Coffea arabica coffee represents between seventy and seventy-five percent of world production[5] and it would be much higher if arabica were not as susceptible to disease as it is.[6]
Before the end of the 19th century, arabica was indeed the exclusive producer of all coffee in the world[7] but the first documented outbreak of coffee leaf rust (CLR) disease decimated crops around the world, prompting many farmers to explore alternative crops.
While some countries almost completely replaced coffee production with alternative crops, Indonesia began introducing robusta, which has both a high yield in fruit and a high level of resistance to CLR. Unfortunately, robusta also produces lower quality coffee. During the first half of the 20th century, East Java pioneered systematic breeding designs on robusta coffee, which would become "exemplary to all subsequent breeding programmes of robusta coffee in India and Africa.[8]" This knowledge of robusta is critical for modern coffee breeding because robusta is the main source of pest and disease traits not found in arabica.[9]
Prior to the mid-1900s, arabica coffee breeding involved simple line selection with an emphasis mostly on favorable adaptation to local growing conditions, fruit yield, and cup quality. But in the late 1970s and 1980s, various countries started breeding programs designed to create cultivars resistant to CLR.[10] The intensity of these later breeding programs was a direct response to the serious threat CLR posed to crops. The results of these and other breeding programs have produced a number of important cultivars worth mentioning (see list below).