Grafting of related plants is relatively easy and has a long history (check on google!). The best known are grafts of high yielding tomato scions onto rootstocks of resistant wild tomato. These grafts are done in vast numbers and give not only vigour and even higher yield but also resistance to all-too-common soil pathogens like Verticillium and Fusarium wilts. These wilts can rapidly kill most tomato varieties.
Grafting is also commonly used to combat waterlogging in tomato growing soils in SE Asia. Some Aubergines make good rootstocks for tomato as they can resist flooding. In reverse, the Aubergine is now grafted on to tomato rootstocks to increase early cropping and yield and to give resistance to soil-borne disease. These really do work.
The tomato-potato grafts have a long history and were usually called Pomatoes. We got interested because these are best grown in the garden and for outdoor growing you need both scion and rootstock to be resistant to blight. Thus we grafted a range of combinations of scion and stock using Sarpo potatoes and blight resistant tomatoes. I guess TomTato is not resistant - pity. If you are interested, why not try it for yourself?
|Charlotte tubers with tomato cv Legend on top|