It's pretty cool. Shows that grafts can be done between some different genera of the same Family (edited here to correct myself), much "wider" than can be done with sexual propagations.
As a viable novelty and as experimentals lots of things can be discovered doing this.
Details about disease and pest resistance can be studied. Things such as, can the top portions of a plant aid in Nematode resistance, Nematodes that affect the roots, or conversely, can the roots aid in resistance to leaf diseases. For example, might some varieties of Potato produce Allelic substances in their roots that travel through the stems to confer resistance to certain rusts or blights?
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Things like this make for wonderful thesis projects for grad students in agriculture and horticulture! "Conferred Resistance" or some name like that for it.
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By the way, this year Burpee Seed was selling Tomato plant seedlings that were grafted to Rootstock Tomatoes, varieties of Tomato especially bred to be great rootstocks.
Both Tomatoes and Potatoes are Perennials. Potatoes being dieback perennials that come back from their tubers similar to Dahlias, but as modified root. Tomatoes are tender short lived Perennials, some varieties more so than others.