Species-specific sequences in the genus Solanum: identification, characterization, and application to study somatic hybrids of S. brevidens and S. tuberosum.

To aid in the identification and analysis of somatic hybrids between potato (Solanum tuberosum, dihaploid line PDH 40) and the non tuber-bearing wild species S. brevidens, a series of species-specific repetitive DNA sequences have been isolated. This was accomplished by making libraries of HaeIII-digested total DNA of S. tuberosum and S. brevidens, by cloning fragments into the SmaI site of plasmid pUC18 and transforming them into E. coli (JM83). The S. brevidens library consisted of 1,000 recombinant clones, and that of S. tuberosum, 700. Nitrocellulose filters with recombinant clones were hybridised to nick-translated total DNA of S. brevidens and also S. tuberosum, and, following autoradiography, clones that hybridised strongly to the DNA of only one of the species were chosen. Two highly repeated S. brevidens clones (pSB1, 400 bp and pSB7,210 bp), one highcopy-number s. tuberosum clone (pST10, 200 bp) and one low-copy-number sequence of S. tuberosum (pST3, 1.5 kbp) were selected for further analysis by Southern hybridisation to digested total DNA. Clone pSB7 gave a ladder pattern on hybridisation to EcoR1-digested total DNA of S. brevidens, with signals at multiples of 200 bp DNA. Using these probes it was possible to verify the hybridity of putative hybrids of dihaploid S. tuberosum and S.brevidens, and to confirm by Southern analysis and by slot blots the parental genome dosage of hexaploid hybrids (two s. brevidens: one S. tuberosum, and vice-versa). The S. tuberosum-specific probe, pSTIO, hybridised with DNA of three other tuber-bearing wild species (S. hjertingii, S. capsicibaccatum and S. berthaultii). A squash-blot procedure was developed using the probes that would allow early identification of somatic hybrid callus. There are a number of useful applications of such species-specific probes in the identification and analysis of somatic hybrids.