Chemogeography and antimicrobial activity of essential oils from 'Geijera parviflora' and 'Geijera salicifolia' (Rutaceae): Two traditional Australian medicinal plants

Abstract

Essential oils were hydrodistilled from 27 specimens of 'Geijera parviflora' Lindl., (Rutaceae) and nine specimens of 'Geijera salicifolia' Schott, collected over a wide geographic range in New South Wales, Queensland and South Australia. Essential oils were produced by traditional hydrodistillation and characterised using GC-MS. From one specimen a serendipitous discovery was made of bioactive coumarins dissolved in the hydrosol, which were the coumarins isopsoralen, xanthyletine and osthole. These coumarins were not present in the essential oil from that specimen. Using essential oil composition from all specimens, principal component analysis (PCA) demonstrated nine clusters for 'G. parviflora' and three for 'G. salicifolia'. Some clusters are representative of previously described chemotypes and some are reflective of possible chemotypes requiring more comprehensive sampling for confirmation. Thus, another three or four possible chemotypes of 'G. parviflora' and one of 'G. salicifolia' have been tentatively identified. Using micro-titre plate broth dilution assays, antibacterial and antifungal activity of all chemotypes was investigated. In this regard, the 'green oil' chemotype, restricted to 'G. parviflora', with major components linalool, geijerene/pregeijerene, 1,8-cineol and bicyclogermacrene, demonstrated the highest antimicrobial and free radical scavenging activity. Thus, in the light of traditional use reports of local analgaesia and bioactivity demonstrated in the current study, oils from select chemotypes of 'G. parviflora' may be useful in suitably compounded lotions and creams designed for topical antimicrobial applications and local pain relief. In addition, because major components are known for insecticidal activities, such lotions may also be useful as topically applied insect repellents.