Genetics of western white pine

Abstract

More than 20 years of investigation on the inheritance of white pine blister rust (Cronartium ribicola) disease resistance, growth, and\r\nother features of the paleobotany, flowering, seed yield, and inbreeding of western white pine (Pinus monticola) are summarized. Megafossil collections indicate that the progenitor of P. monticola (the fossil species P. wheeleri) has been present in and around the present distribution of P. monticola since the early Pliocene to mid-Eocene eras, and that the species has withdrawn into four western North American subpopulations. Special significance is placed upon three megafossil cone collections from eastern Siberia, authoritatively identified as P. monticola. These collections indicate that P. monticola has had opportunity for geneexchange with other Asiatic white pines thathave evolved near the gene-center for C. ribicola. P. monticola is monoecious, precociously female as early as age 7 and remaining so through age 20. Under wide spacing in a cultivated, irrigated, and fertilized seed orchard, grafts produced nine cones per tree 12 years after grafting; in a comparable arboretum seedlings produced 4 ½ cones at age 11, and 20 cones at age 18. Anthesis ( ♂ ) and receptivity ( ♀ ) are simultaneous, with ample overlap for self-pollination.\r\nLong-term average yields for 25-to 70-year-old trees are 28 cones; seed produced by these cones include 104 filled seed per wind-pollinated cone, 88 filled seed per controlled cross-pollinated cone and 47 filled seed per self-pollinated cone. Yields vary greatly between mother trees, localities, and seed years. Selfing results in lower cone and seed yields, and a growth reduction of 30 to 40 percent below that of outcrossed progenies. Needle bundles and cuttings from young trees can be rooted with fair to good success. Greenhouse grafting is highly successful, but in \r\nnorthern Idaho field grafting meets with scant success. P. monticola appears to be noncrossable with P. balfouriana and P. aristata of Subsection Balfourianae, but with at least three species of Subsection Cembrae, sound seed of unverified hybridity have been produced repeatedly. Within Subsection Strobi, repeated crossings with six other species have been successful, but repeated crossings with P. armandii/ and P. lambertiana have failed. Thus there is good prospect for obtaining white pine blister rust\r\nresistance-genes from resistant Eurasian species like P. cembra, P. sibirica, P. koraiensis, P. griffithii and P. peuce. Growth of individual hybrids varies widely depending on the particular parental combinations. The genetic load of P. monticola includes deleterious recessive genes for albinism, dwarfing, curly needles, and a variety of chlorophyll deficiencies. Monoterpenes are under strong genetic control. Variation in growth associated with elevation of seed source appears to occur, especially at the extreme upper and lower elevations. Heritability of height growth is low (5 to 30 percent); heritability of blister rust resistance is high (65 + percent). Four races of C. ribicola characterized by foliage lesion types are recognized, and several recessive and dominant resistance-genes are either recognized or hypothesized. Relative abundance and variety of white pine\r\nblister rust resistance factors present in P. monticola strengthens the hypothesis that P. monticola and C. ribicola have made contact in the past, or that gene-exchange has occurred between P. monticola and resistant Asiatic white pines. Breeding for blister rust resistance is eminently possible. A first-stage program for mass-producing partially resistant F₂ seed is now in the seedling-seed orchard planting stages; a second-stage program has been started for the purpose

Citation

Bingham, R. T.; Hoff, R. J.; Steinhoff, R. J. 1971. Genetics of western white pine. Res. Pap. WO-RP-012. Washington, DC: U.S. Department of Agriculture, Forest Service. 18 p