A total of six transgenic Bt cotton lines (GKsu12, GK19, MR1, GK5, 109B, and SGK1) exhibit high resistance to cotton bollworm (Helicoverpa armigera) from the seedling to boll-setting stages in bioassays with detached cotton leaves. Scientists from Nanjing Agricultural University in China conducted genetics analyses which revealed that the resistance to bollworm in these six Bt cotton lines are controlled by a pair of dominant genes, thus their resistance levels vary as well as Bt toxin content. More tests showed some populations follow the Mendelian segregation for two non-allelic genes, i.e., the inserted Bt gene in GKsu12 is non-allelic to that of SGK1, GK5, 109B, and GK19, and Bt genes in GK19 and SGK1 are likely inserted in the same or in close proximity (genetically closely linked), while some F2 produce abnormal segregation patterns, with a segregation of resistance to cotton bollworm which vary between 15:1 and 3:1, though their Bt segregation fit into 15:1 by Polymerase Chain Reaction analysis, which imply Bt gene silence in these populations. Two genes silence may occur in these populations due to the homologous sequence by crossing since the silenced individuals accounted for 1/16 of the F2 populations for allelic test. The silenced populations further showed that one of their parents all showed high resistance to bollworm.

Read the research article in Transgenic Cotton.