Resistance of Transgenic Hybrid Triploids in Populus tomentosa Carr. Against 3 Species of Lepidopterans Following Two Winter Dormancies Conferred by High Level Expression of Cowpea Trypsin Inhibitor Gene

Hybrid triploid poplars [(P. tomentosa x P. bolleana) x P. tomentosa] genetically engineered with cowpea trypsin inhibitor (CpTI) gene have been out-planted in field for two years. They were used to detect their efficacy against 3 species of poplar defoliators: forest tent capterpillar, Malacosoma disstria Hübner, gypsy moth, Lymantria dispar Linnaeus and willow moth, Stilpnotia candida Staudinger by using detached leaves and for the purpose of identifying the CpTI gene at the molecular level. Foliage of transgenic poplars elicited an increase in larval mortality rate and a decrease in foliage consumption, wet weight gains, faeces excretion, deposited pupae number and pupae weight, thus indicating its effectiveness in affecting the growth, development and fecundity of larvae rather than only directly killing them. PCR and Southern blotting analyses confirmed the stable incorporation of CpTI gene while proteinase inhibitory assays disclosed its high level expression in the two-field-season of transgenic trees. Efficacious insect resistance and higher content of CpTI in foliage were found in transgenic clone TG04, TG07, TG08 and TG71, demonstrating a correspondence between the insect resistance level and the CpTI content in the foliage of transgenic poplar.