Glycoalkaloid providing nematode resistance in tomato is

The glycoalkaloid providing nematode resistance in tomatoes is Tomatine.
Tomatine is a glycoalkaloid, found in the stems and leaves of tomato plants, and fruits at much lower concentrations.
Tomatine plays a major role in the resistance of the tomato plant against fungal, microbial, insect, and herbivore attacks. Tomatine is responsible in tomato plants for resistance against for example the Colorado beetle and snails. It is also a defense against fungi.