Effects of watering interval, timing and duration of water stress on the yield and pyrethrins content of pyrethrum plants

Effects of watering interval, timing and duration of water stress on the yield and pyrethrins content of pyrethrum plants Pyrethrum (Tanacetum cinerariifolium L.) is regarded as a crop with high tolerance to water stress. There is however a lack of quantitative information on the impact of water stress on flower biomass, pyrethrins synthesis, and the accumulation these actives in the flowers during key stages of flower development. There is some evidence that water stress reduces pyrethrum flower dry matter (DM) and pyrethrins yield, yet little is known of the sensitivity of the plant to this. The aim of this trial was to determine the effect of both the severity and duration of water stress at key stages of flower development on yield and pyrethrins content of pyrethrum. The differences in water availability during the flowering phase of crops may explain some variation in flower and pyrethrins yield noted between seasons over the past decade. Drought stress was investigated by conducting pot trials under controlled conditions at the Horticulture Research Centre, University of Tasmania, Hobart, from August to December 2009. Two experiments were conducted concurrently evaluating watering interval (to impose levels of water stress), the duration of water stress, and timing of stress. The first experiment was a 3 x 3 factorial design consisting of three levels of watering interval (3, 4 and 5 days) for a 10 day period at three flower maturity stages (early flowering, FMS (flower maturity stage) 2; mid flowering, FMS 4; late flowering, FMS 6). The second experiment consisted of a 2 x 2 factorial design with two levels of watering interval (3 and 5 days) for a 20 day period at two flower maturity stages (early flowering, FMS 2 and mid flowering, FMS 4). The treatments were applied within a completely randomised design with 11 replicates (pots). Eleven control pots that were watered daily were included in both experiments. The FMS stage for individual plants was based on the primary flowering stem and treatments were applied when at least five replicate plants reached the target FMS. Even though longer intervals between watering resulted in lower pre-dawn leaf water potentials, the plants displayed no visual signs of water stress. Drought stress applied at different FMS stages had the greatest effect on the plant growth and development parameters, when compared with watering interval and duration of water stress. In general, drought applied at FMS 2 did not reduce plant biomass accumulation to the same extent as drought applied at FMS 4 and 6. However, drought applied at this stage of development had a slight influence on pyrethrin synthesis. The higher biomass accumulation of plants that were drought stressed at FMS 2 compared with FMS 4 and 6, maybe due to the longer recovery period. It was concluded that plants grown under field conditions are likely to recover from mild drought stress, particularly during early flowering, but yield will be reduced if plants are stressed at later flowering stages.