Chemosystematic studies in the genus Pseudotsuga. IV. Inheritance and geographical variation in the leaf oil terpenes of Douglas-fir from the Pacific Northwest

Abstract

Quantitative terpene analysis of the leaf oils of 433 wild Douglas-fir trees from 87 northwestern localities, 66 wind-pollinated progenies of 4 trees from Idaho, 100 trees from 5 localities represented in a provenance trial, and 76 trees from four full-sib families of F1 intervarietal crosses allowed assessment of biosynthetic pathways, geographic variation, and modes of inheritance. Hypothetical biosynthetic pathways, derived from the cooccurrence of terpenes implied that the variation in 17 monoterpenes could be represented by three or four biogenetic pathways. As a result, geographic variation between the coastal and Rocky Mountain varieties can be described by the relative percentages of β-pinene, the terpinene–sabinene group of terpenes, the camphene group, and perhaps limonene. An abrupt reduction in the production of the camphene group occurs in going from interior to coastal populations. Moreover, patterns of segregation within four full-sib intervarietal hybrid families suggested that production of high relative percentages of the camphene group was governed by a single dominant gene. The dominant allele is characteristic of the Rocky Mountain variety, but isolated occurrences were also found on dry sites in coastal British Columbia. The recessive allele occurs far into the range of the Rocky Mountain variety. The coastal variety is characterized by the synthesis of relatively large amounts of β-pinene and the terpinene–sabinene group and their mode of inheritance is quantitative. Although concentrations of these terpenes decline towards the Rocky Mountains, genes controlling high amounts occur in populations of Idaho and western Montana. The variation in β-pinene and terpenes of the terpinene–sabinene group does not appear to be clinal. Trees with 5–10% ocimene are predominant in eastern Oregon. This terpene was found only in less than 1% amounts in trees from the coastal region and Montana and was practically absent in a provenance from Arizona. Hence it may serve to differentiate Rocky Mountain populations.