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

Authors: MARCHESE, JOS´E - Federal University Of Technology - Parana; Ferreira, Jorge; MORAES, RITA - University Of Mississippi; DAYAN, FRANK - University Of Colorado; RODRIGUES, MICHELLE - Federal University Of Technology - Parana; JAMHOUR, JORGE - Universidade Federal Do Parana; DALLACORTE, LUCAS - Federal University Of Technology - Parana

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2022
Publication Date: 12/15/2022
Citation: Marchese, J.A., Ferreira, J.F., Moraes, R.M., Dayan, F.E., Rodrigues, M.F., Jamhour, J., Dallacorte, L.V. 2022. Crop phenology and floral induction in different Artemisia annua L. genotypes. Industrial Crops and Products. https://doi.org/10.1016/j.indcrop.2022.116118.
DOI: https://doi.org/10.1016/j.indcrop.2022.116118

Interpretive Summary: Sweet wormwood (artemisia), the only commercial source of the antimalarial artemisinin, presents plants with a wide range of artemisinin concentrations and varying blooming times in the same species. The cross-pollination of desired clones of different cultivars of artemisia to achieve plants with high artemisinin is only possible by synchronizing the flowering of target parent plants. This study evaluated the phenological pattern of artemisia from Chinese and Vietnamese origins to establish a phenological scale for the plant, with the main goal of understanding artemisia flowering pattern and to allow successful cross-pollination and breeding. This scale was based on daily observations and photographs of the plant at specific time intervals. The codes for flower development were assigned a scale from 1 to 17 and the results were presented in a table with these codes, descriptions, and pictures of flowering stages. The scale for the phenological development of A. annua was partitioned in two distinct phases: vegetative phase (with five stages) and reproductive phase (with 12 stages). The most important stages in this phenological scale are stage 04, critical for nitrogen application; end of stage 05 (end of vegetative development), recommended for artemisinin extraction; stage 08-09 - essential oil extraction; stage 09 - pollen collection for outcrossing, and stage 14 - seed harvest. Regarding flowering induction, our experiments showed that A. annua genotypes from different geographic origins flowered at different times even under short days, and that low temperature helped them synchronize their flowering. We also showed for the first time that flowering induced by short-day photoperiod can be reversible if plants are placed back under long photoperiod. This work contains important phenological information for plant breeder to achieve the successful outcrossing of selected artemisia clones that present different photoperiod requirements for flowering. Successful breeding will lead to plants with higher artemisinin yields per plant and per cultivated area benefiting growers of this medicinal crop who depend on high-artemisinin plants to secure their profits.

Technical Abstract: 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.