Abstract: This invention relates to a method of breeding plants to improve a trait of agronomic or horticultural value and plants produced by the method. The invention particularly relates to a method of plant breeding to affect an interaction between a plant and an interacting organism. Interactions that can be modified or affected are the positive beneficial, the negative or deleterious, or a harmless interaction. The breeding method of the invention provides progeny plant line phenotypes toward interacting organisms that exceed the range of phenotypes displayed by the parental strains. The methods of the invention can be implemented with the aid of molecular markers for quantitative trait loci.