ABSTRACT
Just as humans vary in their susceptibility to any disease, so we can observe similar variation in susceptibility/ resistance within a natural population of any plant species. A portion of this variation is caused by the environment, that is to say, by variation in things like the amount of inoculum, the particular microclimates, and the growth conditions encountered by each plant. However, a significant-in most cases the most significant-cause of this variation is the genetic variation among individuals.
