Genetics, Vol. 166, 1405-1418, March 2004, Copyright © 2004

Genetics of Postzygotic Isolation in Eucalyptus: Whole-Genome Analysis of Barriers to Introgression in a Wide Interspecific Cross of Eucalyptus grandis and E. globulus

Alexander A. Myburga,b, Claus Voglc, A. Rod Griffind, Ronald R. Sederoffa,b, and Ross W. Whettena
a Department of Forestry, North Carolina State University, Raleigh, North Carolina 27695,
b Department of Genetics, North Carolina State University, Raleigh, North Carolina 27695,
c Department of Computer Science, University of California, Riverside, California 92521
d CRC for Sustainable Production Forestry and School of Plant Science, University of Tasmania, Hobart, 7001, Australia

Corresponding author: Alexander A. Myburg, Forestry and Agricultural Biotechnology Institute, University of Pretoria, Pretoria, 0002, South Africa., zander.myburg{at}fabi.up.ac.za (E-mail)

Communicating editor: O. SAVOLAINEN

The genetic architecture of hybrid fitness characters can provide valuable insights into the nature and evolution of postzygotic reproductive barriers in diverged species. We determined the genome-wide distribution of barriers to introgression in an F1 hybrid of two Eucalyptus tree species, Eucalyptus grandis (W. Hill ex Maiden.) and E. globulus (Labill.). Two interspecific backcross families (N = 186) were used to construct comparative, single-tree, genetic linkage maps of an F1 hybrid individual and two backcross parents. A total of 1354 testcross AFLP marker loci were evaluated in the three parental maps and a substantial proportion (27.7% average) exhibited transmission ratio distortion ({alpha} = 0.05). The distorted markers were located in distinct regions of the parental maps and marker alleles within each region were all biased toward either of the two parental species. We used a Bayesian approach to estimate the position and effect of transmission ratio distorting loci (TRDLs) in the distorted regions of each parental linkage map. The relative viability of TRDL alleles ranged from 0.20 to 0.72. Contrary to expectation, heterospecific (donor) alleles of TRDLs were favored as often as recurrent alleles in both backcrosses, suggesting that positive and negative heterospecific interactions affect introgression rates in this wide interspecific pedigree.




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