RESPONSES OF CELLS AND PROTOPLASTS OF COFFEA-ARABICA GENOTYPES TO PARTIALLY PURIFIED CULTURE FILTRATES PRODUCED BY COLLETOTRICHUM-KAHAWAE

Hypocotyl-derived calli of genotypes and segregating populations of Co ffea arabica, differing in susceptibility to Colletotrichum kahawae, w ere used to produce cell suspensions and protoplasts which were expose d to partially purified culture filtrates (PPCFs) prepared from the pa thogen. The growth and viability of PPCF-treated cells and protoplasts were measured using packed cell volume, fluorescein diacetate stainin g and a colorimetric assay involving the tetrazolium salt MTT. Differe ntial responses of cells and protoplasts were influenced by genotype, time of exposure and PPCF concentration. Protoplasts of resistant geno types responded differentially from more susceptible genotypes as earl y as 4 h after challenge with the phytotoxin, suggesting that they wer e more sensitive than cell suspensions to the treatments. Protoplasts exposed to PPCFs from C. kahawae may therefore be used to screen and s elect genotypes resistant to, or tolerant of, coffee berry disease.