Genetic transformation and evaluation of two sweet sorghum genotypes for resistance to spotted stemborer, Chilo partellus (Swinhoe)

Sweet sorghum is a climate smart crop with multiple uses. The crop is susceptible to attack by the spotted stemborer, Chilo partellus (Swinhoe). This causes deadheart formation, leading to lodging of plants and consequent high economic losses. Lack of stable sources of resistance make any genetic enhancement through breeding difficult. We report a study to build up host plant resistance using transgenic technology by introducing two different classes of Bt genes (cry1Aa and cry1B) into two elite sweet sorghum genotypes of India (SSV84 and RSSV9). We devised tissue culture methods to suit the genotypes of our interest, SSV84 and RSSV9, and employed two methods of genetic transformation: the particle bombardment and in planta method of Agrobacterium. Modification of in vitro culture methods involved subculture every 3 days in the initial stages of culture and the use of precultured embryos as target tissues. For the in planta method, a floral dip for 1 h in Agrobacterium suspension supplemented with l-cysteine and Tween-20 was used. Sixteen transgenic events were generated; inheritance, integration and stable expression of the transgenes till the T-4 generation were confirmed. The amount of Bt Cry1Aa protein at 25-30 days of growth ranged from 24.8 to 72.8 ng/g of fresh leaf tissue. We recorded 78.4 % larval mortality, reduced leaf damage (3.0 out of 9.0) and reduced feeding (41.0 %) over the controls in insect feed assays. Stable inheritance and expression in the in planta-derived transgenics are presented.