Hybridization among several North American firs. I. Crossability

Controlled pollinations were conducted in spring of 1980, 1981, and 1982 to determine crossability among five species and varieties of Abies in the Balsameae section and white fir (A. concolor (Gord. and Glend.) Lindl.) from section Grandes. Trees representing eastern balsam fir populations (A. balsamea (L.) Mill.), Fraser fir (A. fraseri (Pursh) Poir.), bracted balsam fir (A. balsamea var. phanerolepis Fern.), and white fir were used as female parents and were control pollinated with pollen from two populations each of balsam fir. Fraser fir, and subalpine fir (A. lasiocarpa (Hook.) Nutt.), and one population each of bracted balsam and white firs. Based on viable seed production, eastern balsam × Fraser fir and reciprocals, Fraser × bracted balsam fir and reciprocals, and bracted balsam × subalpine fir were fully crossable. The complete crossability of these taxa suggest that geographic rather than genetic isolation is responsible for their taxonomic separation. Although bracted balsam × balsam fir (Vermont) was fully crossable, the reciprocal cross exhibited partial incompatibility which may be sufficient to maintain the integrity of these two sympatric taxa. Crosses involving white fir and balsam fir from a Minnesota population as male parents yielded a relatively low percentage of viable seed. Those involving white fir probably reflect low intersectional crossability, whereas those with the Minnesota balsam fir population may have been the result of either low pollen viability or low crossability.