ELICITORS OF PLANT DEFENSIVE SYSTEMS REDUCE INSECT DENSITIES AND DISEASE INCIDENCE

Some elicitors of plant defensive systems can induce biochemical chang es that enable the plant to reduce disease incidence; however, little is known about the effect of these induced responses on insect herbivo res, We approached this problem using exogenous field applications of several abiotic elicitors of defensive systems in tomatoes (Lycopersic on esculentum), and evaluated the ability of the elicitors [benzo(1,2, 3)thiadiazole-7-carbothioic acid (S)-methyl ester (BTH, Actigard); Pro benazole; chitosan; salicylic acid: KeyPlex 350; KeyPlex DP2; and KeyP lex DP3] to reduce pest densities and to provide cross-resistance agai nst various insect herbivores and pathogens. Only BTH provided cross-r esistance and significantly reduced the incidence of bacterial spot (X anthomonas campestris pv. vesicatoria), early blight (Alternaria solan i), leaf mold (Fulvia fulva), and leafminer larval densities (Liriomyz a spp.). The effects on leafminer larval densities were more pronounce d during the early stages of plant development. A trend of reduced den sities of whiteflies (Bemisia argentifolii) and powdery mildew (Oidium sp.), although not significant, was also found on the BTH-treated pla nts. Other elicitors had no significant effect on insect populations, but Probenazole and KeyPlex 350 significantly reduced bacterial spot a nd early blight incidence. The antiherbivore effects of BTH on leafmin ers was confirmed in a laboratory two-choice experiment. Adult leafmin ers preferred untreated plants to the BTH-treated tomatoes as oviposit ioning host plants, generally corresponding with larval performance. B TH induced high levels of pathogenesis-related proteins in tomato plan ts including peroxidase, lysozymes, chitinase, and beta-1,3-glucanases . The possible cross-resistance role of these proteins is discussed. T he demonstration that exogenous induction of plant defensive systems i n the field can result in lower damage caused by various pathogens and insects, supports the hypothesis that plant defensive systems may be general.