Recombinant DNA technology has created plants resistant to viruses, bacteria, fungi and insects. At present resistant cultivars have been developed against tomato mosaic virus, tobacco mosaic virus, tobacco mild green mosaic virus, papaya ring spot, delayed blight of potato etc. Australian scientist Sayer has developed a rust resistant wheat variety by introducing the Rus+ resistance gene from Aagilops umbellulata into Kile wheat. American scientists have identified RPS2 and L2 genes that are resistant to viruses, bacteria and fungi. Work is underway to introduce these genes into crop plants.