PARENT SESSION
Oral Session # 21: Herbivory I: Susceptability and Resistance.
Presiding: D Lincoln
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Meeting Room 200.

Induction of systemic acquired resistance in Arabidopsis thaliana benefits Spodoptera exigua but not Trichoplusia ni.

Cipollini, Don^*,1, Enright, Stephanie¹, ¹ Wright State University, Dayton, OH

ABSTRACT- The role of salicylate in plant responses to pathogens has been well documented, but the effects of salicylate on plant responses to insects are not well understood. We examined the effects of salicylate on performance of the generalist herbivores, Trichoplusia ni and Spodoptera exigua, using Arabidopsis thaliana genotypes that varied in their ability to mount salicylate- and jasmonate-mediated responses. Feeding by neonates of T. ni was highest on the salicylate deficient nahG, intermediate on the salicylate insensitive nim1-1, and lowest on the jasmonate response mutant jar1-1, the jasmonate deficient mutant fad, and the Columbia and Wassilewskija wild-types. Growth of T. ni larvae largely followed that pattern. Genotypes varied in defense protein expression, and only peroxidase activity responded consistently to salicylate treatment. T. ni larvae responded positively to the lack of endogenous salicylate signaling in their host plant, but salicylate treatment had no effect on their performance. In a separate experiment, growth of Spodoptera exigua larvae was highest on the Wassilewskija wild-type, intermediate on the Columbia wild-type and the fad, jar1-1, nahG genotypes, and lowest on the nim1-1 mutant. Despite having no discernable effect on defense protein expression, salicylate treatment increased the growth of S. exigua larvae on all genotypes except for nahG, which converts salicylate to catechol. In this study, two generalist insects responded differently to genetic defects in salicylate and jasmonate signaling of their host plants, and only S. exigua was responsive to exogenous salicylate treatment. This illustrates that potential cross-effects of salicylate on insect resistance can occur, but are likely to vary with insect species identity. Moreover, it illustrates that elements of endogenous salicylate and jasmonate signaling both function in resistance of A. thaliana to these insects, perhaps through their control of plant defensive chemistry or other aspects of the suitability of foliage for insect feeding and growth.

Key words: Arabidopsis thaliana, induced resistance, insect herbivores, cross effects