Assessment of somaclonal variability in hop (Humulus lupulus L.) in vitro meristem cultures and clones by molecular methods

In vitro meristem tissue cultures are used for production of virus-free rootstocks of hop (Humulus lupulus L.). Because use of plant tissue cultures is associated with occurrence of somaclonal variability, we assessed somaclonal variability in hop meristem in vitro cultures before and after thermotherapy by different molecular methods (RFLP, RAPD, STS, ISSR and AFLP) and compared it with existing clonal variability of Osvald's clones 31, 72 and 114. No molecular differences were observed between mother plants and in vitro mericlones by RFLP and STS analyses. Amplified molecular differences were found in RAPD and ISSR products of one from five in vitromericlones cvs. Eroica (E5) and Southern Brewer (SB2), respectively. Similarities with mother plants were 0.965 and 0.913 (JSC), respectively. Specific amplified polymorphic products were found for every mericlone and mother plant in AFLP reactions and variability of DNA sequence ranged from 0.824 to 0.993 (JSC). This variability was very similar to determined intra-clonal variability within Osvald's clones 31, 72 and 114 by AFLP analysis. Inter-clonal variability of DNA sequence was exactly higher than intra-clonal variability of DNA sequence in these clones. The molecular differences between Osvald's clone 72 normal and meristem derived were not verifiable. Thermotherapy increased frequency of molecular changes, since amplified differences were found in 14 from 20 in vitro mericlones of cv. Eroica, in 6 from 11 in vitro mericlones of cv. Yeoman and in 15 from 23 in vitro mericlones of cv. Southern Brewer by RAPD and ISSR analyses.