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Random amplified polymorphic DNA (RAPD) markers were analyzed in parents and progeny of four sweetpotato crosses. An average of 69 primers were tested and 23.5% produced well resolved polymorphic banding patterns. Each polymorphic primer had an average of 1.9 polymorphic bands resulting in 0.45 polymorphic fragments per primer tested. Phenotypic segregation ratios of 88% of polymorphic fragments fit those expected for hexaploid Mendelian inheritance. Numbers of linked polymorphic fragments and numbers of linkage groups were 13 and 5 for Cross A, 0 and 0 for Cross B, 23 and 3 for Cross C and 16 and 6 for Cross D. Those results indicated that RAPD markers have potential for a genetic linkage map in sweetpotato; however, many primers must be screened.
Parents and progeny of four biparental crosses were analyzed for RAPD marker segregation. A range of 57 to 122 primers were tested in each cross, with an average of 82. Average polymorphic primers and band numbers were 22 and 53, respectively. Of the 212 polymorphic bands, phenotypic segregation ratios were as follows: 133 fitted 1 dominant: 1 recessive, 58 fitted 3:1, 11 fitted ratios 4:1 to 19:1 and 10 were distorted. The 1:1 and 3:1 ratios were expected for either diploid or hexaploid segregation, and the 4:1 to 19:1 are exclusive to hexploid. A total of 14 pairs of markers were linked at map distances ranging from 2.1 to 36.5 cM. One common pair of linked markers was found in two separate crosses.
RAPD marker analyses were completed on parents and progeny of two sweetpotato [Ipomoea batatas (L.) Lam.] crosses to determine the feasibility of genetic linkage map construction. A total of 100 primers was tested and 96 produced amplified genomic DNA fragments. The average number of polymorphisms per primer was 0.69. A total of 134 polyphorphic markers was observed and 74 (60%) segregated 1 band present : 1 band absent as needed for use in genetic linkage mapping of polyploids. The 60% of RAPD markers that segregated 1:1 shows that genetic linkage mapping of the hexaploid sweetpotato by RAPD marker analysis is feasible. Linkage was determined for all markers that segregated 1:1 and five pairs of linked markers were found. These were the first linked molecular markers found in sweetpotato and they show that construction of a genetic linkage map is feasible. A genetic linkage map will be a valuable tool to assist in genetic improvements.