Comparison of restriction endonucleases and sources of probes for their efficiency in detecting restriction fragment length polymorphisms in lettuce (Lactuca sativa L.).

As a first step in developing a detailed genetic map of lettuce (Lactuca sativa L.), 156 cDNA and 123 genomic DNA clones of lettuce were compared for their efficiency to detect restriction fragment length polymorphism (RFLP) between four lines of lettuce. Polymorphism was detected 2.5 times more frequently with cDNA probes than random genomic probes. Less polymorphism was detected with cDNA clones homologous to single copy than with cDNA clones homologous to multiple copy DNA sequences. A lower percentage of polymorphism was detected with genomic DNA clones homologous to repetitive sequences than with other types of probes. Digests with each of nine restriction endonucleases were compared; increased polymorphism was not correlated with the presence of a CpG dimer in the recognition sequence of the restriction endonuclease. Digests with enzymes recognizing four base pairs, however, displayed RFLPs less frequently. The six pairwise comparisons of the four lettuce lines showed different frequencies of polymorphism which only approximately corresponded to genetic distances obtained from previous isozyme analyses.