TOMATO CHROMOSOME-1 - HIGH-RESOLUTION GENETIC AND PHYSICAL MAPPING OFTHE SHORT ARM IN AN INTERSPECIFIC LYCOPERSICON-ESCULENTUM X LYCOPERSICON-PERUVIANUM CROSS

A detailed map of part of the short arm of chromosome 1 proximal to th e Cf-4/Cf-9 gene cluster was generated by using an F-2 population of 3 14 plants obtained from the cross between the remotely related species Lycopersicon esculentum and L. peruvianum. Six markers that cosegrega te in an L. esculentum x L. pennellii F-2 population showed high recom bination frequencies in the present interspecific population, spanning an interval of approximately 13 cM. Physical distances between RFLP m arkers were estimated by pulsed field gel electrophoresis of high-mole cular-weight DNA and by identifying YACs that recognized more than one RFLP marker. In this region 1 cM corresponded to 55-110 kb. In compar sion with the value of 730 kb per cM averaged over the entire genome, this reflects the remarkably high recombination frequencies in this re gion in the hybrid L. esculentum x L. peruvianum progeny population. T he present data underline the fact that recombination is not a process that occurs randomly over the entire genome, but can vary dramaticall y in intensity between chromosomal regions and among populations.