Graduate Thesis Or Dissertation
 

Genetic variation in phenology of bud and cambial activity in coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco)

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  • Growth phenology (i.e., timing of growth initiation and cessation) is important to adaptation. This study examined the extent of genetic control of bud and cambial phenology and their relationships with stem growth in pole-size Douglas-fir (ages 13 to 16 years) from 60 open-pollinated families. The availability of bud phenology data from two-year-old seedlings of 45 of the 60 families also made it possible to examine the potential of early testing for bud phenology. The difficulty of scoring terminal buds on leaders of large trees and the expense of multiple visits to test plantations to score budburst and budset timing, however, discourage the inclusion of these traits in breeding programs. Thus, the efficiency of two alternative methods of scoring bud phenology was explored. The strong genetic control (h2 > 0.73) and moderate genetic variation in dates of budburst and budset indicate that bud phenology can be readily altered in pole-size trees via selection and breeding. Early testing appears to be effective for both budburst and budset, especially for early culling of families. In both pole-size trees and seedlings, height growth had positive genetic correlations (0.19 < rA < 0.77) with dates of budburst and budset, indicating that selection for greater height growth at either stage will lead to delayed budburst and budset. Delayed budburst reduces risk of spring frost damage, whereas delayed budset increases risk due to damage from late summer drought or early fall frost, especially in seedlings which continue growth until early September. With the exception of the lowest lateral branches, scoring budburst on branches was found to be a very efficient means to rank families and individuals for date of budburst on the leader shoot. Scoring budset on branches may not be as effective since the genetic correlation between dates of budset on branches and the leader appears only to be moderate (rA < 0.70). The proportion of trees in a family which burst (or set) buds on a single scoring date was found to have a strong negative genetic correlation with mean date of family budburst (or budset). Thus, data from a single measurement date is adequate for the purpose of ranking families for bud phenology. In contrast to bud phenology traits, the cambial phenology traits measured in this study in 1987 (i.e., dates of diameter initiation and cessation in the 15th growing season) were weakly inherited (h2 < 0.23). In addition, only weak relationships were observed between diameter growth increment and diameter growth phenology, with diameter increment being more a function of growth rate rather than growth duration in 1987. The estimated genetic correlation between dates of budburst and diameter growth initiation was unexpectedly low (rA = 0.26). Because cambial phenology traits were weakly correlated with diameter growth and budburst timing, selection for greater growth or delayed budburst is expected to produce little correlated response in cambial phenology.
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