Xylem Monoterpenes of Pines: Distribution, Variation, Genetics, Function

Smith, Richard H. 2000. Xylem monoterpenes of pines: distribution, variation, genetics, function. Gen. Tech. Rep. PSW-GTR-177. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; 454 p. Retrieval Terms: Pinus species, pine grafts, bark beetles, western pine beetles, gas liquid chromatography, California. The monoterpenes of about 16,000 xylem resin samples of pine (Pinus) species and hybrids—largely from the western United States—were analyzed in this long-term study of the resistance of pines to attack by bark beetles (Coleoptera: Scolytidae), with special emphasis on resistance to the western pine beetle (Dendroctonus brevicomis). The samples were analyzed by gas liquid chromatography, and the results reported are expressed as normalized monoterpene composition. Optical isomers were not separated. The study covered (a) 19 pine species in California, (b) 86 pine hybrids and 26 parent species at the Pacific Southwest Research Station's Insitute of Forest Genetics, (c) 21 half sibling populations of Pinus ponderosa Dougl. ex Laws., (d) 56 full sibling populations of P. ponderosa, (e) interspecific and intraspecific pine grafts, (f) effects of procedural parameters, and (g) bioassay of resistance to Dendroctonus brevicomis. The results suggested that (a) these monoterpenes and associated hydrocarbons were primarily controlled by genes in pine xylem—hepane, undecane, α–pinene, ß–pinene, 3–carene, sabinene, myrcene, limonene, ß– phellandrene—and evidence strongly suggested a pair of additive alleles for each monoterpene that competes with each other for a fixed amount of a fivecarbon precursor; (b) all of these might also be produced by isomerization and possibly may be byproducts of biosynthesis of other monoterpenes; (c) the quantity of all these can be modified by several environmental factors often associated with forms of stress, and possibly by other minor genetic factors; an (d) these monoterpenes were not controlled by genes in pines but are probably the results of isomerization and byproducts of biosynthesis: α–thujene, nonane, camphene, γ–terpenene, ocimene, α–phellandrene, and terpinolene.