engleski

Management, Genetic Gain and Genetic Diversity in Clonal Seed Orchards in Croatia

In accordance with the delineation of Regions of Provenances of forests in Croatia into ecogeographic seed regions and zones, the following productive clonal seed orchards have been established: three orchards of pedunculate oak (Quercus robur L.), two of narrow-leaved ash (Fraxinus angustifolia Vahl), one of sessile oak (Quercus petraea (Matt.) Liebl, ), one of wild cherry (Prunus avium L.) and one orchard of black pine (Pinus nigra J. F. Arnold). Phenotypical selection and heterovegetative propagation of plus trees, as well as the establishment of clonal seed orchards were launched with the goal of controlling more regular yield periodicity and obtaining forest seed of good genetic quality in the categories Qualified and Tested. The orchards are regularly subjected to pomotechnical treatments, protection and other measures of maintance. Establishment and evaluation of progeny trials are provided for all clonal seed orchards. Different pomotechnical treatments (training systems) were applied to each tree species. For pedunculate and sessile oak oval spindle training system, for narrow-leaved ash spindle pyramid and for wild cherry spindle bush training system. Training systems should provide a strong framework and good light penetration in the canopy. The forming pruning is used to bring the grafts into the required training shape whereas pruning for higher yield maintains the adequate balance between the growth and the seed production. Tree pruning and training started right after the planting with a goal to gain desired canopy shape with well-deployed scaffold branches in the next 7 or 8 years. The main function of pruning is the removal of competing shoots to enforce the growth of remaining desired ones. Pruning intensity, i.e. the relation between vegetative and generative buds in the canopy determines the tree’s condition, density and yield. The balance between vegetative and generative buds can only be achieved by appropriate underground and aboveground tree parts pruning. The evaluation of genetic values of selected clones of pedunculate oak (Quercus robur L.) from seed orchards in progeny tests were also started for the purpose of obtaining increased genetic gain. Three open pollinated progeny trials have been established, representing three seed region at the age of 2 + 18 years (TP1) and at 2 + 7 years (TP2, TP3). The realised gain from the tests and expected genetic gains for height were calculated by three methods which included: realised gain (R) calculated as the difference between means of selected plus tree progenies and means of unselected control plants ; expected genetic gain by individual within provenance mass selection of first generation plus trees at the same ages as those represented in studied trial ; expected genetic gain by backward selection among first generation plus trees. In TP1 i TP3 family effect for height was statisticaly significant for the entire period, showing decreasing trend in TP1 and rising in TP3. Family effect was not significant in TP2, ponting to narrowed individual variability of plus trees in that seed region. High values of environmental variance components and family × block interactions suggest strong environmental influences in that particular trial (caused by flushing phenology), which could have led to underestimation of additive variance. High values of additive coefficients of variation in TP1 and TP3 suggest wide genetic variability of selected plus trees and good adaptability of their progeny to changing environmental conditions. In all trials the estimated expected genetic gains by backward selection among first generation plus trees after open-pollinated progeny testing showed the highest values. Realised gains were not very high during the entire period in TP1, showing the decreasing trend in recent years. In TP3 realised gain is improving, due to higher heritabilities and greater differences between selected and control families. Opposite to that, low heritabilities, non significant family variance component and small differences between selected and control families resulted in little, even negative realised gains in TP2. Genotypes from the clonal seed orchard of wild cherry (Prunus avium L.) was taken for the investigation of genetic variability and consisted of 24 selected plus trees from the area of north-western Croatia. The clones were analyzed by 15 selected microsatellite markers (SSR), chosen by the ECPGR. A wealth of allelic variations was found in SSR loci, while a high degree of polymorphism confirmed the existence not only of extensive morphological but also a very significant genetic diversity. Based on pairwise proportion of shared allele distance (DPSAM) the average genetic distance of 0.573 was calculated. The genetic distance matrix, based on pairwise proportion of shared allele distance (DPSAM), did not show a clear classification of wild cherry individuals with regard to their origin, i.e. region (Koprivnica, Bjelovar, Zagreb). The analysis of molecular variance (AMOVA) revealed a significantly higher percentage (95.88 %) of the total microsatellite diversity caused by the differences among the invidividuals within the regions, compared to that caused by the differences between the studied regions (4.12 %). The  - statistics, amounting to 0.041, was highly significant (P < 0.01) and indicates the existence of specific regional structurality of genetic diversity. Clonal seed orchards are also a nucleus of conservation of forest genetic resource using the ex situ statical method, since the relationship between the size of population and the percentage of preserved heterozygosity is thus reduced to minimal loss of total additive genetic variability. Climate changes and new habitat conditions will pose additional challenges to seed production and forest management ; in turn, this will influence their economic and social benefits, as well as biological diversity of forest ecosystems.

Quercus robur; Quercus petraea; Fraxinus angustifolia; Prunus avium; Pinus nigra; pomotechnical treatments; progeny trials; genetic parameters; genetic diversity

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