Chromosome pairing in Solanum commersonii- S. tuberosum sexual hybrids detected by commersonii-specific RAPDs and cytological analysis

Abstract

BC1 pentaploid to near-pentaploid Solanum commersonii-S. tuberosum genotypes obtained from 3x × 4x crosses have been used for cytological and molecular studies on chromosome pairing and meiotic recombination. Microsporogenesis analysis at diakinesis revealed that chromosomes had a tendency to pair as bivalents, though multivalents were also observed in many cells. Meiosis resulted in a high production of tetrads and pollen stainability was high, ranging from 34.5% to 92.1%. DNA from S. commersonii and S. tuberosum was amplified with 87 decameric primers, resulting in the identification of 26 S. commersonii-specific RAPDs. The analysis of these RAPDs in BC1 genotypes showed that a number of commersonii-specific markers was present in all BC1 genotypes. On the other hand, markers which were missing in one or more of the BC1 genotypes suggested that in some cases homoeologous pairing occurred. Two linked markers were transmitted together in all of the BC1 genotypes except two. This provided evidence that a recombination event between these markers occurred during megasporogenesis of their triploid parents. The possibility of demonstrating other recombination events is discussed.Key words: triploid, pentaploid, microsporogenesis, gene flow, recombination.