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ŠUMARSKI LIST 5-6/2013 str. 33     <-- 33 -->        PDF

Icgen et al. (2006) reported that the majority of genetic diversity present in natural populations of P. brutia appears to be captured in seed orchards and plantations. Also, the results of our study showed that all studied seed orchards have high proportion of gene diversity (Table 1). As a result, different selection methods and management strategies should be applied on seed orchards depending on related species to get maximum genetic gain and maintain high level of genetic diversity.
Kang and Mullin (2007) studied effect of variation in effective clone number on the genetic diversity of Chamaecyparis obtusa seed orchard in Korea over a four-year period. They indicated that gene diversity in seed crop would increase if seeds collected from different years are pooled. Varghese et al. (2006) estimated gene diversity in two 25-years old clonal seed orchards of Tectona grandis in southern India as 0.943 and 0.792, respectively. They reported that improvement in diversity level were inadequate in the second seed orchard, and suggested some measures such as intentional adjustment of ramet numbers of each clone, that can help to reduce the loss of gene diversity during domestication process. The seed orchards in our study are all first generation seed orchards; and management and improvement studies for future seed harvests from the seed orchards are in progress in Turkey (Koski and Antola 2003). However, genetic diversity parameters of seed orchards in this study showed parallelism with previous studies (Godt et al. 2001, Kang et al. 2001b, 2003). Therefore, phenotypic selection, related species fertility and genetic analysis studies should be considered to establish second generation seed orchards.
Genetic diversity parameters of seed orchards were shown not to be significantly different from seed stands and plantations (El-Kassaby and Ritland 1996, Godt et al. 2001, Icgen et al. 2006). Even, the percentages of polymorphic loci in seed orchards were slightly higher than natural stands and plantations (Icgen et al. 2006). These results suggest that large proportion of genetic diversity found within natural populations are captured in seed orchards through practicing phenotypic selection and implementing effective number of clones (Godt et al. 2001, Icgen et al. 2006). Results of this study suggest high proportion of gene diversity in conifer seed orchards in Turkey. However, reduced allelic richness and heterozygosity in seed orchards were also reported (Cheliak et al. 1988, Stoehr and El-Kassaby 1997, Rajora, 1999). Such contrasts may be attributed to the sampling, management practices (especially roguing of seed orchard) and mating system of the species in question (Icgen et al. 2006, Lindgren et al. 2009). These characteristics should be considered to establishment of seed orchards in the future.
Certain conditions should be achieved to obtain expected level of genetic gain from an open-pollinated seed orchards: (a) Seed orchards should be isolated from unwanted pollen sources, (b) Number of clones and ramets per clone in a seed orchard should be high enough depending on species (from 20 to 50 clones), and all clones should contribute relatively equal proportion of male and female flowers, (c) Pollen dispersal period and female receptivity should occur at the same time as much as possible, and (d) Inbreeding and mating among close relatives should be avoided (Fast et al. 1986, El-Kassaby et al. 1989, Kang et al. 2001a). Orchard-management techniques such as selective seed harvesting and genetic thinning (roguing) are used to improve genetic quality of seed orchard crops. In selective seed harvest, selection is applied to seed parents, whereas in roguing selection is applied to both seed and pollen parents. Genetic thinning maximizes the genetic gain from seed orchard crops and effective clone number in orchards (Kang et al. 2001a, Moriguchi et al. 2008, Prescher et al. 2008). The results of this study and previous studies about seed orchards which are discussed above showed that clone number, ramet number, fertility variation of related species, distribution range of related species and different management strategies should be considered to establish tomorrow’s seed orchards.
Future’s seed orchards should be established with phenotypic selection as well as populations’ molecular genetic analysis (especially analysis of adaptive genes). Genetic gain and genetic diversity balance should be considered when establishment of first and/or second generation seed orchards. To capture and manage high levels of genetic variation in seed orchards, high number of populations, covering a wider range of environments and marginal populations of species, should be systematically sampled and genetically analyzed. According to the genetic analysis results, and considering threats such as climate change, seed orchards are established on a wide range of species distribution area depending on their provinces and local growing conditions.
Dr. Kani ISIK (Akdeniz University, Science Faculty, Biology Department, Antalya, TURKEY) and Dr. Juan Jose ROBLEDO-ARNUNCIO (Department of Forest Ecology and Genetics, Forest Research Centre, Madrid, SPAIN) kindly reviewed and edited the earlier version of the manuscript both linguistically and scientifically. Two anonymous reviewers provided valuable comments to improve the manuscript. We gratefully acknowledge the contributions of all these persons.