Résumé
This study presents results of field experiments conducted to identify factors determining kavalactone content and chemotype in
Piper methysticum. The following factors have been studied: (1) the geographical direction of the roots on the plant, (2) the geographical location of the plant, (3) its age, and (4) its organ (roots, stumps, or basal stems). Overall, 185 samples were analysed by HPLC. It appears that the geographical direction of the roots (North, East, South, West) is not significant. Chemotype and kavalactone content variation among clones of a cultivar grown in a common garden is negligible. There is significant variation among different cultivars originating from the same island. The variation within island is comparable to the variation existing within the whole Vanuatu archipelago. For a given cultivar, chemotype is stable across locations. There are however, chemotype differences between organs. Kavalactone content is always higher in the roots than in the stumps and higher in the stumps than in the basal stems. Experimental data obtained from one cultivar indicate that at the juvenile stage (less than 18 months of growth), kavalactone content is still low but increasing progressively: from 3% of dry matter at 10 months to 8% at 17 months. After two years of vegetative growth, the chemotype appears stable and kavalactone content does not increase but rather fluctuates (±2%). Although seasonal factors might have an effect, it is not possible to observe a significant trend. It is confirmed that chemotype is genetically controlled. However, kavalactone content appears to be greatly determined by the growing conditions, either by the local environment or by the agricultural techniques used by the local farmers. Consequently, the selection of the cultivar, its organ and the geographical area of origin are factors contributing directly to quality control in
Piper methysticum.