T.S. Anekonda

Mapping of quantitative trait loci controlling adaptive traits in coastal Douglas-fir. II. Spring and fall cold-hardiness

Abstract Quantitative trait loci (QTLs) affecting fall and spring cold-hardiness were identified in a three-generation outbred pedigree of coastal Douglas-fir [Pseudotsuga meniziesii (Mirb.) Franco var. menziesii]. Eleven QTLs controlling fall cold-hardiness were detected on four linkage groups, and 15 QTLs controlling spring cold-hardiness were detected on four linkage groups. Only one linkage group contained QTLs for both spring and fall cold-hardiness, and these QTLs tended to map in close proximity to one another. Several QTLs were associated with hardiness in all three shoot tissues assayed in the spring, supporting previous reports that there is synchronization of plant tissues during de-acclimatization. For fall cold-hardiness, co-location of QTLs was not observed for the different tissues assayed, which is consistent with previous reports of less synchronization of hardening in the fall. In several cases, QTLs for spring or fall cold-hardiness mapped to the same location as QTLs controlling spring bud flush. QTL estimations, relative magnitudes of heritabilities, and genetic correlations based on clonal data in this single full-sib family, supports conclusions about the genetic control and relationships among cold-hardiness traits observed in population samples of Douglas-fir in previous studies.

Influence of second flushing on genetic assessment of cold hardiness in coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco)

Abstract The consequences of second flushing for fall cold hardiness in coastal Douglas-fir ( Pseudotsuga menziesii var. menziesii (Mirb.) Franco) was investigated in 4-year-old trees from two genetic tests: 42 polycross families in British Columbia and 8 full-sib families in the state of Washington. Cold injury to needle and stem tissues was assessed in October and November in samples of both second-flushed and non-second-flushed shoots from the same trees following artificial freezing. Freeze damage to needles and stems in the second-flushed portion of shoots was 50–60% greater than in non-second-flushed shoots. Great care, therefore, should be taken to consistently sample the same shoot type when comparing cold hardiness of genotypes (or families) using artificial freeze testing. However, because the estimated genetic correlations in freeze injury between second-flushed and non-second-flushed shoots were moderately positive, scoring all trees for hardiness of one shoot type should provide fairly accurate rankings of genotypes for cold hardiness of both shoot types. We recommend scoring non-second-flushed shoots because the frequency of second flushing decreases relatively rapidly with increasing age in coastal Douglas-fir. Hardening of both second-flushed and non-second-flushed shoots was delayed in trees with higher proportions of second-flushed shoots in their crown. Thus, foresters should avoid planting families with high propensity to second flush on high fertility sites (i.e. sites that promote second flushing) susceptible to fall frost events.

Genetics of dark respiration and its relationship with drought hardiness in coastal Douglas-fir

Genetic variation in respiration parameters, and the relationships between respiration and drought hardiness were investigated in coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco). Material included 3-year-old seedlings from 12 families grown under two treatments: control (well-watered) and drought (moderate drought the second growing season followed by severe drought the next year). Respiratory parameters measured were metabolic heat rate (q) and rate of CO 2 production (R CO ). Calculated parameters were the ratio of metabolic heat rate to CO 2 production rate (q/R CO2 ) specific growth rate (R SG ), and Arrhenius temperature coefficients of metabolic heat (μ q ) and CO 2 production (μ CO2 ). Growth traits measured were third-year increments of seedling height and diameter. Means of respiration traits were generally less in the drought treatment than in the control, with the exception of μ q , which increased under drought. Consistent increase in μ q and decrease in μ CO2 values in response to drought appear to suggest a differential influence of drought on the temperature dependence of ATP synthesis in catabolic reactions, and ATP breakdown in anabolic reactions or in futile cycles of dark respiration. Metabolic heat rates measured over a wide a range of temperatures (20 to 55 C) differed significantly between control and drought treatments for the most drought sensitive family, but not for drought hardy families. Variation among the 12 families in q (at 25 C) and μ CO2 were significant (p<0.05) when families were grown in the control treatment. Family means for height increments (r 2 =0.43 to 0.58; p<0.05) related negatively to respiration and diameter increments related positively to respiration traits (r 2 =0.34 to 0.56; p<0.05). Temperature coefficient of CO 2 production rate under control treatment was negatively associated with shoot damage (r 2 =0.34: p<0.05) suggesting that respiration traits may be useful for evaluating drought hardiness in this species.

Extreme growth phenotypes of trees are caused by differences in energy metabolism

Abstract Rapid and slow growth phenotypes of same-age-trees can result from differences in genetic growth potential due to differences in the metabolic properties of the phenotypes or by differences in the match between their metabolic characteristics and environmental factors. In this study, paired rapid and slow growing trees from two species were examined to define physiological properties that determine the growth rate differences. Because plant structural biomass production depends on energy production via aerobic respiratory metabolism, respiration rate and energy use efficiencies of the rapid and slow growing trees were compared. Growth rates were calculated for each tree from the measurements of metabolic heat rates and CO 2 production rates of meristems as functions of temperature. The rates of metabolic heat and CO 2 production by respiration were higher, the energy use efficiency was higher, and the rate of storing chemical energy in structural biomass (calculated growth rate) was higher in the large trees than in the small trees, showing that the respiratory metabolic properties define growth rate differences. Ratios of calculated growth rates of large and small trees varied with temperature. Therefore, classification of trees into rapid growth or slow growth phenotypes is dependent upon growth temperature and the match between metabolic characteristics and environment. These findings suggest that respiratory parameters may be used in identifying trees most suitable for rapid growth in a given environment.