PURIFICATION OF A TOXIN FROM FUSARIUM-OXYSPORUM F-SP LYCOPERSICI RACE-1

Leaf protoplasts from near-isogenic tomato (Lycopersicon esculentum) c ultivars, differing only at the I-1 resistance gene, showing different ial cell death in response to culture filtrates of Fusarium oxysporum f.sp. lycopersici race 1 were used to quantify the toxic activity of c rude and partially purified culture filtrates. Toxic activity was part ially lost after treatment with protease or storage at pK values above neutrality and was completely destroyed by autoclaving. Fractions wit h toxic activity were separated by gel filtration. Following acid nati ve polyacrylamide gel electrophoresis and electro-elution of a desalte d fraction precipitated by 20% saturation with ammonium sulphate from crude culture filtrates, toxic activity was found to be associated wit h a single proteinaceous band with an R(F) value of 0.32. Electrophore sis under denaturing conditions revealed that the toxin was comprised of two bands, with apparent molecular weights 56 and 61 kDa, which sta ined positively for protein. Protoplasts of cv. Ace, lacking resistanc e genes, were sensitive to the toxin, with a LD(50) of 55 ng protein m l(-1) compared with > 22 mu g protein ml(-1) against cv. Royal Ace pro toplasts, possessing the I-1 resistance gene to F. oxysporum f.sp. lyc opersici race 1. Injection of the toxin into tomato plants induced sym ptoms similar to those of natural infection in susceptible cv. Ace, bu t caused no symptom development in resistant cv. Royal Ace. This corre sponded to the cultivar-race interactions observed under field conditi ons.