Transgenic broccoli with high levels of Bacillus thuringiensis Cry1C protein control diamondback moth larvae resistant to Cry1A or Cry1C

A synthetic Bacillus thuringiensis (Bt) cry1C gene was introduced into broccoli (Brassica oleracea ssp. italica) by Agrobacterium-mediated transformation. Twenty-one Cry1C transgenic plants were regenerated from 400 hypocotyl and petiole explants. Variable amounts of stable steady-state cry1C mRNA accumulated in different transgenic plants. Cry1C protein (up to 0.4% of total soluble protein) was produced in correlation with the cry1C mRNA levels. Leaf section and whole-plant bioassays were done using diamondback moth (DBM) larvae from lines susceptible to Bt or resistant to Cry1A or Cry1C proteins (Cry1A(R) or Cry1C(R), respectively). Plants with high levels of Cry1C protein caused rapid and complete mortality of all three types of DBM larvae with no defoliation. Plants with lower levels of Cry1C protein showed an increasing differential between control of susceptible of Cry1A(R) DBM. This study demonstrated that high production of Cry1C protein can protect transgenic broccoli not only from susceptible or Cry1A(R) DBM larvae but also from DBM selected for moderate levels of resistance of Cry1C. The Cry1C-transgenic broccoli were also resistant to two other lepidopteran pests of crucifers (cabbage looper and imported cabbage worm). These plants will be useful in studies of resistance management strategies involving multiple transgenes.