Resistance And Oviposition Performance Of Diamondback Moth To Transgenic Bt Brassica Oleracea L

Along with the expansion of the cultivation of Brassica oleracea in recent years, it is damaged bydiamondback moth (DBM) more and more seriously. Application of chemical insecticides is the mainmethod to control DBM but they pollute the environment and threat human health. It is important tobreed insect-resistant cabbage. However, it is hardly to get insect-resistant Brassica oleracea as thegermplasm resource is limited. Genetic engineering may provide an important approach to getinsect-resistant plants. The commercialization of transgenic crops has reduced the application ofchemicals and provided enormous economic benefits since1996. The durability of Bt crops andresistance of insects are worried by more and more people. Especially, several cases showed that someinsects had developed resistance to Bt crops. The resistance of insects to Bt crops threatens theapplication of Bt crops. It is necessary to understand the mechanism of insect resistance so as to counterthe insect resistance and to keep the durability of Bt crops.In this study, transgenic cabbage and broccoli were used to evaluate their efficacy in controllingdiamondback moth. The inheritance mechanism of DBM to Bt broccoli was obtained. The inheritanceof oviposition preference in DBM to broccoli and cabbage was also studied. Two-locus populationgenetic model was constructed. The main results were as follows.1. Resistance of Bt broccoli to diamondback mothThe resistance of Cry1Ac-susceptible and Cry1Ac-resistant diamondback moth to Bt broccoliexpressing different levels of Cry1Ac protein were evaluated in laboratory and greenhouse. Theconcentration of Cry1Ac protein in the three Bt broccoli lines was167,224, and246ng/g fresh weightrespectively. Untransformed broccoli plants were used as control. Larval survival of diamondback mothon control leaves was not significantly different between resistant and susceptible DBM. The mortalityof susceptible DBM reached100%on all Bt lines. While the resistant DBM could survive on the Btbroccoli expressing167ng/g Cry1Ac protein. The development of susceptible and resistant DBM onintact Bt plants was also tested in greenhouse. The results of greenhouse trial were similar to that oflaboratory tests. It showed that the resistant DBM have developed resistance to the low level of Btbroccoli but the resistance is not high enough to overcome higher level of Bt broccoli.2. The inheritance mechanism of resistance in DBM to Bt broccoliAmerican-resistant and-susceptible strains were used to get F1hybrids and backcross progeny BC1and BC2. The survival of F1, BC1, and BC2on Bt broccoli was evaluated. The results showed thatresistance inheritance of DBM to Bt broccoli was recessive and the resistance gene was controlled byone locus.3. Oviposition performance of DBMThe DBM adults did not discriminate Cry1Ia8cabbage and control. There was no significantdifference in the number of eggs laid by DBM adults among different Bt broccoli lines, either. Theseresults indicate that the introduction of cry1Ia8and cry1Ac gene did not have any adverse effects on oviposition performance of DBM. There was no significant difference in the preference of differentDBM strains. They preferred to lay more eggs on broccoli than that on cabbage. There was nosignificant difference in oviposition preference among different DBM strains. While ovipositionpreference of DBM to broccoli and cabbage was different among DBM individuals from fields. Thepreliminary results showed that the oviposition behavior was influenced by genetic factors.4. Construction of two-locus genetic modelsTwo-locus genetic models were constructed with the resistance and oviposition preference data.The two-locus genetic models were compared to the one-locus model. The results show that theoviposition behavior could delay the evolution of resistance to Bt crops.