Phenological phases of flowering in hop (Humulus lupulusL.) and theircorrespondence with microsporogenesis and microgametogenesis

Hop (Humulus lupulus L.) suffered, as many other crops, a shrinkage of its intraspecific agrobiodiversity. Biotechnological methods of breeding would offer new opportunities to produce improved varieties with interesting phytochemical profiles and adaptable to the challenging conditions of climate change. Doubled haploid (DH) technology could be a useful tool to increase hop agrobiodiversity but, unfortunately, there is a complete lack of information about hop flower biology. For this reason, the main aim of this work is the study of the different phenological phases of flowering in hop and the corresponding developmental stages of microspores/pollen grains contained therein. The results obtained allowed the identification of morphological markers (anther and flower bud length), easy and fast to measure, that would speed up the selection of flower buds containing the highest percentage of vacuolated microspores and young pollen, the stages considered in most species as the most responsive to androgenesis. A further result, derived from the flower bud and anther microscopical observation, evidenced the increase of lupulin glands on bud and anther surface as the bud proceeds in development from microsporogenesis to microgametogenesis.