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ŠUMARSKI LIST 5-6/2013 str. 32     <-- 32 -->        PDF

The estimated proportional gene diversity was in the range of 0.922 to 0.983 (mean 0.973) among the studied seed orchards (Table 1). There was positive correlation between gene diversity and Nc value (r = 0.953, p = 0.0001), and also between gene diversity and Nr value (r = 0.977, p = 0.0001).
Discussion
Rasprava
Plus trees, selected based on their desirable phenotypic characteristics, are used for establishment of clonal seed orchards (Kang et al. 2001b). Genetic thinning and selective harvesting may change clonal ramet proportion in orchards, while, at the same time, they can improve the genetic quality of seed orchards (Kang et al. 2001a, Prescher et al. 2008). Both ramet number variation and ramet fertility of clones contribute to the gene pool in a seed orchard. Therefore, important attention should be given on ramet number variation during seed orchard establishment and management.
In this study, overall mean effective number of clones (Nc) based on variation in the number of ramets was estimated as 27.59. Furthermore, P. sylvestris seed orchards had the highest Nc value (35.55), followed by P. brutia seed orchards (32.89) and finally, P. halepensis seed orchards with the lowest value (6.6). Kang et al. (2001b), working on a 255 conifer clonal seed orchards in Finland, Korea and Sweden, estimated the mean effective number of clones (Nc) as 66, ranging from 10 to 421. Prescher et al. (2008) reported Nc values in Picea abies seed orchard as 19.99 and 22, before and after thinning, respectively.
The Nr was 0.827, with a range from 0.523 to 0.906 in this study. Kang et al (2001b) estimated overall average Nr value as 0.74; Picea abies seed orchards in Sweden had the highest, Pinus koraiensis seed orchards in Korea had the lowest value. Varghese et al. (2006) reported Nr value in two clonal seed orchards of Tectona grandis in southern India as 0.582 and 0.120, respectively. The seed orchard with high Nr value had relatively more number of fertile ramets and better sexual symmetry, both contributing to the higher gene diversity. Results of our study indicate that seed orchards of conifer forest trees in Turkey have relatively high effective number of clones. This implies that Forest Tree Seeds and Tree Breeding Research Directorate have an efficient program for seed orchards establishment and management.
The main reasons for variations in ramet number are graft availability and incompatibility, growth conditions and mislabeling of ramets. Variation in the number of ramets per clones in seed orchards may result unequal production of female flowers, male flowers and gametes. Equal contribution of clones to the formation of the progeny is necessary because the production of genetically superior seeds in the seed orchard through panmictic reproduction is important (Kang et al. 2001a, Lindgren and Prescher 2005). If seed orchards do not reproduce panmictically, some reduction in the expected genetic gains will occur. The quality of a seed produced in seed orchards is determined by many factors, including the rate of pollen contamination from outside sources, degree of self-fertilization, and equality of the clones (in other words ramet number variation) as pollen donors. The level of contribution varies significantly among clones in the seed orchard that have variations in ramet number (Kaya et al. 2006, Funda et al. 2009). El-Kassaby and Cook (1994) studied the within and among clonal variation in reproductive energy and reproductive success, and their impact on the genetic diversity of cone/seed crop in a Douglas fir seed orchard. In that study, the average number of seed-cone producing ramets per clone was ranging between 1 and 15, they observed significant correlation (p≤0.05) between clone size (variable number of seed-cone bearing ramets per clone) and both seed-cone crop size and filled seed yield. Nikkanen and Ruotsalainen (2000) reported that the status number is important measure for describing the genetic diversity of the seed orchard crop. They found that the status number of studied Norway spruce seed orchard was 56 (84% of the number of clones in the orchard) when the ramet number variation per clone was considered.
The mean estimated proportional gene diversity was 0.973 among the seed orchards studied. We found positive correlation between gene diversity and Nc value, and also between gene diversity and Nr value. Gene diversity increases as Nc or Nr increases. Our result in this study is compatible with other studies on conifer seed orchards (Kang and Lindgren 1998, Kang et al. 2001b). Kang and Lindgren (1998) estimated gene diversity in P. densiflora, P. thunbergii and P. koraiensis seed orchards by total strobili production as 0.993, 0.991 and 0.987, respectively. Kang et al (2001b) calculated the estimated mean gene diversity as 0.992 in 255 conifer clonal seed orchards. Differences among clones in fertility and ramet number affect genetic composition of seed orchards and may cause loss in genetic diversity (Kang and Lindgren 1998).
Kang et al. (2003) estimated genetic gain after the implementation of %45 and %70 genetic thinning in a Pinus densiflora clonal seed orchard. They reported genetic gain as 0.07% at initial establishment of orchard, 6.3% at 1st genetic thinning and 11.6% at 2nd genetic thinning. Genetic diversity was estimated in a 13-year old Quercus serrata breeding seed orchard under three selection (roguing) methods (Kang et al. 2007). They calculated genetic diversity loss for individual, family and family + within family selection as 1.05%, 1.72% and 1.29%, respectively. Kang et al. (2007) concluded that genetic gain from seed orchards can be manipulated by using different selection methods, but strong genetic thinning might result in a decrease of genetic diversity.