Growth and sporulation of some pathogenic fungi in the presence of grapefruit extract.

Development of Fusarium oxysporum f. sp. cyclaminis, F. oxysporum f. sp. dianthi, Botrytis cinerea and B. elliptica in the presence of grapefruit extract (GE) was evaluated. Amendment of potato-dextrose agar with 40 micrograms of GE/cm3 inhibited linear growth of tested species at least in 50%. Addition of 40 micrograms of GE/cm3 of medium inhibited spore germination of F. oxysporum f.sp. cyclaminis about 34% whereas germ tube growth was suppressed in 87%. In case of Botrytis species, B. cinerea spores were more susceptible on GE than B. elliptica. They did not germinate, however, at 200 micrograms of GE/cm3. Drenching of peat, artificially infested with F. oxysporum f. sp. dianthi, with GE at conc. 165 micrograms/cm3 resulted in drastical decrease of colony forming unit numbers and this suppressive effect was observed at least 35 days.