Determination of the Volatile Fraction of Polygonum bistorta L. at Different Growing Stages and Evaluation of Its Antimicrobial Activity against Two Major Honeybee (Apis mellifera) Pathogens by Roberto Cecotti a ), Emanuele Carpana b ), Luca Falchero c ) 1 ), Renato Paoletti a ), and Aldo Tava* a ) a ) CRA-FLC Centro di Ricerca per le Produzioni Foraggere e Lattiero Casearie, viale Piacenza 29, IT-26900 Lodi (fax: þ 39-0371-31853; e-mail: aldo.tava@entecra.it) b ) CRA-API Unita ´ di Ricerca per lApicoltura e la Bachicoltura, via di Corticella 133, IT-40128 Bologna c ) Dipartimento di Agronomia, Selvicoltura e Gestione del Territorio, Universita ` di Torino, via L. da Vinci 44, IT-10095 Grugliasco (Torino) The composition of the volatile fraction of Polygonum bistorta L. (also known as bistort or snakeroot) was investigated. Fresh aerial parts of this plant species were collected in the Western Italian Alps during the summer at three different phenological stages, namely vegetative, flowering, and fruiting, and steam-distilled in a Clevenger -type apparatus. The oils accounted for 0.004 to 0.010% of the fresh plant material, and their compositions were determined by GC/FID and GC/MS. The composition of the oils during the vegetative period varied both in quantity and quality; several classes of compounds were found with a predominance of alcohols in the vegetative phase, terpenes and linear-chained saturated hydrocarbons in the flowering phase, while saturated aliphatic acids and their methyl esters were predominant in fruiting phase. The most abundant compounds were 3-methylbut-3-en-1-ol in the vegetative phase, linalool in the flowering phase, and dodecanoic acid and its methyl ester in the fruiting phase. The obtained essential oils were then tested against two major bee pathogens, i.e. , Paenibacillus larvae and Melissococcus plutonius , and against a reference bacterial species, Bacillus subtilis . Data were compared to those obtained with reference standards used against those pathogens such as the essential oils obtained from leaves and bark of Cinnamomum zeylanicum (cinnamon), and the antibiotic oxytetracyclin. Introduction. – Polygonum bistorta L. (Polygonaceae), also known as bistort or snakeroot, is a circumboreal species, whose distribution areal stretches across Europe, from Eastern Portugal to the Pyrenees, the Alps, and the Carpathians [1]; it is also widespread across Russia, where it reaches its easternmost stations in the region of Lake Baikal [2] and in China. This plant species has also been reported in North America [3]. The plant is 20-to-80-cm tall, with a convoluted and hardened rhizome and an erect stem. Basal leaves are lanceolate, 6 – 9-cm long, bluish-green on their lower side, while stem leaves are smaller, 1 – 3-cm long, green to rusty-yellow on the lower side. The inflorescence is a single spike, pink to violet, blooming between July and September; achenes are brownish and triangle-shaped. P. bistorta prefers fertile pastures and other rich soils with plenty of nitrates, such as those located in the sub- alpine plain (900 – 2000 m above sea level), at least in its Southern European stations [4]. CHEMISTRY & BIODIVERSITY – Vol. 9 (2012) 359  2012 Verlag Helvetica Chimica Acta AG, Zürich 1 ) Current address: Chemistry & Biochemistry Laboratory, Department of Agriculture, University of Reading, 1, Earley Gate, P.O. Box 236, Reading RG6 6AT, UK.