Phytophthora cinnamomi Rands, the causal pathogen of phytophthora root rot (PRR) of chestnut, is one of the main obstacles to growth of american chestnut [Castanea dentata (Marsh.) Bork.] in the southern part of its distribution. To facilitate introgression of PRR resistance of chinese chestnut (C. mollissima Blume) into a C. dentata genetic background, we assessed the disease resistance of 10 interspecific hybrid families derived from potentially resistant C. mollissima cultivars. Hybrid progeny were inoculated with P. cinnamomi in the nursery and assessed for root lesion severity after 1 year of growth. Asymptomatic plants were transplanted to a P. cinnamomi-positive orchard and evaluated for survival midway through the following growing season. During the nursery experiment, 8 of 10 hybrid families were not significantly different from susceptible C. dentata controls for average disease resistance scores. However, multiple asymptomatic individuals were identified in each of the eight families. Two of the 10 hybrid families were not significantly different from the resistant C. mollissima and C. henryi controls. In the P. cinnamomi-positive orchard, the prescreened hybrid families displayed a greater proportion of survivors than backcross families that had not been prescreened for P. cinnamomi resistance. Hybrid plants that have survived 2 years of growth in P. cinnamomi-infested potting media and soils represent an important step toward the production of genetically diverse chestnut populations in the southeastern United States that combine the PRR resistance of C. mollissima with the morphology and local adaptation of C. dentata.
M. Taylor Perkins, Anna Claire Robinson, Martin L. Cipollini and J. Hill Craddock
James Hill Craddock, R.J. Sauve, S.E. Schlarbaum, J. Skinner, R.N. Trigiano, M.T. Windham and W.T. Witte
Hand pollinations and honey bees were used to cross Cornus florida cultivars in a series of experiments investigating dogwood pollination biology from a breeding viewpoint and testing the use of insects (domestic honey bees and ladybug beetles as pollinators in dogwood breeding. Experiments were conducted to study possible incompatibility between dogwood cultivars and to determine if self-compatibility and self-fertility occur in Cornus florida. Since 1993, ≈200 seedlings have been produced by hand and insect-mediated pollinations. Honey bees can be used in dogwood breeding. Trees cross pollinated by ladybeetles had lower fruit set than trees cross pollinated by honey bees. Greenhouse forcing to accelerate anthesis and cold storage to delay the onset of bloom of container-grown trees can extend the dogwood breeding season effectively.