The variation of timing of terminal bud set and frost hardening in first-year seedlings of Scots pine (Pinus sylvestris L.) was studied. Both bud set and frost hardiness showed clinal variation with respect to latitude over a steep environmental gradient (60-67°N) in Finland. Northern populations set buds and developed frost hardiness earlier than southern populations. Backcrosses ((north × south) × south) were intermediate or close to the southern parent both in bud set and in frost hardiness between the populations representing the parental origins. In bud set, 36.4% of the total variation was between the populations. The bud set date and development of frost hardiness were highly correlated at the population level (r = 0.69-0.97). Frost hardening started during the bud formation period and accelerated when most of the buds had formed. In backcross progenies, earlier bud set resulted also in earlier development of frost hardiness. This suggests a genetical association between the two traits.Résumé : La variation dans le moment où le bourgeon terminal est formé et la résistance au gel est acquise a été étudiée chez des semis de pin sylvestre (Pinus sylvestris L.) âgés de 1 an. La formation du bourgeon terminal et la résistance au gel montraient une variation clinale par rapport à la latitude le long d'un fort gradient environnemental (60 à 67°N) en Finlande. Les populations septentrionales formaient leur bourgeon terminal et devenaient résistantes au gel plus tôt que les populations méridionales. Les populations issues de rétrocroisements ((nord × sud) × sud) se situaient à mi-chemin ou près des parents d'origine méridionale pour la formation du bourgeon terminal et la résistance au gel comparativement aux caractéristiques des populations dont provenaient les parents. Dans le cas de la formation du bourgeon terminal, la variation entre les populations représentait 36,4% de la variation totale. La date à laquelle le bourgeon terminal était formé et l'acquisition de la résistance au gel étaient fortement corrélées (r = 0,69-0,97) au sein des populations. L'acquisition de la résistance au gel débutait pendant la période de formation du bourgeon terminal et s'accélérait lorsque la plupart des bourgeons étaient formés. Dans les descendances issues de rétrocroisements, l'acquisition de la résistance au gel survenait plus tôt si le bourgeon terminal se formait plus tôt. Les résultats suggèrent qu'il existe une association d'ordre génétique entre les deux caractères. [Traduit par la Rédaction]

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We have examined patterns of variation of several kinds of molecular markers (isozymes, RFLPs of ribosomal DNA and anonymous low-copy number DNA, RAPDs and microsatellites) and an adaptive trait [date of bud set in Scots pine (Pinus sylvestris L.)]. The study included Finnish Scots pine populations (from latitude 60°N to 70°N) which experience a steep climatic gradient. Common garden experiments show that these populations are adapted to the location of their origin and genetically differentiated in adaptive quantitative traits, e.g. the date of bud set in first-year seedlings. In the northernmost population, bud set took place about 21 days earlier than in the southernmost population. Of the total variation in bud set, 36.4% was found among the populations. All molecular markers showed high levels of within-population variation, while differentiation among populations was low. Among all the studied markers, microsatellites were the most variable (He=0.77). Differences between populations were small, GST was less than 0.02. Our study suggests that molecular markers may be poor predictors of the population differentiation of quantitative traits in Scots pine, as exemplified here by bud-set date.

Segregation, homology and linkage of 33 random amplified polymorphic DNA (RAPD) markers were studied in three trees [P304, E1101 and F1 (cross P315 × E1101)] of Scots pine (Pinus sylvestris L.). Markers were selected on the basis of a RAPD map constructed earlier for F1. Markers from three linkage groups were studied in P304 and E1101. In both P304 and E1101, 14 markers (42%) were heterozygous. Segregation deviating from 1:1 was found for three markers in P304 and one marker in E1101. With the restriction pattern test, two out of the 33 loci studied (6%) were found to be not homologous to the corresponding fragment in F1. Both of these loci were heterozygous, and they were not linked to any markers, which confirmed their nonhomology. Homologous heterozygous markers segregating 1:1 were mostly linked with similar order in P304 and E1101 as in F1. The results suggest that it might be necessary to verify the homology of comigrating fragments before using them even across individuals. It will often be desirable to use other codominant markers together with RAPDs.

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