Pre-inoculation treatment of tomato plants with reduced light intensities during daily photoperiods promoted germination and germ tube growth of ' Botrytis cinerea' on the phylloplane, and sporulation potential of the pathogen after leaves were incubated on paraquat chloramphenicol agar medium (PCA). Conidia of the pathogen germinated and grew poorly on leaves of healthy plants. Germination increased two-to-three fold when light intensity during 15 days before inoculation was 135 or 14 [mu]mol.m-2·s -1. Similarly, germ tubes were 16 and 42% longer respectively. Conidiophore production on PCA at the end of 11 days was 20 and 45% higher respectively compared to values for leaves pre-inoculated in 384 [mu]mol.m -2·s-1. Reduced light intensities before inoculation also increase germination, germ tube growth and sporulation potential of the biocontrol agent 'Clonostachys rosea' in tomato leaves.