Abstract
Boreal coniferous species with wide geographic distributions show substantial variation in autumn cold acclimation among populations. To determine how this variation is inherited across generations, we conducted a progeny test and examined the development of cold hardening in open-pollinated second-generation (F2) progeny of Abies sachalinensis. The F1 parents had different genetic backgrounds resulting from reciprocal interpopulational crosses between low-elevation (L) and high-elevation (H) populations: L × L, L × H, H × L, and H × H. Paternity analysis of the F2 progeny using molecular genetic markers showed that 91.3% of the fathers were located in surrounding stands of the F1 planting site (i.e., not in the F1 test population). The remaining fathers were assigned to F1 parents of the L × L cross-type. This indicates that the high-elevation genome in the F1 parents was not inherited by the F2 population via pollen flow. The timing of autumn cold acclimation in the F2 progeny depended on the cross-type of the F1 mother. The progeny of H × H mothers showed less damage in freezing tests than the progeny of other cross-types. Statistical modeling supported a linear effect of genome origin. In the best model, variation in freezing damage was explained by the proportion of maternally inherited high-elevation genome. These results suggest that autumn cold acclimation was partly explained by the additive effect of the responsible maternal genome. Thus, the offspring that inherited a greater proportion of the high-elevation genome developed cold hardiness earlier. Genome-based variation in the regulation of autumn cold acclimation matched the local climatic conditions, which may be a key factor in elevation-dependent adaptation.
Highlights
Seasonal growth cycles are well described for plant taxa distributed in boreal, sub-boreal, and temperate climates
Interpopulational genetic variation for many boreal conifers is greater during autumn cold acclimation than during spring dehardening (Aitken and Hannerz, 2001; Howe et al, 2003)
We investigated the genetic basis of variation in the regulation of autumn cold acclimation using Sakhalin fir
Summary
Seasonal growth cycles are well described for plant taxa distributed in boreal, sub-boreal, and temperate climates. For evergreen coniferous species, cold acclimation often occurs before temperatures drop below freezing (Aitken and Hannerz, 2001; Chuine, 2010). During this acclimation, evergreen plants shift their physiological condition from an active growth phase to a hardening phase that involves some degree of freezing tolerance. Because of a trade-off between growth and risk of freezing damage, the timing of phenological events can be a key driver for adaptation to cold climates During their long evolutionary histories, conifers have acquired an adaptive schedule of cold acclimation to survive under their local environmental conditions, using changes in daylength and/or temperature as regulatory signals (Kozlowski and Pallardy, 2002). It is a consistent trend that populations from high latitudes and elevations exhibit earlier development of cold hardening than those from low latitudes or elevations (Rehfeldt, 1989; Skrøppa and Magnussen, 1993; Oleksyn et al, 1998; Savolainen et al, 2004; Notivol et al, 2007; Mimura and Aitken, 2010)
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