Genetic aspects of phenological distinctions in Scots pine populations | Parastās priedes populāciju fenoloģisko atšķirību ģenētiskie aspekti

The most important aim of seed orchards is the production of genetically superior seed material. Scots pine population flowering time phenology is especially important when selecting clones for seed orchard establishment. In order to obtain the highest quality seed material from seed orchards, it is important that all clones represented in the orchard contribute to seed production. Therefore, synchronisation of flowering time is important. The phenological characteristics of Scots pine (Pinus sylvestris L.) clones were investigated with observations during the spring of 2008 in two seed orchards - Dravas in the western part of Latvia (containing 65 Misa population clones), and Sāviena in the eastern region of Latvia (containing 76 Misa population clones and 86 Smiltene population clones). Phenological observations were made 6 times in the period between the 12th of May and the 3rd of June. At each observation time, the development stage of both male and female strobiles was noted. The pine clones were categorized into 5 female flowering groups (very late, late, medium, early, very early), and 3 male flowering groups (late, medium, early). It has been established, that significant flowering time differences occur both between populations and within populations between different clones. About half of the clones fell into the medium category for both male and female flowering time. Of the Misas clones, 39% of clones fell into the medium category for female flowering time in the Sāvienas seed orchard and 45% in the Dravas seed orchard, while 74% of the Smiltenes clones fell into the medium category for female flowering time (average 53%). The average values for the female flowering groups ''very late'', ''late'', ''early'' and ''very early'' were 5%, 27%, 13% and 1%, respectively. With regard to male flowering time, the size of the medium group in both populations was very similar - 56-57%. The remaining clones were all classified as early flowering, except for one clone from the Misas population, and one from the Smiltenes population. No correlation was found between male strobile number and either male or female flowering time. Overall, the flowering time observations confirmed the hypothesis that early and late flowering clones maintained their phenological characteristics in differing environments (the Misa population clones in the Sāviena and Dravas seed orchards), and that progeny of different populations maintained phenological differences in the same growing conditions (the Misa and Smiltene clones in the Sāviena seed orchard). Therefore, the conclusion can be drawn that these phenological differences are at least partly genetically determined. DNA analysis using chloroplast markers was performed on the Misa clones to determine if population differences could be found between various flowering time groups. The DNA marker analysis showed, that utilising the chloroplast markers, no differences could be detected between both the male and the female flowering groups. This lack of population structure found using the chloroplast markers could be explained by the fact that they are ''neutral'' markers, which do not influence morphological or phenological traits. Therefore, gene expression and allele differences of candidate genes involved in control of flowering time should be investigated in further studies of phenological traits.