Coffee berry disease: rain, public enemy no. 1

This is really a disease that falls from the sky. "Rain spreads coffee berry disease ", as Daniel Bieysse and Christian Cilas from CIRAD and Mouen Bedimo from IRAD* confirm. In Africa, this terrible fungus attacks Arabica coffee trees, and can destroy up to 60% of the crop.
The researchers conducted their experiments over a two-year period, on a small farm in Cameroon 1800 m above sea level. During the first rainy season, 30 coffee trees chosen at random were completely isolated from the rain using a clear plastic sheet. The results were decisive: just 1% of the berries on the protected trees were affected by the disease, compared to 45% for unprotected trees.

The fungus spores are carried by raindrops

The following year, half of the original 30 trees were left totally in the open, while the other 15 were protected on the sides alone. In the latter group, 12% of berries were affected by the disease, half as many as on the unprotected trees. However, on the trees that had never been protected, 53% of berries were contaminated. This clearly shows that the rain is "almost 100% " responsible for disease transmission. What is the explanation for this? The spores of the fungus Colletotrichum kahawae , which appear on the surface of infected berries, are transported and spread to other coffee trees by raindrops. The disease appears on the berries from the 8th week after flowering, and remains present until the 24th week. The infected berries blacken, rot and eventually fall. The disease is primarily seen at between 1400 and 2200 m above sea level, where temperatures are most propitious to its development. The experiment also showed that controlling the fungus one year reduces its spread the following year. Moreover, a canopy comprising shade trees also serves to reduce the intensity of the disease, by reducing the impact of raindrops.

Resistant varieties

New crop management sequences, combining planting shade trees and using resistant varieties in contaminated zones, in agroforest areas, could serve to reduce the need for chemical treatments. To identify sources of resistance to CBD, CIRAD has joined forces with Cameroon, Kenya and Portugal on a programme funded by the EU. Such sources have been identified in wild coffee trees and in an interspecific hybrid (Catimor). In Cameroon, the Java variety, and in Kenya, variety Ruiru 11, have been selected for their worthwhile resistance characters.
The disease is now found in almost every producing country in central and East Africa: Rwanda, Uganda, Tanzania, Ethiopia, Malawi, Zimbabwe and Zambia, and it spreads very quickly. Moreover, while CBD is currently restricted to Africa, it is a potential threat to all the Arabica plantations worldwide. This particularly applies to those in central and Latin America, where the varieties grown are particularly susceptible and are planted at high densities.

* IRAD: Institut de recherche agricole pour le développement, Cameroon.

Literature

Mouen Bedimo J.A., Bieysse D., Nyassé S., Nottéghem J.L., Cilas C., 2010. Role of rainfall in the development of coffee berry disease in Coffea arabica caused by Colletotrichum kahawae , in Cameroon. Plant Pathology, 59, 324-329.