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2nd ISHS Hop Symposium, Melle, Belgium

A Temporary Immersion System for the Effective Micropropagation of Hop

The largest bottleneck for the genetic transformation of hop is the inefficiency of existing regeneration protocols. Successful hop transformation therefore requires large numbers of explants, is time consuming and labor intensive. We developed a fast and efficient shoot regeneration procedure for the ?US Tettnanger? cultivar, starting from green organogenic nodule clusters (GONCs). We induced GONCs under the sole influence of the hormone TDZ on internodal explants. Even though only 56% internodes produced GONCs, all of them were highly regenerative. In combination with a temporary immersion system (TIS), we produced on average 35 shoots per GONC in a single round of regeneration. Our overall regeneration efficiency therefore was 20-fold (35 shoots regenerating from a single GONC, 0.56 GONCs per explant), and compared to our previous report increased 30-fold. This increase could help overcome current limitations in biotechnological applications for hop. The use of a TIS further eliminated bi-weekly tissue transfers and thereby reduced labor and contamination problems. Our procedure, which works through de novo shoot induction via the callus route, seems to have high potential for the generation of virus-free hop material. It will also be useful for the production of large numbers of genetically transformed plants, for example in the arena of pathogen resistance, for improving flavor, or for the development of medicinal hops. Based on our improved regeneration procedure, we expect being able to increase Agrobacterium-based transformation efficiencies from currently 0.4% to 20%. Experiments to test this prediction are currently under way in our laboratory.