9:30 AM - 9:45 AM
[G-03] Nematicidal activity of diterpenoids from algae of the genus Dictyota against Aphelenchoides besseyi
Brown algae of the genus Dictyota (Phaeophyceae) are known to produce secondary metabolites for chemical defense against marine herbivores, several of which have been paid attention to for their potential as insecticides. Aphelenchoides besseyi (Aphelenchoididae) is a widely distributed plant parasitic nematode (PPN) that causes ‘white tip’ disease on rice. Natural product researches for nematicide resources against PPN have been conducted primarily on terrestrial plants. However, the nematicidal activity of marine algae has only been studied in the form of dried algal powder or crude extract, yet to reach the compound level. We attempted to identify nematicidal active compounds against A. besseyi from Dictyota spp. After extraction of fresh D. dichotoma with acetone and chromatographic separation, seven diterpenoids including two new compounds have been obtained from the hexane-soluble fraction. After 96 h of exposure, one of the known diterpenoids, 4β-hydroxydictyodial A, exhibited an LC50 of 1.575 mM, whereas fenitrothion used as a positive control showed 0.022 mM.