Submitted to: Allelopathy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 6, 2008
Publication Date: January 1, 2009
Citation: Hoagland, R.E. 2009. Phytotoxicity of Microbial Antibiotics Helvolic and Fusidic Acids. Allelopathy Journal, Vol. 23, Number 1, pp. 167-174. Interpretive Summary: Helvolic and fusidic acids are steroidal compounds produced by certain fungi including plant pathogens. These compounds have strong antibiotic activity against some bacteria. Helvolic acid has previously been shown to have phytotoxic properties. Research was conducted to determine if these natural products were phytotoxic to some important plant species including weeds and crop plants. Several bioassays to assess phytotoxicity using high purity compounds were used. Neither compound affected seed germination, but both inhibited seedling growth of all species tested except in the weeds sicklepod and helvolic acid treated hemp sesbania. Results are important because they show these compounds have broad range phytotoxicity, may affect plants directly or indirectly (action on soil microorganisms), help explain interactions of microorganisms on plants and microoganisms, and provide insight into the nature of chemical structure and phytotoxicity useful in herbicide design.
Technical Abstract: Various laboratory tests were performed on tissues of several plant species using high purity helvolic acid and a related compound, fusidic acid. Bioassay tests include: germination/growth [hemp Sesbania [Sesbania exaltata (Raf.) Rydb.], sicklepod (Cassia obtusifolia L.), mung bean (Vigna radiata L.), wheat (Triticum aestivum L.), cucumber, (Cucumis sativa L.], leaf disk electrolyte leakage [corn (Zea mays L.), giant ragweed (Ambrosia trifida L.)], and greening of etiolated tissues (hemp Sesbania, sicklepod, wheat (Triticum aestivum L.), mung bean, sorghum (Sorghum vulgare L.) for phytotoxicity of helvolic (0.25 mM) and fusidic (0.5 mM) acids were conducted on these weeds and crops. Fusidic acid reduced chlorophyll accumulation in hemp Sesbania (95%), wheat (70%), mung bean (60%), sorghum (60%), and sicklepod (48%); helvolic acid had only weak effects, except in mung bean. Neither compound affected germination, but both inhibited seedling growth of all species except sicklepod and helvolic acid-treated Sesbania. Both treatments increased electrolyte leakage in corn and giant ragweed leaf disks after a 48-hr exposure. These natural products have broad-range phytotoxicity and may affect plants directly, or indirectly via antibiotic effects on soil/rhizosphere organisms.