THE INVOLVEMENT OF FUSARIC ACID IN THE BULB-ROT OF GLADIOLUS

Tissue cultures of Gladiolus have been used successfully to determine host specific properties of fusaric acid, a phytotoxin produced by Fus arium oxysporum f. sp. gladioli (Mas.) Sny. et Hn. Ten Gladiolus genot ypes, including three wild South African species, varying in resistanc e to Fusarium-rot, were differentiated based on the expressed insensit ivity to fusaric acid. Shoots and callus cultures were challenged in v itro with various concentrations of fusaric acid. The ion-release caus ed by the toxin was measured with callus and intact cormels. In all ab ove mentioned bioassays resistant and susceptible genotypes could be g enerally discriminated. However, only two of the developed bioassays, the shoot assay and the ion-release with intact cormels, gave signific antly coinciding results with the Fusarium-resistance assessed in a gr eenhouse experiment. When using callus tissue in the assays, the obtai ned answer correlated less with the Fusarium-resistance. It is conclud ed that a part of the Fusarium-resistance is based on fusaric acid ins ensitivity.