Isolation of molecular markers for tomato (L. esculentum) using random amplified polymorphic DNA (RAPD).

A new DNA polymorphism assay was developed in 1990 that is based on the amplification by the polymerase chain reaction (PCR) of random DNA segments, using single primers of arbitrary nucleotide sequence. The amplified DNA fragments, referred to as RAPD markers, were shown to be highly useful in the construction of genetic maps ("RAPD mapping"). We have now adapted the RAPD assay to tomato. Using a set of 11 oligonucleotide decamer primers, each primer directed the amplification of a genome-specific "fingerprint" of DNA fragments. The potential of the original RAPD assay to generate polymorphic DNA markers with a given set of primers was further increased by combining two primers in a single PCR. By comparing "fingerprints" of L. esculentum, L. pennellii, and the L. esculentum chromosome 6 substitution line LA1641, which carries chromosome 6 from L. pennellii, three chromosome 6-specific RAPD markers could be directly identified among the set of amplified DNA fragments. Their chromosomal position on the classical genetic map of tomato was subsequently established by restriction fragment length polymorphism (RFLP) linkage analysis. One of the RAPD markers was found to be tightly linked to the nematode resistance gene Mi.