DETACHED BERRIES INOCULATION FOR CHARACTERIZATION OF COFFEE RESISTANCE TO COFFEE BERRY DISEASE

Introgression of resistance to coffee berry disease (CBD), caused by Colletotrichum kahawae, is one of the best control methods for this disease. In a set of three successive experiments, we assessed the efficiency of detached berries inoculation to characterize coffee resistance to CBD. Cvs Ruiru 11 and SL 28 were inoculated with a suspension containing from 10(3) to 10(6) fungal spores ml(-1). The number of infected berries and their degree of infection were assessed and statistically analyzed. Results indicated that berry resistance could be separated into two components: one against the pathogen penetration and the other against its growth in the berries. The existence of a third dynamic component of resistance is suggested: the continued evolution and eventual decrease of resistance during berry expansion and maturation stages. Resistance to C. kahawae penetration was higher in cv. Ruiru 11 than in cv. SL 28, but was bypassed at the highest inoculum concentration tested (106 spores ml(-1)). The resistance of the inner berry tissues to pathogen growth appeared similar in both cultivars, but was broken in cv. SL 28 at the highest inoculum concentration. It is assumed that both forms of resistance could be of quantitative nature because they were modulated by the inoculum concentration. As the varieties were ranked in the same order in the three experiments, it was concluded that the technique is reliable for a relative ranking of the tested cultivars.