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Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and sequences of the 16S and 18S rRNA genes were used to access the effects of actively growing Bacillus thuringiensis (Bt) corn Pioneer 34B24 and Nongda 1246*1482, and plant straw (leaves plus stalks) of Bt hybrid Pioneer 34B24 and Nongda 61 on soil bacterial and fungal communities. Two-way indicator species analysis (TWINSPAN®), and detrended correspondence analysis (DCA) of the DGGE data indicated that neither the actively growing Bt corn nor its straw had any constant apparent effect on the soil bacteria and fungi community structure. The age of the growing plants, or the timing of plant straw decomposition may have more effect on the microbial community than other factors, i.e., the presence of Cry protein, plant hybrid and variety.

In order to control lepidopteran and coleopteran insects, the genes expressing Bacillus thuringiensis ( Bt ) insecticidal proteins have been transferred into crops. Ecological risk assessments of the transgenic plants have included impacts on non-target entomophagous insects, such as parasitoid wasps. Herbivore-induced plant volatiles are considered to be important defensive traits of plants because these compounds play as an important role in recruitment of natural enemies. Here, we evaluated induced volatile emissions of maize seedlings of two Bt cultivars (5422Bt1, event Bt11 and 5422CBCL, event Mon810), and their nearly isogenic non- Bt line 5422. We damaged plants mechanically and then applied with the regurgitant of Spodoptera litura (F.) caterpillars (Lepidoptera: Noctuidae), or treated the plants with the plant hormone jasmonic acid (JA), to trigger similar defensive responses of plants. Compared to the non- Bt isoline 5422 and the Bt maize 5422CBCL, the other Bt maize 5422Bt1 released more (3 E )-4,8-dimethyl-1,3,7-nonatriene (DMNT) when they were all treated by artificial wounds and caterpillar regurgitant; and released more linalool, DMNT and ( E )-β-farnesene when applied with JA solution. As a result, the total volatile emission of the 5422Bt1 was highest. However, the difference in volatile emission did not affect the attractiveness of the Bt maize plants to the egg parasitoid Trichogramma ostriniae Pang et Chen (Hymenoptera: Trichogrammatidae) compared to the nearly isogenic non- Bt plants. The variability of induced volatiles of maize cultivars derived from conventional breeding programs and transgenic methods are discussed.

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