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 Fusarium oxysporum f. sp. gladioli (Mas.) Sny. et Hn. Ten Gladiolus genotypes, including three wild South African species, varying in resistance to Fusarium-Tot. were differentiated based on the expressed insensitivity to fusaric acid. Shoots and callus cultures were challenged in vitro with various concentrations of fusaric acid. The ion-release caused by the toxin was measured with callus and intact cormels. In all above mentioned bioassays resistant and susceptible genotypes could be generally discriminated. However, only two of the developed bioassays, the shoot assay and the ion-release with intact cormels, gave significantly coinciding results with the Fusarium-resistdncs assessed in a greenhouse experiment. When using callus tissue in the assays, the obtained answer correlated less with the /"u.sflr(um-resistance. It is concluded Ihat a part of the Fw5-ar/wm-resistance is based on fusaric acid insensitivity