Published in Probe Volume 3(1-2): January-June 1993
Dr. David B. Neale, Molecular Geneticist
Institute of Forest Genetics
USDA, Forest Service
Albany, CA
Forest trees present many unique and interesting challenges for researchers constructing genetic maps. For example, in forest trees, inbreeding is generally not possible, multigeneration pedigrees are rare, generation times are long, genome sizes are large, and resources are limited.
Recently forest tree genome researchers met to discuss approaches to mapping in trees and to report on the progress of various mapping projects. The meeting was the first Forest Tree Genome Mapping Workshop, one segment of the Plant Genome I Conference held in San Diego, CA. Approximately 80 persons attended the workshop, organized by David Neale (Institute of Forest Genetics, Albany, CA). Fourteen invited speakers participated.
Progress Reports
The workshop opened with a progress report by Toby Bradshaw (University of Washington) on the mapping of Populus (P. trichocarpa x P. deltoides). The map will be used to identify quantitative trait loci (QTL) infuencing growth and form characteristics. Bradshaw noted that severe segregation distortion was observed at one locus, which was attributed to a recessive lethal allele in the P. trichocarpa female parent.
Dario Grattapaglia (North Carolina State University, presented by Ron Sederoff) reported on a 548 RAPD marker map in hybrid Eucalyptus (E. grandis x E. urophylla) based on a pseudo-testcross mapping strategy. This approach avoids the loss of information associated with dominant markers in diploid mapping populations. Andrew Groover (Institute of Forest Genetics) presented preliminary results on the mapping of QTL's influencing wood specific gravity in a 3-generation loblolly pine (Pinus taeda) pedigree.
In another presentation, John Carlson (University of British Columbia) reported on RAPD mapping in white spruce (Picea glauca) and localization of rDNA loci using fluorescence in situ hybridization (FISH). Michael Devey (Institute of Forest Genetics and CSIRO) reported on a novel method to map a dominant gene for resistance to white pine blister rust (Cronartium ribicola) in sugar pine (Pinus lambertiana). His strategy employed bulked segregation analysis of haploid megagametophytes from a mother tree heterozygous for the dominant resistance gene. Ten RAPD markers were very closely linked to the resistance gene.
In addition, Keith Hutchison (University of Maine) described the method of single-stranded conformational polymorphism of RAPD fragments to reveal codominant markers in larch and a method to detect variation by PCR from single pollen grains. Warren Nance (Forest Service) reported on the construction of RAPD maps in slash pine (Pinus eliottii) and automation technology for large-scale mapping projects. David O'Malley (North Carolina State University) presented a RAPD map for loblolly pine based on haploid segregations from a single mother tree. A method to map QTL's in open-pollinated families was also presented. Dave Harry (Institute of Forest Genetics) described approaches to developing codominant PCR-based markers for trees to avoid the limitations imposed by RFLP's and RAPD's. Gavin Moran (CSIRO) reported on mapping in Monterey pine (Pinus radiata) and Eucalyptus nitens in Australia.
Statistical Problems
The second part of the workshop addressed statistical problems specifically related to linkage mapping, QTL mapping, and marker breeding in forest trees.
Steve Knapp (Oregon State University) discussed linkage mapping in outbreeding populations; Tom Mitchell-Olds (University of Montana) addressed similar issues related to QTL mapping. Claire Williams (Weyerhaeuser Company) described how molecular marker information might be incorporated into a loblolly pine breeding program.
Database Development
The last part of the workshop focused on the development of a genome database for forest trees. Brad Sherman (Institute of Forest Genetics) presented an on-line demonstration of APtDB, a Pinus taeda database. He showed how forest tree genome researchers could contribute data to the database and how it could be accessed by users through the Internet.
1994 Workshop
Plans are underway to hold a second workshop at the Plant Genome II meeting in early 1994. Low-density maps have just been completed for a few of the major species. It is expected that by the next meeting many more maps will have been completed, QTL's for important traits will have been identified, and numerous other applications of molecular markers and maps will be commonplace in forest genetics research.