Tomato chromosome 1: High resolution genetic and physical mapping of the short arm in an interspecific Lycopersicon esculentum x L-peruvianum cross

A detailed map of part of the short arm of chromosome 1 proximal to the Cf-4/Cf-9 gene cluster was generated by using an F-2 population of 314 plants obtained from the cross between the remotely related species Lycopersicon esculentum and L. peruvianum. Six markers that cosegregate in an L. esculentum x L. pennellii F-2 population showed high recombination frequencies in the present interspecific population, spanning an interval of approximately 13 cM. Physical distances between RFLP markers were estimated by pulsed field gel electrophoresis of high-molecular-weight DNA and by identifying YACs that recognized more than one RFLP marker. In this region 1 cM corresponded to 55-110 kb. In comparsion with the value of 730 kb per cM averaged over the entire genome, this reflects the remarkably high recombination frequencies in this region in the hybrid L. esculentum x L. peruvianum progeny population. The present data underline the fact that recombination is not a process that occurs randomly over the entire genome, but can vary dramatically in intensity between chromosomal regions and among populations.