IN-VITRO SELECTION OF COFFEA-ARABICA CALLUS FOR RESISTANCE TO PARTIALLY PURIFIED PHYTOTOXIC CULTURE FILTRATES FROM COLLETOTRICHUM-KAHAWAE

Calli derived from hypocotyl explants of a susceptible and resistant g enotype of Coffea arabica were evaluated for their response to differe nt concentrations of partially purified culture filtrates (PPCFs) prod uced by Colletotrichum kahawae which are phytotoxic. The size of calli was measured non-destructively by automated image analysis. Different ial responses of calli ranged from complete necrosis or reduced growth in the susceptible genotype (N39) to an absence of necrosis and rapid growth in the resistant genotype (cv. Hybrido de Timer). Subsequently , one selection cycle in the presence of PPCF was devised and applied to calli of nine C. arabica genotypes. Normal plants were regenerated through somatic embryogenesis of callus lines that survived the phytot oxin treatment and in vitro and in vivo testing of these plants agains t the PPCF showed that increased resistance to the toxin had been obta ined. These studies suggest that in vitro selection of calli may be a feasible approach to acquiring germplasm with improved resistance to c offee berry disease.