Various locations in Switzerland were screened for Petasites hybridus plants with high petasin and low pyrrolizidine alkaloid content. The mean petasin content of the various populations ranged from 7.4 to 15.3 mg/g dry weight in rhizomes and from 3.3 to 11.4 mg/g dry weight in leaves. Mean pyrrolizidine alkaloid content in rhizomes ranged from 5 to 90 ppm whereas leaves contained between 0.02 to 1.50 ppm. These results suggest that leaves might be a preferable source for harvesting compared to the underground organ due to the finding of high petasin contents and consistently lower amounts of toxic pyrrolizidine alkaloids.

We developed an immunoassay with antibodies against retrorsine to detect the closely related senecionine, the main alkaloid in various Asteraceae. Sensitivity is about 23 pg (68 fmol) for senecionine. Cross reactivity of monocrotalin, retrorsine N-oxide, senkirkine (< 0.1%), and seneciphylline (3.6-34.5%) was resolved. The alkaloid content in leaves of Petasites hybridus (Asteraceae) was determined to be 3.86 ppm, calculated as senecionine, which was far less than in rhizomes (104.8 ppm). Additionally, we proved specificity by taking immunograms from different parts of Petasites hybridus. The test is a suitable tool for assessing the toxic potential of medicinal plants containing senecionine.

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Sesquiterpene esters are the active principle in the medicinal plant Petasites hybridus. Two chemotypes, the petasin chemotype and the furanopetasin chemotype, are known, but only the first one is suitable for pharmaceutical purposes. Experimental crossings were performed within and between plants of both chemotypes to study the genetic basis of the occurrence of these sesquiterpenes. The chemotype was determined by TLC in extracts of a small piece of rhizome in the parent plants and the progenies. A model including the combined action of two genes is proposed to explain the inheritance of the chemotypes where the furanopetasin chemotype is under recessive genetic control.