Originally published as Genetics Published Articles Ahead of Print on October 22, 2006.

Genetics, Vol. 174, 1775-1788, December 2006, Copyright © 2006
doi:10.1534/genetics.106.065144

Homeologous Recombination in Solanum lycopersicoides Introgression Lines of Cultivated Tomato

Michael A. Canady¹, Yuanfu Ji² and Roger T. Chetelat³

C. M. Rick Tomato Genetics Resource Center, Department of Plant Sciences, University of California, Davis, California 95616

³ Corresponding author: C. M. Rick Tomato Genetics Resource Center, Department of Plant Sciences, University of California, 1 Shields Ave., Davis, CA 95616.
E-mail: trchetelat{at}ucdavis.edu

A library of "introgression lines" containing Solanum lycopersicoides chromosome segments in the genetic background of cultivated tomato (Lycopersicon esculentum) was used to study factors affecting homeologous recombination. Recombination rates were estimated in progeny of 43 heterozygous introgressions and whole-chromosome substitution lines, together representing 11 of the 12 tomato chromosomes. Recombination within homeologous segments was reduced to as little as 0–10% of expected frequencies. Relative recombination rates were positively correlated with the length of introgressed segments on the tomato map. The highest recombination (up to 40–50% of normal) was observed in long introgressions or substitution lines. Double-introgression lines containing two homeologous segments on opposite chromosome arms were synthesized to increase their combined length. Recombination was higher in the double than in the single segment lines, despite a preference for crossovers in the region of homology between segments. A greater increase in homeologous recombination was obtained by crossing the S. lycopersicoides introgression lines to L. pennellii—a phylogenetically intermediate species—or to L. esculentum lines containing single L. pennellii segments on the same chromosome. Recombination rates were highest in regions of overlap between S. lycopersicoides and L. pennellii segments. The potential application of these results to breeding with introgression lines is discussed.

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