Quantitative genetics of bud phenology, frost damage, and winter survival in an F₂ family of hybrid poplars

Abstract 

We studied the quantitative genetics of bud phenology, fall frost damage, and winter survival in an F₂ family (no. 822) of Populus hybrids derived from a cross between two full-sub F₁ hybrids (P. trichocarpa (Torr. & Gray×P. deltoides Bartr.). Field traits studied included the timing of bud set (BS_F) in Minnesota and Oregon, the timing of bud flush (BF_F) in Oregon, as well as fall frost damage (FD_F) and winter survival (WS_F) in Minnesota. We conclude that Family 822 has substantial genetic variability for all field traits, BS_F and BF_F are under moderate to strong genetic control (H ² _i =0.48–0.80), FD_F and WS_F are under low to moderate genetic control (H ² _i =0.27–0.40), and late bud set is associated with increased frost damage and decreased winter survival. In a warm greenhouse, we measured the timing of bud set and the number of new leaves on trees growing under either an 8-h photoperiod (BS_SD and NL_SD) or a natural photoperiod (NP) from August to December (BS_NP and NL_NP). We found that BS_SD, NL_SD, and NL_NP are under moderate genetic control (H ² _i =0.53–0.70), but the heritability of BS_NP could not be determined because few trees set bud in the warm greenhouse under the NP. By comparing results from the greenhouse experiments with results from the field, we conclude that the genetic correlation between BS_SD and BS_F (0.53–0.60) is relatively modest and that NPs in the fall are relatively ineffective at promoting bud set under warm greenhouse temperatures, although bud set readily occurred in the field. Although, low levels of light pollution in the greenhouse might have affected BS_NP, results from both greenhouse and field experiments suggest that genetic differences in photoperiodic responses play a modest role in explaining genetic differences in the timing of bud set under natural field conditions. Therefore, genetic differences in responses to other environmental factors, such as temperature, deserve greater attention.