| Summary: | Pyrethrin is a specialized metabolite of Dalmatian pyrethrum (<i>Tanacetum cinerariifolium</i> (Trevir.) Sch. Bip.), Asteraceae, known worldwide as an effective bioinsecticide. It consists of six active compounds: Pyrethrin I and II, cinerin I and II, and jasmolin I and II. Pyrethrin accumulates mainly in the flower heads and its content depends on numerous factors, such as the flower developmental stage. This study aims to investigate the accumulation patterns of six pyrethrin compounds in the flower heads of Dalmatian pyrethrum over the eight developmental stages (FS1 to FS8), and to make a comparison in six natural populations. Ultrasound assisted extraction was used to extract the pyrethrin, while qualitative and quantitative analysis was performed by High performance liquid chromatography. The accumulation patterns of different pyrethrin compounds were generally similar and also synchronous between different populations, while the pyrethrin I/pyrethrin II ratio showed irregular patterns. In all populations studied, the highest increase of all compounds was observed from FS1 to FS2. Their concentration continuously increased, reaching the highest values at FS4 stage (2–5 rows of open disc flowers), and generally decreased gradually towards FS6 or FS7 and then stagnated until the FS8 stage. Despite the very similar accumulation pattern of pyrethrin compounds in the different populations, the significant differences in their content suggest a different genetic background. Knowledge of the dynamics of pyrethrin compounds accumulation across flower development stages is valuable for determining the optimal harvest time of pyrethrum flower heads.
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