SYSTEMIC INDUCTION OF ALLELOCHEMICALS IN GLANDED AND GLANDLESS ISOGENIC COTTON BY SPODOPTERA-EXIGUA FEEDING

Induction of systemic resistance to feeding of beet armyworm, Spodopte ra exigua, was investigated in two isogenic lines of Stoneville 213 co tton, Gossypium hirsutum, that differed in the presence of pigment gla nds. In laboratory bioassays, larvae strongly preferred to feed on gla ndless cotton plants when presented a choice between undamaged termina l leaves of undamaged glanded and glandless plants. Feeding damage inf licted by S. exigua larvae on the two oldest leaves of glanded plants seven days prior to feeding bioassays caused larvae to prefer by 33-fo ld the undamaged terminal foliage from undamaged plants compared to th at from damaged plants. Feeding damage on glandless plants caused only a 2.6-fold greater preference for terminal foliage from undamaged pla nts over foliage from previously damaged plants. Extracts of terminal foliage from glanded cotton damaged seven days earlier had significant ly greater quantities of terpenoid aldehydes (hemigossypolone, gossypo l, and heliocides) than did foliage from undamaged glanded plants. Ter penoid aldehydes were undetectable in extracts of both undamaged and p reviously damaged glandless plants. The profile of volatile compounds collected from the headspace of mechanically damaged terminal leaves o f undamaged glanded and glandless plants differed. Both cotton isoline s released large quantities of lipoxygenase products (hexenyl alcohols , acetates, and butyrates), but glandless plants released only small a mounts of mono- and sesquiterpenes compared to glanded plants. Glandle ss plants damaged seven days prior to volatile collection released sig nificantly greater quantities of lipoxygenase products, beta-ocimene, and alpha- and beta-farnesene than did undamaged glandless plants. Pre viously damaged glanded plants released significantly greater quantiti es of all mono-and sesquiterpenes and hexenyl acetates and butyrates, but not alcohols. The relative importance of volatile compounds versus terpenoid aldehydes in induced feeding deterrence in cotton to S. exi gua larvae is still unclear.