9 32.4 11.2 24.3
No. of Mean 108.5 85.1 89.5 152.6 116.6 75.5
fruits / kg CV (%) 20.0 13.6 21.7 27.6 11.4 34.4
Length Mean (mm) 2.1 2.2 2.5 1.8 1.9 2.3
of hilum CV (%) 9.5 12.6 12.8 20.3 12.0 10.3
Width Mean (mm) 1.1 1.2 1.3 1.0 1.1 1.2
of hilum CV (%) 12.3 12.0 11.3 18.1 12.6 9.6
3.2 RAPD analyses
In the dendrogram of Jaccard’s similarity coefficients, five groups were identified and two trees formed individual branches of the dendrogram (Fig. 1).
The first cluster included four genotypes from region B1 with small nuts and strong pellicle penetration. The second and third clusters were made up of small, small-medium and medium nut genotypes from the continental subpopulations A1, A2, A3, B1 and B2. The fourth cluster comprised all the Mediterranean genotypes. One genotype (Koz-1) with large nuts (18.6 g) belonging to the A2subpopulation formed an individual group at the top of the dendrogram and one genotype (Koz-7) with small nuts (10.7 g) and a small hilum formed another individual group at the bottom of the dendrogram (PODJAVORSEK1999).
The clusters based on the RAPDs do not correspond fully with the clusters based on the pomological characters (Fig. 1).
Fig. 1. Dendrogram of the RAPDs analysis. A: origin of genotype, B: cluster assignment according to pomological traits.
4 Discussion
Characterizing Slovenian chestnut cultivars using pomological methods and RAPDs analysis has shown that the genetic variation is smaller among the Mediterranean genotypes than among the continental genotypes. Further, there is a greater genetic similarity among the genotypes of the Mediterranean region C than among the genotypes of the continental populations. RAPDs analysis shows a weak clustering of the subpopulations.
A B
A2 4 B1 6 B1 7 B1 3 B1 6 A2 5 B1 7 B1 6 A2 5 A2 5 A2 5 A3 5 A3 4 B2 7 B2 6 B2 7 B2 7 B2 6 B2 6 A3 5 B1 6 B1 3 B1 6 B1 3 A1 6 B1 6 A1 7 A1 7 A3 5 A3 5 A1 5 A1 7 A3 5 A3 5 A1 3 C 4 C 4 C 4 C 7 C 4 C 4 C 4 C 4 C 4 C 4 A2 5
0.48 0.64 0.80 0.96 1.12
The quality of Mediterranean genotypes is higher than that of the continental ones. Even though the majority of continental genotypes have nuts of small to medium sizes with strong pellicle penetration, some better quality individuals among them could be expected, and were indeed found with a few quality outliers inside the continental subpopulations. Their presence may be due to the human intervention in cultivating chestnut in the past. Given that sweet chestnut is not very adaptable to different edaphic circumstances, we will continue to explore the smaller areas so that the transport at random of specific types from one part of the country to another can be avoided.
Up until now, 17 genotypes have been preselected. Some of them have been multiplied by grafting on germinated seeds and then planted into a trial plot for a final evaluation.
5 References
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Genève. 23 pp.
Accepted 29.4.02
