Two products that are currently available are Virus Resistant Squash (resistant to 2 kinds of viruses) and Rainbow Papaya (resistant to Ringspot Virus). The papaya is often discussed because biotechnology literally saved the Hawaiian Rainbow papaya as well as the Hawaiian economy that depended on this crop. This is actually a great example of how beneficial GM technology can be when viruses or bacteria threaten to wipe out an entire crop.
NewLeaf Plus and NewLeaf Y potatoes were resistant to viruses but are no longer on the market. Simplot has a late blight-resistant potato that was recently deregulated by USDA but is not on the market yet.
Some current crops that are being severely threatened from bacteria or virus infection include: oranges throughout Florida from Citrus Greening, the American Chestnut tree from Chestnut blight and the Cavendish Banana from Tropical Race 4 fungus. All of the crops could be devastated in these regions if a solution is not found.
This question is an important one but requires a nuanced answer. If we are talking about commercial crops, there are only two examples currently grown—some squash and Hawaiian papaya. These plants have been engineered to be resistant to viruses that cause diseases that greatly affect production.
The papaya is probably the best example. Papaya ringspot virus was devastating the crop in Hawaii. The virus is spread by insects, so controlling the virus meant insecticides and then treatment of sick trees. In the early 1990s Cornell University, University of Hawaii and the USDA coordinated a project to introduce virus resistance to the crop using genetic engineering. It worked wonderfully, and has been in place since 1998. There are many good resources online about how it works.
The same technology quickly was applied to squash, which suffers from a variety of viral diseases. GE plum trees are not available, but plants have been engineered and approved that resist the Plum Pox Virus, a pathogen that causes the devastating disease called “Sharka.” We don’t have the disease in the USA, but we’re ready if it does show up.
Sadly, there are many solutions to plant disease problems using genetic engineering that have not been used. There are proven solutions to diseases in world staple crops like bananas and cassava. In the industrialized world a gene from pepper stops bacterial wilts in tomato. Grapes have been engineered to resist vascular diseases. The citrus industry is threatened by a horrible disease, and genetic engineered trees show promise in research trials, but they are not yet available. In all of these cases there is a long and expensive approval process, and in many cases industries avoid use of the technology because of unsure public sentiment.
So where the solutions have been used they are quite successful. Additional technologies could be extremely beneficial and you will see them deployed by small companies and governments that want to help their people and environment. Genetic engineering solutions have the potential to decrease the dependence on insect controls, fungicides and other crop protection. That saves money for farmers and benefits the planet, but most of all ensures food security.