Planting resistant varieties is the most effective and economical means to maintain soybean yields in fields infested with the soybean cyst nematode (SCN), Heterodera glycines. Eggs of SCN hatch in response to root exudates from resistant varieties and the infective juveniles enter the roots of resistant plants as readily as they enter susceptible ones. Host defense responses are activated after nematodes infect roots; nematodes in resistant plants are not able to feed and most eventually starve to death.

Soybean varieties resistant to SCN have been developed using different original sources of resistance. To date, seven plant introductions (P.I.) have been used in breeding programs to develop commercial soybean varieties resistant to SCN. Most of the commercial resistant varieties grown in Wisconsin derive resistance from P.I. 88788. Each of the plant introductions used in breeding programs owe their resistance to different genes or combina tions of genes. Just like soybean plants, SCN are all different and the qualities that make a plant resistant are not equally effective for every nematode that comprise the population of a soybean field.