In vitro leaf-derived organogenesis and somaclonal variant detection in Humulus lupulus L

The exploitation of somaclonal variation potentially could be a valid strategy to overcome the depletion of hop intraspecific agrobiodiversity. To increase somaclonal variation induction, it is possible to resort to several strategies including a differentiated starting explant material such as leaves, roots and stems, an extended time in which cultures are maintained in vitro, and a wellbalanced cytokinin/auxin ratio. In this research, firstly, the influence of growth regulator type and concentration and the effect of the period of in vitro hop leaf culture (6, 12, and 18 wk) were investigated. Secondly, cytofluorimetric and Random Amplification of Polymorphic DNA (RAPD) analyses were carried out to verify the occurrence of somaclonal variation. Adventitious shoots were obtained in all media containing 6-benzylaminopurine (BAP) (except BAP at lowest concentration tested), with no influence detected by culture period. Mutants were detected among regenerants (16.8%) with more than half of the tetraploids obtained from medium containing the highest BAP concentration (35.55 mM). Mutants detected by RAPD analysis were independent of the medium composition and time in culture. A strong influence regarding explant was observed where nearly half of mutants obtained originated from cultured leaf tissues. Further studies are needed to characterize the field performance of mutants.