Disease and insect resistance is governed by

Disease and insect resistance are governed by Plasma genes, Oligogenes and Polygenes.
The plasma gene is an extranuclear determiner of hereditary characteristics with a capacity for replication similar to that of a nuclear gene.
Oligogene is a gene that produces or significantly affects the expression of a qualitative heritable characteristic, acting either alone or with a few other genes.
A polygene refers to a group of genes that when expressed together produce a particular phenotype or trait.