The invention describes a highly improved, reproducible and a consistent method of transformation and regeneration that results in obtaining 12-15% transgenic plants. The present invention relates to a method of selecting genetically transformed Sunflower explants based on their ability to utilize Xylose as a sole carbohydrate source. Further disclosed is the nucleic acid sequence of the Xylose Isomerase gene, vector construction for incorporation of the selection marker gene and the process of Agrobacterium Mediated Transformation of target host plant with the vector comprising the gene encoding the enzyme Xylose isomerase under the functional combination of the heterologous regulatory sequences. Also disclosed is the method of selecting the putative transformants post transformation with the said vector that possess a metabolic advantage of utilizing Xylose as a sole carbon source. Increased efficiency of regeneration, better growth and survival has been observed on subjection to the described method of positive selection. The subject invention alleviates the disadvantages of negative selection methods such as the undesired elimination of the transformed cells and the potential environmental harm caused due to the dispersal of the antibiotic and the herbicide resistant genes.