HOMOEOLOGOUS PAIRING AND RECOMBINATION IN Solanum lycopersicoides MONOSOMIC ADDITION AND SUBSTITUTION LINES IN TOMATO

Department of Vegetable Crops, University of California, Davis, CA 95616

Introgression of S. lycopersicoides chromosome segments into tomato genome was shown previously to cause recombination suppression. In this study, we chose S. lycopersicoides chromosome 7, 8 and 10 monosomic alien addition lines (MAALs) and substitution lines (SLs) in a tomato background to further characterize homoeologous pairing and recombination. Genomic in situ hybridization (GISH) was used to differentiate S. lycopersicoides chromosomes from those of tomato. In the MAALs, three different configurations were formed from the single S. lycopersicoides chromosome and its two tomato homoeologues in meiotic diakinesis/metaphase chromosome spreads: trivalent (III), bivalent + univalent (II + I), and 3 univalents (3I). Among the second category of configuration (II + I), the univalent was from S. lycopersicoides most of the time (90.9% - 99.5%), indicating preferential pairing between homologues. In the SLs, homoeologous chromosomes paired at much higher rates (> 27.3%) due to the absence of homologous partners. Genome-wide analysis of chromosome pairing revealed an increase in the average achiasmate arm frequency for both MAALs and SLs. RFLP analysis of the progeny confirmed that homoeologous recombination is greatly suppressed, particularly on chromosome 10, and more so in MAALs than corresponding SLs.