摘要
Although millions of hectares of cotton and corn carrying Bacillus thuringiensis (Bt) genes are now being grown worldwide, questions remain about the most effective way to delay development of resistant insect pests. In a collaborative project with the Shelton lab at Cornell, we have developed a model system for use in empirical studies of various proposed resistance management strategies. The plant components of the model system are broccoli (Brassica oleracea ssp. italica) lines transformed with cry1Ac or cry1C Bt genes under control of constitutive (35S CaMV) or chemically-inducible promoters. The insect components are susceptible, Cry1A-resistant and Cry1C-resistant populations of the diamondback moth (Plutella xylostella). We identified transgenic lines with high (>1 000 ng/mg total soluble protein) constitutive expression of Cry1Ac or Cry1C proteins and used them in sexual crosses to produce plants expressing both Bt genes. The two-gene plants showed Bt gene expression comparable to the parental lines, i.e. no gene silencing occurred. The cry1Ac+ cry1C plants controlled P. xylostella resistant to Cry1Ac or Cry1C proteins. Chemically inducible broccoli lines that provided insect control after treatment with the crop protectant BTH were also developed. These showed rapid high production of Cry1Ab protein and some signal transduction to untreated or newly formed leaves and heads. Older leaves of these plants produced some Bt protein and retarded insect development even when not induced, so this system may not be suitable for resistance management. Our cry1C broccoli, cauliflower, and Chinese cabbage plants also control other lepidopteran insect pests (Trichoplusia ni, Pieris rapae). A further area of work is production of two types of Bt-transgenic trap crops: glossy leaf collards (B. oleracea ssp. acephala) and Indian mustard (B. juncea). These are more attractive for P. xylostella oviposition than cabbage and also kill all larvae hatched from the eggs laid. Bt-trap crops may offer an attractive combination of biotechnology and biological control, especially when transgenic commercial crops are not accepted. A field test of how well plantings of these materials protect cabbage from insect damage will be conducted in the summer of 2005.
Although millions of hectares of cotton and corn carrying Bacillus thuringiensis (Bt) genes are now being grown worldwide, questions remain about the most effective way to delay development of resistant insect pests. In a collaborative project with the Shelton lab at Cornell, we have developed a model system for use in empirical studies of various proposed resistance management strategies. The plant components of the model system are broccoli (Brassica oleracea ssp. italica) lines transformed with cry1Ac or cry1C Bt genes under control of constitutive (35S CaMV) or chemically-inducible promoters. The insect components are susceptible, Cry1A-resistant and Cry1C-resistant populations of the diamondback moth (Plutella xylostella). We identified transgenic lines with high (>1 000 ng/mg total soluble protein) constitutive expression of Cry1Ac or Cry1C proteins and used them in sexual crosses to produce plants expressing both Bt genes. The two-gene plants showed Bt gene expression comparable to the parental lines, i.e. no gene silencing occurred. The cry1Ac+ cry1C plants controlled P. xylostella resistant to Cry1Ac or Cry1C proteins. Chemically inducible broccoli lines that provided insect control after treatment with the crop protectant BTH were also developed. These showed rapid high production of Cry1Ab protein and some signal transduction to untreated or newly formed leaves and heads. Older leaves of these plants produced some Bt protein and retarded insect development even when not induced, so this system may not be suitable for resistance management. Our cry1C broccoli, cauliflower, and Chinese cabbage plants also control other lepidopteran insect pests (Trichoplusia ni, Pieris rapae). A further area of work is production of two types of Bt-transgenic trap crops: glossy leaf collards (B. oleracea ssp. acephala) and Indian mustard (B. juncea). These are more attractive for P. xylostella oviposition than cabbage and also kill all larvae hatched from the eggs laid. Bt-trap crops may offer an attractive combination of biotechnology and biological control, especially when transgenic commercial crops are not accepted. A field test of how well plantings of these materials protect cabbage from insect damage will be conducted in the summer of 2005.
