Morphological, phytochemical, and genetic variation in Hawaiian cultivars of 'Awa (kava, Piper methysticum, Piperaceae)

Standardized morphological descriptions, quantitative phytochemical analyses (HPLC) of major kavalactones and DNA fingerprinting (AFLP) were utilized to define the extent of variation existing between Hawaiian cultivars of Piper methysticum. For each cultivar, morphotypes and chemotypes were compared to their respective genotypes. Overall, 63 samples were analyzed for their kavalactone content and composition (44 root samples, 6 stump, 5 basal stem, 7 leaves and 1 peelings). Results obtained from different cultivars planted in an homogeneous environment (soil and climate) are quite variable for the kavalactone content of their roots. Total kavalactone content decreases when shade increases over the plants. Total kavalactone content markedly increases with fertility, irrigation and in a cultivated type of habitat. However, kavalactone content appears to be independent of the age of the plant. For all cultivars analyzed, total kavalactone content decreases from the roots to the stump; the basal stems and the leaves exhibit the lower concentration. It is also observed that there is a correlation between the total kavalactone content and the size of the roots: smaller roots tend to have a higher kavalactone content. Peelings of the bark had a higher kavalactone content than the stump and represent a very interesting by-product for the extraction industry. Chemotypes are similar in the roots and the stump, while they differ in the aerial parts where the concentrations in dihydrokavain and dihydromethysticin increase. DNA samples were extracted from fresh leaves collected on 22 accessions. Most accessions, representing all Hawaiian morphotypes were monomorphs for the 21 pairs of primers assayed. Kava in Hawai’i is a species with an extremely narrow genetic base. Morphological and phytochemical variation is obviously controlled by very few genes. Most cultivars representing different morphotypes are most likely somatic mutants from a common clonal source introduced by Polynesians during early settlements.