Analysis of nrDNA ITS Sequences in Ipomoea batatas and its Relative Wild Species

In this study, the internal transcribed spacer of nucleus ribosome DNA (nrDNA ITS) copies from Ipomoea batatas and its wild relatives were cloned and sequenced to analyze their phylogenetic relationships. For the first time, we report on the nrDNA ITS sequences isolated from I. batatas ‘Xushu18’ and its relative wild species (I. triloba (DOM), I. cordatotriloba (MEX), I. nil (PER), I. nil (JPN), I. hederacea Jacq. (USA), I. hederacea Jacq. (HK)), an interspecific hybrid 67-1 (I. batatas ‘Xushu18’ × I. hederacea Jacq.), and a backcross line (67-1 × I. batatas ‘Xushu18’). Analysis showed that the nrDNA ITS sequences ranged from 570 bp to 600 bp. Among them, the ITS1 fragments ranged from 185 bp to 209 bp, with GC content of 53.11%-61.83%; the ITS2 regions ranged from 214 bp to 226 bp, with GC content of 61.21%-72.89%; the 5.8S sequences were 165 bp, with GC content of 54.55%-55.76%. Furthermore, the informative sites of I. batatas and its wild relatives lay in the ITS1 and ITS2 regions; in contrast to other Ipomoea germplasms, there was a 6-8 bp deletion in the ITS2 of I. wrightii. Phylogenetic analysis revealed that I. batatas ‘Xushu18’ had closer phylogenetic relationships with the wild relatives of I. triloba, I. cordatotriloba, I. lacunosa, and I. trifida than I. wrightii, I. pes-tigridis, I. grandifolia, I. nil, I. hederacea, and I. purpurea. Moreover, the interspecific hybrid and the backcross line had closer phylogenetic relationships with I. batatas ‘Xushu18’, compared to I. hederacea.