Crop phenology and floral induction in different Artemisia annua L. genotypes

Artemisia annua L. (sweet wormwood or artemisia), the only commercial source of the antimalarial artemisinin (ART), has genotypes with a wide range of ART concentrations and varying blooming periods. This makes the cross-pollination of high-ART genotypes difficult unless the flowering of selected parents is synchronized. In this study, we evaluated the phenological pattern of artemisia to establish a phenological scale that will allow successful cross-pollination and breeding. The scale was based on daily observations and photographs of the plant at specific time intervals and was divided into two distinct phases: the vegetative phase (with five stages) and the reproductive phase (with 12 stages). Although short days induce flowering, our experiments with Chinese and Vietnamese genotypes of artemisia demonstrated that genotypes from different geographic origins are better synchronized on both short days and low temperatures, with the Chinese genotype requiring only short days to flower and the Vietnamese genotype requiring short days and low/moderate temperatures to reach full flowering. We also noticed that Chinese plants flowering under short days can be reversed to the vegetative stage if plants are exposed to long photoperiod early enough. Finally, plants growing under long days, in the vegetative phase, have higher densities of glandular trichomes and higher concentrations of ART when compared to plants grown under short days and induced to flower. These observations suggest that the further from the inductive photoperiod the transplantation to the field occurs, the higher the concentration and yield of ART.