Transformation of an Australian Cotton Cultivar: Prospects for Cotton Improvement Through Genetic Engineering

Somatic embryogenesis and regeneration of whole plants is a highly genotype-dependent process in cotton. We have identified at least one highly regenerable Australian cultivar, Siokra 1-3, which is a sister line to the current major variety being grown in Australia. A number of plants have been regenerated and although some are showing abnormal pollen development, most can produce fertile seed when selfed or crossed with a normal pollen donor. Agrobacterium tumefaciens has been used to efficiently produce fertile transgenic Siokra 1-3 plants expressing novel genes such as the bacterial neomycin phosphotransferase or the β-glucuronidase. This is the first example of the transformation of an elite commercial cultivar. Critical factors in the transformation are the use of a supervirulent disarmed Ti-plasmid with a binary transformation vector, and a highly regenerable genotype of cotton. Bacterial concentration at the time of infection, tissue age, kanamycin selection regime, and co-cultivation support and media composition all have an influence on transformation efficiency and were optimised in our protocol. The ability to transform an elite Australian cultivar of cotton paves the way for agronomic improvements through genetic engineering. We have concentrated on increasing the tolerance of Australian cotton to the herbicide 2,4-D (to protect it from spray drift damage from adjacent cereal crops), and increasing its tolerance to insect pests, such as Helicoverpa armigera, using BT-toxin genes, protease inhibitors and other novel insect resistance genes.