Plant Genome I Conference
Town & Country Conference Center, San Diego, CA, November, 1992.
PG-I: 79pg1
RAPD MAPPING AND TREE IMPROVEMENT
D. Grattapaglia 2, J. Chaparro 3, P. Wilcox 1, S. McCord 1,
D. Werner 3, H. Amerson 1, S. McKeand 1, F. Bridgwater 1, L
McIntyre 2, R. Doerge 4, B. Weir 4, R. Whetten 1, D.
O'Malley 1, & R. Sederoff 1,2. Departments of Forestry 1,
Genetics 2, Horticulture 3,& Statistics 4 . North Carolina State
University, Raleigh, N.C. 27695-8008.
Time is the major barrier to genetic improvement of forest
trees. Forest trees have long generation times and many
commercially important traits are differentially expressed in
juvenile and mature stages. In comparison with annual crops,
marker aided breeding has greater potential for forest trees
because of the difficulty of evaluating genetic potential
when trees are in the juvenile state. Forest trees generally
have high levels of genetic heterogeneity and markers have high
levels of linkage equilibrium. Few extended pedigrees are
available, therefore it is useful to obtain detailed maps for
individual trees to apply molecular markers to specific breeding
problems. RAPD markers made possible the genomic mapping of
single trees using the pine megagametophyte, which is composed
of maternally derived haploid tissue. A moderate density
genetic map for loblolly pine was constructed (230 markers: 9cM
average distance). The advantages of mapping with RAPD markers
in the conifer haploid megagametophyte can be extended to mapping
in diploids. RAPDs can be used in diploids if informative
markers are selected using a pseudotestcross strategy. A wide
full sib cross between two closely related species of Eucalyptus
was screened for RAPD markers where one parent is heterozygous
and the other is null for specific markers, analogous to a
testcross. In this way, two maps were generated simultaneously
for both diploid parents (501 markers; 8cM average). In peach,
bulked segregant analysis was used for targetted mapping around
known loci. Markers were identified flanking a morphological
trait and an isozyme locus. Genetic markers flanking traits
expressed at maturity should be valuable for early selection of
marketable traits, such as nectarine in variety conversion.
Genetic markers for morphological traits can be directly a
efficiently identified in F2 breeding populations. Two projects
in progress will be discussed that attempt to dissect complex
traits in loblolly pine. Within half sib analysis will be used
to dissect quantitative components (QTLs) for early height growth
and a full sib crosses will test an oligogenic model for
resistance of loblolly pine to fusiform rust disease.
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