Commercial production of transgenic Bt insect-resistant cotton varieties and the resistance management for bollworm (Helicoverpa armigera Hubner)

Commercial production of transgenic Bt insect-resistant cotton varieties and the resistance management for bollworm (Helicoverpa armigera Hubner)

There are currently three kinds of transgenic Bt insect-resistant cotton germplasm lines, Shanxi 94-24, Zhongxin 94 and R19, in China. They showed high resistance to the neonate larvae of bollworm (Helicoverpa armigera). Transgenic Bt insect-resistant cotton varieties or hybrids have been bred using the three kinds of germplasm lines as parents. Our researches reveal that there exist different expressions in resistant level at different developmental stages in the three categories of germplasm lines. When neonate larvae are fed with leaves of cotton plant at the seeding stage with less than 10 leaves on the main stem, the mortality of the neonate larvae is 100%, but the resistance level will decline at later season. When Bt gene has been transferred to the cotton genome, it can be steadily transferred to the progeny, the level of resistance to bollworm keeps fundamentally uniform. Such insects as tobacco budworm (Heliothis virencens) in laboratory directive selection are very apt to produce resistance to the Bt insecticidal crystal protein. From the present crop system of cotton region in the Yangtze and Yellow River Valleys, and the expression characteristic of transgenic Bt resistant cotton, we suggest that the resistance to toxin protein in bollworm is not apt to be produced if the transgenic Bt insect-resistant cotton varieties are released and grown in the regions except in the Xinjiang cotton region. The managing strategies to delay or retard the resistance are discussed.