Toward the construction of a molecular map of cassava (Manihot esculenta Crantz): comparison of restriction enzymes and probe sources in detecting RFLPs.

The construction of a detailed genetic map of cassava (Manihot esculenta Crantz), classified as a tetraploid species, depends on the ability of cloned sequences to detect polymorphisms. As a first step in developing this map, 200 cloned nuclear sequences generated with different restriction enzymes were hybridized to total digested DNA from eleven cultivated lines and one wild Manihot species, M. aesculifolia. Polymorphism was detected less frequently with both BamHI and EcoRI genomic probes than with PstI, HindIII and XbaI genomic probes. DNA digested with HpaII, DraI and TaqI displayed less polymorphism, whereas DNA digested with EcoRI and EcoRV displayed more polymorphism like that found in lettuce, rice and tomato (Landry et al., 1987; McCouch et al., 1988; Miller and Tanksley, 1990). Four-cutter restriction enzymes displayed less frequency of polymorphism when compared with six-cutter restriction enzymes. Polymorphism displayed by DraI was extremely low, indicating that regions rich in adenine and thymine may not be hot spots for mutation in cassava. Polymorphism detected between cultivated genotypes and M. aesculifolia was dramatically higher than that found among cultivated genotypes.