棉 花 学 报 Cotton Science 2007，19(2)：88-92
Inheritance Analysis and Resistance of the Transgenic Cotton Harboring Bt+Sck Double Genes to Helicoverpa armigera Abstract：At present，scientists are engaged in engineering plants with two or more resistant genes in order to delay and prevent the adaptation in pest species，prolong the usage of life span of transgenic plants and broaden resistant spectrum. Thus，the Bt and Sck （modified CpTI gene）gene，driven by CaMV35S promoter and CLCuV promoter （PRPB），respectively，were transformed into the cotton genome (Sumian 16) by pollen-tube pathway-mediated method in our lab. Five transgenic cotton plants (T0) were obtained by Kanamycin screening. The results of PCR and Southern hybridization indicated that the exogenous genes were stably integrated into cotton genome. Laboratory bioassays showed that the mortality of bollworm larvae ( Helicoverpa armigera ) accounted for more than 90% at peak flowering and boll developing stage after 5 d fed with new expanded leaves on main stem nodes of the two transgenic plants，312-5 and 332-2，which had higher efficiency against neonate larvae than bivalent transgenic cotton sGK321 (unpublished data). The homologous lines (312-5 T2 and 332-2 T2 ) were obtained in the second generation progeny plants (T2) from the self-fertilized transformed parent tested by Kanamycin resistance and bollworm bioassays. In the present work，these two transgenic homologous lines showed high efficiency to bollworm by insect bioassays. The insect-resistant and susceptible plants were segregated out in F2 populations produced between homologous transgenic lines (312-5 T2，332-2 T2) and three cultivars (Sumian16，R19 and sGK321). The plants with three and four in leaf damage index and 3rd instar larvae survival were classed as the susceptible and those of one and two in leaf damage index and no 3rd instar larvae survival as the resistant after 5d feeding in laboratory bioassays. According to this standard，segregation of resistant and susceptible plants fits 3∶1 ratio in F2 populations crossed among the two homologous transgenic lines and Sumian 16，respectively. This result indicated that the resistance of homologous transgenic lines to Helicoverpa armigera was controlled by one pair of dominant genes. The populations of (312-5T2×sGK321) F1，(332-2T2×sGK321) F1，(312-5T2× R19)F1and (332-2T2× R19)F1 had the same resistant level to bollworm as their parents. It meant that in heterozygous status，there was no co-suppression phenomenon which caused gene silence and resistance decrease. Additionally，there were 112 vs. 12 and 187 vs. 20 resistant and susceptible plants segregated out respectively for (312-5T2×sGK321) F2 and (332-2T2×sGK321) F2. These values closely fit 15∶1 segregation ratio. These results showed independent inheritance or different chromosome insertion of Bt genes for transgenic homologous lines and sGK321 strains. Segregation of resistant and susceptible plants also fit 15∶1 ratio in (312-5T2× R19)F2 population，indicating independent inheritance or different chromosome insertion of Bt genes for 312-5T2 and R19. In the population of (332-2T2× R19) F2，all the plants were resistant to bollworm，implying linkage inheritance or the same chromosome insertion of Bt genes for 332-2T2 and R19. So the two homozygous transgenic lines (312-5T2 and 332-2T2) were valuable to develop new transgenic cotton varieties with high efficiency against cotton bollworm. |