Wild service tree is one of the valuable economical and medicinal species in the north forests of Iran distributing from Astara to Golidaghi as scattered and more or less as small groups in mixed beech, hornbeam and oak stands (Espahbodi et al., 2003). It is a tall tree and obtains 34 m in height and 100 cm in diameter at breast height (Poormajidian, 1999). Its economical importance is mainly due to wood quality, especially its attractive design (Lanier, 1993). It increases biological values of forest and has especial importance in afforestation and tree breeding (Demesure et al., 2000). Regarding to its high value and also the hazards threatening it, seedling production and afforestation with this species is of essential important. Breeding is a method that increases output and decreases production costs. Among different aspects of breeding, selection is one of the simplest ones. In tree improvement programs, selection of the best genotypes and using them as parents in producing high-quality trees is emphasized. Phenotype variance provides relative importance of genotype and environment and also their interaction effects (Tabaei Aghdaei and Jafari, 2000).
Heritability is a portion of phenotype variety in progenies (Mirmohammadi Meybodi and Mirlohi, 2000). The amount of heritability explains measure of variety which is related to genetic differences among individuals; it is also transferable to future generations. By determining heritability of each trait, the study of traits which have been mostly under control of gene can be limited. In the time of selection seed bearer trees, if attention is paid to higher heritability of seedling characteristics, superior and more qualified seedlings will be produced. Thus, costs decrease and production increase. Generally, this research by doing a 3-year progeny test with aim of determining heritability of qualitative and quantitative characteristics of wild service tree (Sorbus torminalis L. Crantz) tries to take a small step in order to reserve, improve and develop this valuable species.
MATERIALS AND METHODS
Research methodology: Seeds after collecting from 20 parent trees (genotype)
located in Sangdeh forest (1600-1800 m a.s.l., north of Iran) were sown in Orimelk
nursery (1550 m a.s.l.). The data of climate of nursery is given as Table
1. The seedlings grown were replanted in second year in the nursery as randomized
complete blocks design with three replications.
|| Nursery climatic information
According to Cornelius et al. (1996a) in every replication from each
genotype 10 seedlings (progeny) were replanted with distance of 0.5 m from each
other. During doing the progeny test (years 2 and 3) weeds were removed four
times per year and seedlings irrigated once a week. At the end of third growing
season collar diameter (in millimeter), height (in centimeter), angle of longest
branch (in degree) and branch number of seedlings were recorded. Vitality of
seedlings was noted based on Savolainen et al. (2004).
Data analysis: At first for studying the effect of genotype and progeny
analysis of variance was conducted. Since for each parent tree in every replication
10 seedlings were measured in this model 10 progenies per each parent tree were
nested as equation 1 (beneath formula):
By PROC GLM process (SAS institute, 1989) variance was analyzed and effects
of replication, genotype and their mutual effects were investigated. Because
progeny test was Half-sib and model of plan was as nested design, variances
were analyzed into different components by calculating the expectation referring
to nested plans. By using expectation formulas of each characteristic environment
and genetic variances were separated and heritability of characteristics was
calculated manually as Eq. 2 (beneath formula) using Falconer
(1996) method. In this equation δ2p is Phenotype variance, δ2g
is genetic variance and h2 is heritability.
SAS software (SAS Institute, 1989) was used to conduct the analyses.
Results indicated that difference of genotypes for angle of longest branch was significant among progenies (p<0.05). Vitality, collar diameter and branch number of genotypes did differ significantly (p<0.05) (Table 2).
High significance of differences of genotypes showed a suitable variety in
characteristics measured. Comparison of means of genotypes showed that progenies
of trees 3, 11 and 17 with grade of 4.5 had the highest vitality. Progenies
of trees 2 and 18, respectively with 15.9 and 15.6 mm had the highest collar
diameter. Progenies of trees 15, 19 and 20, respectively with 84.3, 86.9 and
84.5 cm in stem height produced tallest seedlings. Likewise, progenies of trees
10, 18 and 20, respectively with 13.3 and 12.9 had the most frequent branch
number and progenies of tree 2 with 67.2 degree had the greatest angle of longest
branch (Table 3).
|| Results of analysis of variation for each seedling characteristic
|** Difference of means in level (p<0.01) was significant,
*Difference of means in level (p<0.05) was significant, ns Difference
of means was not significant
|| Results of comparison of means for each seedling characteristic
|Different letter (s) in column are significantly different
|| Separated variation of seedling characteristics
|| Plus trees for seed selection
|Different letter (s) in column are significantly different
|| Heritability of seedling characteristics
By using expectation formulas of each characteristic, variances were separated (Table 4). Results indicated that the lowest heritability allocated to angle of the longest branch (0.003) and branch number (0.07). Heritability of collar diameter, vitality quality and stem height was 0.22, 0.20 and 0.17, respectively (Fig. 1).
As the results indicated in Table 5 progenies of trees 2,
11, 12, 18, 19 and 20 compared to other progenies of trees are in better situation.
Therefore these trees can be introduced as plus trees for sowing seed and producing
Heritability of branch number and angle of longest branch was lower in comparison with heritability of other characteristics recorded. Such a result related to branch number was reported for many species. Toky et al. (1996) about three-year progeny test of Albizia lebbek (L.) Benth reported that heritability was lower in branch number than in height and collar diameter and biomass. In other hands, heritability in angle of branch was relatively high.
Cornelius et al. (1996b) in a 2-3-year progeny test on Alnus acuminata Kunth. displayed that heritability of branch angle (0.62) was higher than those of height (0.45) and diameter at breast height (0.15). One of the reasons for low heritability of branch number was high environment effects especially competition for receiving light available. Most of branches are destroyed as affecting the competition and natural pruning. Under environmental competition variance severely increases. Since sorbus torminalis has high tendency to light, therefore under competition conditions heritability changes.
Because amount of heritability explains capacity for transferring the existing genetic variety to progenies, its high quantities in studying characteristics confirm the possibility of characteristic improvement using individual selection. Related to this matter collar diameter, height and vitality have suitable genetic variety. High heritability in these characteristics reveals that heritability is transferable to progenies and if tree improvement projects are performed, especially using different selection procedures, promotion in poverty of created populations will be expected.
Regarding to our short time (3-year) study we are not able to judge surely on introducing plus tree. But according to Wu view (1998) and Danusevicius and Lindgern (2003) very weak genotypes can be identified and eliminated. This reality besides of genetic gain can decrease the costs of plantation and maintenance and field preparation for progeny test. Thus, considering the results of this research, if seeds are provided from genotypes of 2, 11, 12, 18, 19 and 20 of Sangdeh population, genetic gain as well as production of high quality seedlings will be promising.
At the end it should be declared that this study needs to repeat measurement
in next years and up to sexual maturity (near 20 years). Thus the trend of heritability
variations of seedling characteristics and early selection of genotypes (parent
trees) will be assessed.