Morphological and genetic analysis of inflorescence and flower development in hemp (Cannabis sativa L.)

Hemp (Cannabis sativa) is one of the oldest cultivated crops, and its myriad of uses have fascinated humans for millennia. In contemporary agriculture, the seeds are used for high-quality oil, human food, and nutritional supplements. From female inflorescences, secondary compounds (cannabinoids, terpenes, and flavonoids) are isolated that are implicated to have a wide range of medicinal applications. These elements provide hemp with significant market and research value and emphasise the need to thoroughly understand reproductive development in hemp. Here, we present a detailed morphological and molecular analysis of hemp inflorescence and flower development of the cultivar FINOLA. Hemp is unusual among flowering plants as it is dioecious, i.e. develops male and female plants. We define eight landmark events in male and female flower development and show that developmental differences between male and female plants extend beyond floral morphology, additionally comprising inflorescence structure as well as flowering time. Further, we demonstrate that the time of activation of key reproductive developmental regulators is significantly different in male and female hemp plants. Our comparison of male and female hemp plants shows that developmental pathways diverge very early, already at the two-leaf stage, laying a basis for further exploration into the genetics of sex determination of C. sativa.