Effects of density on dry matter yield on the yield and pyrethrins content of pyrethrum plants in Tasmania

Effects of density on dry matter yield on the yield and pyrethrins content of pyrethrum plants in Tasmania Variation in plant architecture, crop biomass, flower yield, pyrethrins content and pattern of pyrethrins accumulation has been reported between pyrethrum varieties (Ikahu and Ngugi 1988; Ikahu et al. 1994; Parlevliet et al. 1979). It is unknown whether these differences in response between varieties affect the optimum planting density to maximise crop growth, yield and pyrethrins content of pyrethrum. Thus there is a need for a detailed evaluation of the impact of planting density and breeding line on the partitioning of dry matter (DM) between plant components and flower pyrethrin content of pyrethrum. The response of 19 selected lines of pyrethrum to three plant densities was examined in a field trial at a research farm (41°10'S, 146°40'E) in northwest Tasmania in the 2008-09 growing season. The three plant densities were; low (40 x 40 cm; 16 plants/m2), medium (35 x 35 cm; 25 plants/m2) and high (25 x 25 cm; 44 plants/m2) with plots arranged in a randomised complete block design in four blocks. The experiment assessed the effects of family and density on DM partitioning at different flower maturity stages (FMS) and flower pyrethrin content. Plant stand density was shown to have a significant effect on DM partitioning. High leaf and stem numbers, and high flower DM yield recorded per plant at low plant stand densities was compensated by plant number at higher densities. There was no significant difference in the concentration of pyrethrins (mg/g dry weight) due to the effects of plant stand density. However, Total flower DM and pyrethrin per unit area was significantly higher at the at high plant stand density. No significant differences in DM accumulation were found between pyrethrum genotypes and there were no density by genotype interactions. In conclusion, stand density affected stem and flower number and mean flower weight, but not total flower pyrethrins content.