Plant & Animal Genome VI Conference

W104

COMPREHENSIVE INTROGRESSION OF THE Solanum lycopersicoides GENOME INTO TOMATO VIA SEGMENTAL SUBSTITUTION LINES

C.M. Rick Tomato Genetics Resource Center, Dept. of Vegetable Crops, University of California, Davis, CA 95616

In order to expand the gene pool available to tomato breeders and geneticists, we are attempting to introgress whole chromosomes and/or chromosome segments from the related wild nightshades Solanum lycopersicoides and S. sitiens. A male-fertile F₁ L. esculentum x S. lycopersicoides hybrid enabled, for the first time, extensive backcrossing to tomato at the diploid level (Euphytica 95:99-108). Recombination in the BC₁ generation was relatively normal over most of the genome, despite reduced pairing in the F₁; the resulting genetic map comprised 1216 centiMorgans -- comparable to existing maps from more closely related Lycopersicon species. However, in later backcross generations, recombination in certain regions was reduced 100 fold or more. A group of approx. 300 backcross inbred families (BC₂F₅) generation were surveyed for introgressed S. lycopersicoides markers. From this group were selected a subset of 71 homozygous lines, each possessing a unique S. lycopersicoides segment (average length=23cM), which together cover approx. 70% of the donor genome. An additional 26 heterozygous (segregating) introgressions (average length=41cM) were also selected to provide complete genome representation. Each line contains on average 1.2 homozygous introgressions and 1.7 heterozygous ones, with an average recurrent parent genome proportion of 97%. Barriers to the fixation of certain genetic markers were encountered, such as skewed transmission, suppressed recombination, male-sterility (particularly in homozygotes), lack of vigor, and other defects. Single-segment introgressions are currently being identified in BC₃F₂ families. Rich in phenotypic and genotypic variation, these lines are expected to be useful for breeding and genetic studies directed at disease resistances (including CMV, Botrytis cinerea, Xanthomonas campestris pv. vesicatoria, etc.), cold tolerance, and other traits identified in this wild relative.