Induced resistance in soybean: Studies with the Mexican bean beetle and the soybean looper

Induced resistance in soybean (Glycine max), cv 'Williams 82', to the soybean looper (SBL) (Pseudoplusia includence) and the Mexican bean beetle (MBB) (Epilachna varivestis) was investigated. An increased level of antifeeding effect in soybean can be induced by previous insect herbivory as well as by mechanical injury. There seems to be no interplant transfer of inducing signals, as uninjured plants growing in the same pots as injured plants are not induced. Various induction factors were compared and the results suggest that: (1) the strength of resistance induced by mechanical injury seems to depend on the number of injured cells in contact with healthy cells, and not on the amount of total leaf area lost; (2) resistance induced by SBL herbivory results from a combination of mechanical injury and some yet unidentified factors in the larval regurgitate. The impact of induced resistance on food consumption and utilization of MBB and SBL was studied using standard gravimetric technique. Induced resistance has a significant retarding impact on growth and development of MBB and SBL, and significantly affects most indices of food consumption and utilization, except total food consumed. The impact on MBB fitness is greater than that on SBL. Study of soybean phytochemical profiles (fraction of phenolic compounds) using HPLC revealed twelve peaks and showed that increase of three and two peaks from leaf samples of induced plants was significantly correlated with antifeeding activity of leaf samples to MBB and SBL respectively. It has been reported that ozone increased acceptability of soybean plants to MBB. The effect of ozone on induced resistance was studied and the results suggest that (1) ozone decreases soybean resistance to insect herbivory and overrides induced resistance; and (2) induced plants are more sensitive to ozone influence and ozone exposure results in a lower resistance in injured plants than in uninjured plants. A conceptual model was presented in an appendix to describe the ecological significance of induced resistance to MBB as a preliminary step to build a microcomputer model and simulation of the impact of induced resistance in soybean to insect herbivores.U of I OnlyETDs are only available to UIUC Users without author permissio