Submitted to: Entomologia Experimentalis et Applicata
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/19/2000
Publication Date: 4/30/2001
Citation: Interpretive Summary: Plants have several different ways to resist insect attacks and pathogen infections. These can include the production of secondary plant metabolites, e.g., phytoalexins that can act as antibiotics, behavioral modifiers, etc.; defensive proteins that can act to prevent infection by attacking the pathogen or insect directly; or by killing the tissue surrounding the pathogen or insect, i.e., necrosis. Exactly how these defensive systems are activated in the plant is still a question under study. Here we use salicylic acid analog (i.e., BTH also called Actigard and BION; a plant chemical that thought to signal defenses for pathogen infections) applied to cotton to determine if it gives results similar to those caused by insect herbivory. The results show little effect of the BTH on various insect behaviors (oviposition, host preference, etc.) for cotton bollworms as compared to the effects of insect feeding by whiteflies on the host plant. These tests support the idea of two or more signaling pathways to activate various plant defenses. The information indicates that it may be possible to activate specific pathways through the use of specific activators/elicitors.
Technical Abstract: Whether or not chemical changes in plants in response to pests (insect and pathogens) are general or specific remains unclear. Some evidence indicates that an induced response (IR) to arthropods via the octadecanoid pathway represents a distinct mechanism from the salicylic acid-based pathway of induce systemic resistance (ISR) to pathogens. To further test this hypothesis young cotton seedlings were activated with benzo (1,2,3) thiadiazole-7-carbothioic acid (S) methyl ester (BTH), an elicitor of ISR. The enzymatic activities of a number of pathogenesis related (PR) proteins in young and old leaves of control and BTH treated plants were measured. BTH applications elicited marked increases in the activity levels of chitinase, peroxidase, and ß-1,3-glucanase both locally and systemically. The highest levels of induction were detected systemically in young leaves. Except for some local effects on whitefly oviposition, the induction of ISR by BTH-induction had no effect on either host preference of whiteflies Bemisia tabaci (Gennadius) or on feeding efficiency of cotton bollworms Helicoverpa armigera Hubner. We conclude that ISR induction via the salicylic acid pathway in 'Acala' cotton has negligible effect on the tested insect herbivores.