New Concepts in Breeding for Disease Resistance

Any scientific discipline has a basis in theory, and theory may be defined as a coherent system of concepts. Breeding plants for resistance to crop parasites embraces several disciplines within crop science and conceptually, these disciplines have developed at different rates. The major concepts in genetics were developed some three quarters of a century ago, while those in epidemiology were developed only recently, largely as a result of the work of Van der Plank (17-20). The conventional approach to breeding for resistance is consequently based almost exclusively on genetic theory; cru­ cial aspects of epidemiological theory have been ignored for the obvious reason that they were unknown. These new aspects of epidemiology, and their likely influence on plant breeding, were reviewed recently [Robinson (14)], and the present paper is an attempt to expand some of the more interesting of those ideas. While knowledge of this recent review would be an advantage, this is not essential as its important features are summarized here.