Quillaja lancifolia Immunoadjuvant Saponins Show Toxicity to Herbivores and Pathogenic Fungi

Saponins from leaves of <i>Quillaja lancifolia</i>, a native species from southern Brazil, show potent immunoadjuvant activity in experimental vaccine formulations. The accumulation of the immunoadjuvant saponin fraction QB-90 is induced in cultured leaf disks and seedlings by several stresses and stress signaling molecules, such as osmotic agents, salicylic acid, jasmonic acid, mechanical damage, ultrasound, UV-C radiation, and high light irradiance. These observations suggest a role in plant defense. To further examine this possibility, an investigation of the potential inhibitory role of <i>Q. lancifolia</i> saponins on plant and human pathogenic fungi and two herbivore models was carried out. The screening tests showed that saponin-rich fractions, particularly QB-90, were able to significantly inhibit the growth of <i>Bipolaris micropus</i>, <i>Curvularia inaequalis</i>, <i>Fusarium incarnatum</i>, and <i>Cryptococcus gattii</i> R265. The same metabolites acted as deterrents against the generalist mollusk and insect herbivores <i>Helix aspersa</i> and <i>Spodoptera frugiperda</i>, respectively. Significant reductions in consumption of leaf area and larvae body weight were recorded. Taken together, these data indicate a role for <i>Q. lancifolia</i> saponins in plant defense against diverse herbivores and fungi, having potential as a natural pest control agent and/or as a molecular platform for the development of new environmentally friendly biocide molecules.