The effects of explant source and hormone content on plant regeneration and induction of tetraploids in Humulus lupulus L.

Abstract

Shoot regeneration was induced after long-term culture of stem- and petiole-derived callus of Humulus lupulus cv. ‘Iunga’. The effects of explant type and plant growth regulators on the regeneration efficiency and polyploid induction were estimated. Callus initiated from stem fragments showed significantly higher shoot regeneration than that obtained from petioles. Both types of explants were able to regenerate shoots if cultured in the presence of auxin and cytokinin. The mean number of shoots per explant ranged from 6.2 to 21.8 for stem-derived callus and from 1.0 to 14.6 for petiole-derived callus. The highest number of shoots from stem-derived callus was obtained on Murashige and Skoog (MS) medium containing 14.23 μM zeatin riboside and 0.57 μM indole-3-acetic acid (IAA), while MS medium supplemented with 8.87 μM 6-benzylaminopurine (BA) and 0.57 μM IAA produced the highest shoot regeneration in petioles. Flow cytometry revealed that long-term callus cultures, over 23 wk old, led to DNA amplification and formation of tetraploids among the regenerated plants. However, there was a distinct inter-explant diversity in the frequency at which polyploid lines regenerated. The highest number of tetraploids, 9.4%, was obtained from petiole-derived callus, and the number of polyploids was clearly enhanced by the addition of IAA to the regeneration medium.