Chemical and physical pre-treatments to improve in vitro seed germination of Humulus lupulus L., cv. Columbus

The most widespread breeding method for hop (Humulus lupulus L.), based on the selection of interesting genotypes within segregating progenies, is a time consuming process, requiring no less than 8-10 years. The process is further slowed down by the very low germination percentage of hop seeds. This study provides an efficient protocol to obtain, in a relatively short time and out of the natural season, a high number of" hop seedlings, cv. "Columbus, evaluating the influence of several pre-treatments (timing of chemical scarification, cold stratification, imbibition in water and in gibberellic acid solutions) on in vitro hop seed germinative power; moreover, the application of a sex-linked molecular marker allowed the precocious individuation of seedling gender. At the end of the study, an efficient protocol to obtain a high in vitro hop seed germination percentage was set up, resorting to a chemical scarification with sulfuric acid and the use of gibberellic acid; moreover, in a relatively short time, it was possible to determine the sex ratio of cv. "Columbus" obtained seedlings, that was around 70% of females and 30% of males. Further studies will be carried out to increase the final germination percentage and to individuate a sex-linked marker, based on morphological or physiological characters.