ABSTRACT
This chapter discusses a historical view on resistance work and, afterwards, to highlight basic research fields. History of resistance breeding has suggested that high levels of resistance based on major genes is generally less durable than resistance based on minor genes. Vertical resistance was supposed to be monogenic resistance, giving complete protection to avirulent races, whereas horizontal resistance was considered as generally polygenic, with quantitative expression. The horizontal resistance concept has stimulated studies on incomplete or partial resistance in several host-pathogen systems, especially those where durability of resistance is of great importance. Genetic descriptors of resistance are monogenic/polygenic or major/minor gene resistance. Several coffee expeditions were undertaken to collect cultivated or spontaneous C. arabica types in Ethiopia, generally with the purpose of finding new sources of resistance to leaf rust.
