New Developments in the Production of Herbicide-resistant Sugarcane

In a previously reported model study, sugarcane was genetically engineered with the pat gene conferring resistance to the herbicide Buster®. The sugarcane cultivar used in that work was NCo310, which is no longer grown commercially but responds well to tissue culture and transformation. The field performance of the herbicide resistant sugarcane was assessed and stable transgene expression observed over several ratoons with repeated herbicide application. However, the cost of the Buster® herbicide is particularly high. The use of a cheaper herbicide known to be as effective as Buster® could increase the returns per Rand spent on weed control by up to six times. More recently, therefore, a gene conferring resistance to a cheaper herbicide has been introduced routinely into commercial cultivars N12 and N19, which constituted 32% and 16% respectively of cane harvested in South Africa in 2000-01. Gene delivery by microprojectile bombardment was accomplished using five plasmid constructs, each containing the same herbicide resistance gene and the antibiotic selectable marker gene nptII, but differing in promoter characteristics. Plantlets were regenerated via either direct or indirect somatic embryogenesis and selection carried out on medium containing the antibiotic geneticin. Putatively transformed plants were subjected to herbicide spraying in the glasshouse where to date 52% have survived a sub-lethal dose, which severely damaged control plants. Results have suggested that N19 is more amenable to transformation and regeneration than N12. In addition, it has been shown that the promoters chosen to drive the gene of interest and selection gene are of great importance. In this study CaMV 35S promoter derivatives proved to be effective in the genetic environment of sugarcane.