CHARACTERIZATION OF ACTIVE COMPOUNDS IN RESISTANCE-INDUCING PLANT EXTRACTS OF REYNOUTRIA SACHALINENSIS (F. SCHMIDT) NAKAI
CHARACTERIZATION OF ACTIVE COMPOUNDS IN RESISTANCE-INDUCING PLANT EXTRACTS OF REYNOUTRIA SACHALINENSIS (F. SCHMIDT) NAKAI A SCHMITTl, KH GANSBAUER2, O VOSTROWSKI2, J HUBERl , and HJ BESTMANN2 l Biological Research Centre for Agriculture and Forestry, Institute for Biological Control, 64287 Darmstadt, Germany; 2FA-University Eriangen-Nurnberg, Institute for Organic Chemistry, 91054 Eriangen, Germany Background and objectives Extracts from Reynoutria sachalinensis are known for their resistance-inducing properties in several plant-pathogen interactions. The plant extracts are used against powdery mildew fungi or grey mould in vegetables and ornamentals. In greenhouse-grown cucumbers the efficacy against, Spaerotheca fulinginea reached more than 90%. Former investigations on active compounds in the plant extract excluded proteins and salts spp.. However, the nature of the resistance inducing compounds in R. sachalinensis was not elucidated. The objective of this study therefore was to isolate and identify relevant compounds in this plant. Results and conclusions An aliquot of dried plant power from R. sachalinensis was extracted in a soxhlet apparatus with organic solvents. The sequential extraction was performed with hexane, chloroform, ether and methanol. The methanol extract was finally washed with an unpolar solvent for further purification. All extracts that resulted from soxhlet extraction underwent efficacy trials in the system cucumber - S. fuliginea. From these the methanol extract showed highest efficacy. For further studies this extract was hydrolized, since from former work it was known that acid hydrolysis enhances the activity of R. sachalinensis extracts. The HPLC profile of the two resulting fractions showed that after hydrolysis the number and highth of peaks was enhanced to a large extend. Also, on thin layer chromatograms (TLC) the unhydrolised methanol fraction could not be separated in the given solvent system, whereas after hydrolysis two yellow bands could be seen. These bands and the rest of the TLC-plate were reeluated and bioassayed against S. fuliginea on cucumber. Band 1 reached an efficacy of 83%, while band 2 and the rest of the TLC-plate had no influence on the development of the pathogen. Investigations by GC-MS and comparison with known compounds lead to the identification of the two anthrachinones physcion (band 1) and emodin (band 2). Bioassays on cucumber with synthetically produced physcion and emodin supported these findings; only physcion reduced the development of powdery mildew on cucumbers, while emodin did not. Both compounds could be identified in the HPLC profile of the hydrolised, but not in the unhydrolised methanol extract, indicating that the aglyca have been released by acid hydrolysis from a bonded form. In literature there are reports about the occurrence of physcion and emodin and their glycosides in R. sachalinensis. Therefore, the activity in this fraction could either be due to the physcion glycoside or to other compounds not yet determined. Further investigation will be necessary to clarify this question. References 1. Kowalewski AK, Herger G, 1992. Mededelingen de Faculteit van de Landbouwweien-schappen Universiteit Gent - Beigi6 57/2b, 449-56.