To improve insect pest resistance of cotton, scientists at Huazhong
Agricultural University in China used gene stacking strategy. First, they
introduced Cry9C from Bacillus thuringiensis into cotton (cultivar Simian-3)
through Agrobacterium-mediated transformation. The intergration and
expression of the gene were confirmed by PCR and RT-PCR. The transgenic
plants exhibited moderate toxicity to cotton bollworm (Heliothis armigera)
but strong toxicity to cotton leafworm (Spodoptera litura) compared with the
transgenic plants expressing Cry 1Ac. Then they pyramided Cry9C gene and Cry
2A or Cry 1Ac, respectively by sexual crossing.

Results showed that the expression of Cry9C protein in the progenies of the
first generation had a similar level as the parent plants indicating the
high heritability of Bt genes. Progenies from both Cry9CxCry 2A and
Cry9CxCry 1Ac showed better resistance to cotton leafworm than their
parents. Based on the results, successful incorporation of gene pyramiding
technology can provide a new solution of developing multiple resistance
management strategies.

[link.springer.com]