Coffee berry disease in Kenya. I. Colletotrichum spp. colonizing the bark of Coffea arabica

Several species ofColletotrichum occur in maturing bark ofCoffea arabica branches in Kenya. TheColletotrichum population inhabits the bark tissue external to the developing phellogens in the cortex. TheColletotrichum species are unable to invade green bark tissue, where the phellogen has not yet been differentiated, while colonization ceases on the phelloderm of the true bark. Only one of theColletotrichum species discussed in this paper,C. coffeanum, can infect green coffee berries. Shortly after the initiation of the first phellogen in the cortex the parasite is in a small area in the bark. It cannot be found in bark tissues where more phellogens have been formed and where the colour of the bark has changed from yellow-green to brown or black. From the bark ofC. liberica trees, grown in Kenya, andC. arabica cv. ’lsBourbon’, grown in greenhouses in the Netherlands one of the saprophytic components of theColletotrichum population could be isolated. It was impossible to induce ddie-back symptoms or mere infection by inoculation of green internodes even after wounding of live branches ofC. arabica with any of theColletotrichum components colonizing the bark. It is suggested that die-back systems of coffee in Kenya are primarily caused by unfavourable growing conditions.