Diversity in bean Caffeine content among wild Coffea species: Evidence of a discontinuous distribution

Caffeine is a metabolite of great economic importance, especially in coffee. Previous evaluations have already focussed on wild species of coffee trees, but this assessment included six new taxa from Cameroon and Congo and involved a simplified method that generated more accurate results. Two main results were obtained: (1) Cameroon and Congo were found to be a centre of diversity, encompassing the entire range of caffeine content; (2) four groups of coffee tree species - CAF1, CAF2, CAF3 and CAF4 - were established on the basis of discontinuities in the caffeine content range. The trace levels of caffeine in CAF1 is due to an absence of accumulation in beans - a factor that is controlled by a major gene. The other classes, i.e., CAF2, CAF3 and CAF4, were characterized by the extents of their caffeine accumulation. Caffeine content was found to increase twofold from CAF2 (0.55% dmb) to CAF3 (1.1% dmb) and from CAF3 to CAF4 (2.3% dmb). This discontinuous distribution is discussed from an evolutionary standpoint.