Efficient production of viroid-free German hops using meristem culture and M-bridge technique

Hop (Humulus lupulus L.) is a critical component of the brewing industry, contributing to the flavor, aroma, and stability of beer.
However, viroid infections, particularly citrus bark cracking viroid (CBCVd) and hop stunt viroid (HSVd), pose significant threats to hop cultivation, leading to reduced yield and quality.
Additionally, hop latent viroid (HLVd) has been shown to diminish alpha acid concentrations and alter terpene profiles in some aroma hop cultivars.
In this study, we developed an efficient protocol for producing viroid-free German hops using meristem culture combined with the M-bridge technique.
Two German hop cultivars, ‘Callista’ and ‘Tettnanger’, were sterilized, dissected under a binocular microscope, and cultivated in liquid Murashige and Skoog (MS) medium supplemented with B5 vitamins, 0.1 mg L^‑1 indole-3-acetic acid, 0.1 mg L^‑1 gibberellic acid, and 0.5 mg L^‑1 6-benzylaminopurine.
The use of the M-bridge technique, where “M” refers to the folding of the filter paper, allowed slow absorption of liquid nutrients without damaging the fragile meristem, significantly increased the survival rate of meristematic explants.
For ‘Callista’ and ‘Tettnanger’, the survival rates in a standard semi-solid medium were 21.9 and 24.4%, respectively.
In contrast, using the cotton bridge technique achieved 92.9 and 88.9%, and the liquid M-bridge medium resulted in 96.3 and 94% survival, respectively.
After six months of cultivation, plantlets were tested for viroid presence by RNA extraction and RT-qPCR, confirming the elimination of viroids.
After confirmation of viroid-free status, plantlets underwent root treatment with 1.5% Previcur^® fungicide, were transplanted into autoclaved soil, and grown under controlled conditions for acclimatization.
Following this, all ‘Callista’ and ‘Tettnanger’ plants were tested for viroids.
All ‘Tettnanger’ plants retained HLVd, however seven ‘Callista’ plants were free of all tested viroids.
This protocol provides a reliable and effective method for producing viroid-free hops, safeguarding the future of hop cultivation in Germany.

International Symposium on Biotechnological Tools in Horticulture

S. Jagani, M.H. Hagemann, U. Born, S. Hegele

meristem culture, M-bridge technique, hop latent viroid, RNA extraction, RT-qPCR, viroid elimination, hop tissue culture, hop cultivation

https://doi.org/10.17660/ActaHortic.2026.1454.13