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.



[link.springer.com]