IN-VITRO SCREENING OF COFFEE GENOTYPES FOR RESISTANCE TO COFFEE BERRYDISEASE (COLLETOTRICHUM-KAHAWAE)

An in vitro protocol was developed to screen Coffea arabica genotypes for resistance to coffee berry disease caused by Colletotrichum kahawa e. Initially, cultural conditions which influenced the growth of isola tes of C. kahawae on agar media suitable for callus growth were determ ined. The growth of the fungus on the callus derived from susceptible and resistant genotypes was then assessed. This ensured that no detrim ental competition for nutrients between the pathogen and the calli occ urred. Optimisation of the concentration of the phytohormones added to the media, the temperature and incubation period were found to be imp ortant in the expression of differential responses of calli to inocula tion with the pathogen as detected by measurement of hyphal growth. Th e screening of calli of nine C. arabica genotypes showed that this met hod identified genotypes highly resistant or susceptible to the diseas e and was sufficiently sensitive to distinguish those genotypes with m oderate or low resistance.